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.

The research presents the inter-comparison of atmospheric variables measured by 9 automatic meteorological stations. This set of data was compared with the measurements of other meteorological stations in order to standardize the values that must be adjusted when taken to different areas. The data of a set of a total of 9 GMX500, which measures conventional meteorological variables, and 10 WS100 sensors, which measures precipitation parameters. The automatic stations were set up at the Huancayo Observatory (Geophysical Institute of Peru) for a period of 5 months. The data set of GMX500 were evaluated comparing with the average of the 9 sensors and the WS100 was compared with a optical disdrometer Parsivel2. The temperature, pressure, relative humidity, wind speed, rainfall rate, and drop size distribution was evaluated. A pair of GMX500 sensors presented high data dispersion, it was found found that the errors came from a bad configuration; once this problem was solved, good agreement was archived, with low RMSE and high correlation. I was found that the WS100 sensors overestimate the precipitation with a percent bias close to 100% and the differences increase with the greater intensity of rain. The DSD retrieved by WS100 have unrealistic behavior with higher concentrations in diameters of 1 mm and 5 mm, in addition to a flattened curve.

It has been shown that the Micro-Rain Radar (MRR) can be used to derive rainfall rates every 10 m over a depth of 1.28 km using the mean vertical air velocity corrected Doppler raindrop fall speed spectra. Furthermore, it has been shown that by assuming a reasonable advection velocity for the rain, these data can be analyzed to produce spatial radial power spectra often readily fit using a power function. Previous work has shown, however, that each spectrum applies only to each particular set of data and usually lacks the statistical qualifications necessary to be considered generally applicable. However, this limitation does not preclude the potential existence of other generalizations that can be used to explore the rainfall formation processes. The intent of this study, then, is to perform an initial look for such possible behaviors using time-height profiles of the rainfall rate. It is found that once the rainfall rate, R, exceeds about 20 mm h-1, there is, apparently, an associated flattening of the spectra with increasing R so that the smaller scales play an ever increasingly important role in such rain near the ground perhaps reflecting the increasing importance of such scales in the formation of pockets of more intense convective rain. The true generality of this finding needs additional scrutiny using more data particularly from two spatially separated MRR as is currently under preparation.

A realistic approach for gathering high-resolution observation of the rainfall rate, R, in the vertical plane is to use data from vertical pointing Doppler radars. After accounting for the vertical air velocity and attenuation, it is possible to determine the fine, spatially resolved drop size spectra and to calculate R for further statistical analyses. The first such results in a vertical plane are reported here. Specifically, we present results using MRR-Pro Doppler radar observations at resolutions of ten meters in height over the lowest 1.28 km as well as ten seconds in time over four sets of observations using two different radars at different locations. Both correlation functions and power spectra are useful for translating observations and numerical model outputs of R from on one scale down to other scales that may be more appropriate to particular applications such as flood warnings and soil erosion, for example. However, it was found in all cases that while locally applicable radial power spectra could be calculated, because of statistical heterogeneity, most of the power spectra lost all generality and proper correlation functions could not be computed in general except for one 17 minute interval. Nevertheless, these results are still useful since they could be combined to develop catalogs of power spectra over different meteorological conditions and in different climatological settings and locations. Furthermore, even within the limitations of these data, this approach is being used to gain a deeper understanding of rainfall to be reported in a forthcoming paper.

It is important to understand the statistical-physical structure of the rain in the vertical so that observations aloft can be translated meaningfully into what will occur at the surface. In order to achieve this understanding, it is necessary to gather high temporal and spatial resolution observations of rain in the vertical. This can only be accomplished using radars. It can be achieved by translating radar Doppler spectra into drop size distributions which can then be integrated to calculate variables such as the rain fall rate. A long-standing difficulty in using such measurements, however, is the problem of vertical air motion which can shift the Doppler spectra, and, therefore, significantly alter the deduced drop size distributions and integrated variables. In this work, we illustrate the improvement in measured rain structures using a new approach for removing the effect of mean vertical air motion. It is demonstrated that the new approach proposed here not only produces what appear to be better estimates of the rainfall rates, but, also as a consequence, provides estimates of the temporal and spatial regionally coherent updraft and downdrafts occurring in the precipitation. Furthermore, the technique is readily applicable to other radars especially those operating at non-attenuating frequencies.