A21E-0765
Towards a realistic deposition coefficient expression for cirrus cloud modeling
Ice crystal deposition (condensation) coefficients affect ice crystal shape and size, two parameters that are important for cloud processes and cloud radiative impacts. Moreover, due to their effect on crystal mass uptake, deposition coefficients affect both the supersaturation at the crystal surface and the ambient supersaturation in the cloud. However, deposition coefficients are sensitive to the surface supersaturation (a fact that is widely ignored), which makes it difficult to use realistic deposition coefficient values in cloud models. The goal of our work is to find a realistic expression for the ice deposition coefficient that can be easily inserted into existing cloud models. For simplicity, we assume that only one coefficient applies to the entire surface, an assumption that gives a reasonable approximation for spherical and isometric crystal shapes. After relating the surface supersaturation to the ambient supersaturation, we determine a general expression for the deposition coefficient as a function of the ambient supersaturation and ice crystal size. Using an adiabatic parcel model with binned microphysics (Kay et al., 2006), we demonstrate the influence of a realistic deposition coefficient on ice crystal nucleation and growth.Finally, we assess if a more realistic deposition coefficient can help explain recent observations of high ice supersaturation in cirrus.
A21E-0766
Towards understanding the impact of TTL cirrus clouds on troposphere-to-stratosphere transport
Although it is well accepted that air enters stratosphere through the tropical tropopause by large-scale upwelling, the detailed mechanisms of troposphere-to-stratosphere transport (TST) remain unclear. Recently, Corti et al. postulated that the radiative heating effect of cirrus clouds in the tropical tropopause layer (TTL) can be an important factor in affecting the rate of TST. Their results were confined to a one-dimensional view which may arguably apply to tropical-mean conditions. To examine the validity of this postulation in the real atmosphere, we use new observations of TTL cirrus acquired from Aura MLS and CALIPSO, along with trajectory analyses, to examine the impact of cirrus on TST when horizontal displacements of air parcels and spatial and temporal variations of cirrus distributions are taken into account. The trajectories of air parcels are sorted according to the cirrus cloud occurrence frequency and a set of cloud-influenced TST pathways are identified. Our preliminary analysis shows that the radiative heating associated with cirrus can contribute to a faster ascent of air from the troposphere to stratosphere, and that the spatial and temporal variations of cirrus impacts are significant.
A21E-0767
The influence of convection on the water vapor and isotopic composition of the upper TTL and tropical stratosphere
We use recent in-situ observations of tropical H2O and HDO from the NASA WB-57 aircraft, coupled with a back trajectory model of convective influence, to study the effects of convection on air ascending into the tropical stratosphere. Data are presented from both the CR-AVE and TC4 campaigns to show differences in the convective influence between the wintertime and summertime. We measure heavy isotopic compositions of stratospheric water vapor as compared to the expected value from Rayleigh distillation. We also see surprisingly little isotopic gradient between the regions and seasons sampled, even though water vapor shows the expected seasonal and altitude dependence. We examine the possibility that stratospheric isotopic homogeneity is indicative of significant exchange between the midlatitudes and tropical upper troposphere. Back-trajectories suggest that a large fraction of sampled tropical air has recently traveled through latitudes higher than the subtropical jet.
A21E-0768
Investigating In-cloud Relative Humidity and Thin Cirrus in the Upper Tropical Atmosphere Using AIRS, CALIPSO, and MLS
We investigate vertical and horizontal distributions of tropical oceanic thin cirrus optical and microphysical properties observed by the Atmospheric Infrared Sounder (AIRS). These properties are related to thermodynamic quantities, i.e., relative humidity with respect to ice (RHi), and cloud top temperature derived from the AIRS Level 2 operational soundings. Differences between all sky and in-cloud RHi are explored and possible mechanisms that explain these anomalies are discussed. Furthermore, we evaluate the hypothesis that many of the observed clouds are physically much thinner than the nominal resolution of AIRS, which may lead to dry biases of in-cloud RHi. To test this we exploit the co-located AIRS RHi and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) cloud thickness. Finally, we diagnose the ability of AIRS to measure water vapor in the Tropical Tropopause Layer (TTL) using co- located observations from the Microwave Limb Sounder (MLS). From this, a combined AIRS-MLS RHi product is used to investigate joint distributions of cirrus microphysical and optical properties, and RHi in the TTL.
A21E-0769
A numerical study of tropical cross-tropopause transport by convective overshoots
Observations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case was investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation reproduced the measurements along the flight track fairly well. A reasonable agreement with MSG observations was also achieved: the 10.8-micron brightness temperature (BT) minimum of 187 K was reproduced (a value 6 K colder than the environmental cold-point temperature) as was the positive BT difference between the 6.2- and 10.8-micron bands, an overshoot signature. The simulation produced several overshooting plumes up to 410 K yielding an upward transport of water vapour of a few tons per second across the tropical tropopause. The estimated mass flux agrees with those derived from over tracer budgets, indicating that convection transports mass across the tropopause. http://mesonh.aero.obs- mip.fr/chaboureau/PUB
A21E-0770
Dehydration processes in the Indian monsoon anticyclone : Lagrangian analysis and sensitivity to vertical wind fields.
