A31C-0096
Turbulence and Ozone Measurements during BAQS-Met.
Simultaneous radar and ozonesonde measurements are presented for the period from June to August 2007 for south-western Ontario, as part of the Border Air Quality Study. Data were recorded in the region around the Great-Lakes, to the north of Lake Erie and east of Lake Huron. This study involved a multiplicity of measurements of atmospheric constituents, but here we concentrate on winds, turbulence strengths, and ozone concentrations. Measurements were made with a windprofiler radar and ozonesondes, as well as a ground-based Brewer spectrophotometer. Data include not only surface information but also measurements from higher altitudes, up to the tropopause in some cases. We investigate correlations between turbulence strengths and transport rates, cases of tropospheric intrusions of ozone from the stratosphere, the general impact of ozone variability, as well as general inter-seasonal variability.
A31C-0097
Gravity Wave Relations in Density Coordinates and Application to Constant Density Balloon Data
Super pressure balloons that are constrained to float on constant density surfaces have been used in a number of campaigns for gathering data for studies of stratospheric dynamics. The natural coordinate system for analyzing data from balloons that float at constant density is one where density, rather than geometrical height or pressure is the vertical coordinate. We show the equations of motion derived for constant density coordinates and show the gravity wave relations derived from them. Using these relations, we analyze data from the CNES VORCORE campaign, in which a total of 27 balloons circulated in the Antarctic polar stratospheric vortex during the late summer and spring of 2005. For this campaign, horizontal wind and pressure data were suitable for gravity wave analysis and we give relations for deducing the quantities (e.g., temperature and vertical wind fluctuations) required to calculate the momentum, heat and energy fluxes. We apply these relations to VORCORE data and show the results of flux calculations for balloon trajectories in various regions of the vortex.
A31C-0098
Model Study of Waves Generated By Convection With Direct Validation via Satellite
Atmospheric gravity waves are a common feature of the middle atmosphere, and play an important role in shaping the mean flow in this region. Gravity waves generated in the troposphere can influence the flow in the stratosphere due to the vertical transfer of momentum associated with the waves. In the tropics specifically, gravity waves are believed to contribute to the forcing of the QBO. Understanding the sources and generation mechanism of gravity waves is crucial to modelling of the middle atmosphere circulation. Convection is a particularly important source in the tropics due to the deep cumulus convection as well as the lack of topography which precludes any topographic wave generation. In the case of convectively generated waves the source can vary in both time and space, generating waves through a wide range of phase speeds, frequencies and vertical and horizontal scales. In this research we examine an event on January 12, 2003, when convective waves were clearly generated by a period of extremely intense rainfall near Darwin, Australia. To model this event we use a three dimensional, nonlinear, non-hydrostatic, cloud resolving model forced by latent heating derived from high resolution precipitation radar observations. Since the model is forced with observed precipitation patterns, the generated wave field can be compared directly to observations. This approach, using prescribed heating, gives us both an understanding of the mechanism of wave generation and the means to validate the model results with satellite data. We directly compare the model output to a satellite observation of the same gravity wave event, using an observation from the Atmospheric Infrared Sounder (AIRS) instrument on the Aqua satellite. The comparison provides a validation of the model method of forcing the waves with a prescribed heating field. The model method further provides a means of evaluating and improving the parameterizations developed for global model studies. We find good comparison between the modelled wave field and the satellite radiances. Both the wave patterns and wave amplitudes in the model and satellite observation correspond well. This indicates that latent heating from the convective storm is the major source of forcing for the observed waves. An interesting fact is that the precipitation responsible for this particular wave observation is a weak rain event following a much larger rain event earlier in the day. This underscores the potential for sampling biases associated with precipitation variability, wave intermittency, and the 12-hour sampling frequency of the satellite.
