A24B-01 INVITED
Cloud Occurrence and Cloud Properties from the A-Train: The relationship between cloud microphysics, cloud radiative forcing, and cloud geometric properties
The diverse array of instruments sensing the earth from the A-Train provides opportunities to quantify the occurrence, properties and effects of clouds. The great strength of the A-Train instrument suite extends from the diversity of the measurements and the combination of active and passive remote sensing. This opportunity for increasing our understanding can best be realized by considering the A-Train as a unified observational platform where the data streams from individual instruments are combined. This synergistic approach allows for description of the vertical profile of cloud physical properties. For instance, the radar reflectivity profile from Cloudsat and the attenuated backscatter profile from CALIPSO not only allows for the creation of an authoritative description of hydrometeor layers through the vertical column and over the entire earth but also provides unique information about the microphysical properties of these clouds. Combined with passive measurements from MODIS, CERES, and AMSR-E, a physically consistent vertical profile of cloud microphysical properties can be derived. I will describe an experimental approach to this problem and show results validated with data collected during field campaigns. The statistical distributions of cloud occurrence, cloud properties, and associated radiative forcing over several climatically important regions will be examined and compared.
A24B-02
Variability of radiation properties for different cloud types observed by CERES
This study evaluates the variations of cloud properties for different types of clouds using the Cloud and Earth's Radiant Energy System (CERES) Single Scanner Footprint (SSF) data obtained by both CERES and MODIS measurements from the NASA EOS satellites during January 1, 2003 to December 31, 2005. Generally, same types of clouds from different preferred areas have different radiative fluxes due mainly to the differences in solar insulation and local atmospheric profiles. When the same types of clouds are analyzed in the same boreal seasons, although there are large differences in cloud covers, the differences in radiation fluxes of these clouds are remarkably reduced. The inter-annual variations in the mean liquid water path (LWP) and ice water path (IWP) estimates for maritime straticumulus and anvil clouds, respectively, are very small, at least for these normal climate years, even the probability density functions show large variability in both LWP and IWP values. The area-to-area variability for the same type of clouds is as large as seasonal variability. Anvils in North Atlantic storm track regions have the largest seasonal variability, while the clouds off the coast of California exhibit minimal variations.
A24B-03
Relationships among MISR, OMI and CALIOP Cloud Occurrence Frequency Observations
Cloud detection depends on instrument sensitivity and thresholds used to separate between clouds and clear sky. Cloud occurrence frequency (COF), as a result, can vary substantially among observations from different instruments as well as with the same instrument if different cloud-detecting thresholds are used. With the launch of powerful CALIPSO cloud/aerosol lidar (CALIOP), we can quantitatively evaluate the clouds as observed by passive imagers such as MISR and OMI in terms of instrument sensitivity and cutoff optional depth. In this study we focus on cloud climatology for January 2008, in which MISR COF is typically 1-2 percent in the upper troposphere whereas CALIOP COF shows 10-20 percent instead. Using different cloud- detecting thresholds, we found that MISR COF would match well to a CALIOP COF if the threshold of 0.004- 0.005 1/km/sr be used in the attenuated 532nm perpendicular backscatter. This higher threshold is much higher than what CALIOP sensitivity can provide for cloud detection, explaining most of the large differences between MISR and CALIOP COFs. At this threshold, the optical depth for the integrated backscatter above cloud top is approximately 0.12-0.15, which is consistent with MISR detection limit. We will discuss more detailed analyses of COF observations from these sensors.
