A51A-0737 0800h
Effects of ozone, cloud and snow surface on surface UV irradiance
Total solar irradiance(TSO), total UV irradiance(TUV) and erythemal UV irradiance(EUV) measured at King Sejong station($62.22\deg$S, $58.78\deg$W) in west Antarctica have been used together with total ozone, cloud amount and snow cover to examine the effects of ozone, cloud and snow surface on these surface solar irradiance over the period of 1998$\sim$2003. The data of three solar components for each scan normalized to the mean Sun-Earth distance(1AU) were grouped by cloud amount, n in oktas(0$<=$n$<$3, 3$<=$n$<$4, 4$<=$n$<$5, 5$<=$n$<$6, 6$<=$n$<$7 and 7$<=$n$<=$8) for the solar zenith angle(SZA) over the range of $45\deg$ to $75\deg$. The radiation amplification factor(RAF) is used to quantify ozone effect on EUV. RAF of EUV decreases from 1.51 to 0.94 under clear skies but increases from 0.94 to 1.85 under cloudy skies as SZA increases. It decreases from 1.51 to 1.01 as cloud amount increases. The effects of cloud amount and snow surface on EUV are estimated as a function of SZA and cloud amount after the normalization of the data to the reference total ozone of 300 DU. In order to analyze the transmission of solar radiation by cloud, regression analyses have been performed for the maximum values of solar irradiance on clear sky conditions(0$<=$n$<$3). On cloudy conditions the maximum and minimum transmission can be regarded as thin and thick cloud covers, respectively. The maximum regression values for the clear sky cases were taken to represent minimum aerosol conditions for the site and thus appropriate as a normalization(reference) factor for the other regressions. In comparison with the three components of the solar irradiance under thin and thick cloud covers, it is found that the transmission is the largest in TUV and the smallest in TSO among the three components of the solar irradiance for the specific SZA. We also noted that the transmission by thin cloud covers is enhanced significantly due to multiple scattering and reflection by the clouds. The relative difference between snow surface and snow-free surface in EUV slowly increases from $9%$ to $20%$ as total ozone increases from 100 DU to 400 DU under partly cloud conditions(3$<=$n$<$6) at SZA $60\deg$. The snow effects on TUV and TSO are relatively high with $32%$ and $34%$, respectively, under clear sky conditions, while the effects changes to $36%$ and $20%$ for TUV and TSO, respectively, as cloud amount increases.
A51A-0738 0800h
Radiative Effects of Stratus Cloud Subgrid Scale Variability Observed by MODIS
Marine boundary layer are important to the planetary energy balance because they cover large regions of the oceans and possess an albedo that is considerably larger than underlying ocean surface. General circulation models (GCM) typically ignore the horizontal variability of cloud liquid water path within these clouds, and previous studies differ on the importance that this variability has on the solar albedo and, therefore, its possible impact on the simulated climate. We use MODIS cloud retrievals for five prominent stratus regions to resolve this issue. The parameters for this study are obtained from a companion study that analyzes 4 years of MODIS cloud properties (see presentation by Vogelmann et al.). For each scene with the area of a GCM gridbox, the probability density function of the MODIS pixel-scale optical depths is fit using a gamma distribution. Radiative transfer calculations using DISORT are used to determine the differences in cloud albedo when the variability is treated versus when it is ignored. We find that, when the cloud regions are carefully screened, the effects of the albedo differences are generally small and ignoring the variability in models does not present a large radiative effect.
