Abstract:

Statistical information of shallow cumuli is extracted from the SPolKa data. The data contains echo fields at different snapshots in time. The area distribution of echoes appears to be a power law upto 10 km 2 . This power law is robust, that is, it does not sway with environmental conditions. The area distributions of big echoes vary with the level of moisture. At time it appears to be another power law with different and varying exponent which approaches that of smaller echoes as the air is getting wetter. The size which separates these two regimes is called the scalebreak.

The temporal behaviors of the whole fields are studied via tracking algorithm. The contribution of isolated echoes - ones which through out their lifetimes do not split or merge with other echoes - is contrast to that of systems. Isolated echoes are less numerous, cover much less area and have shorter lifespan. Allowing an echo field to develop reveals that unlike increasing environmental moisture, it is the area distribution of small echoes which evolves with time, while of the big echoes remains comparatively unchanged.

The divergences of radial velocities are proxies to the behaviors of vertical transportations inside echoes. The number of echoes with negative total transportations are found to be as many as echoes with positive transportations; statistically neither the updraft nor the downdraft dominates the vertical mass flux. Echoes can either start off with strong negative or positive buoyancy and become weaker until in some cases the signs even reverse.

Finally the simulation of the optical array probe determines the forward matrix which can be used to convert the drop size distribution into the image area distribution. As well it can be used in approximating the drop size distribution from the image area distribution. The result is promising; our conversion algorithm performs rather well, and in most cases the sampling errors are even bigger than the error due to this new conversion technique.