A24B-04
Evaluation of AMSR-E and MODIS Liquid Water Path Retrievals in Warm Clouds
This study evaluates liquid water path (LWP) estimates in warm oceanic clouds from the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E) and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments aboard the Aqua satellite. One year of AMSR-E Wentz retrievals and coincident, co-registered MODIS retrievals have been analyzed both for operational (vertically homogeneous) and adiabatic optical retrieval models. Dependence of LWP on factors such as cloud fraction, water vapor amount, presence of ice clouds or absorbing aerosols, solar and view geometry, as well as cloud heterogeneity has been investigated and will be presented. In non-precipitating clouds, microwave and optical datasets are generally well correlated, with a coefficient of 0.72 when all scenes are considered, and 0.83 for overcast cases. Overall, AMSR-E LWP overestimates MODIS by 15-25 g/m2 in annual and monthly means due to a high bias rapidly increasing with decreasing cloud fraction, but also depending on water vapor amount. In overcast cases, however, the adiabatic optical model results in excellent agreement between the datasets, with monthly biases within 5 g/m2, and an annual bias of only 0.3 g/m2. Zonal means show relatively good agreement in the summer hemisphere; however, in the winter hemisphere, MODIS LWP sharply increases toward the poles in contrast to AMSR-E. This behavior points to significant 3D optical effects at large solar zenith angles. In addition, the discrepancy between microwave and optical estimates, and the view angle dependence of MODIS retrievals, are generally more pronounced for heterogeneous than homogeneous cloud scenes, especially at low sun, further indicating that 3D effects can be important under certain solar/view geometries. In precipitating clouds, AMSR-E suggests a much faster LWP increase with rain rate than does MODIS. This and an assumed rain-no rain threshold of 180 g/m2 result in AMSR-E LWP being significantly overestimated in warm precipitating clouds, but increasingly underestimated in thick non-precipitating clouds with optical thicknesses above 30. Based on these results we recommend a simple modification to the cloud LWP-rain rate formula currently implemented in the Wentz algorithm, which might yield better agreement between AMSR-E and MODIS retrievals under warm rain conditions.
A24B-05
Utilizing the multiangular information of PARASOL oxygen A-band measurements to infer macrophysical properties of cloud structures
Getting informations about the vertical structure of cloud covers (altitude, geometrical thickness, multilayer features) is of high interest for different applications (vertical profile of radiative heating rate in the atmosphere, weather forecast). We show here interest in the multiangular character of PARASOL measurements in the oxygen A-band to infer macrophysical properties of cloud structures. Our idea is to detect from this satellite passive sensor multilayers clouds and to retrieve simultanously cloud-top pressure and its geometrical thickness. We will show results of simulation, and analyses of PARASOL data, and comparisons with other satellite (CALIPSO, CLOUDSAT) and ground measurements.
A24B-06 INVITED
Characterization of the Chemical and Optical Properties of Cloud-Processed Aerosols: first results from the Cumulus Humilis Aerosol Processing Study of June 2007 (CHAPS)
Considerable progress has been made in the analysis and reduction of observations coming from the
Cumulus Humilis Aerosol Processing Study (CHAPS) of June 2007. This campaign was designed to
characterize and contrast freshly emitted aerosols below, above and within fields of fair weather cumulus in
the vicinity of Oklahoma City (OKC), OK, and to look for changes in the cloud microphysical structure
associated with these clouds.
Since the campaign, we have found clear evidence of the Oklahoma City plume despite the extensive
precipitation that occurred during the study, with elevated CO levels found in many of the boundary layer
clouds downwind of this mid-size North American city. Areas of elevated CO were frequently co-located with
regions in which the number density of particles less than 0.17um were an order of magnitude greater than
corresponding measurements collected in air outside of the plume region, suggesting that fresh particles
associated with urban activities were indeed being sampled by instruments aboard the Department of Energy
G-1 aircraft. Estimates of the activation efficiency of aerosols within clouds have been developed by
examining the ratio of aerosol number density as estimated by a condensation particle counter (CPC)
sampling behind a Counterflow Virtual Impactor, which allowed only cloud drops into the sampling stream,
and the total number of aerosols measured by a Passive Cavity Aerosol Spectrometer Probe (PCASP)
mounted on the outside of the aircraft. The first look at aerosol composition from an Aerodyne Mass
Spectrometer that alternated sampling between the CVI and a standard inlet has not yet suggested any
significant differences in the fractional composition of aerosols measured upwind-, downwind-, below- or
above-cloud; in all cases sulfate and organics dominated the mass, although elevated NO3 levels were
detected in aerosol measured behind the CVI during in-cloud sampling.
Observations from the CHAPS ground site just north of OKC included a MicroPulse LIDAR (MPL) with
pointing and scanning ability; this flexibility allowed CHAPS scientists to identify streaks of enhanced aerosol
backscatter below clouds that we think are due to aerosols within the thermal roots of fair weather cumulus
that are growing as a result of the increased relative humidity typically found in upper boundary layers.
