A33F-01 INVITED
Assessing the Vertical Structure of Global Atmospheric Radiative Heating Using CloudSat
It is well known that clouds and precipitation exert a profound influence on the propagation of radiation through the Earth's atmosphere. In fact, feedbacks between clouds, radiation, and precipitation represent one of the most important unresolved factors inhibiting our ability to predict the consequences of global climate change. By virtue of its sensitivity to both clouds and precipitation, CloudSat is uniquely suited to addressing the problem of quantifying their role in modifying the vertical structure of atmospheric radiative heating on global scales. The CloudSat radiative fluxes and heating rates product leverages CloudSat's unprecedented cloud and vertical structure information to infer profiles of longwave and shortwave radiative heating in the atmosphere at a resolution that has not been possible until now. This presentation will describe the underlying physical bases of the algorithm, summarize early efforts to evaluate the products, and highlight preliminary findings from the analysis of the first year of CloudSat data. Emphasis will be placed on the problem of assessing the varying impacts of clouds with different morphologies on the vertical distribution of radiative heating in the atmosphere over different regions of the globe.
A33F-02
Radiative Impacts of Misclassification of Cloud Thermodynamic Phase
Cloud thermodynamic phase is one cloud observation among a set necessary to monitoring cloud-climate feedbacks. Together with cloud height, temperature, thermodynamic phase,and optical properties such as effective radius and optical thickness, cloud phase is necessary to model the radiative impacts of clouds. While much progress has been made in recent years in satellite-based cloud phase determination using near-infrared measurements of reflected solar radiation, most infrared-based techniques still rely on a priori assumptions of relationships between cloud phase and cloud temperature. We will present a new method for retrieving cloud phase using infrared satellite observations from the MODIS and AIRS instruments. This method does not depend on an assumed relationship between cloud phase and temperature, making it useful for studying potentially mixed-phase clouds with temperatures between 255 and 265 K. This method will be applied to several case studies using MODIS and AIRS data, allowing relationships between cloud phase, height, and temperature to be determined. These relationships will be used as input to a broadband radiative transfer model to address the following question: "What are the radiative impacts of misclassification of cloud thermodynamic phase?" In particular, we will address the effects of redistributing water vertically and between phases. For each set of relationships, longwave and shortwave cloud forcing will be calculated at the surface of the earth, the top of the atmosphere, and the atmospheric layers in between.
A33F-03
Cirrus Radiative Flux Study at SGP Using Radar/Lidar/AERI Derived Cloud Properties
The role that clouds play in the Earth's radiative balance represents a major source of uncertainty in understanding climate and climate change. A large part of this uncertainty lies in the modeling of the cloud, which requires assumptions and simplifications of the cloud morphology. In this study uniform cirrus cloud events at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site are investigated using various data sources (including 3 mm and 8 mm radar, lidar, AERI, and combinations thereof) to derive cloud microphysical and optical properties. The results of a flux closure study are presented where observed top-of- atmosphere and surface flux measurements are compared with computed fluxes. Computed heating rates are compared with the ARM Broadband Heating Rate Profile (BBHRP). Results indicate that combinations of measurement types are needed to accurately characterize thin cirrus. Radar alone can miss significant upper level cirrus impacting the computed fluxes and heating rates. Vertical distribution of cirrus extinction and particle size is significantly less important than the total optical depth in computing heating rates.
A33F-04
Radiative Heating Profiles for Tropical Cloud Regimes
Radiative heating is important for its effects on atmospheric circulation and cloud evolution in addition to its central role in influencing the atmospheric temperature structure. The vertical distribution of radiative heating is determined by the vertical profile of gases such as water vapor, ozone and CO2 as well as by clouds. The Atmospheric Radiation Measurement (ARM) program operates sites around the world which provide measurements of surface radiative fluxes and various measurements of the atmospheric state that effect surface fluxes. Continuously operating millimeter cloud radars at each site provide the means to derive vertical profiles of cloud properties. In previous work, we have used these cloud profiles in combination with profiles of temperature and humidity from radiosondes to calculate radiative flux profiles using a 4-stream radiative transfer model at the three tropical ARM sites: Manus, Nauru, and Darwin. In the current study, we will use the vertical profiles of cloud properties at these sites to segregate the data into distinct cloud regimes. By compositing radiative heating profiles in different regimes, we will define characteristic radiative heating profiles of each cloud regime. Analysis of the data in terms of cloud regime provides datasets which can be more easily compared with climate model results.
A33F-05
The Sensitivity of Shortwave Radiative Forcing and Heating Rates to the Aerosol Vertical Profile
We are investigating the sensitivity of the shortwave aerosol radiative forcing and the heating rate profile to the vertical profile of aerosol optical properties (extinction, single-scattering albedo, and asymmetry parameter), solar geometry and surface albedo for clear-sky conditions. Total uncertainties in modeled local diurnally averaged direct radiative forcing (DRF) at the surface and top of the atmosphere (TOA) due to uncertainties in the input parameters mentioned above range from 0.2 to 1.3 W m-2 (42 to 20%) depending on location (from tropical to polar sites), solar zenith angle, surface reflectance, aerosol type, and aerosol optical depth. The largest contributor to total uncertainty in DRF is usually single scattering albedo; however decreasing measurement uncertainties for any property would increase accuracy in DRF. Comparison of two radiative transfer models (RRTM_SW and SBDART) suggests the contribution of modeling error is small compared to the total uncertainty although comparable to uncertainty arising from some individual properties. In this presentation we are assessing the results not only at TOA and the surface but throughout the vertical profile. As inputs, we are using slightly idealized case studies from SAFARI-2000 (Southern Africa), ACE-Asia (Sea of Japan, 2001), ARM Aerosol IOP (Oklahoma, 2003), and RADAGAST (Niger, 2006). These case studies encompass a wide range of aerosols including marine, local and transported smoke, dust, and pollution aerosols. Initial results indicate that the shape of the aerosol extinction profile has very little impact on TOA and surface forcing. However, as long as the aerosol is not purely scattering (i.e single-scattering albedo < 1), the shape of the extinction profile is important for the vertical profiles of forcing and heating rates. In contrast, the shape of the aerosol absorption profile has a slight impact on TOA and surface forcing but is the main driver for the forcing and heating rate profiles. Unfortunately, the vertical profile of aerosol absorption is a quantity that is currently measured with rather large uncertainties only. We also show actual measurements of up and down-welling spectral flux profiles from the 2003 ARM Aerosol IOP and our attempts at deriving heating rate profiles from these.