During Asian monsoon season, the large-scale monsoon flux generates a persistent anticyclonic circulation at the tropopause over the sub-tropical part of Asia (15°N to 40°N). The anticyclonic region is associated with a large water vapor maxima, which can hardly be explained by the seasonal variation of tropopause temperatures alone. In the upper troposphere, the moistening effect of deep convective events in the anticyclone has been pointed out by Randel and Park (JGR, 10.1029/2005JD006490, 2006). However, at higher levels the deep convective area is separated from the anticyclonic region (Park et al., JGR, 10.1029/2006JD008294, 2007). The large-scale circulation (slow ascent and anticyclonic barrier) seems hence essential to explain the water vapor distribution observed at 100 hPa (MLS/AURA or MIPAS). In this context, the ability of the large-scale wind fields to represent the water vapor distribution has been studied from back-trajectories. The calculations have been performed over three summers (1998, 1999 and 2000) using two representations of the vertical wind in the ERA-40 dataset and the new ERA-Interim: the "classical" wind (from divergence equation) and the diabatic wind (from temperature tendency equation). Coupled to a simple microphysical model, back-trajectories can reconstruct water vapor maps (Fueglistaler et al., JGR, 10.1029/2004JD005516, 2005). Here, the comparison to MLS/AURA retrievements at 100 hPa shows that : if "classical" wind calculations exhibit large discrepancies, diabatic winds accurately reconstruct the location and the concentration of the indian monsoon water vapor maxima without represented small-scale micro-physic. Investigating transport and dehydration processes along trajectories (intersection with isentrops, clouds from CLAUS,...) the Lagrangian approach offers a synthetic scenario. After being quickly lifted by deep convection over the Bay of Bengal until 350-360 K, most of the parcels are freezed-dry around 370 K above the Bay of Bengal, experimenting the coldest region of the TTL in summer. In the meantime, parcels trapped in the anticyclone avoid this "cold trap", and are freezed-dry westward of it in warmer regions. Hence, the water vapor anomaly in the anticyclone is not explained by a special convective regime, but by the particular horizontal advection through the TTL in the anticyclone ("warm trap"). Complementary results on the sensitivity of our results to the level of sursaturation, and to variations from ERA- 40 to ERA-Interim will be presented.
A21E-0771
Water and Relative Humidity at the Tropical Tropopause
Aircraft data of total water and water vapour from SCOUT-O3 (Australia), TROCCINOX (Brazil), AMMA (West Africa) and APE-THESEO (Indian Ocean) will be analyzed for the ice water content of cirrus and RHice at very low temperatures. Formation of ultrathin cirrus clouds and freeze-drying results in very low mixing ratios, sometimes below 2 ppmv. Deep convection leads to injection of moist air into the TTL and lower stratosphere. We will discuss the local cloud formation and dehydration processes as well as those having occurred before the observations analyzing the airmass history along backward trajectories.
A21E-0772
A Study of Dehydration, Low Temperatures and Supersaturations in the Tropical Tropopause Layer both Inside and Outside of Clouds.
There are substantial, and longstanding, discrepancies among instruments on satellites, balloons, radiosondes, and aircraft as to the levels of supersaturation of air parcels in the Tropical Tropopause Layer (TTL), particularly for measurements of water vapor volume mixing ratio lower than 10 parts per million by volume (ppmv). The discrepancies are due both to the difficulty of making the measurements in situ and to the difficulty of calibrating hygrometer instruments in the laboratory. We have developed a new calibration system for laser hygrometers that has allowed us to analyze data from the Jet Propulsion Laboratory Laser Hygrometer (JLH) and derive water vapor volume mixing ratios with an uncertainty of 7%, and relative humidity over ice with an uncertainty of 10%. The Costa Rica-Aura Validation Experiment (CR-AVE) was a NASA aircraft mission to characterize composition, clouds, and humidity in the TTL. In January and February 2006, a high-altitude NASA WB-57F aircraft made a series of flights from San Jose, Costa Rica, into the TTL over the equatorial Eastern Pacific Ocean. Several of these flights were characterized by unusually cold and highly supersaturated conditions near the tropical tropopause. New laboratory calibration measurements have been applied to the CR-AVE data. We analyze the updated water vapor and relative humidity along the aircraft flight path derived from water vapor concentrations measured by JLH and static temperature provided by the Meteorological Measurement System (MMS) on the aircraft.
A21E-0773
Tropical Tropopause Layer Cirrus Clouds as Seen by Cloudsat and Calipso
Cirrus clouds in the tropical tropopause layer (TTL) are posited to play an important role in the physics and chemistry of the air that eventually enters the stratosphere and in the Earth's radiation balance; but their location and tenuous nature have made them difficult to observe and, as a result, more poorly understood than other types of cloud. The advent of the A-Train sensors, however, now affords unprecedented views of these clouds and the opportunity to shed new light on their possible formation mechanisms and on their various possible radiative impacts. Toward this end, radar and lidar data taken from aboard the CloudSat and Calipso satellites are here used to demonstrate statistics of the seasonal and spatial variability of TTL cirrus clouds along with their tendency to occur with other, lower clouds.
A21E-0774
A-Train Observations of Stratosphere-Troposphere Exchange During 2006
Studies of jet stream and frontal boundary dynamics with atmospheric tracer measurements provide insight to the coupled stratosphere-troposphere system. A-Train satellite instruments possess the horizontal and vertical resolution along with temporal and spatial coincidence necessary to identify stratospheric intrusions, investigate their three-dimensional structure, and estimate cross-tropopause exchange. We present results from our analysis of tropospheric chemistry and dynamics using AIRS and Aura instruments to observe stratospheric intrusions along the polar jet during the 2006 Intercontinental Chemical Transport Experiment Phase B (INTEX-B) field experiment. Focusing on April-May 2006, we explore the temporal and spatial evolution of STE events over the Pacific Ocean originating off the eastern coast of China and traveling along the storm track to the North American west coast. With the broad swath of AIRS and the higher vertical resolution of Aura instruments like TES, ozone and water vapor retrievals show typical features of stratosphere-troposphere exchange in the UTLS near dominant meteorological structures. Analyses of in-situ and aircraft remote sensing measurements of these trace gases compare well with the satellite observations.
