A23E-01 INVITED
Aerosol Indirect Effects on Warm Clouds as Observed by the A-Train Satellites
Collocated observations obtained from four sensors orbiting in NASA's A-Train constellation of satellites are used to examine the indirect effects of aerosol on the albedo of warm, low clouds composed of water droplets and rain. These observations are used to provide estimates of aerosol indirect forcing given certain, clearly stated caveats. These estimated forcings are provided for raining and non-raining clouds and for different conditions of thermodynamic stability. We find that the sensitivity of the cloud albedo, as observed by CERES, to aerosol varies according to these various conditions and does not simply correlate with decreased particle size. Since the observations are grouped in terms of cloud water path and the occurrence of precipitation, we are able to quantify the Twomey effect, demonstrate effects of aerosol on cloud liquid water and introduce an entirely new indirect effect of aerosol on warm clouds associated with the delayed precipitation production evident in the observations. Our findings are consistent with and verify a number of conjectured effects of aerosol on low clouds, such as the effect of enhanced entrainment on cloud liquid water, reduced probability of precipitation among others. We find that the total estimated global indirect forcing is -0.7 Wm-2 with about a 1/3 of this forcing being contributed by the new indirect effect introduced. It will be argued this estimated global forcing is likely to be an upper bound on the actual global indirect forcing.
A23E-02 INVITED
Evaluating the Impact of Aerosols on the Onset and Microphysical Properties of Rainfall off the Coast of China
Differences in satellite rainfall estimates from the Tropical Rainfall Measuring Missions (TRMM) precipitation radar (PR) and microwave imager (TMI) provide compelling evidence for the large- scale modification of precipitating clouds by aerosols off the coast of China. The role of aerosols in modifying cloud properties over this region is examined using a combination of satellite observations from TRMM and CloudSat along with cloud resolving model (CRM) simulations. Coincident TRMM/CloudSat observations for a case from 3 April 2007 show striking differences in both rain area and rainfall intensity from the TMI, PR, and CloudSat retrievals. Observations from the 94-GHz CloudSat radar, which is highly sensitive to the onset of rain, confirm the presence of widespread light rain/drizzle containing relatively small drops below the ~17 dBZ PR detection threshold. For pixels with reflectivities above the PR detection threshold, large differences are present in the satellite rain intensity estimates, which are consistent with either a decrease in the mean drop size, an increase in ratio of cloud water to rain water, or both. Idealized cloud resolving model (CRM) simulations initialized for the 3 April 2007 case are generally consistent with the observations indicating high aerosol concentrations leading to an overall increase in the ratio of cloud water to rain water for developed systems, as well as a delay in the onset of warm rain. Based on the combination of observations and CRM simulations, it is hypothesized that the observed satellite rainfall differences may be due to an increase in the ratio of cloud water to rain water leading to an overestimate in rain intensity by the CloudSat/TMI retrievals and/or a decrease in the mean drop size leading to an underestimate by the PR retrieval.
A23E-03 INVITED
Evaluation of CRM-Simulated Cloud and Precipitation Structures Using Multi-sensor TRMM Retrievals: Implications for Model Development
Cloud resolving models are typically used to examine the characteristics of clouds and precipitation and their relationship to radiation and the large-scale circulation. As such, they are not required to reproduce the exact location of each observed convective system, much less each individual cloud. Some of the most relevant information about clouds and precipitation is provided by instruments located on polar-orbiting satellite platforms, but these observations are intermittent 'snapshots' in time, making assessment of model performance challenging. In contrast to direct comparison, model results can be evaluated statistically. This avoids the requirement for the model to reproduce the observed systems, while returning valuable information on the performance of the model in a climate-relevant sense. The focus of this talk is a model evaluation study, in which updates to the microphysics scheme used in the Goddard Cumulus Ensemble (GCE) model are evaluated using statistics of observed clouds, precipitation, and radiation. We first present the results of multiday simulations of organized deep convection using the current GCE cloud microphysical scheme. Statistics of TRMM multi-sensor derived clouds, precipitation, and radiative fluxes are used to evaluate the GCE results. Results of simulations using a new single- and double- moment bulk cloud microphysical scheme are then presented, and these simulations are compared with observations and with the control simulation. We conclude with a demonstration of how data assimilation techniques can be used to examine uncertainty in model parameterizations, and provide a pathway toward model improvement.
A23E-04 INVITED
GCSS/WGNE Pacific Cross-section Intercomparison: Tropical and Subtropical Cloud Transitions
In this presentation I will discuss the role of the GEWEX Cloud Systems Study (GCSS) working groups in paving the way for substantial improvements in cloud parameterization in weather and climate models. The GCSS/WGNE Pacific Cross-section Intercomparison (GPCI) is an extension of GCSS and is a different type of model evaluation where climate models are analyzed along a Pacific Ocean transect from California to the equator. This approach aims at complementing the more traditional efforts in GCSS by providing a simple framework for the evaluation of models that encompasses several fundamental cloud regimes such as stratocumulus, shallow cumulus and deep cumulus, as well as the transitions between them. Currently twenty four climate and weather prediction models are participating in GPCI. We will present results of the comparison between models and recent satellite data. In particular, we will explore in detail the potential of the Atmospheric Infrared Sounder (AIRS) and CloudSat data for the evaluation of the representation of clouds and convection in climate models.