A31C-0099
On the Wave Spectrum Generated by Latent Heating
Waves generated by convective heating in the troposphere propagate upward through the equatorial stratosphere. These waves are responsible for driving the quasibiennial (QBO) and semiannual (SAO) oscillations. The equatorial wave spectrum is very rich, consisting of Rossby, Kelvin, and gravity waves over a large range of wavelengths and frequencies. It remains an open question as to what range of scales is required to provide the necessary wave driving for the QBO and SAO. In order to examine this question, we use observations of convective activity to drive a realistic simulation of the equatorial wave spectrum. High resolution data of rainfall rate and infrared cloud top brightness temperature derived from TRMM (Tropical Rainfall Measurement Mission) and geostationary satellite observations have been used to construct estimates of latent heating and cloud top height every 3 hours on a .25 x .25 longitude-latitude grid. Heating profiles are constructed using a model of convective heating. (The effect of stratiform heating is considered in another paper submitted to this session). This heating is then used to force a primitive equation model, and the wave spectrum is derived from the response. In this study we examine how the wave spectrum depends on model resolution. We find that the waves so generated in a model with T40 horizontal resolution with vertical grid spacing at .75 km is insufficient to drive a QBO. However, a QBO-like oscillation can be produced by artificially enhancing the eastward wave amplitudes by a factor of 2 and the westward wave amplitudes by a factor of 3. Higher resolution simulations (up to T120) do not contribute sufficient additional momentum flux. One possibility is that the 'missing flux' arises from gravity waves at horizontal scales much smaller than we can simulate or at higher frequencies than the TRMM sampling rate. Another possibility is that the wave spectrum is significantly strengthened by the inclusion of stratiform heating.
A31C-0100
Upper Troposphere/Lower Stratosphere (UTLS) Trace Gas Evolution in Recent Satellite Datasets: Relationships to Stratospheric and Upper Tropospheric Jets
A method has been developed for categorizing the location and characteristics of upper tropospheric jets and of the lower reaches of the stratospheric polar night jet (PNJ) that extend into the upper troposphere/lower stratosphere (UTLS). This method is applied to define the position, width and dynamical characteristics (e.g., windspeed/direction, potential vorticity, temperature, static stability, etc) of the primary subtropical jet (STJ) core, as well as similar information on multiple jets in the extratropical (ET) UTLS. The PNJ in the UTLS is characterized at each level by its position, width, and dynamical characteristics. Jet characteristics during quasi-isentropic stratosphere-troposphere exchange (STE) events and seasonal evolution of jet structure are investigated in Goddard Earth Observing System Version 5 (GEOS-5) and other meteorological analyses. Satellite trace gas measurements from several current instruments, including the Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and the Aura High Resolution Dynamics Limb Sounder (HIRDLS), are studied to further our understanding of the seasonal evolution of the ET tropopause layer in relation to the STJ and the tropopause.
A31C-0101
Layering Occurrence and Characteristics in Ozonesonde Profiles in the Upper Troposphere/Lower Stratosphere Region
Vertical profiles, as observed in ozonesonde data, display instances of both well-mixed and layered environments. Layers can develop as a consequence of a number of transport processes, including detrainment, tropopause folding, and wave breaking. We have developed and used a layer identification method that does not rely on filtering or on use of a default ozone distribution. We will present results on the occurrence of layers, specifically their frequency and vertical distribution. This will include a breakout using established criteria in ozone variation, water vapor and static stability, and their co-variation with respect to ozone. The contribution of layering to the overall ozone variability will be noted. This and related factors will be detailed as a function of height and also of height relative to the thermal tropopause (WMO criterion). The relationship between the thickness (extent in height) of layers and their amplitude (ozone increment) will be discussed. The underestimation of peak ozone values and corresponding overestimation of minimum ozone values in layers caused by the moderate time response of the ozonesonde instrument as it ascends through the profile can be approximated using this relationship by taking account of the rise rate. The impact of this effect on estimates of the variability of lower stratospheric ozone will be discussed. The ozone profile data used cover a period of several years and are from sites around the United States.
A31C-0102
The Origins of Poleward-extending Thin Laminae of Low Ozone Seen by HIRDLS
The high vertical resolution (~1 km of data from the High Resolution Dynamics Limb Sounder (HIRDLS)shows frequent thin layers, or laminae, of low ozone extending along isentropic surfaces from the low latitude upper troposphere into the mid-latitude lowermost stratosphere. These are seen most clearly in ozone and nitric acid. Previous studies of wave dynamics in the UTLS suggest that the meteorological situation in the lower troposphere could create conditions in which the potential vorticity (PV) contours in the upper troposphere (potential temperatures 330K-360K) would be distorted and break in a poleward direction. This permits the transport of air from low latitudes with low PV and low ozone to extend in thin layers poleward. Here we show how well the laminae can be explained and predicted by these meteorological mechanisms. The frequency of these events increases from January through April, then decreases. The laminae occur at preferred locations, notably over the North Atlantic-European and the Eastern Pacific regions.
A31C-0103
Low-ozone bubbles observed in the TTL during TC4 campaign.