A33F-06
Atmospheric Heating by Saharan Dust and Its Implication on the Temperature Profiles over the Tropical Cyclone Main Development Region
We have investigated anomalies in atmospheric temperature profiles that are associated with Saharan dust over the tropical cyclone main development region (10°-20°N, 20°-30°W), using temperature data from Atmospheric Infrared Sounder (AIRS) and aerosol data from Moderate Resolution Imaging Spectroradiometer (MODIS). We find that Saharan dust is associated with a vertical temperature structure that has a warm anomaly lying above the marine boundary layer (~850 hPa) and a cold anomaly throughout the middle troposphere (~350-600 hPa). We then estimate dynamical and dust radiative heating of the atmospheric column. The dynamical heating is estimated using wind and temperature data from NCEP reanalysis, while the dust radiative heating is computed using the NASA/GSFC CLIRAD radiative transfer model for both shortwave and longwave. Dust particle size distributions and vertical concentration profiles for use in the radiative transfer calculations are prescribed according to the simulation of the MATCH dust transport model. The warm anomaly in the lower tropsphere can be explained by the dynamical and dust radiative heating. For air columns with aerosol optical thickness greater than one, the dust heating rate is at least 20% of the dynamical heating rate in the lower troposphere. The cold anomaly in the middle troposphere cannot be explained by dynamical or radiative heating. Suppression of deep convection probably plays an essential role in cooling the middle troposphere over the dust layer by reduction of latent heat release. We will also investigate the sensitivity of dust radiative heating rate using assumed particle shapes for dust.
A33F-07
Atmospheric Solar Absorption measurements in the lowest 3-km of the atmosphere with small UAVs
This paper reports unique measurements of atmospheric solar absorption and heating rates in the visible (0.4- 0.7 ƒÝm) and broadband (0.3-2.8 ƒÝm) spectral regions using vertically stacked multiple light weight autonomous unmanned aerial vehicles (UAVs) during the Maldives autonomous UAV campaign (MAC). The UAVs and ground based remote sensing instruments determined most of the parameters required for calculating the albedo and vertical distribution of solar fluxes. Measured fluxes have been compared with those derived from a Monte-Carlo radiative transfer algorithm which can incorporate both gaseous and aerosol components. The analysis focuses on a cloud-free day when the air was polluted due to long range transport from India, and the mean aerosol optical depth (AOD) was 0.31 and mean single scattering albedo was 0.92. The UAV measured absorption AOD was 0.019 which agreed within 20% of the value of 0.024 reported by a ground based instrument. The observed and simulated solar absorption agreed within 5% above 1.0 km and aerosol absorption accounted for 30% to 50% of the absorption depending upon the altitude and solar zenith angle. Thus there was no need to invoke anomalous or excess absorption or unknown physics in clear skies, provided we account for aerosol black carbon. The diurnal mean absorption values for altitudes between 0.5 and 3.0 km msl were observed to be 41¡Ó3 Wm-2 (1.5 K/day) in the broadband region and 8¡Ó2 Wm-2 (0.3 K/day) in the visible region. Future investigations into the atmospheric absorption in cloudy skies will characterize the spatial and temporal variation of the cloudy atmosphere in sufficient detail to simulate the vertical distribution of net solar fluxes to permit comparison with the collected radiative observations. This next phase will utilize 4 stacked UAVs to observe the extended cloud decks off the coast of California. A combination of observations and models will then be used to assess if the amount of solar absorption observed to occur in cloudy atmosphere can be accounted for without invoking unknown or anomalous physics.
A33F-08
RADAGAST: Modelling Surface and TOA Fluxes to Estimate Atmospheric Flux Divergence
The ARM mobile facility deployment to Niger, during 2006, was chosen partly to complement the GERB broadband radiation budget instrument on Meteosat-8. This afforded the opportunity of combining radiation measurements at the top of atmosphere (GERB) and at the surface (AMF). Using the AMF instrumentation, the modelling of these fluxes in the atmospheric column over Niamey has been initiated. The aim is to create a framework that ensures consistency between the surface and TOA components in the atmospheric radiation budget. We achieve this by utilising satellite retrievals to characterise the spatial inhomogeneity and thus produce estimates of the surface and TOA fluxes that are most consistent with the measurements. Examples of the modelling in this framework are shown, and the method illustrated. The result of this modelling is to produce surface and TOA fluxes that can be combined to produce the divergence values under a variety of atmospheric conditions (e.g. aerosol loading, various cloud types). Initial results of the resultant divergence values for the whole of 2006 will also be shown.