Assessment of Satellite Precipitation Products in Relation with
Orographic Enhancement Over the Western United States
Abstract
Different precipitation products are assessed for their skill in
capturing orographic precipitation over the western United States using
two popular methods. The first method defines orographic indices using
orographic enhancement and moisture content that represents the amount
of moisture advected over sloping terrain. In contrast, the second
method classifies precipitation events into orographic and
non-orographic events. NCEP Stage-IV product used as a reference. All of
the evaluated products show more significant errors for the orographic
than the non-orographic events. The Global Precipitation Mission (GPM)
Dual-frequency Precipitation Radar (DPR), combined radar and radiometer
(COMBINE), Microwave Humidity sounder (MHS), and GPM Microwave Imager
(GMI) severely underestimate the precipitation rates, especially for
heavy precipitation (> 4 mm/day), whereas infrared
precipitation of the Integrated Multi-satellite Retrievals for GPM
(IMERG-IR) and a reanalysis product (ERA5) show relatively better
estimation. Satellite products tend to show a lower fraction of
precipitation occurrence and amount for orographic than no-orographic
classes. It was found that rate BIAS varies with seasons, so in cold
seasons satellite precipitation products tend to underestimate while in
warm-season they (except DPR) tend to overestimate precipitation amount.
Most of the satellite products severely underestimate precipitation
volume at relatively colder surfaces (< 10
0C) and lower TPW (<15mm), but ERA5 shows
little rate BIAS in such cases. The underestimation tends to be larger
for orographic than non-orographic events. In contrast, ERA5 shows
relatively large underestimation at warmer temperatures
(>20 0C), where satellite products tend
to overestimate precipitation amounts.