An Evaluation of the interactions of outgoing long wave radiation (OLR) with Vegetation, Non-vegetated and snow covered areas in India
-.M.Pavalavanni, Hydrabad, India-
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The outgoing long wave radiation (OLR) is one of the most important components in the global energy balance for the Earth-Atmosphere system. Both spatial and temporal variations of long wave radiation have direct implications on the climate. This study aims to evaluate the interactions of OLR with vegetation, non-vegetated and snow covered areas in India. For this purpose OLR data derived from KALPANA-1 and Sea WiFs  satellite products has been used.

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  The response of Outgoing Long wave Radiation with vegetation, non-vegetated and snow covered area is evaluated through observations made out of Normalized Difference Vegetation Index calculated for the entire stretch of India from SewWiFS data. 

The period of observation is the monthly average of OLR and NDVI observed during 2009. The results indicate that ‘the non vegetated open land and ‘tar’ desert has a high OLR, consistent with dry, cloud free and warm conditions. From the study it is observed that the vegetation cover and OLR response are indirectly related.  Further, it is clear from the study that the wetness in the soil affects the interactions of OLR. Lower the wetness higher will be the OLR.  The snow surface and ice interaction is so unique with OLR. Though wet the ice and snow have high albedo and so high OLR response.

Average Outgoing   Long wave Radiation Across Indian States

  

The graph shows the average out going long wave Radiation (OLR) in different states.  From the graph it is clear that Gujarat and Rajasthan has the maximum LOR, where the condition of desert is prevalent.  The areas where non-vegetated land is high such as Madhya Pradesh, Maharastra, the  OLR is high.  In states like Kerala, Utranchal, Meghalaya, Sikkim and Nagaland where vegetative area is very high the OLR is low. Very low OLR is observed especially in north eastern states such as Arunachal Pradesh, Assam, Manipur and Mizoram where they receive very heavy rainfall.  A moderate OLR is registered in Himachal and Jammu and Kashmir where snow covered peaks are prevalent.

Results


From the study the following conclusions are derived as conclusion:

• High OLR is observed in Thar Desert of Rajasthan and low OLR is observed in Jammu Kashmir.
• The OLR distribution is strongly influenced by seasons such as summer, winter, spring and autumn.
• In summer due to  less dense seasonal crops and plantation canopy, dry soil and more non vegetated area induce high OLR.
• The dense forest vegetation canopy maintain soil moisture even in summer season, thus in these areas OLR is in medium category.
•  Snow covered areas have low OLR.
•  In monsoon season, the rainfall is more that provide wet soils with very dense vegetation canopy results in low OLR.
•  In spring season, haze and mist particles strongly absorb Long wave Radiation and thus acts as barrier for OLR.
• The observations of OLR  reveals that the vegetation is not the single most controlling factor for OLR,  rather it is a controlling factor when the soil moisture is high.

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 Author : Mr.M.Pavalavanni, Core Logic, Hydrabad, India

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