A23E-05
Three-way, Statistically-based Comparison of Convective Clouds and Precipitation in Satellite Observations, GEOS-5 Retrospective Analyses, and Cloud Resolving Model Simulations.
High-resolution satellite datasets such as those from the CloudSat and TRMM instruments provide an
unprecedented view of global cloud and precipitation fields. We will combine these observations with new
global 0.5x0.66 retrospective analyses from the Goddard Earth Observing System version 5 (GEOS-5) to
examine convective events and their parameterized counterparts in atmospheric models. We show, for
example, that simple predictors of convective cloud depth based on analyzed profiles of temperature and
humidity do a good job of describing the statistics of cloud depth-scales obtained from CloudSat radiances.
At the same time, comparisons with parameterized convection in the global model indicate possibly significant
differences in character between parameterized and observed convection. Cloud resolving model
simulations are used to examine uncertainties arising from satellite sampling, and to examine relationships
with other important, unobserved variables such as convective mass flux
http://gmao.gsfc.nasa.gov/systems/geos5/geos5_research
A23E-06
Comparisons of Cloud Structure from Satellite Estimates to ECMWF and GMAO Analyses, 20th Century IPCC AR4 Climate Simulations, and GCM Simulations
To assess the fidelity of general circulation models (GCMs) in simulating cloud liquid water, liquid water path (LWP) retrievals from several passive satellites and the vertically-resolved liquid water content (LWC) from CloudSat are used. Comparisons are made with ECMWF and MERRA analyses, climates simulations utilized from the IPCC 4th Assessment, and three GCM simulations. There is considerable disagreement amongst the LWP estimates and amongst the modeled values. Better agreement is found between the two analyses and CloudSat LWP/LWC when cases with surface precipitation are excluded. The upward vertical extent of LWC from the GCMs and analyses is greater than CloudSat estimates. The largest values in the CloudSat LWP/LWC occur over the planetary boundary-layer stratocumulus regions; this feature is not as evident in the analyses or models. We therefore examine the cloud structure along a Northern Pacific Ocean cross- section encompassing both the ascending and descending branches of the Hadley Circulation, covering stratocumulus, trade-wind shallow cumulus and deep cumulus from low sea surface temperature (SST) to high SST regions during June, July and August (JJA) 2006. The results show that the total ice water content (IWC) values from CloudSat are much larger than the IWC values from the ECMWF analysis and GCMs by a factor of two. Better agreement is found between CloudSat IWC values and the values from ECMWF and two GCMs when only non-precipitating and non-convective CloudSat retrieval profiles are considered. Both analyses and models show a deepening of the vertical extent of LWC as it transitions from a low SST to a higher SST region, while the CloudSat LWC exhibits little variation in the vertical depth of LWC. Better agreement is found between the total CloudSat LWC and the values from ECMWF analyses and models. All the models show bias high LWC than non-precipitating conditions of CloudSat LWC estimates over low SST stratocumulus cloud region. Large peak values are evident in the total CloudSat LWC and models LWC over the boundary-layer stratocumulus regions. The vertical extent of LWC from the GCMs and analyses are greater than CloudSat estimates over the high SST region, i.e., the tropical ascending branch. CloudSat profiles are classified into six cloud types that include high-level cirrus clouds, middle-level cumulus, altostratus, altocumulus and deep cumulus clouds from the sub-tropics to the equator. Stratocumulus clouds are dominant over the low SST region in a persistent and geographically separated way, along this cross- section. The issues of representing LWC/IWC and precipitation are discussed in making comparisons between satellite data and models.
A23E-07
A-Train observation of warm cloud microphysical processes and its application to evaluation of model parameterizations
The combined use of CloudSat-observed radar reflectivity and the columnar effective radius obtained from combined microwave-shortwave analysis is suggested as a way of examining warm cloud microphysical processes. Theoretical relationships of radar reflectivity as a function of effective radius for constant number and mass concentrations are employed as proxies for condensation and coagulation processes, respectively. The joint relationship between these quantities obtained from A-Train observations illustrates the sixth power and cubic dependencies of layer-mean radar reflectivity on columnar effective radius, implying the condensation and coagulation processes occurring on global scale. This method is further applied to results from cloud-resolving models for evaluating how the microphysical processes are represented by parameterizations in the models. The joint statistics of radar reflectivity and columnar effective radius obtained from NICAM (Nonhydrostatic Icosahedral Atmospheric Model) and RAMS (Regional Atmospheric Modeling System) models are compared with those obtained from A-Train observations. The result shows substantial differences in statistical relationship of reflectivity and effective radius between different models as well as between the models and the observations. These differences illustrate how the model physics of warm cloud processes differs with parameterizations based on single and double moments, and provide a hint at how the parameterizations can be improved.