A51A-0739 0800h
Parameterization of radiative properties of cirrus clouds
The goal of this work is to parameterize the bulk scattering properties of ice clouds in the spectral range from 0.2 to 99 microns, that is, from the ultraviolet to the far-infrared. To this end, a database has been developed of single scattering properties for six ice crystal habits (hexagonal solid and hollow columns, aggregates, plates, three-dimensional bullet rosettes, and droxtals). For ice crystals with size parameters smaller than 15, the scattering properties are computed by using the finite-difference time domain method. For larger ice crystals, the composite method is used, and is based on a combination of an improved geometric optics method and an equivalent Lorenz-Mie solution. Ice crystal habit mixtures are determined from analysis of in situ data obtained from several field campaigns. The in situ data consist of particle size distributions, ice water content, and median mass diameter. Instead of using a fixed habit mixture for all the size distributions obtained from in situ sampling, a habit mixture is determined for each size distribution to minimize differences between the calculated (from ice crystal models) and inferred (from in situ measurements) ice water content and median mass diameter values. Based on the inferred habit mixtures, a mean habit mixture ratio is formed. We will show that the statistical scattering properties of the habit mixture ratios for mid-latitude cirrus (FIRE-I, FIRE-II, and ARM IOP) are quite different from the ice clouds sampled during polar and tropical region field campaigns. Based upon these mixture ratio distributions and the single scattering property database, the radiative properties of ice clouds are parameterized as functions of effective size, ice water content and spectral band. Furthermore, the parameterization is implemented in several radiative transfer schemes commonly used in climate models.
A51A-0740 0800h
Effective Mueller Matrix for Light Scattering by ice Clouds Using the Monte Carlo Method
The effective Mueller matrix is obtained using a Monte Carlo method developed by Kattawar, Tynes and Adams. Five ice crystal habits are considered with varying percentages within ice clouds (obtained from previous studies) in the tropics and middle latitudes. Averaging of the single scattering properties, including size distribution, of these habits at wavelengths 0.532 um and 1.064 um is performed using Yang and Liou's improved geometrical-optics method. Sensitivity of the effective Mueller matrix to ice crystal habit is investigated using the radiative transfer code.
A51A-0741 0800h
Estimation of Dynamical Parameters in Atmospheric Data Sets
In this study a new technique is used to derive dynamical parameters out of atmospheric data sets. This technique, called the structure tensor technique, can be used to estimate dynamical parameters such as motion, source strengths, diffusion constants or exponential decay rates. A general mathematical framework was developed for the direct estimation of the physical parameters that govern the underlying processes from image sequences. This estimation technique can be adapted to the specific physical problem under investigation, so it can be used in a variety of applications in trace gas, aerosol, and cloud remote sensing. The fundamental algorithm will be extended to the analysis of multi-channel image sequences and to provide solutions to the extended aperture problem. In this study sensitivity studies have been performed to determine the usability of this technique for data sets with different resolution in time and space and different dimensions.
A51A-0742 0800h
Improvement of Madden-Julian Oscillation Simulation in NCAR CCM3
The Madden Julian Oscillation (MJO) is the most prominent mode of intraseasonal variations in the tropical region. It plays an important role in climate variability and has a significant influence on medium-to-extended range weather forecasting in the tropics. Since its discovery by Madden and Julian over three decades ago, MJO has continued to be a topic of significant interest due to its complex nature and the wide range of phenomena it interacts with. In contrast to observational studies, the progress in numerical simulations of MJOs is much slower, particularly in global climate models (GCMs). GCMs have had difficulty in simulating the observed characteristics of the MJO. Recently, we revised the Zhang-McFarlane convection scheme in the NCAR CCM3 to address the model's deficiency in simulating the intraseasonal variability and MJO. In comparison with the observation and the standard CCM3 simulation, we find that the revised Zhang-McFarlane scheme produces a much-improved simulation of the intraseasonal variability and MJO. For instance, the surface wind and precipitation patterns in the composite MJO simulated by the revised Zhang-McFarlane scheme are in the better agreement with the observations than the standard CCM3 in many important aspects, including the amplitude and eastward propagation characteristics. Examination of convective heating from both deep and shallow convection indicates that near the mature phase of the MJO, shallow convection develops ahead of the deep convection. This is consistent with the recent observations and theoretical development that shallow convection helps to precondition the atmosphere for MJO by moistening the lower troposphere.We are currently investigating the possible mechanisms of the MJO in the model to understand what is responsible for the improved simulation of the MJO. Details will be presented at the meeting.
