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| Titel |
Scoping a field experiment: error diagnostics of TRMM precipitation radar estimates in complex terrain as a basis for IPHEx2014 |
| VerfasserIn |
Y. Duan, A. M. Wilson, A. P. Barros |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 19, no. 3 ; Nr. 19, no. 3 (2015-03-25), S.1501-1520 |
| Datensatznummer |
250120667
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| Publikation (Nr.) |
 copernicus.org/hess-19-1501-2015.pdf |
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| Zusammenfassung |
A diagnostic analysis of the space–time structure of error in quantitative
precipitation estimates (QPEs) from the precipitation radar (PR) on the
Tropical Rainfall Measurement Mission (TRMM) satellite is presented here in
preparation for the Integrated Precipitation and Hydrology Experiment
(IPHEx) in 2014. IPHEx is the first NASA ground-validation field campaign
after the launch of the Global Precipitation Measurement (GPM) satellite. In
anticipation of GPM, a science-grade high-density raingauge network was
deployed at mid to high elevations in the southern Appalachian Mountains,
USA, since 2007. This network allows for direct comparison between
ground-based measurements from raingauges and satellite-based QPE
(specifically, PR 2A25 Version 7 using 5 years of data 2008–2013). Case
studies were conducted to characterize the vertical profiles of reflectivity
and rain rate retrievals associated with large discrepancies with respect to
ground measurements. The spatial and temporal distribution of detection
errors (false alarm, FA; missed detection, MD) and magnitude errors
(underestimation, UND; overestimation, OVR) for stratiform and convective
precipitation are examined in detail toward elucidating the physical basis
of retrieval error.
The diagnostic error analysis reveals that detection errors are linked to
persistent stratiform light rainfall in the southern Appalachians, which
explains the high occurrence of FAs throughout the year, as well as the
diurnal MD maximum at midday in the cold season (fall and winter) and
especially in the inner region. Although UND dominates the error budget,
underestimation of heavy rainfall conditions accounts for less than 20%
of the total, consistent with regional hydrometeorology. The 2A25 V7 product
underestimates low-level orographic enhancement of rainfall associated with
fog, cap clouds and cloud to cloud feeder–seeder interactions over ridges,
and overestimates light rainfall in the valleys by large amounts, though
this behavior is strongly conditioned by the coarse spatial resolution (5 km) of the topography mask used to remove ground-clutter effects.
Precipitation associated with small-scale systems (< 25 km2)
and isolated deep convection tends to be underestimated, which we attribute
to non-uniform beam-filling effects due to spatial averaging of reflectivity
at the PR resolution. Mixed precipitation events (i.e., cold fronts and snow
showers) fall into OVR or FA categories, but these are also the types of
events for which observations from standard ground-based raingauge networks
are more likely subject to measurement uncertainty, that is raingauge
underestimation errors due to undercatch and precipitation phase.
Overall, the space–time structure of the errors shows strong links among
precipitation, envelope orography, landform (ridge–valley contrasts), and
a local hydrometeorological regime that is strongly modulated by the diurnal
cycle, pointing to three major error causes that are inter-related: (1)
representation of concurrent vertically and horizontally varying
microphysics; (2) non-uniform beam filling (NUBF) effects and ambiguity in
the detection of bright band position; and (3) spatial resolution and ground-clutter correction. |
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