Diurnal Cycle of Precipitation over the Americas Based on CMORPH

1
Diurnal Cycle of Precipitation over the Americas
Based on CMORPH
Vernon E. Kousky, John E. Janowiak and Robert
Joyce Climate Prediction Center, NOAA
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CMORPH (CPC Morphing technique)
Uses IR data along with passive microwave data to
create global rainfall analyses (60N-60S) at high
spatial and temporal resolution. CMORPH uses
IR only as a transport vehicle, i.e. IR data are
NOT used to make estimates of rainfall when
passive microwave data are not available. The
underlying assumption is that the error in using
IR to transport precipitation features is less
than the error in using IR to estimate
precipitation.
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Rationale

• Passive microwave (PMW) data provide much better
  rainfall estimates than IR but these data are
  spatially and temporally incomplete (instruments
  on polar- orbiting platforms)
• IR data are abundant both in space time (polar
  geostationary platforms)
• CMORPH combines the superior quality of the
  PMW-derived precipitation estimates with the
  excellent sampling characteristics of the IR data

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Specifics

• Spatial Grid 0.0728o lat/lon (8 km at equator)
• Temporal Resolution 30 minutes
• Domain Global (60o N - 60o S)
• Period of record Dec. 2002 present

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Diurnal Cycle of Precipitation South America

• Computed seasonal mean precipitation (for each
  30-minute analysis time plus daily total)
• Computed the seasonal mean percent of total daily
  rainfall for each 30-minute (48 fields per day)
  and each 3-hour period (8 per day)

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South America DJF 2002-2003
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Percent Total Precipitation Diurnal Cycle DJF
2002-03
4
5
6
4
5
6
La Plata Basin
1
2
3
2
1
3
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Time-Longitude Section (20-30S) Diurnal Cycle of
Precipitation
Time
Nocturnal Maximum just east of the Andes
Afternoon maximum over southern Brazil
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Diurnal Cycle DJF 02-03 03-04
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South America DJF 2002-03 2003-04
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Time (UTC) of Max. Precipitation South America
DJF 2002-03
18-21 UTC
00-03 UTC
12-15 UTC
06-09 UTC
06-09 UTC
12-15 UTC
00-03 UTC
18-21 UTC
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Time (LST) of Max. Precipitation South America
DJF 2002-03
15-18 LST
21-24 LST
08-11 LST
03-06 LST
02-05 LST
09-12 LST
20-23 LST
15-18 LST
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Mean Diurnal Cycle MAM 2003
Sea breeze induced convection near the coast on
Day 1 propagates westward reaching the western
Amazon Basin on Day 3.
Day 1
Day 2
Day 3
Day 4
E. Coast
W. Coast
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Central America/ Mexico JJA 2003
15
United States JJA 2003
16
US/Central Amer./ Mexico JJA 2003
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Conclusion

• The CMORPH precipitation analyses provide the
  temporal and spatial resolutions necessary to
  describe the diurnal cycle in precipitation.
• A significant diurnal cycle in precipitation is
  found over continental regions and even over
  oceanic areas at some distance from the coasts.
• The diurnal cycle of propagating features, such
  as the sea-breeze front, is well captured in the
  CMORPH analyses.

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Western Africa JJA 2003
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Southern Africa DJF 2002-2003
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Southeast Asia JJA 2003
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Indonesia JJA 2003