Monthly and Daily Variations in down ward Long wave Radiation and Its Relationship with Atmospheric Temperature and Water Content in desert and Mediterranean Climates
Journal Title: IOSR Journal of Environmental Science, Toxicology and Food Technology (IOSR-JESTFT) - Year 2019, Vol 13, Issue 1
Abstract
Knowledge of downward atmospheric radiation in the range λ= 4–100 μm is vital for several applications. In this study, longwave (LW) radiation datafrom desert (Riyadh, Saudi Arabia) and Mediterranean (Adelaide, Australia) climates are used to characterize seasonal and daily variations. At both sites, the LW radiation shows a maximum in summer and a minimum in winter. The monthly changes in the LW radiation were about 22% for Adelaide, and 36% for Riyadh. When considering these seasonal variations, it was found that during winter and summer, the variations inLW radiation were confined to between 2% and 4%. However, during the transition seasons (spring and autumn) the LW radiation varies considerably. In Adelaide, spring and autumn change by about 8% and 10% respectively. In Riyadh, the LW radiation varies by about 12% in both seasons. At both sites, the LW radiation has aminimum value in the early morning, around 06:00 local time, and reaches its maximum at around 13:00. The daily changes in the LW radiation were 13.5% for Riyadh and 10% for Adelaide. Obviously, the monthly and diurnal variations of the LW radiation closely follow the temperature variations rather than the water content. The influence of screen temperature (T) and atmospheric moisture on LW radiation are examined for each site. The screen level water vapour pressure (e) and the precipitable water vapour (PWV) areusedas two different representative measuresof the atmospheric water contents. PWV is calculated using radiosonde observations from both sites. It is clear thatthe LW radiation correlates better with T than e, and better correlation between LW and e was apparent in Adelaide than in Riyadh. When using the PWV as a measure of thetotal atmospheric water content, the correlation between LW radiation and this variable improves significantly for both sites. Regression analyses are carried out between LW radiation and temperature and water vapour pressure at screen level (T, e), LW radiation and screen temperature and PWV (T, PWV) for eachsite individually, and data arecombined from both sites. Statistical indicators such as mean bias error (MBE), root mean square error (RMSE), mean percentage error (MPE), and student t-tests are used to assess these regressions. Both schemes give good predictions for the measured data, although the model containing(T, PWV) shows better statistics (better predictions) for the three datasets in comparisons with the model using (T, e). For instance, the model containing (T, e) gives a RMSE of 19.38 Wm-2 for Riyadh, 20.52 Wm-2 for Adelaide, and 22.419 Wm-2 for the combined data from both sites. Using the scheme comprising (T, PWV) reduces the RMSE values by 16% for Adelaide, 34% for Riyadh, and 14% for the combined data. Finally, several previously developed models areused to calculate the LW radiation for the three datasets (Adelaide, Riyadh, and the combined data from both sites). Nineteen models with different functional forms and different meteorological variables areselected and used. We find that the predictability of these models varies from one dataset to another. While some models show adequate prediction forone site, they fail forthe other. However, some models give reasonable estimates when the measured data from both sites are combined.
Authors and Affiliations
Maghrabi A. H. , Odah S. H
Keywords
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- EP ID EP444640
- DOI 10.9790/2402-1301014456.
- Views 170
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Monthly and Daily Variations in down ward Long wave Radiation and Its Relationship with Atmospheric Temperature and Water Content in desert and Mediterranean Climates
Knowledge of downward atmospheric radiation in the range λ= 4–100 μm is vital for several applications. In this study, longwave (LW) radiation datafrom desert (Riyadh, Saudi Arabia) and Mediterranean (Adelaide, Australia...