In the summer of 2007 the NASA DC8 aircraft took part in the Tropical Composition, Clouds and Climate Coupling (TC4) campaign based in Costa Rica. Multiple in-situ and remote-sensing instruments aboard the aircraft were set to measure atmospheric composition of the TTL. The partial ozone column above the aircraft products were derived from the CCD Actinic Flux Spectrometer (CAFS) instrument (R. Shetter, NCAR) measurements as part of the continuous validation of the Aura ozone products. Both the stratospheric ozone columns derived from the CAFS measurements and the Differential Airborne Lidar (DIAL) ozone profile measurements aboard the NASA DC8 aircraft detected atypical ozone variability in the tropical tropopause layer (TTL). Analysis of the in-situ aircraft data and the data above the aircraft are performed with regards to the TTL properties that are found to be influenced by both slow ascent and by rapid transport in the deep convection conditions. The transport trajectories and correlated measurements of the boundary layer tracers suggest strong connection of the deep convective processes regularly observed near the south boarder of Mexico in July 2007 and the low-ozone episodes observed in the TTL near the coast of Ecuador.
A31C-0104
Seasonal and Spatial Distribution of Lower Stratospheric Lamina as Observed by HIRDLS and Modeled by the Global Modeling Initiative
Laminar isentropic exchange of air masses is an important transport pathway between the tropical upper- troposphere/lower-stratosphere and the extratropical lower stratosphere. Seasonal, global observations of this process have previously been difficult due to the high vertical resolution needed to resolve the laminar events. The High Resolution Dynamic Limb Sounder (HIRDLS) on NASA's Aura satellite is capable of observing these events with 1 km vertical resolution. We have developed a systematic algorithm to detect lamina in along-track HIRDLS observations of the lower stratosphere. We present the seasonal and spatial characteristics of these intrusions using both ozone and nitric acid observations. At the same time, we compare the observed distributions from those calculated by the Global Modeling Initiative combined tropospheric-stratospheric model. This Chemical Transport Model (CTM) is driven by Aura time period meteorological fields obtained from the GEOS-4 system of NASA/Goddard Global Modeling and Assimilation Office (GMAO). Such comparisons bring out the successes and limitations of the model in representing isentropic transport between the tropics and extratropics.
A31C-0105
Troposphere-stratosphere exchange - constraints from water vapour
Transport into the stratospheric 'overworld' is thought to occur predominantly across the tropical tropopause, whereas transport into the lowermost stratosphere may also occur through quasi-horizontal transport on isentropic levels between 300 and 380K potential temperature. The distribution of stratospheric water vapour is sensitively dependent upon the detailed temperature history of air parcel trajectories, and combined with a Lagrangian study can be used as a tracer for quantifying the relative importance of cross-isentropic mass flux and quasi-isentropic mass flux into the stratosphere. Here we combine measurements from the Microwave Limb Sounder on board of AURA satellite, with trajectory calculations to diagnose the pathways of troposphere-stratosphere exchange. Trajectories are calculated using winds and diabatic heating rates from the new interim reanalysis currently carried out at the European Centre for Medium-range Weather Forecast.
A31C-0106
Upper Tropospheric Humidity and Clouds as seen from the AIRS and MLS
The Atmospheric Infrared Sounder (AIRS) provides high spatial coverage and temporal resolution of water vapor (H2O) through the depth of the troposphere. However, AIRS loses sensitivity in the tropical tropopause layer (TTL), thereby missing a significant population of supersaturated layers. Previous studies have shown that inclusion of the Aura Microwave Limb Sounder (MLS) H2O retrievals primarily modifies the supersaturated portion of the global relative humidity (RHi) distribution, i.e. the MLS/AIRS RHi distribution, relative to AIRS alone, is skewed toward higher RHi and more frequent supersaturation. Combining H2O profiles in a rigorous manner, accounting for differences in horizontal and vertical resolution, as well as H2O sensitivity overlap regions, may add substantially to our knowledge of upper tropospheric humidity (UTH). We investigate the utility in the AIRS and MLS averaging kernels as a means to stitch the profiles in a consistent manner. With this combined H2O product we investigate upper tropospheric humidity (UTH) in and outside of clouds and determine its joint relationships with retrieved TTL cirrus microphysical and ice water content from AIRS and MLS. Furthermore, we investigate the observed differences in the supersaturated portion of the RHi distribution between the Northern and Southern hemisphere (NH and SH). With this combined dataset, we test the hypothesis that differences in seasonal temperature variations between the NH and SH can explain much of the contrast between the hemispheric UTH.
A31C-0107
Recent measurements by laser hygrometers in the upper troposphere and lower stratosphere.