A21E-0775
Quantifying the deep convective flux of CO into tropical upper troposphere: A modeling analysis of Aura-MLS CO Measurements
Dramatic enhancement of CO over the Amazon was observed by Aura-Microwave Limb Sounder (MLS) at 147 hPa during September-October 2005. It is known that widespread deep convection in the tropics can efficiently deposit surface biomass burning emissions in the upper troposphere. Using 5-day running averages of MLS CO at 1-day interval, we estimated the convective vertical CO fluxes by subtracting the horizontal flux terms and net chemical production/loss from total CO tendency. Our results suggest that the abrupt enhancement of the 147 hPa CO concentrations over the Amazon is associated with the dramatic increase of deep convective CO fluxes. This conclusion is supported by CO fluxes derived from the GEOS-Chem global 3-D chemistry and transport model results simulated for the same time period. The model is driven by assimilated meteorological data and includes 2005-specific biomass emissions constrained by satellite observations. Model results show consistent spatiotemporal distributions as the MLS-derived CO fluxes. The increase in the deep convective CO fluxes during September-October 2005 are further investigated by examining MODIS fire counts and MLS cloud ice data (ice water content), indicators for the intensity of biomass burning and deep convection, respectively, for the corresponding period. The strength of deep convection during the aforementioned time period is also examined using NCEP convective mass flux.
A21E-0776
Zonally asymmetric forcing of the stratosphere: Ozone and volcanic aerosols
Often studies concerning troposphere-stratosphere interaction are based on zonally symmetric features (e.g. zonal mean wind, Northern Annular Mode etc.). Also model simulations, used to study the effects of stratospheric ozone depletion or volcanic eruptions generally are forced by zonal symmetric anomalies. In many cases these simulations partly fail to reproduce the observed anomaly patterns. Reasons can be manifold, reaching from missing processes, model biases and inadequate surface conditions (to name but a few), to inadequate forcing. Here we will use two examples showing that the zonally asymmetric part of forcing in the UTLS, even if it only represents a fraction of the zonal mean forcing, may contribute significantly to the resulting anomaly pattern and amplitude. The examples are trends in stratospheric ozone representing decadal variability and volcanic aerosol representing interannual variability. Basically it could be any radiatively active substances, including water vapour. Our results show that: (i) zonally asymmetric forcing at the tropopause contributes an important part of observed climate change in the stratosphere, (ii) at least the recent volcanically induced climate anomalies cannot be understood based alone on zonally symmetric analysis, and (iii) if coupled climate-chemistry models shall reproduce observed features, planetary wave forcing, e.g. due to interannual (El Nino) or decadal (PDO, ADO) must be considered.
A21E-0777
The Spontaneous Formation of a Tropopause Inversion Layer in Simple, Dry, Atmospheric General Circulation Models
The key factors contributing to the formation and maintenance of the recently discovered extra-tropical tropopause inversion layer are presently unclear. In this study, it is shown that such a layer can form as a consequence of the turbulent dynamics of synoptic-scale baroclinic eddies alone, in the absence of explicitly parameterized, small-scale, radiative-convective processes. A simple general circulation model, initialized from a state of rest, and driven with idealized forcings, is found to spontaneously develop an inversion layer above the tropopause under a wide variety of parameter choices and model resolutions. Furthermore, such a model is able to capture, qualitatively, both the latitudinal and (in part) the seasonal dependence of the observed tropopause inversion layer. However, the inability of our simple model to capture some detailed quantitative features strongly suggestes that other physical processes, beyond balanced synoptic-scale dynamics, are likely to play an important role. http://www.columbia.edu/~lmp/pubs.html
A21E-0778
Lidar cirrus cloud and aerosol measurements in the tropopause region
Cirrus cloud can be formed in the upper troposphere by ice particles through nucleation processes. Currently, it is not well understood about the details of the homogeneous or heterogeneous processes. The nucleation of cirrus clouds by sulfate aerosols has been suggested as a possible path. By using a lidar at 532 nm, cirrus cloud and stratospheric aerosol (SA) in the UT/LS are measured. Polarization measurements were employed to distinguish their difference of particle shapes. Lidar backscattering coefficients shows an anti-correlation between both. This suggests that more or larger aerosol particles result in small cirrus cloud particles. The cirrus clouds in the tropopause region are also compared with HALOE cirrus cloud and water vapor data. Results show that in summer months higher probability for observation cirrus clouds is caused by the presence of water vapor in the tropopause region.
A21E-0779
Statistics of Tropospheric and Stratospheric Layers From 1994 to 2007 Over Southwestern Ontario Using Lidar Backscatter Measurements
The Purple Crow Lidar (PCL) is a laser radar which has been in operation since 1992 from the Delaware Observatory, a University of Western Ontario research facility near London, Canada (42.87°N, 81.38°W, 225m elevation). The PCL has a large power-aperture product due in part to its use of a 2.6m diameter telescope. The PCL was designed for temperature measurements in the stratosphere, mesosphere and lower thermosphere. However, the system also measures total backscatter from near the surface to about 18km altitude. Measurements on 450 nominally "clear" nights have been analyzed to determine the occurrence of tropospheric and stratospheric layering events. Cloud or layers were measured having a top altitude above 7.5km on about 200 of these nights and above 12.5km on 63 nights. Of these events, there are 9 above 7.5km altitude that exhibit features that are consistent with layers, that is they produce a significant increase in the scattering ratio profile, are diffuse and lacking in vertical or temporal structure, are very narrow (less than a few hundred meters) and exist for hours. There are 5 layers that exceed 12.5km altitude and are likely in the stratosphere. Furthermore, 4 of these 5 layers occur over a period of a week in late June and early July, 2002. These layers are probably connected with pyroCb events resulting from intense fires in Manitoba and Saskatchewan. The other stratospheric layer occured on the night of May 5, 2007. We will refine our technique of discriminating between layers and clouds, as well as investigate the relation of these events to fires.
