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Analysis of rain types and their Z-R relationships at different locations in the high andes of southern Ecuador

Abstract:

Information on the spatiotemporal rainfall occurrence, its microphysical characteristics, and its reflectivity-rainfall (Z-R) relations required to provide rainfall mapping based on rain radar data is limited for tropical high mountains. Therefore, this study aims to analyze rainfall types in the Andes cordillera to derive different rain-type Z-R relations using disdrometer observations at three study sites representative for different geographic positions and elevations (2610, 3626, and 3773 m MSL). Rain categorization based on mean drop volume diameter (Dm) thresholds [0.1 < Dm (mm) ≤ 0.5; 0.5 < Dm (mm) ≤ 1.0; 1.0 < Dm (mm) ≤ 2.0] was performed using drop size distribution data at a 5-min time step over an approximate 2-yr period at each location. The findings are as follows: (i) Rain observations characterized by higher (lower) Dm and rain rates are more frequent at the lower (higher) site. (ii) Because of its geographic position, very light rain (drizzle) is more common at higher altitudes with longer-duration events, whereas rainfall is more convective at the lower range. (iii) The specific spatial exposition regarding cloud and rain formation seems to play an important role for derivation of the local Z-R relationship. (iv) Low A coefficients (≤60) for the first rain type resemble typical characteristics of orographic precipitation. (v) Greater values of A (lowest and highest stations for Dm > 1.0 mm) are attributed to transitional rainfall as found in other studies. (vi) Rain-type Z-R relations show a better adjustment in comparison with site-specific Z-R relationships. This study is the first contribution of Z-R relations for tropical rainfall in the high Andes.