We have recently developed a new water vapor instrument with improved electronics, and new calibration techniques for laser hygrometers. This has resulted in more accurate and precise aircraft water vapor measurements in the upper troposphere and lower stratosphere. This is critically important for studies of climate, cloud microphysics, and radiation balance, all of which depend on knowing water vapor concentrations and relative humidity in the tropical tropopause layer. This presentation will show the quantitative figures of merit and recent lab and field measurements from the Unmanned Aerial System Laser Hygrometer (ULH) to demonstrate its accuracy and precision. ULH is a new laser hygrometer developed by JPL for faster, more precise measurements of atmospheric water vapor. ULH data rates as fast as 20 Hz allow spatial resolution of 10 meters or less, which is particularly important for ice cloud studies. ULH has been flight tested on the NASA WB-57F high-altitude aircraft during the NASA Newly- Operating and Validated Instruments Comparison Experiment (NOVICE), in preparation for future science flights on the Global Hawk Unmanned Aerial System (UAS). This presentation will also show measurements from the JPL Laser Hygrometer (JLH), which has flown on the WB-57F aircraft since 1999. JLH recently participated in the AquaVIT international water vapor instrument intercomparison in Karlsruhe, Germany. In this experiment, JLH was mounted inside the AIDA aerosol chamber, for a series of blind comparisons of hygrometer measurements at pressures, temperatures, and water mixing ratios representative of the troposphere and lower stratosphere.
A31C-0108
A Novel Method for Assessing the Accuracies of In Situ Measurements of Water Vapor in the UT/LS
We report on results from a series of flights of the NASA WB57F Aircraft into the exhaust plumes of rockets as part of the Plume Ultrafast Measurements Aquisition (PUMA) campaign. It is found that the emission ratio of vapor vapor to CO2, along with highly accurate measurements of CO2 can be used to constrain the abundances of H2O in the plume, such that the highly linear correlation between these two species can be used to determine the accuracies of total H2O measurements in the very dry upper troposphere and lowermost stratosphere. In addition, as the plume disperses evaporation of ice provides a fundamental thermodynamic constraint on water vapor abundances that is an independent test of instrument response. These plume observations provide a unique in situ, flight-based test of instruments to a level of accuracy that is very likely not possible in other types of measurement programs, such as in-flight intercomparisons or comprehensive laboratory calibrations. We propose a low-cost program focusing on flights through plumes of rockets and aircraft in the UT/LS that could resolve the longstanding disagreements between different in situ water vapor instruments.
A31C-0109
Analysis of Processes Controlling Seasonal and Inter-annual Variability of Tropical Upper Tropospheric Humidity
We analyse seasonal and inter-annual variability of tropical upper tropospheric humidity based on measurements by the Microwave Limb Sounder (MLS) on board of the Aura spacecraft for the period of August 2004 ¡§C December 2008. We use trajectory calculations based on winds and diabatic heating rates from the new interim reanalysis currently carried out at the European Centre for Medium-range Weather Forecast (ECMWF). The relations of the humidity variations to the tropical circulation variations due to El-Nino/Southern Oscillation (ENSO), Indian/Southeast Asian monsoon, and possible influences from the stratospheric processes are examined in detail. In particular, we address the question to what extent the observed humidity variations are related to temperature variations, and to what extent they arise from variations in circulation, or possibly cloud microphysical processes.
A31C-0110
Observational estimation of the 'cold trap' dehydration in the tropical tropopause layer: The water vapor match
Stratospheric water vapor is controlled by the degree of dehydration the air parcels experienced on their entry into the stratosphere. The dehydration takes place in the tropical tropopause layer (TTL) over the western Pacific, where the air parcels are exposed to the lowest temperature during horizontal advection (cold trap hypothesis (Holton and Gettelman, 2001; Hatsushika and Yamazaki, 2003)). While, simplified treatment of the dehydration processes combined with trajectories reproduce water vapor variations reasonably well (Fueglistaler et al., 2005), extreme super saturation has been often observed in the TTL (Peter et al., 2006). Thus observational data are needed to quantify the efficiency of dehydration. We have been conducting the project Soundings of Ozone and Water in the Equatorial Region (SOWER) using chilled-mirror hygrometers in the western Pacific. Hasebe et al. (2007) suggested that the water content in the observed air parcels on many occasions was about twice as much as that expected from the minimum saturation mixing ratio during horizontal advection prior to sonde observation. To make this argument more quantitative, however, it is necessary to estimate the changed amount of water vapor by repeated observation of the same air parcel, the water vapor match. The match pairs are sought from the SOWER campaign network observations with the use of isentropic trajectories. For those pairs identified, extensive screening procedures are performed to verify the representativeness of the air parcel and to check possible water injection by deep convection. The match pairs are rejected when the sonde-observed temperature does not agree with spatio-temporary interpolated temperature of the ECMWF analysis field within a reasonable range, or the ozone mixing ratio is not conserved between the paired observations. Among those survived, we sought the cases which showed statistically significant dehydration. We estimated the ratios of the water mixing ratio observed by the first and the second sondes and the minimum saturation mixing ratio during advection. This gives the range of the maximum value of relative humidity with respect to ice. The range of 1.5 - 2.6 was found for the match pair on 362 K that showed a dehydration from 6.0 to 3.5 ppmv.
