Working Paper Article Version 1 This version is not peer-reviewed

Rainfall Characteristics in the Central Andes of Peru from a Vertically Pointed Profile Rain Radar and In-situ Field Campaign

Version 1 : Received: 4 September 2019 / Approved: 6 September 2019 / Online: 6 September 2019 (03:49:02 CEST)

How to cite: Kumar, S.; Del Castro, C.; Valdivia Prado, J.M.; Flores Rojas, J.L.; Callañaupa Gutierrez, S.M.; Moya Alvarez, A.S.; Villalobos Puma, E.; Martinez Castro, D.; Silva, Y. Rainfall Characteristics in the Central Andes of Peru from a Vertically Pointed Profile Rain Radar and In-situ Field Campaign. Preprints 2019, 2019090066 Kumar, S.; Del Castro, C.; Valdivia Prado, J.M.; Flores Rojas, J.L.; Callañaupa Gutierrez, S.M.; Moya Alvarez, A.S.; Villalobos Puma, E.; Martinez Castro, D.; Silva, Y. Rainfall Characteristics in the Central Andes of Peru from a Vertically Pointed Profile Rain Radar and In-situ Field Campaign. Preprints 2019, 2019090066

Abstract

The present study uses the 3 years of data from a vertically pointed profile Radar (VPPR) at the mountain site (Huancayo at 3.2 km msl; HYO) in Peru to investigate the precipitation characteristics/patterns including diurnal variation, bright band (BB) characteristics and vertical structure of rain (VSR). VPPR provides continuous 1­min profiles of radar reflectivity (Ze), rain rate (RR), liquid water content (LWC) and Doppler velocity. At the same time, field campaign data are used to investigate the role of the surface and atmospheric variables in generating the rainfall and organization of the cloud systems over HYO. The precipitation shows the bimodal distribution; frequent and higher RR during afternoon and nighttime. The BB height also shows a diurnal pattern and BB height is higher during the afternoon and nighttime compared; and follows the diurnal heating of the Andes. More than 70% BB height lies between ~4.3­4.7 km and only 20% BB has altitude higher than 5 km. The austral summer monsoon (December to March months) have higher intense vertical profiles (higher Z e ) compared to pre monsoon seasons (September to November) and shows the nega­tive gradient for most of the altitude. The RR and LWC show the opposite characteristics, and both have a positive gradient below the 6 km altitude and then negative gradient above 6 km altitude. The raindrop size distribution (DSD) parameters show most of the variation below the freezing level, and a higher concentra­tion of large sized of hydrometeors are observed for higher RR, however the dominant modes of Dm are less than 1 mm. The changes in the VSR in DSD parameters are significant for the RR>20 mm/h, whereas for RR<2 mm/h the vertical structure in DSD parameters do not have much differences during monsoon and premonsoon seasons. Satellite and reanalysis data reveal the short periods of convective activity with higher ac­ cumulated rainfall over HYO compared to stratiform precipitation, which is more common in the nighttime and sustain for many hours. Wet spells (higher rainy days) have low pressure circulation, which favours the transport of moisture from the Amazon to the central Sierra of Peru, while the anticyclonic circulation at high levels favours the divergence at higher pressure levels and, enhances the convective in the region. During the dry spells, low level weaker circulation at the west of Brazil, restricts the transport of moisture to the central Sierra, while the circulation at high levels does not favor rain processes. The improved understanding of the tropical Andes precipitation would be very important for assessing climate variability and changes as well as to forecast precipitation using the numerical models.

Subject Areas

MIRA35c; diurnal variation; DSD parameters; convective rain and bright band

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