Find in Library

The mean properties of tropical cirrus, such as cloud top, cloud base, optic centre, cloud strength/optical depth, asymmetry factor and cloud depolarization, as well as their heterogeneities are examined using lidar observations over 281 nights from a tropical station Gadanki (13.5&deg; N, 79.2&deg; E) during the period 1998&ndash;2002. This study shows that as the cloud optical depth (&tau;_<I>c</I>) increases the cloud becomes more asymmetric in its scattering property. The amount of asymmetry is less than 2% for very low values of (&tau;_<I>c</I> and increases nonlinearly with an increase in (&tau;_<I>c</I>. The physical properties of these clouds also show significant variation with different time scales during the course of each night. On average, while the short-term variations in (&tau;_<I>c</I> are in opposite phase with those of the asymmetry factor (ξ) and volume depolarization ratio (δ), the long-term variation in (&tau;_<I>c</I> extending over a night are found to be in opposite phase with that of ξ and in-phase with that of δ. The short-term variations in δ and (&tau;_<I>c</I> were attributed to possible changes in the cloud particle orientation and the long period variations to cloud evolution process. The value of δ shows a pronounced variation along the vertical, with low values near the cloud top and cloud base and high values in the middle, which is attributed to the cloud dynamics.