Spatial distribution of radar bright band intensity

Abstract

A radar bright band is a region of enhanced reflectivity in the radar echo. During precipitation, the falling snowflakes start melting when they encounter a warmer layer below freezing. The snowflakes' refractive index and diameter are higher than the snow above. Below the melting layer, where the melting is over, these snowflakes become raindrops that fall faster. So, the number of drops/volume reduces. Since the back-scattered power from the target is directly proportional to the refractive index of the target and the 6th power of its diameter, the reflectivity in the melting region is higher than above and below it. The paper investigates Bright Band Intensity (BBI) derived from 2A23 V6 of the Precipitation Radar (PR) onboard the Tropical Rainfall Measuring (TRMM) in 35N-35S and 180E – 180W from 1999-2002, 2007, and 2008. The study shows that the bright band's occurrence is more over the ocean (mainly the Pacific) than on the continent. Thus, the Pacific Ocean plays a crucial role in weather and climate. It shows substantial seasonal variations. The BBI minima, in particular, show prominent belts across the two hemispheres and show North-South migration with the season in a direction opposite to the Inter Tropical Convergence Zone (ITCZ) and the solar movement. The longitudinally averaged BBI minima occur in the higher latitudes in both hemispheres. The longitudinally averaged BBI maxima in the Northern Hemisphere (NH) occur at low latitudes, and in the Southern Hemisphere (SH), at high latitudes. The BBI (rainfall) maxima are higher in the winter (summer) hemisphere. The BBI maxima and minima, as also the rainfall maxima and minima, occur in opposite hemispheres. Over a location, the daily BBI maximum does not necessarily correspond to the maximum rainfall. But the maxima of longitudinally averaged BBI and rainfall occur in the same hemisphere, so also the minima.