http://asp.labworks.org/
A24B-07
Lidar observations of aerosols near clouds during CHAPS/CLASIC
Data collected by two lidar systems during the CHAPS/CLASIC missions are used to examine the behavior of aerosols in "transition zones" of a few kilometers to several tens of kilometers away from clouds. The lidar measurements are unaffected by cloud adjacency effects, are less susceptible to cloud contamination than passive satellite measurements, and possess high vertical and temporal resolution to capture variations in aerosol optical properties near clouds. The ground-based U.S. Department of Energy Atmospheric Radiation Measurement Climate Research Facility Raman lidar provides a detailed view of the variability of aerosols and water vapor near clouds at or near the top of the Planetary Boundary Layer. Aerosol and water vapor properties in the vicinity of clouds at the top of the daytime boundary layer are examined using 10 second profiles of aerosol backscattering, water vapor mixing ratio, and relative humidity, and 1 minute profiles of aerosol extinction in conjunction with continuous Total Sky Imager images of cloud cover. Data from the NASA Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) collected during CHAPS/CLASIC are also used to examine the variability of aerosol optical properties near clouds. The LaRC airborne HSRL measures aerosol backscatter and depolarization at 532 and 1064 nm and aerosol extinction at 532 nm. Preliminary results using these Raman lidar and HSRL data show that aerosol backscatter and extinction 1-2 km from clouds were approximately 25-40% smaller than immediately adjacent to clouds. The variations in aerosol optical thickness are smaller, typically around 10-15%, since the changes in aerosol backscatter and extinction were generally confined to the top of the boundary layer. Variations in the Raman lidar aerosol backscatter and extinction measurements were typically confined to the altitude range between 200-400 m below cloud base and 200 m above cloud base. Raman lidar observations show relative humidity decreased by 5-15% within this same region suggesting that variations in backscatter and extinction near clouds were caused in part by hygroscopic aerosol growth. The HSRL aerosol depolarization measurements also suggest that aerosol nonsphericity changed in response to variations in relative humidity. This presentation will discuss the use of these lidar measurements as well as airborne in situ measurements to study the behavior of aerosols near clouds.
A24B-08
Investigation of Southern Great Plains Atmospheric Moisture Budget for CLASIC
The Cloud and Land Surface Interaction Campaign (CLASIC) was conducted over the Southern Great Plains (SGP) ARM Climate Research Facility (ACRF) during June 2007. The investigation described here is designed to provide larger-scale background information for the CLASIC 'Science Questions' that focus on the roles of cumulus convection and land cover variation in relation to the SGP atmospheric moisture budget. Moisture budget analysis is an important tool for studying surface-atmosphere interactions, since the linkages among atmospheric dynamics, water vapor field, surface conditions, and precipitation are constrained by the moisture continuity equation. We use the methods of a recently completed investigation of the moisture budget over the Midwestern Corn Belt (Zangvil et al.,J. Climate, 2001, 2004). In the past, some researchers have interpreted the moisture flux divergence term (MFD) in the traditional moisture budget formulation as a precipitation source. Our research has shown that the externally advected or locally evapotranspired origins of precipitation need to be expressed in terms of an inflow/outflow moisture budget formulation that is defined at the boundaries of the study area. We present an analysis of the moisture budget terms related to both formulations for several contrasting May-June periods over the SGP, including the very wet 2007 season when CLASIC was conducted. Emphasis is given to (1) investigation into the potential nonlinearities in the MFD term and its components of horizontal moisture divergence and horizontal moisture advection, and (2) a spectral analysis highlighting phase shifts among the moisture budget components. Data sources include the North American Regional Reanalysis (NARR) with high temporal (3 hour) and spatial (32 km) resolution, NWS recording raingauges, and special ARM CLASIC observations. With comparisons to our previous Midwestern moisture budget study, this project also will help to assess the uniqueness of the CLASIC land-atmosphere-interaction results, especially concerning the role of the horizontal moisture advection term.
A24B-09
Overview of the MODIS Airborne Simulator (MAS) Instrument and Cloud Products during CLASIC/CHAPS
During CLASIC/CHAPS, the NASA high-altitude ER-2 aircraft flew 6 dedicated science flights observing a variety of boundary layer clouds as well as ice cloud systems. On board the ER-2 was the MODIS Airborne Simulator (MAS) imager as well as other remote sensing instruments. MAS is a grating spectrometer with 50 spectral bands from the visible through the infrared and 50 meter spatial resolution at the ground. Many of the ER-2 flights were coordinated with a variety of in situ aircraft in the greater Oklahoma CLASIC/CHAPS operational area. In addition, the ER-2 coordinated with the NASA Aqua satellite platform on three occasions; Aqua flies one of the two Moderate Resolution Imaging Spectroradiometer (MODIS) instruments. An assessment of the MAS solar reflectance band calibration derived from these MODIS underflights will be discussed. A cloud retrieval algorithm nearly identical to that used for operation processing of MODIS data has been applied to MAS observations. Results from selected flight tracks will be shown.