HR: 1340h
AN: A43C-0110    [Abstracts]
TI: Analysis of Trends and Solar Cycle Effects in the TOMS and SBUV(/2) UV Effective Reflectivity Datasets
AU: * LLOYD, S A
EM: STEVEN.LLOYD@JHUAPL.EDU
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AB: Amid the flurry of publications in the past few years, both in favor and against the new theory of cosmic ray modulation of climate mediated by ion-induced cloud formation, it is still abundantly clear that there are a number of relevant satellite datasets that have yet to be applied to this problem. We have analyzed the Total Ozone Mapping Spectrometer (TOMS) and Solar Backscatter UltraViolet (SBUV and SBUV/2) UV effective reflectivity datasets as surrogates for total cloud cover to determine a correlation between solar cycle and reflectivity, and have further investigated the issue of discontinuity or long-term drift in the ISCCP dataset. The series of TOMS and SBUV(/2) instruments provides a 27-yr record of direct observations of effective UV reflectivity across the globe. Since ISCCP provides estimates of cloud amount and cloud optical depth as separate parameters, it is necessary to convolve these two derived quantities to get a measure of cloud reflectivity. TOMS and SBUV(/2) provide well-calibrated, direct measurements of effective reflectivity or albedo in the near UV, which might well prove to be a better measure of effective cloud cover. While other TOMS and SBUV(/2) data products are somewhat sensitive to the degradation of the instruments' diffuser plates, observations of absolute reflectivity are routinely calibrated against geographic locations with well-known surface reflectivity, such as cloud-free scenes of open ocean (low reflectivity) and cloud-free scenes of ice sheets (high reflectivity). This frequent absolute calibration provides a stable record of global effective reflectivity over 27 yr. We have investigated the correlation of UV effective reflectivity (as a surrogate for effective cloud cover) with galactic cosmic ray (GCR) fluxes and other surrogates of solar activity as a function of solar cycle and latitude. This dataset also provides insight into the issue of long-term changes in the effective albedo of the Earth (i.e.``global dimming''). Marsh and Svensmark [2003] presented results indicating that while their claim of a good statistical correlation between low clouds as determined by the ISCCP-D2 dataset and GCR exists for the period 1983-1994 [Marsh and Svensmark, 2000], this correlation breaks down for the subsequent period 1995-2001. They claim that the ISCCP intercalibration between September 1994 and January 1995 resulted in a calibration discontinuity or long term drift in at least one of the satellite datasets, using differences between ISCCP and SSMI data in the period after 1994 to support their claim. We have used the 27-yr TOMS and SBUV(/2) reflectivity datasets with their stable calibration to further investigate the issue of a possible discontinuity or long-term drift in the ISSCP cloud data.
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005