Diurnal Cycle of Precipitation over the Americas Based on CMORPH
Vernon E. Kousky, John E. Janowiak
and
Robert Joyce
Climate Prediction Center, NOAA
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.
CMORPH (CPC Morphing technique)
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
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
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)
South America: DJF 2002-2003
Percent Total Precipitation: Diurnal Cycle DJF 2002-03
1 2 3
4 5 6
1 2 3
4 5 6
La Plata Basin
Time-Longitude Section (20-30S) Diurnal Cycle of Precipitation
Nocturnal Maximum just east of the Andes
Afternoon maximum over southern Brazil
Time
Diurnal Cycle DJF 02-03 +
03-04
South America: DJF 2002-03 2003-04
Time (UTC) of Max. Precipitation: South America – DJF 2002-03
00-03 UTC
00-03 UTC
06-09 UTC06-09 UTC
12-15 UTC
12-15 UTC
18-21 UTC
18-21 UTC
Time (LST) of Max. Precipitation: South America – DJF 2002-03
21-24 LST
20-23 LST
03-06 LST02-05 LST
09-12 LST
08-11 LST
15-18 LST
15-18 LST
Mean Diurnal Cycle: MAM 2003
Day 1
Day 2
Day 3
Day 4
E. Coast
Sea breeze induced convection near the coast on Day 1 propagates westward reaching the western Amazon Basin on Day 3.
W. Coast
Central America/ Mexico: JJA 2003
United States: JJA 2003
US/Central Amer./ Mexico: JJA 2003
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.
Western Africa: JJA 2003
Southern Africa: DJF 2002-2003
Southeast Asia: JJA 2003
Indonesia: JJA 2003