**5. Conclusions**

land is higher than during other time periods. On the other hand, over the ocean, the diurnal

The diurnal cycle of the DI to DD ratio is similar to the rain top height pattern. The ratio of DI to DD over land is relatively small when the rain top height is high, namely, between 13 and 18 LT. For the entire dataset (without diurnal classification), ratio of DI to DD for 01–06 LT, 07–12 LT, 13–18 LT, and 19–24 LT are 1.30, 1.29, 1.25, and 1.25, respectively. Deep convective has a slightly dominant DI, with a ratio of DI to DD being 1.34, 1.31, 1.18, and 1.28, respectively. Moreover, the shallow convective rain has a larger ratio, in which the ratio for each hour is 4.99, 4.72, 4.22, and 4.77, respectively. On the other hand, the ratios for stratiform rain

The summary of the aforementioned discussion is given in **Figure 11**. Two major peaks are observed, in which one is over land and the other is over ocean. Furthermore, the rain top height increases with increasing time, particularly between 12 and 24 LT. During this period, the reflectivity gradient is less positive or more negative, which is an indication of the reduction of raindrops toward the surface due to evaporation, particularly small-sized raindrops. Disdrometer observations in Sumatera have shown that the raindrop spectra from noon to evening contains less small-sized drops (<2 mm) than at other hours [37]. Between 00 and 12 LT,

**Figure 11.** Diurnal variation of number of radar reflectivity profile (a), the ratio of DI to DD (b), mean VPRG (c), and mean RTH (d). Symbols of S, D and SH indicate stratiform, deep and shallow convective, respectively. Left *y* axis is for

variation in rain top height is not obvious.

86 Engineering and Mathematical Topics in Rainfall

shallow convective rain.

are 0.62, 0.60, 0.56, and 0.59, respectively (**Figure 10**).

The vertical structure of radar reflectivity has many applications, but it has not been comprehensively analyzed on the IMC, which is a region with complex precipitation formation due to the interaction of local circulation dominantly affected by the topography and some global circulations. In this chapter, we present the statistical analysis of seasonal and diurnal variations of such a profile. The gradient is calculated using a linear regression of radar reflectivity as a function of height, in which the positive gradient is denoted as DI and the negative gradient is the DD of radar reflectivity toward the surface. In general, the pattern of reflectivity gradient in this work is similar to that previously found on a global scale, in which the dominant DI is observed in the oceans and DD is observed predominantly on land. However, the diurnal and spatial variations in the gradient shows interesting feature. For convective rainfall, the ratio of DI to DD increases during the wet season such as DJF, whereas during the drier season (MAM and JJA), the number of DD pattern increases, especially over land as the rain top height increases due to the prevailing land-based convection. The stratiform rain does not show a significant seasonal variation, which is consistent with some previous studies on the seasonal variation in raindrops over the IMC. The vertical structure of radar reflectivity shows significant diurnal variations, and the pattern is similar to the land-ocean convection migration, which has been previously reported in some studies. The smallest DI ratio, especially over land, is observed during intense solar radiation. This indicates the reduction of raindrop concentration due to evaporation, especially small-sized raindrops, which are seen from a deficit of such raindrops during this period. The results in this chapter will be useful for the quantitative estimation of rainfall based on weather radar, particularly over the IMC.
