A31D-01
Chemical Isolation in the Asian Monsoon Anticyclone observed in Atmospheric Chemistry Experiment (ACE-FTS) data
Evidence of chemical isolation in the Asian monsoon anticyclone is presented using chemical constituents obtained from the Atmospheric Chemistry Experiment Fourier Transform spectrometer instrument during summer (June-August) of 2004-2006. Carbon monoxide (CO) shows a broad maximum over the monsoon anticyclone region in the upper troposphere and lower stratosphere (UTLS); these enhanced CO values are associated with air pollution transported upward by convection, and confined by the strong anticyclonic circulation. Profiles inside the anticyclone show enhancement of tropospheric tracers CO, HCN, C2H6, and C2H2 between ~12 to 20 km, with maxima near 13-15 km. Strong correlations are observed among constituents, consistent with sources from near-surface pollution and biomass burning. Stratospheric tracers (O3, HNO3 and HCl) exhibit decreased values inside the anticyclone between ~12-20 km. These observations are further evidence of transport of lower tropospheric air into the UTLS region, and isolation of air within the anticyclone. The relative enhancements of tropospheric species inside the anticyclone are closely related to the photochemical lifetime of the species, with strongest enhancement for shorter lived species. Vertical profiles of the ratio of C2H2/CO (used to measure the relative age of air) suggest relatively rapid transport of fresh emissions up to tropopause level inside the anticyclone.
A31D-02
Lagrangian Diagnostics of Tropical Deep Convection and its Effect Upon Upper-Tropospheric Humidity
This study combines geostationary water vapor imagery with optical cloud property retrievals and microwave sea surface observations in order to investigate in a Lagrangian framework (i) the importance of cirrus anvil sublimation on tropical upper-tropospheric humidity, and (ii) the sea surface temperature dependence of deep convective development. Although an Eulerian analysis shows a strong spatial correlation of 0.8 between monthly mean cirrus ice water path and upper-tropospheric humidity, the Lagrangian analysis indicates no causal link between these quantities. The maximum upper-tropospheric humidity occurs approximately 5 hours after peak convection, closely synchronized with the maximum cirrus ice water path, and lagging behind it by no more than 1.0 hour. Considering that the characteristic e-folding decay time of cirrus ice water is determined to be about 4 hours, this short time lag does not allow for significant sublimative moistening. Furthermore, a tendency analysis reveals that cirrus decay and growth - in terms of both cloud cover and integrated ice content - is accompanied by drying and moistening of the upper troposphere, respectively, a result opposite that expected if cirrus ice were a primary water vapor source. In addition, it is found that an 2 degree-C rise in sea surface temperature results in a measurable increase in the frequency, spatial extent, and water content of deep convective cores. The larger storms over warmer oceans are also associated with slightly larger anvils than their counterparts over colder oceans; however, anvil area per unit cumulus area, that is, cirrus detrainment efficiency decreases as SST increases.
A31D-03
Analysis of Overshooting Convection in the Tropics Using ISCCP B1 Data
The ISCCP B1 satellite data is sub-sampled in time and space to 3-hour and 10km resolutions, making it useful in the detection of overshooting convection and its role in upper tropospheric and lower stratospheric (UT/LS) water vapor exchange. The geostationary satellite infrared radiances in the IR window at 11µm and the water vapor absorption band at 6.7µm have been inter-calibrated against channels 8 and 12 of NOAA-17/HIRS and converted to brightness temperatures. Data from these two channels are used to perform an analysis of overshooting cloud tops in the global tropical band between 15N and 15S for the period June 2006 through May 2007 using the Schmetz et. al (1997) approach. The temporal and spatial distribution of overshooting cloud top events will be presented and analyzed in the context of the UT/LS water vapor exchange.
A31D-04 INVITED
The effects of convective ice lofting on H2O and HDO in the tropical tropopause layer
We have derived a climatology of TTL-penetrating convective events from measurements of Ice-water content (IWC) from the Microwave Limb Sounder onboard NASA's Aura spacecraft. Using this climatology, we have added convective ice lofting to a Lagrangian trajectory model of TTL water vapor (H2O) and its stable isotopologue, HDO. The Lagrangian model has been previously shown to accurately simulate H2O in the TTL and lower stratosphere. We show here that the model without convective lofting does a poor job reproducing the observed HDO depletion (dD) in the TTL. When convective ice lofting to altitudes below the cold point (the point where air experiences its lowest H2O saturation mixing ratio) is added to the model, there is little change in H2O in the lower stratosphere, but a large change in dD throughout the TTL that brings the model into better agreement with measurements. Thus, convective ice lofting has the capacity to improve the model's dD simulation while not significantly degrading the agreement between simulated and measured H2O. Convective ice lofting to altitudes above the cold point, on the other hand, has a large effect on lower stratospheric H2O, suggesting that changes in convection reaching these altitudes could drive changes in lower stratospheric H2O. This suggests a mechanism by which lower stratospheric H2O trends may be at least partially decoupled from tropopause temperature trends. Such a disconnection was suggested by previous observations of simultaneously increasing stratospheric H2O and a cooling tropical tropopause.