A21E-0780
The structure of the Tropical and Extratropical Tropopause Layer: 1960-2100
An analysis of the chemical and dynamical structure of the tropical and extratropical tropopause regions from observations and coupled chemistry climate models of the middle atmosphere is presented. The analysis uses detailed results from 2 models and long term simulations from a multi-model ensemble. Models are compared to observations from individual soundings to reanalyses. Variability from daily to interannual time-scales (including the effects of convection and waves) is analyzed. Global models are found to reproduce most scales of variability. Global tropopause trends are examined, including the effects on the UTLS of projected changes to greenhouse gases and halogens (affecting climate and ozone). Models are able to reproduce some aspects of observed trends in tropopause structure in the tropics and extratropics, such as tropopause height trends, but not changes in the meridional extent of the tropics. Future trends in the UTLS to 2100 are explored. Simulations indicate increases in tropopause height and slight increases in tropical tropopause temperature, and increases in the height of convective outflow in the tropical tropopause layer.
A21E-0781
The influence of photolytic effects on modeled lightning-produced nitric oxides for the 10 July STERAO case
On July 10, 1996 a convective system developed in the late afternoon over the Cheyenne Ridge near the southern Wyoming-Nebraska border and was observed as part of the Stratospheric-Tropospheric Experiment: Radiation, Aerosols, and Ozone (STERAO) project. The cells moved in a south to southeastward direction crossing into northeastern Colorado before dissipation occurred in the evening hours. One of the main goals of STERAO was to investigate the role thunderstorms play in the redistribution of chemical species in the troposphere. A particular concern in the program was the distribution of odd nitrogen species; primarily focusing on NOx (NOx = NO + NO2) production by lightning and the transport of NOx into the troposphere and lower stratosphere based on the structure of the convective systems. We simulated this well documented storm with our three-dimensional Storm Electrification Model (SEM) with an explicit lightning scheme, which includes chemistry. The NO production is based on the energy dissipation of the lightning discharge including both a pressure dependence and a scheme that accounts for the cloud radiative effects on the chemical rate of photolytic reactions. This scheme is based on the actinic flux in the upper, middle, and lower portions of the thundercloud. The use of such a scheme allows for the effects of radiation transfer on the production of NOx from lightning. The chemical scheme incorporates nine chemical species, including NO, NO2, O3, CO, and CH4. These chemical species take part in eighteen chemical reactions, which include three that are photolytic. We focus our simulations on the production of NOx, with the goal of comparing the production based on three simulations: one with a clear sky photolytic scenario, another using the radiative transfer scheme, and the last scenario with the photolytic reactions turned off to simulate nighttime conditions. This modeling work is currently underway and the most recent results will be presented.
A21E-0782
Equatorial Waves Excited by Convection Studied With the Whole Atmosphere Community Climate Model (WACCM)
Transient fluctuations of convection are an efficient mechanism for the excitation of equatorial waves. Vertically propagating waves transport energy and momentum upward and are an essential factor in coupling the troposphere to the stratosphere and upper atmosphere. Many climate models underestimate the convective variability at time scales shorter than 2 days, therefore severely impacting wave excitation. Here we used the Whole Atmosphere Community Climate Model (WACCM) to study the excitation of waves under different convective parameterizations. Unlike other convective parameterizations, the scheme by Tiedtke (1989) efficiently excites high frequency waves (Kelvin and inertia-gravity) that are able to propagate into the stratosphere and beyond. The horizontal resolution has an impact on the type of waves excited. A low-resolution (4x5) simulation produces a realistic spectrum of Kelvin waves, which are characterized by large scales, but gravity waves are deficient. A higher resolution (1.9x2.5) simulation, however, generates gravity waves with spectral power comparable to that derived from satellite observations. Using WACCM allows us to (1) Compare the dynamical perturbations simulated in the model to observations (e.g., the SABER/TIMED mission); and (2) study the impact of wave activity on the dynamics of the middle atmosphere.
A21E-0783
Exploratory Analysis Of The 3D Cloud Resolving Model Simulations of TOGA COARE: Preliminary Results
Global climate model studies suggest that cumulus momentum transport (CMT) in tropical oceanic convective cloud systems plays a significant role in the tropical mean circulation and transient variability. CMT is difficult to measure directly and can depend on the detailed structure and organization of the convection. Yet there have been comparatively few evaluations of CMT parameterizations and the assumptions underlying them using 3D cloud resolving model (CRM) simulations. We have analyzed CMT in a four month 3D 64x64x64 gridpoint CRM simulation of TOGA COARE with 1 km horizontal resolution. An additional 256x256x64 large-domain simulation was performed for a 10 day subperiod with strong convection combined with substantial mean vertical zonal wind shear, conditions favorably for strong CMT. Both simulations were identically forced with prescribed vertical motion, horizontal temperature and moisture advection, and relaxation of the domain-mean wind profile to observations on a one-hour timescale. Both were initialized with small amplitude white noise, but spun up realistic convection in less than a day. The domain-mean CMT in the small and large domain simulations for the 10-day common simulation period was compared. The two simulations showed remarkably similar CMT profiles on daily-mean timescales, suggesting that mesoscale contributions to CMT of scales greater than 64 km were small. The skill of a downgradient mixing-length parameterization CMT = Mc*L*DU/Dz was also tested. Here , Mc is convective mass flux, dU/dz is mean vertical shear, and L is a mixing length for updraft zonal velocity perturbations associated with entrainment and horizontal pressure gradient accelerations. This was done by regressing CMT at each height was regressed against Mc*DU/Dz at the same height across all 3D model snapshots over the 10 days. The correlation coefficient describes the accuracy of this downgradient parameterization, and L was calculated as the regression slope. In the upper troposphere (above 6 km), a good linear fit was obtained with L around 1.5 km, but in the mid-troposphere (3-5 km altitude). Binning methods to understand the relative contributions of unsaturated air, saturated updrafts and saturated downdrafts, and principal component analysis of the CMT profiles over the full 120-day record are in progress and will be also reported on.
