ROLE OF METEOROLOGY AND LITHOLOGY IN THE TEMPORAL VARIATION OF THE OUTDOOR RADON LEVEL

The outdoor radon concentration was monitored together with the meteorological parameters at two contrasting complex topographies: sub-Alpine basin (SA) and sub-Mediterranean valley (SM) in winter (December 2017–February 2018) and summer (June–August 2018). The time series for each site and each season are evaluated in three different ways: (i) clear-sky and cloudy condition together, (ii) clear-sky conditions only (cloud cover <20%) and (iii) cloudy condition only (cloud cover >20%), and compared to the expected atmospheric boundary layer (ABL) ‘mixing volume’ caused by meteorological changes. The results have confirmed the sensitivity of diurnal and seasonal radon concentration to the expected ABL ‘mixing volume’ at the two selected sites. The relationship is more pronounced in calm clear-sky conditions. Cloudy conditions are associated with fast weather changes, when the ABL is well mixed and hourly mean radon concentrations do not follow the typical diurnal trend.

Comparison of UV Index and Total Ozone Column of Aura/OMI and Ground Measurement from Nepal Himalayas

Ground UV index and total ozone measured from four stations of Nepal Himalaya using NILU UV Multiband Filter Radiometer (MBFR) were compared with that of the Aura/OMI satellite products using the data from October 2008 to December 2010. The main goal of the validation was to find how the satellite products deviate with that of ground measurement in the mountainous sites where the stations have unique set of geographical and environmental conditions. The altitudes of the stations vary from 72 m to 2850 m in a short span of horizontal distance. The comparison was done for clear-sky and cloudy-sky condition using Cloud Transmission Factor (CLT) as a proxy. It was found that UV indices estimated by the satellite have higher values compared to ground instrument. The relative difference (bias) of the four stations are varied from 34.5 ± 24.0% to 47.9 ± 17.4% for cloud free condition and from 106.4 ± 81.44 % to 286.4 ± 254.8% for cloudy condition. The correlation coefficients are more than 0.8 for cloud free condition. The total ozone column comparison showed the mean relative difference (bias) range from -2.17 ± 3.52% to 2.97 ± 3.92% under cloud free condition and -4.42 ± 5.64% to 1.36 ± 6.14% under cloudy condition. The possible factors for this discrepancy are discussed and some important factors are highlighted. DOI: http://dx.doi.org/10.3126/jie.v8i3.5938 JIE 2011; 8(3): 114-129