A31D-05
Using CALIPSO and MLS Data, Along With in Situ Isotope Measurements, to Constrain Simulations of TTL Transport, Cloud Formation, Dehydration
Recent datasets produced by satellites and airborne science campaigns provide unprecedented, detailed information about clouds, water vapor, and water vapor isotopes in the tropical tropopause layer (TTL). We now have, for the first time, data products that can adequately constrain detailed numerical simulations of TTL transport, water (condensed and vapor), and isotopes. We will use comparisons between observed and simulated cloud, water vapor, and isotope fields to address several outstanding science questions: Are high supersaturations in the TTL indicated by in situ measurements consistent with the cloud frequency and regional distribution indicated by CALIPSO? Is injection by deep convection an important source of TTL water and clouds (particularly above the cold point)? How do TTL vertical ascent rates (ranging from relatively slow ascent indicated by radiative transfer calculations to relatively rapid ascent indicated by CO2 tracer clock calculations) affect the comparison between simulated and observed TTL fields? How important are small-scale gravity waves for reproducing the regional cloud distributions in the TTL indicated by CALIPSO?
A31D-06
A Satellite Analysis of the Evolution of Tropical Deep Convection, Upper Tropospheric Clouds, and Humidity
The ability of the Earth to regulate its energy budget is strongly dependent on the concentration of water vapor in the atmosphere. Increases in humidity at upper levels of the troposphere have a greater radiative impact on the climate than equivalent increases closer to the surface. In this study, I investigate the evolution of the moisture and cloud distribution in deep convective systems over the tropical Pacific using retrievals of water vapor, temperature, and cloud properties from AMSR-E, AIRS, and MODIS. Using a compositing technique centered in space and time on locations having high rain rates, I have identified systematic lags in both the fractional coverage of anvil clouds and in the moistening of the upper troposphere following peak convection. Anvil cloud fractions peak 3 hours after the strongest convection while the upper troposphere is most humid 9-15 hours following the strongest convection. Composited vertical velocity profiles from the ERA-40 Reanalysis show anomalous ascent in the upper troposphere following peak convection, which likely has a role in sustaining the moist signature aloft. Correspondingly, clear-sky outgoing longwave radiation remains significantly reduced for several hours after the convection, indicating that the sustained moist anomaly at upper levels continues to affect the local radiation budget well after the convective event.
A31D-07
Cirrus Observations in the Tropical Tropopause Layer Over the Western Pacific
Cirrus clouds in the tropical tropopause layer (TTL), between 14 and 17 km, are keys for the dehydration of the air entering the stratosphere and for the Earth's radiation budget. In this presentation, we will discuss three-campaign results of ship-borne lidar measurements over the western Pacific, in relation to large-scale dynamics and transport. A polarization lidar was continuously operated on the Japanese research vessel MIRAI in three one-month campaigns. The locations and time periods are: 2.0N, 138.0E, 9 Nov. to 9 Dec. 2001 (MR01); 2.0N, 138.5E, 15 Nov. to 14 Dec. 2002 (MR02); and 7.5N, 134.0E, close to Palau, 14 Dec. 2004 to 11 Jan. 2005 (MR04). Three hourly intensive radiosonde soundings were also made on the vessel during all these campaigns. In the MR01 campaign, the tropopause region was cold, but the TTL was often clear with some Sub-Visual Cirrus (SVC). Potential vorticity data (with RDF method) and trajectories show that the TTL in this period was strongly affected by dry air transport from the northern mid-latitude lower stratosphere. In the MR02 campaign, a packet of large-amplitude Kelvin waves primarily controlled the generation and disappearance of cirrus in the TTL. In the MR04 campaign, a cold phase of Kelvin waves resulted in cirrus generation in the TTL, and outflow from the SPCZ also caused optically very thick TTL cirrus in early January 2005. A clear diurnal variation of TTL cirrus, an apparent descending motion at night, was also observed in early January 2005.
A31D-08
Equatorial Waves in the Lower Stratosphere Observed by the High Resolution Dynamics Limb Sounder
Previous studies have shown Kelvin waves detected in radiosonde and GPS profiles modulate the climatological tropopause temperature structure. Temperature fluctuations caused by equatorial waves of all scales are also important components in determining the observed frequency and geographical distribution of tropical cirrus cloud formation. The High Resolution Dynamics Limb Sounder (HIRDLS) provides observations of wave-induced temperature fluctuations over a broad range of horizontal and vertical scales. Zonal modes with wavenumbers 1- 8 and small-scale gravity waves with 200 km along-track wavelengths are resolved by HIRDLS with fine 1.2 km vertical resolution. HIRDLS is an infrared limb-scanning instrument that can observe wave structures in the middle atmosphere down to cloud-top altitudes. The resolution is higher than previous satellite limb scanning techniques with the exception of GPS. HIRDLS and GPS have very different horizontal sampling characteristics: HIRDLS has 1-degree meridional resolution near the equator with 24-degree spacing between orbits and typically 650 profiles per day in the 10S-10N latitude band. GPS in comparison samples randomly, and the previously analyzed combined SAC-C and CHAMP data sets in 2001-2002 gave 20-30 profiles per day between 10S-10N latitudes. We will report on the properties of equatorial waves observed by HIRDLS in the lower stratosphere, with special emphasis on Kelvin waves and the annual cycle.