A21E-0784
Upper Tropospheric Water Vapor Variation Over Asian Monsoon During Northern Summer 2007
The observation of water vapor by the balloon-borne hygrometer, Snow White (hereafter SW; purchased from Meteolabor Inc.), was conducted at the Bangladesh Meteorological Department in Dhaka (90.23°E, 23.43°N, 9mSL) from March to July of 2007 in order to quantitatively investigate the upper tropospheric water vapor variation during the Asian summer monsoon. The six and four radiosondes (Vaisala RS80 and RS92) with SWs were launched in the pre-monsoon (March-May) and monsoon (June-July) periods, respectively. The launch time was approximately 12:30 LST. The upper tropospheric water vapor data for quantitative discussion was obtained by all of the radiosonde measurements except for two. The averages of tropopause temperature and humidity in the pre-monsoon period were higher (~ 1 K) and moister (~ 2 ppmv) than those in the monsoon period because the active convections occurred more frequently during the pre-monsoon period. During the middle of pre-monsoon period when the westerly jet moved southward to Bangladesh, the middle and upper tropospheres were quite dry (< 20 %) and the convections were suppressed. In conclusions, the upper tropospheric water vapor is closely related to the activities of localized convections and westerly jet which is a north part of monsoon circulation, especially during the pre- monsoon period. In the presentation, the comparisons of observational data from SW, H-Humicap from RS80 and RS92 and satellite observations (EOS MLS and AIRS) and the water vapor variation over the Asian monsoon region inferred from the satellite observations will also be discussed.
A21E-0785
HDO:H2O ratios in the tropical UTLS from the ACE-FTS
HDO and H2O profiles can provide constraints on the role of convection, slow ascent and descent and the evaporation of precipitation on the water budget. The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) has recorded high spectral- and vertical-resolution profiles throughout the tropics since 2003. We will present HDO and H2O profiles retrieved from spectra measured by the ACE-FTS in the tropics, and will compare these results to the ACE version 2.2 retrievals and the GISS ModelE.
A21E-0786 [WITHDRAWN]
A Global Mass Circulation Paradigm for the Stratosphere-Troposphere Coupling
Using the NCAR/NCEP reanalysis, we here present evidence suggesting that the out-of-phase relationships of temperature anomalies both between the low and high latitudes and between the stratosphere and troposphere are intimately related to the meridional and downward propagation of anomalies of both signs. The temperature anomalies propagate poleward and downward above the tropopause and propagate equatorward below the tropopause. The characteristic time scale for anomalies of one polarity to propagate from the equator to the pole (or the half period of the complete cycle) is about 40-70 days. The relatively slow meridional propagation helps to explain the well-known seesaw oscillatory pattern between low and high latitudes found in monthly data. The equatorward propagation in the troposphere is synchronized with the poleward propagation of the stratospheric temperature anomalies of the opposite sign in both low and high latitudes, responsible for the out-of-phase relation between the stratospheric and tropospheric temperature anomalies in the polar region. Accompanied with warm (cold) anomalies is a successive levelling (steepening) of isentropic surfaces propagating poleward and downward. The zonal wind anomalies follow the poleward and downward propagating temperature anomalies of the opposite sign. A global mass circulation paradigm is proposed to qualitatively explain the simultaneous meridional and downward propagation of circulation anomalies that appears responsible for the annular mode variability. The global mass circulation paradigm also relates the stratosphere-troposphere coupling in the extratropics to heating anomalies in the tropics via the tropical-extratropical coupling in the stratosphere. When the mass circulation is weaker, the isentropic surfaces in the extratropical stratosphere (troposphere) are steeply (gently) sloped, corresponding to the positive phase of the annular mode. The cold air mass is effectively imprisoned within the polar cap when the mass circulation is weaker, responsible for warm surface temperature anomalies prevailing in the extratropics. Meantime, the weaker mass circulation also implies a temporary reduction of air mass supply over the polar cap, leading to a negative surface pressure anomaly. The warm anomalies brought by the stronger mass circulation cause a lowering of isentropic surfaces in the polar stratosphere, resulting in more gently sloped isentropic surfaces in the extratropical stratosphere. This corresponds to the negative phase of the annular mode in which the meridional temperature gradient in the extratropical stratosphere is weaker accompanied with a weakened polar jet and a falling of the tropopause. The stronger warm air branch of the mass circulation aloft requires a strengthening of the compensating equatorward advancement of the surface air mass, causing massive cold air outbreaks in the extratropics. The more air mass aloft brought by the stronger mass circulation contributes to a rising of the surface pressure over the polar cap till the surface cold air moves out. This explains why the surface pressure anomalies in high latitudes are positive during the negative phase of the annular mode.
A21E-0787
Rayleigh Lidar study of upper stratospheric thermal structure and long term trends over a sub-tropical station Mount Abu (24.5o N, 72.7o E, MSL height 1.7 Km)
Stratosphere plays very vital role in deciphering various geophysical phenomena taking place in the Earth's atmosphere. It is also a well known reservoir of ozone which protects us from the hazard of the UV radiation emanating from the Sun. For more than two decades, Rayleigh Lidar has become a dynamic atmospheric probe for providing height profile of temperature in the middle atmospheric region. A Nd: YAG laser based Rayleigh Lidar was set up, at a high altitude observatory near Mount Abu (24.5o N, 72.7o E, altitude1.7 km), in the Indian sub-tropical region, to study the Earth's neutral atmospheric temperature structure. The system is transmitting pulses of 7 ns duration at a frequency of 10 Hz with average power about 350 mJ at 532 nm. For the study of temperature climatology in the stratosphere, we have used the Rayleigh lidar data collected for about seven years from 1997 to 2003. The temperature profiles are derived from photon count profiles followed by Hauchecorne and Chanin (1980). The systematic and statistical errors in deriving temperature are found to be less than ~1 K below 50 km. The monthly mean temperature profiles obtained are compared with three different model atmospheres (CIRA-86, MSISE-90 and Indian low latitude model). Below the stratopause, model temperatures are in agreement with the observed values. To study the year to year variability, mean monthly temperature profiles have been estimated for different years. The variability is least around 40-50 km with a value of 5 K. The mean stratopause height and its temperature are found to be 48 km and 270 K respectively. Interesting features, like the double stratopause structure around 40-52 km has also been found. For the study of long term changes in the thermal structure of the Stratosphere, consistently good data series for 1997-2006 has been investigated. Monthly mean temperature profiles for each month individually have been used to remove seasonal variability. A multivariable analysis is used to consider natural variability (Solar Cycle and QBO) and similarly the changes in stratospheric ozone concentration due to anthropogenic activity have also been taken into account in trends estimations. We have selected different height regions 36-40, 41-45 and 46-50 km for trends analysis. Linear Regression analysis is applied to calculate temperature trend in different altitude regions. Considering the imprints of seasonal, QBO and solar cycle variability, a linear decreasing temperature trend in stratospheric temperature has been found using the data from 1997-2006. In this paper, long term trends in temperature at a subtropical high altitude station will be presented and discussed.
