Analysis of cumulus solar irradiance reflectance (CSIR) events

Clouds are extremely important with regard to the transfer of solar radiation at Earth's surface. This study investigates Cumulus Solar Irradiance Reflection (CSIR) using ground-based pyranometers. CSIR events are short-term increases in solar radiation observed at the surface as a result of reflection off the sides of convective clouds. When Sun-cloud observer geometry is favorable, these occurrences produce characteristic spikes in the pyranometer traces and solar irradiance values may exceed expected clear-sky values. Ultraviolet CSIR events were investigated during the summer of 1995 using UVA and UVB pyranometers. Observed data were compared to clear-sky curves which were generated using a third degree polynomial best-fit line technique. Periods during which the observed data exceeded this clear-sky curve were identified as CSIR events. The magnitude of a CSIR event was determined by two different quantitative calculations. The MAC (magnitude above clear-sky) is an absolute measure of the difference between the observed and clear-sky irradiances. Maximum MAC values of 3.4 Win⁻² and 0.0169 Wm⁻² were observed at the UV-A and UV-B wavelengths, respectively. The second calculation determined the percentage above clear-sky (PAC) which indicated the relative magnitude of a CSIR event. Maximum UV-A and UV-B PAC magnitudes of 10.1% and 7.8%, respectively, were observed during the study. Also of interest was the duration of the CSIR events which is a function of Sun-cloud-sensor geometry and the speed of cloud propagation over the measuring site. In both the UV-A and UV-B wavelengths, significant CSIR durations of up to 30 minutes were observed. C 1997 Elsevier Science B.V.     

Detection and monitoring of offshore oil seeps using ERS/ENVISAT SAR/ASAR data and seep-seismic studies in Krishna–Godavari offshore basin,India

An attempt has been made to use synthetic aperture radar (SAR) data for detection and monitoring of offshore oil seeps in the eastern offshore areas of the Krishna–Godavari Basin, which has been supplemented and correlated with collateral free-air gravity and seismic data. Images of the study area obtained from ENVISAT ASAR image mode were processed and analysed in detail. A number of natural oil seepages were identified and distinguished from pollution and biogenic slicks. These were subsequently studied using different parameters to assign various degrees of confidence. The repetitiveness of the identified seepages was studied and a total of five areas of seep repetitions had been recognized in the study area. The seeps that are repeated in images of different dates are more likely to be of natural origin than others. Simulation and modelling of a particular oil slick arising has been attempted over the Krishna–Godavari offshore using MIKE 21 software.     

A hybrid technique for computing the monthly mean net longwave surface radiation over oceanic areas

Summary Global maps of the monthly mean net upward longwave radiation flux at the ocean surface have been obtained for April, July, October 1985 and January 1986. These maps were produced by blending information obtained from a combination of general circulation model cloud radiative forcing fields, the top-of-the-atmosphere cloud radiative forcing from ERBE and TOVS profiles and sea surface temperature on ISCCP C1 tapes. The fields are compatible with known meteorological regimes of atmospheric water vapor content and cloudiness. There is a vast area of high net upward longwave radiation flux (> 80 W m^–2) in the eastern Pacific Ocean throughout most of the year. Areas of low net upward longwave radiation flux (< 40 Wm^–2) are the tropical convective regions and extra tropical regions that tend to have persistent low cloud cover. The technique used in this study relies on GCM simulations and so is subject to some of the uncertainties associated with the model. However, all input information regarding temperature, moisture and cloud cover is from satellite data having near global coverage. This feature of the procedure alone warrants its consideration for further use in compiling global maps of the net longwave radiation at the surface over the oceans.With 9 Figures     

Climatology of cloud and radiation fields in a numerical weather prediction model

Summary Satellite-derived datasets are used to verify the cloud cover and radiation field generated by a T62 (horizontal resolution) version of the operational global model at the National Meteorological Centre (NMC). An ensemble of five day forecasts for July 1985 is used, as well as 30 day climatological forecasts for July 1985, October 1985, January 1986, and April 1986.Monthly averages of radiation fields are compared with Earth Radiation Budget Experiment (ERBE) data. For the four months examined, clear-sky outgoing longwave radiation (clear-sky OLR) and absorbed shortwave radiation (clear-sky SW) tend to agree roughly with ERBE. Model global mean OLR, however, exceeds that of ERBE by 10 W m^–2.Comparison of effective cloud cover to corresponding fields cataloged by the International Satellite Cloud Climatology Project (ISCCP C1) reveals deficiencies in the amount of supersaturation cloudiness and the vertical distribution of convective clouds. Large inaccuracies in model radiation fields are closely related to deficiencies in the cloud parameterization. An inventory of model cloudiness, in comparison to satellite data, is conducted.With 18 Figures