A51A-0743 0800h
MEASUREMENT OF HEAT, MOISTURE AND MOMENTUM FLUXES USING FLUX \- GRADIENT METHOD AND BOWEN \- RATIO METHOD.
Using a set of data from Nigeria Micrometeorological Experiment \(NIMEX\-\1\) recently conducted between 15th February and 10th March, 2004 at a tropical field site in Ile\-\Ife \(7.55o N, 4.56o E\), in the south-western Nigeria, Bowen Ratio and Flux\-\Gradient methods were used to calculate heat, moisture and momentum turbulent fluxes in the surface layer. The profile measurements of temperature, moisture and wind up to 15metres height using sensitive instruments such as cup anemometers, Frankenberger\-\type psychrometers and a windvane were sampled at every second and stored as 1 minute averages. The turbulent fluxes of heat, moisture and momentum were measured directly using eddy covariance system consisting of an ultrasonic anemometer and a krypton hygrometer \(sampled at 16Hz and 8 Hz respectively\) . The results obtained using the two methods mentioned above showed good agreement in the turbulent fluxes measured. There was also no significant difference when compared with the turbulent fluxes obtained from the ultrasonic and krypton hygrometer results.
A51A-0744 0800h
Modeling daily and seasonal relationships between air and ground temperatures using a time-dependent thermal diffusivity in the shallow subsurface
Subsurface temperatures have been inverted to reconstruct temperature histories at the ground surface on centennial time scales. These ground surface temperature (GST) histories in turn have been used to estimate SAT changes at times prior to instrumental records, assuming close coupling between SAT and GST at long time scales. This assumption has been the subject of some debate because ground temperatures in the upper few meters of the subsurface are influenced not only by SAT, but also by insulating effects of winter snow cover, latent heat effects associated with winter ground freezing and spring thawing, and summer evapotranspiration. Here we describe a simple way of accounting for these effects in terms of a time-dependent thermal diffusivity in the upper meter of the subsurface. The thermal diffusivity, defined as the ratio of the thermal conductivity to the volumetric heat capacity, is parameterized in terms of daily SAT, precipitation, and snow cover. The insulating effect of snow cover is equivalent to a reduction of the thermal conductivity, whereas latent heat effects are equivalent to an increase of the volumetric heat capacity; both lead to a reduction of the thermal diffusivity. We model subsurface temperatures by driving the subsurface with the SAT as the surface boundary condition, along with a variable diffusivity in the upper meter of the subsurface that changes according to daily precipitation, snow cover and SAT. We illustrate the method by comparing observed and calculated temperatures, using observational data from Fargo, North Dakota for 1981-82 and 1982-83, two very different meteorological years at this site. The time-dependent diffusivity model accurately simulates the observed temperatures in both of the years investigated, and performs significantly better than a model in which a single diffusivity is used for all depths and at all times. Because the time-dependent diffusivity model is parameterized in terms of archived meteorological variables, it shows promise as a means of investigating relationships between GST and SAT at long periods, the timescale relevant to the question of how well a GST history represents the SAT history.
