Effect of low-level flow and Andes mountain on the tropical and mid-latitude precipitating cloud systems: GPM observations

Abstract

The effect of different directional South American low-level flow (SA-LLF) and topography on the near surface rainfall characteristics are validated in the present study. The near surface precipitation characteristics of the precipitating cloud systems (PCSs) are investigated under the influence of low-level flow (LLF) at 850 hPa and topography. Global precipitation measurement dual precipitation radar (GPM-DPR) data is used to define the PCSs. The PCSs consist of valuable information, including radar reflectivity (Ze), rain rate (RR), storm top height (STH), and DSD (drop size (Dm) and drop concentration (Nw) parameters). For LLF, we considered wind data at 850 hPa and for each PCS, the average wind angle is calculated using U and V component of wind component from European Center for Medium-Range Weather Forecast Interim data. Based on the direction of the topography, the LLF is divided into upslope, downslope, easterly and westerly LLF. The transported moisture from the Amazon to east of the Andes and strength of LLF decides the precipitation characteristics over tropical and mid-latitude PCSs. The zonal variation over the SA continent shows that the easterly and northerly LLF consist of higher fraction of PCSs with largest area (> 2000 km2). The RR and Dm are higher at the eastern flank of SA Andes, and higher RR is observed in northerly and easterly LLF and shows the role of the moisture convergence near the eastern flank of Andes. However, the differences in the near surface rainfall parameters are higher when the LLF direction is considered along the perpendicular direction of the topography. The analysis reveals that mountain and directional LLF can alter the precipitation characteristics, and mostly, the eastern flank of Andes has higher RR and Dm compared to western flank of the Andes, and highest for the orographically moisture loaded upslope and easterly LLF in tropical PCSs. Tropical PCS has higher probability of bright band and warm rain compared to mid-tropical latitude PCSs and even higher in upslope and easterly LLF. The variation in DSD parameters with RR and STH revealed the role of the LLF and complex orography in the microphysical evolution of the precipitation and suggested that it is much required to investigate them in the numerical models.