A23E-08
Application of the CloudSat and NEXRAD Radars Toward Improvements in High Resolution Operational Forecasts
As computational power increases, operational forecast models are performing simulations with higher spatial resolution allowing for the transition from sub-grid scale cloud parameterizations to an explicit forecast of cloud characteristics and precipitation through the use of single- or multi-moment bulk water microphysics schemes. Investments in space-borne and terrestrial remote sensing have developed the NASA CloudSat Cloud Profiling Radar and the NOAA National Weather Service NEXRAD system, each providing observations related to the bulk properties of clouds and precipitation through measurements of reflectivity. CloudSat and NEXRAD system radars observed light to moderate snowfall in association with a cold-season, midlatitude cyclone traversing the Central United States in February 2007. These systems are responsible for widespread cloud cover and various types of precipitation, are of economic consequence, and pose a challenge to operational forecasters. This event is simulated with the Weather Research and Forecast (WRF) Model, utilizing the NASA Goddard Cumulus Ensemble microphysics scheme. Comparisons are made between WRF-simulated and observed reflectivity available from the CloudSat and NEXRAD systems. The application of CloudSat reflectivity is made possible through the QuickBeam radiative transfer model, with cautious application applied in light of single scattering characteristics and spherical target assumptions. Significant differences are noted within modeled and observed cloud profiles, based upon simulated reflectivity, and modifications to the single-moment scheme are tested through a supplemental WRF forecast that incorporates a temperature dependence within the slope parameter of the snow crystal size distribution.
A23E-09
Application of TRMM PR and TMI Measurements to Assess Cloud Microphysical Schemes in the MM5 Model for a Winter Storm
A midlatitude frontal precipitation system was observed by the Tropical Rainfall Measuring Mission (TRMM) satellite on February 19, 2001 in the Eastern Pacific. The TRMM microwave imager (TMI) and the precipitation radar (PR) provided detailed observations of a narrow cold-frontal rainband (NCFR) and a wide cold-frontal rainband (WCFR). The Penn State University/National Center for Atmospheric Research mesoscale model (MM5) is used to study the microphysical characteristics of the precipitation system. The mesoscale simulations have been incorporated into a radiative transfer model to calculate brightness temperatures at TMI frequencies and reflectivity at the PR frequency. The purpose of this study is to evaluate the performance of the cloud microphysical schemes in the MM5 model using the combination of TMI and PR observations. Five available schemes in MM5 Version 3-7-4 are investigated, including simple ice, Reisner 1 mixed-phase, Goddard microphysics, Reisner 2 graupel, and Schultz microphysics. In addition, two sensitivity simulations for the Goddard scheme were carried out. The study reveals that the majority of the schemes are capable of reproducing the emission from the rain layer. The outcomes of the schemes in the ice layer vary significantly. Tentative explanations for the differences in the ice layer will be discussed.
A23E-10
Analysis of Precipitation Characteristics Within an African Easterly Wave: A Multi-Platform Perspective
The NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign was conducted primarily to explore the relationship between African Easterly Waves (AEWs) and tropical cyclogenesis in the Atlantic basin, as well as the role of the Saharan Air Layer (SAL) in modulating the intensity of the waves and incipient tropical cyclone growth. The NASA TOGA C-band radar was deployed near Praia, Republic of Cape Verde ( approximately 600 km west of Dakar, Senegal) from 16 August to 16 September 2006. This location provided a unique opportunity to observe the transition of continental convection over Africa into the maritime environment. The primary objective of TOGA was to document convection and accompanying mesoscale processes associated with passage of large-scale disturbances (i.e., AEWs) over the region. Herein, we describe the evolution of convection embedded within an AEW that passed through the region sampled by TOGA on 2-3 September, 2006. This AEW may have been the precursor to hurricane Gordon, the most intense tropical cyclone in the Atlantic basin during the 2006 season. Although the circulation center was located several hundred kilometers south of the Cape Verde Islands, the TOGA radar sampled extensive precipitation associated with the wave passage. Convective echoes, embedded within the stratiform precipitation region, produced significant flash flooding in the nearby city of Praia. The NASA DC-8 flew a series of coordinated flight tracks through the AEW on 3 September and collected a suite of in-situ and remote sensing observations. The DC-8 also coordinated observations with TOGA in order to provide a more detailed picture of the precipitation structure of the AEW. A spiral descent was performed within a broad area of stratiform precipitation near TOGA and dropsondes were launched to sample environmental winds and thermodynamic structure. In this study, the TOGA observations are combined with observations from the NASA 2nd generation airborne precipitation radar (APR-2), as well as in-situ and dropsonde observations from the NASA DC-8, to examine the microphysical characteristics within the AEW. Moreover, precipitation radar (PR) data from a Tropical Rainfall Measuring Mission (TRMM) overpass several hours after the coordinated aircraft-ground radar sampling are used in conjunction with the University of Utah TRMM precipitation feature database to help place the 2-3 September event in context of the TRMM climatology for this region.