Advances in Engineering Advances in Engineering features breaking research judged by Advances in Engineering advisory team to be of key importance in the Engineering field. Papers are selected from over 10,000 published each week from most peer reviewed journals.
Journal of Climate, May2013, Vol. 26 Issue 9, p2719
Kato, Seiji; Loeb, Norman G.; Rose, Fred G.; Doelling, David R.; Rutan, David A.; Caldwell, Thomas E.; Yu, Lisan; Weller, Robert A.
NASA Langley Research Center, Hampton, Virginia and
Science System & Applications Inc., Hampton, Virginia and
Science System & Applications Inc., Lanham, Maryland and
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts.
Abstract
The estimate of surface irradiance on a global scale is possible through radiative transfer calculations using satellite-retrieved surface, cloud, and aerosol properties as input. Computed top-of-atmosphere (TOA) irradiances, however, do not necessarily agree with observation-based values, for example, from the Clouds and the Earth’s Radiant Energy System (CERES). This paper presents a method to determine surface irradiances using observational constraints of TOA irradiance from CERES. A Lagrange multiplier procedure is used to objectively adjust inputs based on their uncertainties such that the computed TOA irradiance is consistent with CERES-derived irradiance to within the uncertainty. These input adjustments are then used to determine surface irradiance adjustments. Observations by the Atmospheric Infrared Sounder (AIRS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) that are a part of the NASA A-Train constellation provide the uncertainty estimates. A comparison with surface observations from a number of sites shows that the bias [root-mean-square (RMS) difference] between computed and observed monthly mean irradiances calculated with 10 years of data is 4.7 (13.3) W m−2 for downward shortwave and −2.5 (7.1) W m−2 for downward longwave irradiances over ocean and −1.7 (7.8) W m−2 for downward shortwave and −1.0 (7.6) W m−2 for downward longwave irradiances over land. The bias and RMS error for the downward longwave and shortwave irradiances over ocean are decreased from those without constraint. Similarly, the bias and RMS error for downward longwave over land improves, although the constraint does not improve downward shortwave over land. This study demonstrates how synergetic use of multiple instruments (CERES, MODIS, CALIPSO, CloudSat, AIRS, and geostationary satellites) improves the accuracy of surface irradiance computations.
Additional information
The Clouds and the Earth’s Radiant Energy System (CERES) is a National Aeronautics and Space Administration (NASA) satellite project that provides observations of Earth’s radiation budget at the top-of-atmosphere and surface. The CERES instrument is a broadband scanning radiometer that measures radiances in the shortwave (0.3 to 5 micrometre), total (0.3 to 200 m) and window (8 to 12 micrometre) spectral regions, which are used to determine reflected solar and emitted thermal irradiances over a range of spatial and temporal scales. Currently, two instruments are operating on the Terra satellite in a 10:30 AM sun-synchronous orbit, two instruments are on the Aqua satellite in a 1:30 PM sun-synchronous orbit, and one instrument is on the Suomi NPP satellite, also in an afternoon sun-synchronous orbit. Surface irradiances are computed using surface and cloud property data inferred from imagers flying on the same satellite as CERES instruments as well as from geostationary satellites. Atmospheric temperature/humidity data is from reanalysis and infrared sounder measurements.
The surface irradiance data product described in the paper entitled “Surface irradiance consistent with CERES-derived top-of-atmosphere shortwave and longwave irradiances” is available from a NASA Langley Research Center web site (http://ceres.larc.nasa.gov/order_data.php) under the name “EBAF-surface”. This data product contains monthly 1°´1° gridded mean surface shortwave (solar) and longwave (infrared) up and downward irradiances under all- and clear-sky conditions from March 2000 through (currently) September 2012. The time period covered by the product is regularly updated. The latency of data release is 6 months to 1 year. The product is developed for climate research but its use can be extended to other areas that require stable and accurate surface irradiances. The estimated uncertainty in surface irradiances is discussed in the paper. Figure 1 shows the downward transmitted solar and emitted infrared irradiances at the surface averaged over 10 years from the data product.
The CERES project also distributes surface irradiances at higher temporal and spatial resolutions. The CERES SYN1deg data product contains 3-hourly surface irradiances in daily files. The CRS product contains instantaneous surface irradiance at a CERES footprint resolution (~20 km) in hourly files. Instantaneous and gridded surface irradiances are also available with a shorter latency, 1 week after data are produced, from CERES FLASHFLUX data products (FLASH_SSF and FLASH_TISA). These products are available from (http://ceres.larc.nasa.gov/compare_products-ed2.php).
