Geoscience Reference
In-Depth Information
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90°N
60°N
30°N
Equator
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90°S
Figure 2.25 Zonally averaged precipitation climatology in
mm/day for the annual mean (black line), December-January-
February (DJF) mean (dotted line), and June-July-August (JJA)
mean (gray line).
China, and Europe—for centuries, other regions—such as the South Pacific
Ocean—have very few direct measurements of precipitation available. The sat-
ellite era has produced global precipitation data sets, but there are still uncer-
tainties associated with translating the radiative fluxes measured by satellites
into precipitation and with producing adequate global coverage.
Figure 2.25
displays zonal mean precipitation rates for DJF, JJA, and the
annual average. The values are from a global precipitation climatology (1979-
2011) developed at the National Oceanic and Atmospheric Administration's
(NOAA's) Climate Prediction Centers (CPC)
2
by combining measurements
from five satellites with rain gauge measurements made at weather stations
and on ships around the world. Note the following:
• High precipitation rates near the equator mark the ITCZ, where the low-
level winds converge (see
Figs. 2.11
and
2.13)
. Tropical precipitation rates
are about three times those in middle latitudes.
• Precipitation rates are not at a maximum on the equator. Rather, the highest
precipitation rates in each hemisphere tend to occur about 7° of latitude
away from the equator.
• The summer tropical precipitation maximum in the Northern Hemisphere is
significantly larger than that in the Southern Hemisphere.
• Precipitation rates have a local minimum in the subtropics.
• Secondary precipitation maxima occur in middle latitudes, between 35° and
55°, depending on season.
• Lowest precipitation rates are found in high latitudes. With precipitation
rates under 0.5 mm/day, it takes many hundreds of years to accumulate snow
and ice in these regions.
2
This data set is known as the CPC Merged Analysis of Precipitation (CMAP).
