Abstract
Most civil aviation aircraft are equipped with meteorological radar working at the X-band ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> ≈ 10 GHz; λ ≈ 3.2 cm) . These radars use a small antenna and, thus, a large beamwidth, around 3°-4°, for observations over long distances (up to 350 km). In the presence of microphysical inhomogeneities inside a radar sampling volume, as filling by different hydrometeor categories, radar reflectivity measurements are biased. An important bias occurs when a radar cell is cut by a nonresolved layer of melting snowflakes whose attenuation is high compared to those of rain and dry snow. This paper illustrates the effects in precipitation-attenuation correction schemes (PACS) of the inhomogeneity associated with the 0 °C isotherm. It proposes a method to take into account these effects in PACS. Adaptation of the method to other frequency bands and ground-based radar observations is easy.
Highlights
T HE RADAR equation used for quantitative interpretation of precipitating system radar observations, and notably for correction of attenuation by precipitation, implicitly assumes that the radar resolution volume Vr is homogeneously filled by the meteorological target
This paper proposes a way to compute attenuation by a layer of melting snow and to take into account the corresponding contribution in precipitation-attenuation correction schemes (PACS), when the radar cell is too large to observe the melting layer in detail
The degradation of reflectivity fields at long distances carried by a large value of θ3 dB is illustrated with the example of a squall line occurring in Georgia (USA), on May 2, 2003
Summary
T HE RADAR equation used for quantitative interpretation of precipitating system radar observations, and notably for correction of attenuation by precipitation, implicitly assumes that the radar resolution volume (the radar cell) Vr is homogeneously filled by the meteorological target. This is not always true, because the scattering medium inside a radar cell may be composed of various hydrometeors with different electromagnetic properties [1], [2]. This paper proposes a way to compute attenuation by a layer of melting snow and to take into account the corresponding contribution in precipitation-attenuation correction schemes (PACS), when the radar cell is too large to observe the melting layer in detail. It is valuable for ground-based radar observations and other frequency bands
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