A31C-0111
Use of ADEOS-II/GLI Radiometric and Geometric Characteristics for the Simulation of Moisture Variations in the Upper Troposphere
This study is an examination of the performance of radiative transfer models in the simulation of variations of the upper tropospheric relative humidity (UTRH) observed by satellites. For this purpose, upper tropospheric water vapor simulations are produced by the radiative transfer code (RSTAR6b) using radiance observations of the water vapour channel (6.7 µm) of the Global Imager (GLI) onboard ADEOS-II satellite. The geographical area covered by these simulations is the Sea of Japan and surroundings. Based on the GLI sensor radiometric and geometric characteristics, we describe the methodology and calculations made to estimate the UTRH from satellite brightness temperature observations. The average correlation obtained between these two parameters is above 0.65. Then the model outputs of the satellite UTRH retrievals are compared with corresponding UTRH from the NCEP/NCAR re-analysis data weighted by the water vapour channel of the GLI weighting function. Results are interpreted in terms of proximity with cloud formations.
A31C-0112
What governs the isotopic composition of water vapor in the tropical tropopause layer?: Insights from a simple model
We make use of a simple one dimensional model to investigate the comparative role of deep convection and large scale processes in determining the isotopic composition of water vapor in the tropical tropopause layer. The model uses a simplified convective code based on the continuously entraining plume scheme and an idealized view of the large-scale environment in the tropics. We find that such an approach renders the problem of diagnosing local tendencies in the isotopic ratios more tractable. We show that the observed enrichment of the isotopic composition at high altitude in the tropics cannot be explained without taking into account the re-evaporation of ice from the convective outflows. We also show that the isotopic composition of the vapor is strongly dependent on the effective ice retention rate integrated throughout convective towers.
A31C-0113
HOxotope Total Water Isotopologues Instrument Performance and Results from TC4
We present measurements of total water isotopologues (condensed and vapor phases) from the upper troposphere and lower stratosphere that were obtained by the HOx total water isotopologues instrument (HOxotope) onboard the NASA WB-57 aircraft during the TC4 field campaign. Measurements of the relative abundance of HDO and H2O serve as a sensitive indicator of the convective history of an airmass. The instrument's performance measuring water vapor is evaluated by intercomparison with the Harvard Water Vapor instrument and the condensed phase performance is evaluated by intercomparison with University of Colorado's closed-path laser hygrometer (CLH). Additionally, isotopologue measurements by Hoxotope and ICOS are used to quantitatively constrain parameters of cirrus cloud formation during TC4.
A31C-0114
Measurements of Isotopic Composition of Water Vapor Using CIMS From the NASA DC-8 During TC4
Measurements of the isotope ratio of water vapor in the tropical troposphere were performed from the NASA DC-8 aircraft platform during the TC4 campaign in 2007. Measurements were conducted in-situ using a chemical ionization tandem mass spectrometry system. Using the global meteoric relationship, the data are used to calculate the ratio of HDO to H2O and δD in the water vapor. The tropospheric δD observations are discussed in the context of a simple model for Rayleigh fractionation. The data are also compared to data from two water isotope measurements aboard the high altitude NASA WB-57 aircraft, providing a surface-to-stratosphere profile of δD as well as an opportunity for instrument intercomparison.
