Rainfall Characteristics in the Mantaro Basin over Tropical Andes from a Vertically Pointed Profile Rain Radar and In-Situ Field Campaign

Abstract

Information on the vertical structure of rain, especially near the surface is important for accurate quantitative precipitation estimation from weather and space-borne radars. In the present study, the rainfall characteristics, from a vertically pointed profile Radar in the Mantaro basin (Huancayo, Peru) are observed. In summary, diurnal variation of near-surface rainfall and bright band height, average vertical profiles of the drop size distribution (DSD), rain rate, radar reflectivity (Ze) and liquid water content (LWC) are investigated to derive the rainfall characteristics. Diurnal variation of rain rate and bright band height show the bimodal distribution, where frequent and higher rain rate occurred during the afternoon and nighttime, and more than 70% bright band height found between 4.3–4.7 km. The average vertical profiles of Ze show the opposite characteristics above and below the melting level (ML) and depend on the near-surface rain rate. For example, the average Ze profiles have a negative gradient above the ML, whereas below, the ML, the gradient depends on the near-surface rain rate. The rain rate and LWC show the opposite behavior, and both consist of a positive (negative) gradient below (above) the ML. The vertical growth of DSD parameters depend on the near-surface rain rate, and a higher concentration of large-sized of droplets are observed for higher near surface rain rate, however, the dominant modes of droplets are <1 mm throughout the vertical column. However, the most significant variation in DSD growth is observed for near-surface rain rate ≥20 mm/h. These findings suggest using different retrieval techniques for near surface rain estimation than the rest of the vertical profile and high rain rate events. The improved understanding of the tropical Andes precipitation would be very important for assessing climate variability and to forecast the precipitation using the numerical models.

Calibration of X-Band Radar for Extreme Events in a Spatially Complex Precipitation Region in North Peru: Machine Learning vs. Empirical Approach

“…highest beam elevation of 3800 m at the full range (100 km) is almost always be typical altitude of the melting layer as reported by [12] for the Andes.…”

“…Bright-band effects are rarely seen in the radar data because of the low elevation of the radar site and the sharp pencil beam (2 • vertical) with a center elevation of 0 • . The highest beam elevation of 3800 m at the full range (100 km) is almost always below the typical altitude of the melting layer as reported by [12] for the Andes.…”

“…Andrieu et al [10] analyzed the characteristic problems in mountain terrain, while Amitai [11] addressed specific issues for the tropics. Kumar et al [12] have pointed out the geometric issues of beam broadening and weakening of the signal with distance. More recently, many of these correction procedures have been integrated into comprehensive software products, such as the processing software supplied by radar manufacturers [13], national weather services [14], or community efforts such as PyRad [15] or ωradlib [16].…”

High Impact Weather Events in the Andes

“…The central Andes witness convective (30%) and stratiform (70%) precipitation, contributing with 63.3 and 36.7% of total rain, whereas in the Amazon-Andes transition those percentages and the contribution to cumulative rain attain similar values (31 and 69%, respectively). Over the central Peruvian Andes, and using a vertically pointed profile rain radar installed in the Mantaro Basin, Kumar et al (2020) show that most of the bright band height (an indication for the melting zone) over this region vary between 4.3 and 4.7 km. An example of the vertical profile of radar reflectivity is shown in Figures 6E,F.…”

A Comparative Study on the Vertical Structures and Microphysical Properties of Stratiform Precipitation over South China and the Tibetan Plateau

“…Compared with conventional scanning weather radars, vertically pointing short-wave radars have advantages in the observation of stratiform precipitation vertical structures because of their higher spatiotemporal resolution and sensitivity. For instance, Kumar et al [12] used gradients in profiles of radar reflectivity and Doppler velocity from a Kaband Doppler radar to identify the BB, noting that radar reflectivity significantly increases with decreasing height above the BB, whereas vertical variations of it below the BB depend on rain rate. Jha et al [13] and Devisetty et al [14] suggested that an appropriate threshold value of −22 dB for the radar linear depolarization ratio, measured using a Ka-band zenith radar, can be associated with the top and bottom heights of the BB.…”