A34D-01 INVITED
Radiative Energy Budget in the Tropical Upper Troposphere and Lower Stratosphere
The radiative heating rates in the tropical upper troposphere and lower stratosphere (UTLS) play a critically important role in the tropical troposphere-to-stratosphere transport. In this presentation I will review recent efforts to quantify the radiative heating rates in the UTLS and discuss the challenges in radiative transfer modeling and observations of atmospheric states and clouds in this region.
A34D-02 INVITED
Improved Understanding of Far-Infrared Radiative Processes in the Earth's Atmosphere
Longwave radiative cooling in the upper troposphere significantly influences Earth's climate. With water vapor dominating this cooling, the spectral regions in which the greatest upper tropospheric cooling occurs are opaque when viewed from the vast majority of surface locations. While the opacity of the lower atmosphere is a formidable obstacle in studying upper tropospheric radiative processes from the surface, a greater obstacle has been the lack of radiometric instrumentation in the most critical spectral region for these processes, the far- infrared (λ > 15 μm). These obstacles have led to a relatively high uncertainty in our knowledge of upper tropospheric radiative processes. In the spring of 2007, the Radiative Heating in Underexplored Bands Campaign (RHUBC) was conducted at the Atmospheric Radiation Measurement Program's (ARM) North Slope of Alaska Climate Research Facility (NSA). The experiment was designed to make detailed observations of the downwelling infrared radiation in the pure rotation (17--100 μm; 100--600 cm-1) and the 6.7 μm (1350--1850 cm-1) ν2 water vapor bands under the extremely dry and cold conditions found at the NSA location. High-spectral-resolution observations were collected by two state-of-the-art Fourier Transform Spectrometers: the ARM AERI-ER (400-- 3000 cm-1) and the Imperial College TAFTS (80--650 cm-1). Also, three state-of-the-art microwave radiometers observing emission at 183 GHz were deployed to the NSA site during RHUBC. From these microwave measurements, the total atmospheric water vapor column can be accurately retrieved. With numerous radiosondes launched in conditions with less than 3 mm of total precipitable water vapor, RHUBC provided the opportunity for extensive clear-sky high-spectral-resolution comparisons between model calculations and measurements. This presentation will discuss the infrared radiance measurements, radiative transfer models and specification of the atmospheric state used in these radiative closure studies, as well as the initial efforts to reduce key uncertainties in water vapor spectroscopy. RHUBC is anticipated to improve calculations of polar surface radiative fluxes and mid-to-upper tropospheric radiative cooling, ultimately resulting in improved simulations of Earth's present and future climate. http://science.arm.gov/rhubc/
A34D-03
A comparison of clear-sky OLR between CERES measurements and model calculations and the dependence of OLR on temperature and water vapor
We compare nighttime clear-sky outgoing longwave radiation (OLR) from a model calculation against measurements from the Clouds and the Earth's Radiant Energy System (CERES) data set. Our model calculation is driven by profiles of temperature and water vapor from the Atmospheric Infrared Sounder (AIRS). Using several different radiative transfer models, we find an offset between the model and measurements, with the model tending to predict higher OLR by about 5 watts per square meter. Although this can be explained by uncertainties in the data and model, it is also possible that there is some missing process in the model. We also explore how the atmosphere regulates OLR by looking at the gradients between the dry subtropics and the moist convective regions. We see how changes in water and temperature oppose each other, and how changes in water begin to dominate around 299 K, where the so-called supergreenhouse effect occurs.
A34D-04
Cloud Structure Anomalies Over Tropical Pacific During 97/98 El Nino
A merged satellite data set has been used to study cloud structure and outgoing longwave radiation (OLR) changes over the tropical Pacific Ocean during the strong 1997/98 El Niño. This data set provides radiative fluxes at the top of the atmosphere in addition to cloud fraction, cloud-top altitude and cloud optical depth, all on a one-degree by one-degree grid and as monthly means for the first eight months of 1998. This time period includes much of the 1997/98 El Niño, which reached peak intensity in March 1998 and had essentially subsided by August 1998. The west-to-east shift of the center of convection that occurred during the El Niño resulted in cloud fraction, cloud-top altitude and cloud optical depth all increasing in the eastern equatorial Pacific while decreasing in the western tropical Pacific, and for both regions all three cloud parameters are strongly correlated with each other. OLR changes over the eastern Pacific are also investigated. For all sky OLR change, though highly correlated with sea surface temperature (SST), is mainly driven by cloud altitude and cloud fraction change. Clear sky OLR change is mainly due to moisture change. SST and lapse rate have much smaller effect on OLR change.