A31C-0115
Simulations of Clouds and Water Vapor in Boreal Summer Tropical Tropopause Layer with a Microphysical Model
The Tropical Tropopause Layer (dubbed the TTL), roughly between 13 and 18km altitude, is one of the coldest parts of the earth's atmosphere. In contrast to the rest of the global tropopause region, radiative heating rates are positive and mean vertical motion is upward. It is thus the pathway for constituents into the stratosphere, and the cold temperatures lead to the well-known very dry stratospheric conditions. This simple picture is made more complicated by the interaction of convective injection, horizontal advection through cold regions (and consequent dehydration), slow ascent, and constraints on the nucleation of ice crystals. All these processes have significant effects on the water vapor distribution. Simulations of the boreal winter TTL have shown that including microphysics and convection in trajectory- based calculations moisten the TTL by about 1 ppmv, improving agreement with observations. Simulated horizontal distributions are also improved. In the boreal summer, the distribution of radiative heating rates strongly affects simulated water vapor and clouds. Generally, simulated water vapor values are wetter than observations, while the model simulates fewer clouds than observed. The implication is that gravity wave amplitudes are too low and that convective injection is inadequate. Results will be presented using: (1) modified convective injection based on analyses of CLOUDSAT and CALIPSO measurements, and (2) modified gravity wave parameterizations.
A31C-0116
Heat balance and isotopic composition in the tropical tropopause layer (TTL) of a mock- walker circulation
Cloud-resolving model simulations over a large-scale gradient in sea surface temperature (SST), dubbed a mock "Walker" circulation, connects the convection over warm SSTs to the subsiding flow over cooler SSTs and provides a framework for exploring the effects of tropical convection and the large-scale circulation on the TTL. The focus of the present work is on a series of simulations in this framework, performed using the System for Atmospheric Modeling (SAM, Khairoutdinov & Randall 2003) in two-dimensional domains with widths of up to 8192 km, horizontal grid sizes of 1-2 km, and vertical grid sizes of 300-400 m in the tropopause layer. A reverse circulation above the mock-Walker circulation in the troposphere is found, and its effect on the maintenance of the TTL is explored. In addition, simulations that include stable water isotopes (HDO and H218O) of water vapor and all hydrometeors (cloud water, cloud ice, rain, snow and graupel) and their microphysical interactions and fractionation are detailed. The roles of fast (convection) and slow (advection) processes in fixing the fractionation of water vapor in the TTL is explored.
A31C-0117
Convective and stratiform heating profiles estimated from TRMM rain rate data for realistic forcing of equatorial atmospheric waves
The latent heat released in tropical convection is the source for a variety of equatorial waves that both influence the formation of cirrus clouds and drive global-scale circulations in the middle atmosphere. Global models used for climate and data assimilation have sufficient resolution to describe many of these waves, yet the realism of the wave modes appearing in these models is not enerally well validated against observations. We have developed a global model for very realistic representation of quatorial waves that can be directly compared to observations. The model is forced with latent heating derived from the Tropical Rainfall Measurement Mission (TRMM) satellite gridded rainfall product (3B42) with .25 x .25 degree and 3-hourly resolution. Convective and stratiform heating profiles are estimated from the TRMM 3B42 data, which is then used as the forcing for equatorial atmospheric waves in a global spectral model. The vertical structure of heating is one of the important factors to impact the characteristic of the waves. Since the stratiform clouds, having relatively shallow heating structures, are widespread in tropics, the stratiform type heating as well as the convective type heating are considered to make the full convective plus stratiform latent heating profile (CSH). For the stratiform heating, the lookup table of the melting level and the precipitation at melting level depending on the surface rain rate and the precipitation top height are made from TRMM instantaneous swath data. The CSH profile is updated every 3 hours from TRMM 3B42 rainrate data and forced in a version of the model with a horizontal resolution of T40 (approximately 3 x 3 degrees). A broad spectrum of Kelvin, mixed-Rossby, equatorial Rossby, and gravity waves are generated in the model. Equatorial inertia-gravity waves with smaller vertical wavelength are enhanced in the stratosphere by using the CSH profile instead of the convective-only heating profile.
A31C-0118
Joint ARM/GCSS/SPARC TWP-ICE CRM Intercomparison Study: Description, Preliminary Results, and Invitation to Participate
The 2006 Tropical Warm Pool - International Cloud Experiment (TWP-ICE) is 'the first field program in the
tropics that attempted to describe the evolution of tropical convection, including the large-scale heat,
moisture, and momentum budgets at 3-hourly time resolution, while at the same time obtaining detailed
observations of cloud properties and the impact of the clouds on the environment' [May et al., 2008]. A cloud-
resolving model (CRM) intercomparison based on TWP-ICE is now being undertaken by the Atmospheric
Radiation Measurement (ARM), GEWEX Cloud Systems Study (GCSS), and Stratospheric Processes And
their Role in Climate (SPARC) programs. We summarize the 16-day case study and the wealth of data being
used to provide initial and boundary conditions, and evaluate some preliminary findings in the context of
existing theories of moisture evolution in the tropical tropopause layer (TTL). Overall, simulated cloud fields
evolve realistically by many measures. Budgets indicate that simulated convective flux convergence of water
vapor is always positive or near zero at TTL elevations, except locally at lower levels during the driest
suppressed monsoon conditions, while simulated water vapor deposition to hydrometeors always exceeds
sublimation on average at all TTL elevations over 24-hour timescales. The next largest water vapor budget
term is generally the nudging required to keep domain averages consistent with observations, which is at
least partly attributable to large-scale forcing terms that cannot be derived from measurements. We discuss
the primary uncertainties.
