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Diurnal Cycle of Precipitation over the Americas

This study analyzes the diurnal cycle of precipitation over the Americas using the CMORPH technique. The analysis combines infrared (IR) and passive microwave data to create high-resolution global rainfall analyses. The study finds significant diurnal cycles in precipitation over both continental and oceanic regions.

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Diurnal Cycle of Precipitation over the Americas

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  1. Diurnal Cycle of Precipitation over the Americas Based on CMORPH Vernon E. Kousky, John E. Janowiak and Robert Joyce Climate Prediction Center, NOAA

  2. 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.

  3. 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

  4. 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

  5. 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)

  6. South America: DJF 2002-2003

  7. Percent Total Precipitation: Diurnal Cycle DJF 2002-03 4 5 6 4 5 6 La Plata Basin 1 2 3 2 1 3

  8. Time-Longitude Section (20-30S) Diurnal Cycle of Precipitation Time Nocturnal Maximum just east of the Andes Afternoon maximum over southern Brazil

  9. Diurnal Cycle DJF 02-03 + 03-04

  10. South America: DJF 2002-03 2003-04

  11. 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

  12. 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

  13. 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 W. Coast E. Coast

  14. Central America/ Mexico: JJA 2003

  15. United States: JJA 2003

  16. US/Central Amer./ Mexico: JJA 2003

  17. 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.

  18. Western Africa: JJA 2003

  19. Southern Africa: DJF 2002-2003

  20. Southeast Asia: JJA 2003

  21. Indonesia: JJA 2003

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