Abstract
In this paper, some distinctive features of the vertical profile of precipitable liquid water content (LWC) with considerable respect to rain rates (R) and radar reflectivity (Z) obtained in a tropical location are presented. Assessment of LWC allows applications in the specific area of flight icing severity, aviation safety as well as signals traversing through the atmosphere. The parameters were typically measured using vertically-pointing Micro Rain Radar (MRR) over a period of 2 years (2011-2012) at Akure, a tropical location of Nigeria. The radar scanned at every 10 seconds and integrated over one minute samples to reduce event logging error associated with the instrument. The vertical profile of the LWC typically reveals a prominent seasonal variation. However, majority of the LWC profiles has low LWC, less than 0.1 gm−3 while the maximum observed LWC is about 3.18 gm−3. A strong like hood relation was observed between the melting layer height and the LWC, with the LWC reaches peak at the considerable height of about 4160 m which coincides precisely with the freezing height level (rain height of ~4520 m) of the study location. Good correlation was also observed between the LWC and R in most of the heights considered. The results obtained will assist system engineers to assess the level of absorption, reflection and attenuation of electromagnetic signals as a result of precipitable LWC along the transmitting paths. The novelty of the present work is in the area of linking LWC and Z as against usual relation between Z and R.
Highlights
The liquid water content contained in the precipitation size drops can be estimated from the drop-size distribution, as well as the rainfall rate
The novelty of the present work is in the area of linking liquid water content (LWC) and Z as against usual relation between Z and R
The profile shows a seasonal variation in the monthly mean result, as higher values are obtained at the rainy season months and lower values in the dry months which are one of the features of tropical climate
Summary
The liquid water content contained in the precipitation size drops can be estimated from the drop-size distribution, as well as the rainfall rate. The mass of water per cubic meter of air space is essential for many applications and is a more fundamental parameter of the distributions than the rainfall rate. It has been noted that very high values of precipitable water content up to about 10 gm−3, and extremely high values of cloud droplet water content, are mutually exclusive and cannot coexist. This is because the collection of small cloud droplets by the precipitation droplets is effective and rapid. For the typical raindrop spectrum associated with a precipitable water content of about 10 gm−3, the time to completely sweep the volume of cloud droplets is approximately 30 secs or less (Foote & Dutoit, 1969)
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