http://www.giss.nasa.gov/~fridlind/twp-ice
A31C-0119
Coarse-scale Convective Transport of CO and O3 Over 36 Hours Above Southern United States
Ozone distribution in the UTLS region is an important factor in the heat budget for the LT. Above areas with heavy industrial activities and other anthropogenic sources, the UT can potentially experience anomalously high pollutant composition when deep convection extracts boundary layer air and detrains it at high altitude. Though healthy for boundary layer air quality, such migration of pollutants complicates the ozone budget in UTLS. Therefore reliable budgets require dependable models for chemical transport in the region of convection and reactions. Detailed dynamic scheme that resolve convection show great promise for accurately simulating and understanding the transport of relevant chemical constituents, while parameterized convective schemes are still required for coarse resolution simulations. While there is an abundant choices of heavily tested microphysics and grid-scale dynamic schemes, some convective parameterization methods call for more validations. This is a much more prominent issue in lower resolution runs, where sub-gridscale convection transports of trace gases must be parameterized and seldom assessed. In this way, measurements of the chemical species under such settings can provide a critical test of the fidelity of convective transport schemes. Coarse-resolution (Δ x=36km) simulations using Weather Research and Forecasting model coupled with Chemistry (WRF-chem) are done to quantify how well different convective parameterization schemes performed. Results are compared to observation of CO and O3 profile from Tropospheric Emission Spectrometer (TES). We focus on the case of the 36 hour period in the southeastern United States on Aug 23-24, 2006, which coincides with heavy convective activity over Oklahoma and Arkansas. Using the Grell-Deveyi parameterization scheme in a low resolution simulation, result shows large amount of water vapor transported into the UTLS region, where it is retained further at this level by the summer anticyclone of Southern United States centered above Houston, TX. Yet, no comparable amount is observed in another simulation done without any convective parameterization. The TES CO data suggest these convective anomalies indeed occur, and as such the transport of chemical CO and O3 that accompanies the water vapor detrainment provides a strong local enhancement of the ambient concentrations because of the rapid ventilation of pollutants emitted from the surface. This work highlights the need to understand the convective transport in regional trace gas budgets, and that some care is needed to ensure the convective transport is adequately accounted for in models where horizontal resolutions are limited above the typically scale of a convective system.
A31C-0120
Lightning-generated NOx seen by OMI during NASA's TC4 experiment: First results
We present here case studies identifying upper-tropospheric NO2 produced in convective storms during NASA's Tropical Composition, Cloud and Climate Coupling Experiment (TC4) in July and August 2007. DC8 aircraft missions, flown from the mission base in Costa Rica, recorded in situ NO2 profiles near active storms and in relatively quiet areas. We combine these data with measurements from the Ozone Monitoring Instrument (OMI) on the Aura satellite to estimate the amount of NO2 produced by lightning (LNO2) above background levels in the regions influenced by storms. In our analysis, improved off-line processing techniques are employed to minimize known artifacts in the OMI data. Information on lightning flashes (primarily CG) observed by the surface network operated by the Instituto Costarricense de Electricidad are examined upwind of regions where OMI indicates enhanced LNO2. Comparisons of the observed flash data with measurements by the TRMM/LIS satellite instrument are used to obtain the lightning detection efficiency for total flashes. Finally, using the NO/NO2 ratio estimated from DC-8 observations, we estimate the average NOx production per lightning flash for each case in this study. The magnitudes of the measured NOx enhancements are compared with those observed by the DC-8 and with similar OMI measurements analyzed in mid-latitude experiments.