A21E-0788
Observation of quasi-biannual oscillation (QBO) in ozone concentration and its implication in the tropopause temperature over Banchio (24.44 N 121.45 E), Taiwan
Abstract: We have studied the characteristics of tropopause for 21 years (1985-2005) and ozone concentration for 14 years (1992-2005) over Banchio (24.44 N, 121.45 E), Taiwan by using radio and ozone sonde measurements, respectively. The observation reveals that the annual oscillation is dominating in cold point tropopause (CPT) height, whereas quasi-biannual oscillation (QBO) is dominating on CPT temperature. Further analysis shows there is no direct correlation between tropopause height and temperature in terms of oscillation. In the present study, we have tried to explain the causative mechanism for the presence of different oscillating nature in tropopause height and temperature by using ozone concentration and out going long wave radiation (OLR) in light of present understanding. The OLR data has been taken from NCEP/NCAR Reanalysis monthly means. The details will be discussed and presented in the conference.
A21E-0789
Effects of volcanic eruptions on temperatures near the tropical tropopause: A model-data comparison
Although the volcanic eruption of El Chichon produced a clear warming at the tropical tropopause, there is a surprising lack of warming after the Pinatubo eruption in both radiosonde and reanalysis data. Here we compare the response at 100 mb in the tropics in radiosonde data to the response in 20th century runs from six models in the AR4 model archive. The models all show substantial warming after Pinatubo, similar to that shown in models and data after El Chichon. Most models also overestimate the stratospheric warming after Pinatubo, but even those that underestimate the response at 50 mb show significant warming at 100 mb. In the mid-troposphere, the models appear to underestimate the extent of amplification of surface cooling after the eruptions. Possible causes of these differences include changes in ozone and water vapor following the eruption, which were not included in the AR4 model runs, as well as interannual variability from the QBO or ENSO. We investigate the effects of these differences on temperature trends.
A21E-0790
Comparison of CHAMP Radio Occultation Climatologies of the UTLS to Operational ECMWF Analyses and Forecasts
In recent years radio occultation (RO) data have become an integral part of monitoring the atmosphere because of their high vertical resolution, high precision (<0.5 K), and inter-comparability between different satellite missions. Data from the CHAllenging Minisatellite Payload (CHAMP) satellite are now available for more than six years providing the first opportunity to create RO based climatologies. We present temperature climatologies and systematic differences of selected seasons compared to operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). In general, we find good agreement with systematic differences below 0.5 K. Exceptions are: altitudes above 30 km, where CHAMP climatologies are about 1 K warmer than ECMWF analyses; the austral winter polar vortex where deviations of more than ±3.5 K exist; and the tropical tropopause region which is up to 2 K colder in the ECMWF analyses until the beginning of 2006 due to limitations in resolution of the analyses. Here we present first results of CHAMP climatologies compared to ECMWF climatologies obtained from 24 hrs and 36 hrs forecast files. Within this time the forecasts are expected to have uncoupled from the initial analyses still representing a physically reasonable state of the atmosphere but presumably free of biases of the analysis. In turn, deviations of RO climatologies compared to ECMWF forecasts are expected to decrease considerably. Additionally, since mid-December 2006 RO data of various satellites including the CHAMP satellite are assimilated into ECMWF operational analyses rendering these not anymore independent from RO data. (CHAMP RO climatologies presented for the year 2007 are thus referenced to forecast fields.)
A21E-0791
Sensitivity of the climatic impact of Mt. Pinatubo eruption to the phase of the Quasi Biennial Oscillation
The quasi-biennial oscillation (QBO) is the dominant mode of variability in the equatorial stratosphere. Planetary wave activity is much less in the easterly phase of the QBO compared to the westerly phase. These different phases of the QBO have different effects on the stratospheric extratropical circulation. Here, we try to evaluate the sensitivity of the effect of large volcanic eruptions on the high latitude circulation to the QBO phase. Mt. Pinatubo erupted on June 15, 1991 during the easterly phase of the QBO at 30 hPa and the change to the westerly phase took place in Aug 1992 at 30 hPa and remained in the same phase till May 1993. It would be interesting to understand the climate impact of Mt Pinatubo eruption if it had erupted during the opposite shear. Here, in this study, a sensitivity analysis is carried out to understand the effect of the QBO phase on the response of the extratropical circulation to the Mt. Pinatubo eruption. For this, the middle atmosphere version of the general circulation model (MA)ECHAM5.4 is employed to carry out ensemble simulations for two years (June 1991 - May 1993) following the eruption. Two sets of experiments were performed - one with the QBO in the phase as observed and the other with an opposite QBO phase. The model is forced by zonally averaged values of aerosol extinction, single scattering albedo and asymmetry parameter and volcanically induced ozone anomalies. The differences in the responses will be discussed. The model is able to simulate the tropical and extratropical responses to Mt. Pinatubo eruption most realistically when all the known processes are included.