A34D-05
Diagnosis of the Course Vertical Profile of Radiative Heating with CERES Surface and Atmosphere Radiation Budget (SARB) for Terra and Aqua
The vertical profiles of SW and LW fluxes (surface, 500 hPa, 200 hPa, 70 hPa, and TOA) have been computed over the globe with the Langley Fu-Liou (FL) code and inputs for clouds from MODIS (Minnis et al.), aerosols from the MODIS-Atmosphere Team and the NCAR Model for Atmospheric Transport and Chemistry (MATCH), temperature and humidity from GEOS-4, and ozone from SMOBA (mostly SBUV). Surface spectral albedo for the ice-free ocean was based on Jin et al.; clear-sky broadband CERES SW observations and a look-up table to FL were used to develop surface albedo elsewhere. Tuned (i.e., based on adjustments to cloud properties) and untuned fluxes were compared with CERES at TOA for every footprint. Systematic validation with independent broadband SW and LW measurements at 60 sites worldwide has been a severe teacher on disparate accounts: RMS discrepancies of calculations with observations show that computed instantaneous diabatic profiles with clouds have limited meaning. For clear footprints over land, time-mean computed and observed surface insolations often agree, but this is partly due to offsetting errors in the code and aerosol inputs (MFRSR and Cimel photometers show MODIS Collection 4 land optical depths are too high). CERES broadband SW TOA observations appear to be low by 2-3 percent. Matched surface and TOA validation indicates, however, the LW profiles merit attention on the monthly scale: the interannual variability of surface LW downwelling compares astoundingly well with collocated ARM measurements of E13 and C01 (RMS of retrieval and measurement less than RMS of measurements). On both the interannual (deviation of an individual month from the calendar monthly mean) and synoptic (snapshot deviation from the mean of the individual month) scales, layer radiative heating correlates with layer water vapor more strongly than with layer temperature; and coherence in the upper troposphere exceeds that in the lower troposphere. Clouds introduce noise and reduce the correlation of layer radiative heating with water vapor, but all-sky regressions can have more slope than do clear-sky regressions, so total radiative divergence explained by fluctuations of water vapor increases in a cloudy sky. We will summarize such profile results from sites where matched TOA and surface validation give sufficient confidence. http://www-cave.larc.nasa.gov/ceres/
A34D-06 INVITED
Evaluation of shortwave flux profiles in the Hadley Center Global Environmental Model (HadGEM1) with CERES TRMM products
The value of checking the shortwave fluxes produced by a climate model with reliable data at both the surface and top of atmosphere (TOA) is well recognized. An examination of the full vertical profile of shortwave fluxes, however, provides further insight on the integrated effects of cloud and aerosol processes, as well as the distribution of water vapor, on fluxes in the model; and will be helpful for improving the simulation of the present- day climate and the predictions of climate change. Cloud and the Earth's Radiant Energy System (CERES) on TRMM satellite provides broadband TOA observations in low and mid latitudes from January 1998 to August 1998. CERES's surface and atmospheric radiation budget (SARB) group also calculates fluxes at the surface, 500 hPa, 200 hPa, 70 hPa, and TOA, using inputs of cloud and aerosol optical properties derived from the narrowband VIRS imager on TRMM; and an operational aerosol assimilation. Validation of the SARB calculations are extensive at the TOA, where each footprint in the complete domain is compared with explicit broadband observations by CERES; at the surface, the computed fluxes are routinely compared with quality measurements at ground 50 sites; these checks establish the uncertainties of the computed fluxes within the atmosphere. To compare these flux profiles with those from HadGEM1, we developed a method to correct the insufficient diurnal coverage of CERES on TRMM, since TRMM spacecraft does not provide a true diurnal coverage. The diurnal coverage corrected monthly-mean shortwave flux profiles in the tropics are compared with those from HadGEM1 for clear sky and all sky conditions. The differences at each level are analyzed and the causes are discussed.
A34D-07
Relationships between ISCCP Cloud Cover Amounts and Energy Budget Terms from the NASA/GEWEX SRB
The ISCCP (International Satellite Cloud Climatology Project) has now produced over 20 years of global cloud data which is used as an input for computing the Earth's radiative energy budget by the NASA/GEWEX SRB (Surface Radiation Budget.) Since both of these mutidecadal records are being used to analyze long-term global trends, it is important to understand the degree to which the two records are linked. We present the results of a study comparing the trends in total cloud amount and the amounts of high, middle, and low clouds from ISCCP to the trends in surface solar fluxes and atmospheric absorption in the SRB. In particular, we will demonstrate that the "geo artifacts" observed in the ISCCP cloud data do not control the long-term trends in the SRB downwelling solar flux at the surface. We will also show the contributions of each cloud type to both the ISCCP "artifact" and the column energy budget.
A34D-08
Ship based cloud and radiation measurements on the Atlantic Ocean
Clouds remain one of the biggest obstacles in our understanding of the coupled ocean-atmosphere climate system. Because of the strong inhomogeneity of cloud pattern on those scales that are relevant for the radiative transfer processes it is clear that subgrid-scale processes must be accounted for in radiative transfer parameterizations. Combined observations of cloud physical and radiative properties are a key to adjust or to validate such parameterizations. In spring and in fall 2007 the cruises ANT-XXIII-10 and ANT-XXIV-1 of the German research vessel Polarstern from South Africa to Germany and back have been utilized to perform continuous measurements of the radiation budget at the sea surface and the corresponding cloud properties under tropical, subtropical and mid-latitude climate conditions. For the first time, a multichannel microwave radiometer has been operated under open ocean conditions to obtain profiles of humidity, temperature, as well as liquid water path and water vapor path with 1 Hz temporal resolution. Cloud cover, cloud type and cloud bottom height have been obtained from continuous sky imaging and ceilometer measurements. Satellite based surface radiation budget estimates from Meteosat-7 SEVIRI measurements provided by the Climate Monitoring - Satellite Application Facilities CM-SAF have been compared to ship based measurements. Differences between the two will be discussed in terms of climatological and meteorological conditions. The high resolution ship based observations of cloud and radiation properties have been applied to improve exisiting surface radiation parameterizations with special considerations of rapid fluctuations due to the dynamics of clouds. Both campaigns in 2007 are test phases for the German national project OCEANET where temporarilly high resolved measurements of the chemical and biological composition of the upper ocean are combined with energy- and CO2-flux measurements at the ocean surface to improve our understanding of ocean-atmosphere interactions. To this end intensive measurements during six Atlantic transects of RV Polarstern between 2008 and 2010 will be performed.