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