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| Titel |
The Dual Wavelength Ratio knee: a signature of multiple scattering in airborne Ku-Ka observations |
| VerfasserIn |
Alessandro Battaglia, Simone Tanelli, Gerald Heymsfield, Lin Tian |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088840
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| Publikation (Nr.) |
 EGU/EGU2014-3007.pdf |
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| Zusammenfassung |
| Deep convective systems observed by the HIWRAP radar during the 2011 MC3E field
campaign in Oklahoma provide the first evidence of multiple scattering effects
simultaneously at Ku and Ka band. One feature is novel and noteworthy: often, in
correspondence to shafts with strong convection and when moving from the top of the cloud
downward, the dual wavelength ratio (DWR) first increases as usual in Ku-/Ka-band
observations, but then it reaches a maximum and after that point it steadily decreases all the
way to the surface, forming what will be hereinafter referred to as a knee. This DWR knee
cannot be reproduced by single-scattering theory under almost any plausible cloud
microphysical profile, on the other hand it is explained straightforwardly with the help of
multiple scattering theory when simulations involving hail-bearing convective cores with
large horizontal extents are performed. The DWR reduction in the lower troposphere (i.e.,
DWR increasing with altitude) is interpreted as the result of multiple scattering
pulse stretching caused by the highly-diffusive hail layer positioned high up in the
atmosphere, with Ka multiple scattering typically exceeding that occurring in the Ku
channel.
Since the effects of multiple scattering increase with increasing footprint size, if multiple
scattering effects are present in the aircraft measurements, they are likely to be more
pronounced in the space-borne dual-frequency Ku - Ka radar observations, envisaged for
the NASA-JAXA Global Precipitation (GPM) Measurement Mission, whose launch is
expected in February 2014. Our notional study supports the idea that DWR knees will be
observed by the GPM radar when overflying high-density ice shafts embedded in
large convective systems and suggests that their explanation must not be sought
in differential attenuation or differential Mie but via multiple scattering effects. |
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