A21E-0792
Kinetics of HO2 reactions in the upper troposphere and lower stratosphere
Reaction kinetics of HO2 complexes with small organic molecules are investigated at conditions relevant to the upper troposphere and lower stratosphere (UTLS). At the lower temperatures associated with higher altitudes, these HO2 adduct species can play a significant role in kinetic mechanisms. Using a turbulent flow tube reactor capable of operating at temperatures as low as 200 K and pressures ranging from 60 to 200 Torr we have been able to improve the understanding of HO2 kinetics in the UTLS. An elementary reaction rate mechanism for HOx and single carbon species has been constructed to both guide experiments and interpret the results. Previous ab initio studies have determined that there is a potentially significant pathway from the reaction of the HO2•H2O adduct with HO2 to form O3 and 2 H2O. An upper bound on this proposed ozone branching ratio has been measured at conditions relevant to the UTLS. The reaction network of HO2 + HCHO has been explored as well and the rate of HCOOH formation has been measured at a range of temperatures and pressures.
A21E-0793
Mountain Wave Propagation Across the Tropopause
Using observations from the NSF/NCAR Gulfstream V and U. Wyoming King Air research aircraft in the Terrain- Induced Rotor Experiment, wave properties over the Sierra Nevada are analyzed for six cases with cross-barrier flow. Energy and momentum fluxes were compared to those predicted by existing theory and idealized model simulations. The Eliassen-Palm linear relation between momentum (MF) and energy flux (EF) was verified using the aircraft data. Spatial, Fourier, and wavelet techniques are employed to document spatial and temporal wave evolution and associated vertical fluxes. In one case (RF10), MF was found to vary as a function of height. The Eliassen- Palm relation stipulates that MF should be independent of height and this vertical variation of MF appears to be a violation of existing theory for a steady, upward propagating wave. In the case of RF10, systematically reversed momentum and energy fluxes were consistently found in the stratosphere above 12km. Spectral techniques also suggest the possible presence of a fluxless trapped wave riding just above the tropopause. Results are compared to known and modeled solutions for vertically propagating mountain waves. Secondary wave generation is examined as a possible result of wave breaking and interactions with the tropopause inversion layer.
A21E-0794
Correlating Polar Stratospheric Cloud Occurrence at the South Pole with Transport and Polar Geopotential Height Anomalies
In a recent paper, we describe the macrophysical and thermodynamic properties of polar stratospheric clouds (PSC) at the South Pole based on continuous eye-safe lidar measurements made over five seasons (2000, 2003-2006). In this paper, we describe the relationship between PSC occurrence and the propensity for transport within the austral polar vortex. The southern lower-stratospheric polar airmass may be approximated as a closed system from May to September. Saturation vapor pressures for background concentrations of sulfuric and nitric acid and water vapor are reached either through radiational cooling or isentropic lift. Once nucleated, PSC acquire fall-velocities that remove these compounds from these heights. Satellite measurements (e.g., MLS) depict the widening proximity of the depleted airmass through the polar night. Yet, our measurements show that PSC occurrence can occur up to 20 km late in the season, which suggests replenishment of these species in air originating near the edges of the vortex. We examine 120-h back-trajectories during July and August and temperature histories to identify conditions and circumstances favorable to this occurring. Furthermore, we describe geopotential height anomalies averaged along 60° - 90° S, and compared to a twenty-year mean, as a proxy for the dynamic character of the polar vortex. Negative/positive anomalies indicate a strong/weak and deep/shallow vortex where its circulation inhibits/promotes meridional transport, replenishment and the likelihood of PSC at South Pole. We test this hypothesis using our dataset and reach conclusions on the influence of the polar vortex on total PSC observed each season, which, in turn, may influence the severity of annual ozone losses.
A21E-0795
Experimental and theoretical investigations of the rate constant for the reaction of the hydroxyl radical with methyl ethyl ketone
Methyl ethyl ketone (MEK) or 2-butanone is a high-volume industrial solvent with a production rate greater than 70 million lbs yr-1. It is also a photo-oxidation product of several volatile organic compounds (VOCs) in the atmosphere. MEK is removed from the atmosphere primarily by its reaction with hydroxyl (OH) radical. As a result, knowledge of the chemical mechanism and temperature dependence of this reaction is important as MEK may be transported to the upper troposphere and influence the chemistry of this region of the atmosphere. We present absolute measurements of the rate constant and the kinetic isotope effect for the reaction of MEK with OH radicals at low pressure and over the temperature range 263-388 K using a discharge-flow technique coupled with resonance fluorescence detection of OH radicals. Theoretical studies of the potential energy surface suggest that the reaction of MEK and OH proceeds by H-abstraction mediated by the formation of a 7- membered hydrogen-bonded complex. This mechanism is similar to that of several other atmospherically relevant oxygenated VOCs such as acetone, acetic acid and hydroxyacetone. The influence of the pre-reactive complex on the temperature dependence for this reaction will be discussed.
A21E-0796
Hybrid Kriging Cubic Spline Interpolation Algorithm for Display of Global Airglow Measurements
A Kriging interpolation technique has been applied to two-dimensional data from SABER (Sounding of the Atmosphere using Broadband Emission Radiometry), a ten-channel infrared radiometer aboard NASA's TIMED (Thermosphere Ionosphere Mesosphere Energetics and Dynamics) satellite. These data are indicative of hydroxyl Meinel airglow emissions from the Earth's mesosphere. A hybrid Kriging cubic spline interpolation algorithm has been developed for the purpose of globally displaying the measurements. Kriging interpolation gives a minimum mean-squared error (MMSE) approximation for unknown data values using unevenly sampled spatial data points at specific latitude and longitude locations. Due to the great number of calculations and long processing time required to perform high-resolution Kriging interpolation, a hybrid technique was created which uses the Kriging estimates at a certain resolution as the input to another interpolator. A cubic-spline technique was then used to enhance the resolution of the overall image from the processed data. The hybrid interpolation technique performs well when compared with Kriging interpolation, and the processing time for each image is drastically reduced.