A31C-0121
Estimating the production of lightning NOx from satellite observations of NO2
The amount of nitrogen oxides (NOx=NO+NO2) produced by lightning is a key uncertainty for the assessment of tropospheric ozone production. In this study, we discuss the potential and limitations of satellite observations of NO2 to estimate lightning NOx (LNOx). Despite the mean NO2 enhancements due to lightning being rather small (compared to strong anthropogenic sources), LNOx has been identified clearly in satellite observations which show (a) average column enhancements over lightning active regions as well as (b) a direct enhancement for measurements coinciding with thunderstorms in space and time. The task is to transfer these qualitative findings to quantitative estimates that actually improve our knowledge of LNOx production. In a model study, we assess the sensitivity of NO2 satellite observations for LNOx under cumulonimbus cloud conditions: a cloud resolving model, providing profile information on NOx, NO2, and clouds, was used to derive synthetic "satellite measurements", i.e. slant column densities of NO2 for cloudy sky, involving the Monte-Carlo Radiative Transfer Model McArtim. From this study we find on average a "sensitivity" of 0.46 (0.37-0.55), i.e. the observed slant column of NO2 is expected to be 46% of the vertical LNOx column. Hence, a strong thunderstorm should result in a clear column enhancement for direct satellite overpass. Several such satellite measurements coinciding with lightning have been found over tropical oceans. Continental thunderstorms, however, are missed due to the fact that current UV/vis instruments measure in the morning (GOME, SCIAMACHY, GOME-2) or shortly after noon (OMI), whereas continental lightning activity peaks in late afternoon. To study LNOx over continents, one has to relate the observed NO2 columns to LNOx produced the previous day(s). In addition, one has to keep in mind that in particular over continents, convection of anthropogenic NOx might interfere with LNOx. We present estimates of LNOx production for both, freshly produced LNOx as well as aged LNOx, from the relation of observed NO2 column enhancements to flash rates from LIS, NLDN, and WWLLN. From the studies performed so far, we find LNOx per flash productions that correspond to a global release of about 1-2 Tg [N]/yr. This is significantly lower than the often used estimate of 5 Tg [N]/yr. Ongoing studies have to deal with the rather high variability of the NO2 columns. In addition, systematic regional (and possibly seasonal) differences of the LNOx production, which have been discussed recently, are analyzed. In particular for this, the time series with global coverage available from satellite shows its high potential.
A31C-0122
Tropical Thin Cirrus in AIRS Measurements: Retrieval and Radiative Forcings
We developed an efficient thermal infrared radiative transfer model on the basis of the delta-four-stream approximation to facilitate high-spectral-resolution remote sensing applications under cirrus cloudy conditions in the Atmospheric Infrared Sounder (AIRS) data. Multiple scattering contributions from cirrus cloud particles have been found to be important in thermal infrared cloudy spectra, especially when cirrus cloud optical depths are larger than 0.3. We selected a number of nighttime thin cirrus scenes over the Atmospheric Radiation Measurement program's Tropical Western Pacific sites from AIRS datasets and applied this radiative transfer model to the selected cases to determine cirrus optical depth and mean effective ice crystal size and habit factor. For retrieval, we followed an approach using look-up tables constructed from numerous in situ ice particle size and shape measurements over tropical cirrus clouds. Solar and infrared radiative forcings and heating rates produced by thin cirrus in the tropical atmosphere have been analyzed using the retrieved cirrus optical and microphysical properties along with a modified Fu and Liou broadband radiative transfer scheme. Subsequently, we carried out comparison of cirrus retrieval results and computed broadband fluxes to those determined from available ground-based cloud radar and pyrgeometer measurements to check consistency between the two. Finally, we will report on the impact of tropical thin cirrus on atmospheric heating and surface radiative forcing on the basis of the present analysis.
A31C-0123
OSIRIS 7-year subvisual cirrus climatology
Subvisual cirrus clouds are routinely seen as enhancements in the limb-scattered sunlight profiles observed with the InfraRed Imager subsection of the OSIRIS instrument. The equivalent vertical optical depths of the clouds seen in this dataset are in the range 10-5 to 10-3. OSIRIS, an instrument on the Odin satellite, makes measurements at 0600 and 1800 local time, and has been in operation since 2001, providing a long-term data record. In this poster, highlights from the OSIRIS subvisual cirrus climatology are presented.
A31C-0124
'NAT-like' particles in TTL clouds observed from space?
A classification technique shown to be effective on Polar Stratospheric Clouds has been applied to spaceborne observations of lidar depolarization and backscattering ratios from CALIOP within tropical cloud layers with temperatures below 200K (June 2006 to May 2008) to infer the presence of HNO3-containing (i.e. 'NAT-like') particles. Results suggest the importance of HNO3- containing particles within clouds seems roughly anticorrelated to the cold cloud cover itself, with such particles representing 2 to 8% of cold cloud particles for the period of most active convection (January to March), reaching a maximum of approximately ~20% in June. The total number of HNO3-containing particles seems relatively constant within cloud layers.