A51A-0745 0800h
Seasonal Difference of Air Parcels Arriving at the Japan Area Between Summer and Winter
General increase in atmospheric air pollutants from Eastern Asia is expected to continue in the near future. Since anthropogenic and natural aerosols are widely distributed around the Japan area and the interannual and seasonal variability occurred, it is important to examine source and transport pathway of continental and marine air mass arriving at the Japan area. Examining probability distribution of transport pathway of the air parcels arriving at the Japan area, relationship between atmospheric circulation and the source and transport pathway of the air parcels were investigated. In this study, air parcel's trajectories were calculated using wind fields in sigma coordinate. The seven day backward air parcel's trajectories arriving at two areas, which are south (32.5N, 131.0E) and north of Japan (43.5N, 142.5E) in boundary layer, were calculated each day from January to December 2001. The probability of transport pathway was estimated by counting the trajectories in 2.5 degrees longitude-latitude columns at a grid. The grid point values of geopotential height and wind component from the NCEP/DOE AMIP-II re-analysis data were used. It was found out that the probability distribution of transport pathway of air parcels arriving at those areas was changed with season. The source and transport pathway of air parcel arriving at those areas were greatly different especially in summer and winter, although the south of Japan is close to the north of Japan in the global scale. In winter the south of Japan was strongly influenced by continental air mass from the Eurasia. However, the marine air mass from the Sea of Okhotsk and near Alaska was frequently transported toward the north of Japan. In winter, passage of extratropical cyclone around the Japan area, effluent of Siberian anticyclone, and development of the extratropical cyclone over the Okhotsk Sea played important roles in transport of air parcel arriving at the Japan Area. In summer, transport of marine air mass from East China Sea and Pacific Ocean toward the south of Japan was prevailed, although continental air mass from the east coast of Asian continent including Japan and Korea were often transported to the north of Japan. It was found out that the features of air parcel transport in summer were associated with activity of the Pacific high and weak westerly flow around the Japan area. It is suggested from these findings that the knowledge of geographical location of a specified area is important when we examine the transport mechanism on the atmospheric circulation system.
A51A-0746 0800h
Ozone Feedback Effects on the Quasi-Biennial Oscillation of Zonal Wind in the Equatorial Stratosphere
Feedback effect of ozone on the quasi-biennial oscillation (QBO) of zonal wind is investigated with a 3-D chemical transport model of Meteorological Research Institute, MJ98-CTM. The dynamical module (MJ98) is a spectral global model of T42 truncation with 68 layers extending from the surface to 0.01 hPa (about 80 km), wherein the vertical spacing is 500m in the stratosphere. To reproduce QBO in zonal wind, Hines gravity wave (GW) drag is incorporated with enhanced GW source in the tropics. Further, the horizontal diffusion is weakened to 180 hrs at the maximum wavenumber of 42 in the middle atmosphere, while a conventional value of 18 hrs is used in the troposphere. MJ98 successfully reproduces a zonal wind QBO with a period of about 27 months in the equatorial stratosphere without trend, though the strength is somewhat smaller than observations. To the dynamical module of MJ98, a chemical transport module (CTM) is coupled and the radiative heating effect of ozone QBO on the dynamical QBO is explored. The CTM module treats 34 long-lived species including 7 families, and 15 short-lived species with 79 gas phase reactions, 34 photochemical reactions and 9 heterogeneous reactions on polar stratospheric clouds and sulfate aerosols. Transport scheme is a flux form semi-Lagrangian type in the vertical and, at once, a simple semi-Lagrangian type in the horizontal with cubic interpolation. Two runs are made for more than 10 years: one is a non-interactive ozone run and the other is an interactive ozone run. It is found that the interactive ozone elongates the QBO period from 27 months to about 4 years. Detail analysis of the ozone feedback effects on QBO is made in the presentation.
A51A-0747 0800h
Examination of the Volcanic Ash Transport from the July, 2003 Soufriere Hills Volcanic Eruption
The Soufriere Hills Volcano is located on the southern half of the Caribbean island of Montserrat. Montserrat is situated in the northern part of the Lesser Antilles, and is one of the volcanic islands formed along the junction of the Atlantic tectonic plate and the Caribbean plate. The Soufriere Hills Volcano began eruptions in 1995. Periods of small to moderate sized explosions followed. On July 12, 2003, a lava-dome of the volcano collapsed and led to several days of explosions that rocked the island and injected ash into the atmosphere. This work presents an analysis of satellite and in-situ observations and trajectory modeling to examine regional transport of the volcanic ash and its impact on regional aerosol distribution.