A21E-0797
Observation of Large Amplitude Inertial Gravity Waves and Their Link to the Upper Tropospheric Jet
We examined large amplitude lower stratospheric gravity wave events from radiosonde measurements conducted over a US mid-latitude site in winter. Using the combined hodograph and wavelet analysis, we derived the complete set of wave parameters and found that the waves had intrinsic frequency of 1.3-1.5 f (where f is the Coriolis parameter), vertical wavelength of 2.1-2.7 km, horizontal wavelengths of 400-500 km, and total energy density of up to 50 J/kg. Also, the intrinsic propagation directions were estimated to be toward the Northwest. The derived wave parameters allow us to trace the possible sources of the events using the ray-tracing technique. We concluded that the waves were very likely originated from the upper tropospheric jet exit region via the spontaneous imbalance mechanism. We also compared various diagnostic tools to quantify unbalanced flow, and compared our observations with existing model studies on inertial gravity waves generated from jet streaks.
A21E-0798
Protonation of Alcohols in Sulfuric Acid Solutions at UT/LS Conditions
The protonation of several small alcohols (ethanol, 2-propanol, and 1-butanol) in cold sulfuric acid aqueous solutions was measured using variable temperature 13C nuclear magnetic resonance (NMR) spectroscopy. The acidity of the sulfuric acid + deuterium oxide solutions ranged from 43 to 81 weight percent (wt %) H2SO4. The pKBH+ values, which are a measure of the acidity of each alcohol, range from -2.0 for butanol at room temperature to -2.2 for ethanol at -20°C. The protonation enthalpies of the three alcohols over the temperature range of 22°C to -35°C were found to be small and negative, ranging from -1.8 kJ mol-1 for 2-propanol to -2.3 kJ mol-1 for ethanol. A small, negative protonation enthalpy means that the degree of protonation of the alcohol slightly decreases as temperature decreases. The pKBH+values and protonation enthalpies are used to predict the form of dissolved alcohols in sulfate aerosols. For typical upper troposphere/lower stratosphere (UT/LS) conditions (40-70 wt % H2SO4 and 220 K), all three alcohols increase from approximately 10% protonated in 40 wt % H2SO4 to over 60% protonated in 70 wt % H2SO4. The percent of protonated alcohol depends more strongly on m*, the slope factor of the excess acidity treatment, than on pKBH+ values. This relationship may reflect solvation effects. The treatment of strongly acidic, non-ideal solutions as applied to organic solutes in sulfate aerosol particles will be discussed.
A21E-0799
Uptake and Reactions of Formaldehyde, Acetaldehyde, Acetone, Propanal and Ethanol in Sulfuric Acid solutions at 200-240 K: Implications for upper tropospheric aerosol composition
The production of light absorbing, organic material in aerosol that is normally considered to be transparent in the UV and visible wavelength regions has significant implications for biogeochemical cycling and climate modelling. Production mechanisms likely involve carbonyl compounds such as formaldehyde, acetone, acetaldehyde and propanal that are present in significant quantities in the upper troposphere (UT). In this study, we have performed experiments focusing on a class of acid catalyzed carbonyl reactions, the formation of acetals. R2C=O + 2R'OH --> R2C(OR')2 + H2O Using a Knudsen cell apparatus, we have measured the rate of uptake of formaldehyde, acetaldehyde, acetone, propanal, and ethanol into sulfuric acid solutions ranging between 40-70 wt% of acid, containing 0-0.1 M of ethanol, acetone or formaldehyde at temperatures of 220-250 K. For all reactant pairs, the aldol condensation path, including self reaction, should be insignificant at the acidities studied. Evidence for reaction between organics was observed for all pairs, except those involving propanal which were likely limited by the very low solubility. We attribute enhanced uptake to the formation of acetals, such as 1,1-diethoxyethane and 2,2- diethoxypropane, among others. Enhanced uptake was observed to proceed on timescales > 1 hour and sometimes shows complex dependence on acidity that is likely related to speciation of the individual carbonyls in acidic solution. The acetal products do not absorb in the visible but are less volatile than parent molecules, allowing for accumulation in sulfuric acid particles, and enhanced uptake. Cross reactions of carbonyls with alcohols in sulfuric acid medium have not been previously measured, yet methanol and ethanol show high solubility and are present at significant concentrations in the UT. Thus even at slow reaction rates, the acetal reaction has ample starting material and proceeds under conditions common to the UT. We will present results for the enhanced uptake of carbonyls in the presence of alcohols, derive rate constants, and discuss the atmospheric impact of the acetal reaction path.
A21E-0800
Cirrus Clouds, Equatorial Kelvin Waves and Dehydration in the Tropical Tropopause Layer
A number of field-campaigns in the tropics have been conducted in the past years with the mobile LIDAR systems MARL and ComCAL of the Alfred Wegener Institute aboard the research vessel Polarstern in the tropical Atlantic and at Paramaribo in Suriname. The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). We investigated the occurrence of clouds in the TTL with a newly developed trajectory model and found that ice particles form in slow ascent and efficiently dehydrate the air. The Lagrangian temperature history thus defines the water vapour transported to the stratosphere in the tropics. Radiosonde as well as ECMWF operational analysis data show a strong influence of eastward moving equatorial Kelvin waves on the temperature at the tropical cold point tropopause (CPT). We find a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus. This finding suggests an influence of Kelvin wave activity on the dehydration characteristics of the TTL
A21E-0801
Laboratory Growth of Ice Crystals Under Simulated Polar Stratospheric Cloud and Upper Tropospheric Conditions at Temperatures Below -70 C
A static diffusion chamber has been used to grow ice crystals at temperatures between -70 C and -85 C under controlled conditions of temperature, pressure, and ice supersaturation. Growth conditions for Type 1 polar stratospheric cloud and tropical cirrus particles have been simulated. Linear, projected area, and volume growth rates are presented. Martian ice crystal simulations may also be presented.