A51A-0748 0800h
Prolonged stratospheric warming in the 2003-2004 winter and its relation to interannual variability
The 2003-2004 Arctic winter was remarkable in the approximately 50-year record of meteorological analyses. A major warming beginning in early January 2004 led to nearly two months of vortex disruption with high-latitude easterlies in the middle to lower stratosphere. We show the unique characteristics of vortex evolution and wave propagation during the warming period in 2003-2004 in comparison with previous years. Examination of past variability shows that the recent frequency of major stratospheric warmings (seven in the past six years) is unprecedented, and lower stratospheric temperatures were unusually high during six of the past seven years. This recent cluster of warm winters is examined in relation to the historical record, with attention to the evolution of winds, temperatures and wave propagation. Possible implications for changes in interannual variability and for determination and attribution of trends are discussed.
A51A-0749 0800h
Using a Geographic Information System to Improve Satellite Estimates of Rainfall over the Tibetan Plateau
While it is very important to obtain accurate estimates of precipitation over the Tibetan Plateau for the understanding of hydrological and climatological processes, it is also difficult to study spatial variability in precipitation in this region due to sparse distribution of rain gauges and complex terrain characteristics. Satellite rainfall estimates have been proven very useful in filling gaps where gauge data are not available. Common satellite sensor systems include visible light, near and thermal infrared, and passive microwave sensors. However, in previous validation studies, the effects of complex terrain and high elevation have not been fully examined. This study examines the potential of spatial modeling using a geographic information system (GIS) to improve the rainfall estimates based on Special Sensor Microwave/Imager (SSM/I) over the Tibetan Plateau. The SSM/I is a passive microwave sensor system on board of the U.S. Defense Meteorological Satellite Program (DMSP) satellites. The data go back to July 1987. The 1° x 1° monthly SSM/I rainfall estimates are based on the algorithm developed at the National Environmental Satellite, Data and Information Service (NESDIS) of NOAA. When using SSM/I estimates to predict station precipitation directly, the coefficients of determination (R$^{2}$ values) range from 0.005 to 0.624, with a mean of 0.334 for all the months of the year during the study period of 1987-1999. When terrain and location variables obtained from the GIS are added to the models, the R$^{2}$ values improve up to 0.739 with a mean of 0.590 for all the months. The models for the winter months generally produced the worst performance due to the effect of snow and ice on ground. These terrain and geographic variables represent the effects of orographic forcing of topography, rain barrier/rain shadow, direction of moisture-bearing winds, and distance to the sources of moisture over the Tibetan Plateau. Results form this study suggest that region-specific algorithms are necessary for the SSM/I precipitation estimates over the Tibetan Plateau and that topographic analysis based on GIS can contribute significantly in improving the performance of SSM/I estimates. A similar approach is also used to examine the data from the Tropical Rainfall Measuring Mission's TMI sensor system. In additional to terrain and geographic variables, other variables representing local and regional atmospheric circulation patterns will also be considered in the future modeling effort. We hope that these empirical relationships obtained through this study will be useful in developing improved and region-specific algorithms to estimate precipitation over the Tibetan Plateau. As a result, an improved spatial data set of precipitation for the Plateau can be constructed by integrating satellite estimates and gauge observations to facilitate future studies of spatial and temporal variation of precipitation over the Tibetan Plateau.
A51A-0750 0800h
Application of GIS for Data Quality Monitoring in the NPOESS Ground Data Processing System
Geographic Information System technology is applied to perform Data Quality Monitoring functions for the National Polar-Orbiting Environmental Satellite System (NPOESS) and NPOESS Preparatory Project (NPP) Ground Processing Systems. A GIS-based design provides broad capabilities for automated data quality checks and data quality notifications on sensor data products within the first 24 hours of satellite data production. This design supports remote sensor and ancillary data ingest and management, with flexible data display, processing and interactive editing in a spatial/relational environment, and can be quickly adapted to changes in satellite remote sensor operations. Time is critical in an operational environment, so a "Sensor Space" projection is used to minimize coordinate transformations and increase processing performance. The Data Quality Monitoring capability provides a quick look at both data and analysis products, and can support System Test by filtering and preprocessing the NPOESS/NPP products for further off-line Calibration and Validation analysis. An interface to Interactive Data Language (IDL) is included to support heritage IDL algorithms and exploit the combined capabilities for image (IDL) and vector (GIS) processing.
A51A-0751 0800h
Tracking Summer Storms: A Climatological Overview and Variability in the North Atlantic
Numerous studies on storm track climatology, variability and relation to the large scale flow have been investigated with respect to the winter season. However, to our knowledge, hardly any such investigations have been done related to the summer season. In this study we present some climatologic properties of summer storm tracks based upon ensemble statistics of many individual storm tracks calculated by means of a feature tracking algorithm. NCEP/NCAR reanalysis data during 1949 - 2002 provided by the NOAA-CIRES Climate Diagnostics Center has been used as input to the tracking method. The 850hPa relative vorticity is used instead of the more often used Mean Sea Level Pressure (MSLP) because it is not an extrapolated field to any large extent, and is less influenced by the background flow than fields such as MSLP and geopotential height. Furthermore, it focuses on smaller scale synoptic activity than these other fields with the advantage that a higher number of storm trajectories can be identified. The summer storm track variability in the North Atlantic, its spectral properties, as well as relations with large scale flow properties will be presented.
A51A-0752 0800h
Synoptic Weather Typing and its Application to the Assessment of Climate Change Impacts on Human Mortality in South Central Canada
A synoptic climatological classification approach, using a combination of principal components analysis, an average linkage clustering procedure (hierarchical clustering), and discriminant function analysis (nonhierarchical reclassification), was used to automatically classify distinctive synoptic categories for the period 1953-2001 at each of four selected cities (Montreal, Ottawa, Toronto, and Windsor). Elevated mortality within the identified synoptic weather types were shown to be associated with temperature extremes (heat and cold) and air pollution. Statistical downscaling methods were used to downscale GCM scenarios for the Canadian GCMs (CGCM1 IPCC IS92a & CGCM2 IPCC SRES A2/B2) and the U.S. GCMs (GFDL R30 Coupled Climate Model IPCC SRES A2/B2). The discriminant function analysis was then used to project the future weather types. The projected air pollution concentrations were estimated using the historical regression models from weather typing applied to the downscaled climate change scenarios. This model can also incorporate various air pollution emission scenarios. Two independent approaches were used to assess climate change impacts on elevated mortality for two-time windows (2040-59, 2070-89): 1) comparison of future and historical within-weather-type frequencies and 2) using elevated mortality prediction algorithms (e.g., heat/air pollution-health prediction models). The latter has accounted for not only changes in frequency of future weather types but also changes in future air pollution concentrations. The expected mortality rates due to modeled global warming and pollutant effects for both warm and cold seasons were then estimated. Preliminary results show that under climate change, the future total seasonal elevated mortality rates caused by extreme weather would be increased in summer and decreased in winter due to the expected rise in temperatures.
A51A-0753 0800h
Influence of Extreme Meteorologic Events on the Heat Budget of Tampa Bay
For the period of May 2002 to present, as part of the Bay Regional Atmospheric Chemistry Experiment, an observational tower has been maintained in Middle Tampa Bay that is equipped with sensors measuring meteorological and air-water turbulent flux parameters. A SeaGauge sensor monitors water temperature, salinity, and water level, and a sonic anemometer measures the three dimensional wind speed and the turbulent flux of momentum and sensible heat. Sensible and latent heat fluxes are calculated following the TOGA COARE model (Sea-Mat Air-Sea Toolbox V. 2.0). We focus on hurricane season 2004 to investigate the effects of tropical storm systems on a semi-tropical estuary. Verification for our model results comes from the directly measured sensible heat flux at the tower and the results from the NOAA Buoy Model (Mizak, 2004).