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

2. Motivation The diurnal cycle is fundamentally important throughout the Tropics and Subtropics (and in middle latitudes in summer). A better understanding of the diurnal cycle, and its variability, will lead to better short-range forecasts. There is a need to develop a benchmark for evaluating the diurnal cycle in numerical models.

3. 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)

4. 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

5. Specifics Spatial Grid: 0.0728 o lat/lon (8 km at equator) Temporal Resolution: 30 minutes Domain: Global (60 o N - 60 o S) Period of record: Dec. 2002 – present For more information about CMORPH: http://www.cpc.ncep.noaa.gov/products/janowiak/cmorph.html

6. Methodology The seasonal mean precipitation rates, from CMORPH, are computed for each time interval (1-h or 3-h). The mean daily precipitation rates are computed by summing the 1-h rates. In the absence of any diurnal variability, the same amount of rainfall would be expected during each time interval (e.g., 100/24 = 4.2% for 1-h intervals and 100/8 = 12.5% for 3-h intervals). Brown (green) colors are used to depict times when the observed % is less (more) than the expected values (precipitation uniformly distributed throughout the 24-h period).

7. Global: June-August

8. Land Areas Many land areas experience a late night/ early morning minimum and a late afternoon/ early evening maximum in precipitation. (Add 5-8 hs for LST) Southeast Asia, India, Malaysia & Indonesia

9. Ocean Areas Many ocean areas experience a late night/ early morning maximum and a late afternoon/ early evening minimum in precipitation. (Add 5-8 hs for LST) Southeast Asia, India, Malaysia & Indonesia

10. Southeast Asia, India & Indonesia

11. Animation India

12. Indonesian region

13. Animation Malaysia/Indonesia/Phili ppines

14. Many land areas experience a late night- early morning minimum and a late afternoon- early evening maximum in precipitation. (5-8 LT) (18-21 LT) North & Central America: Land Areas

15. North & Central America: Ocean Areas (5-8 LT) (18-21 LT) Many nearby ocean areas experience a late night- early morning maximum and a late afternoon- early evening minimum in precipitation.

16. North & Central America: JJA 0304 (1mm/d mask)

17. South America: December-February

18. Comparison: CMORPH and Gridded Analyses (DJF 0203+0304) CMORPHGridded CMORPH over estimates precipitation by 40-50% over Brazil. The bias is being corrected using station observations.

20. Land Areas Many land areas experience a late night- early morning minimum and a late afternoon- early evening maximum in precipitation. (6-9 LT) (18-21 LT) However, some land areas experience a late night- early morning maximum and a late afternoon- early evening minimum in precipitation.

21. Ocean Areas (6-9 LT) (18-21 LT) Many nearby ocean areas experience a late night- early morning maximum and a late afternoon- early evening minimum in precipitation.

22. South America: DJF 0203-0405 (1mm/d mask)

23. Diurnal Cycle DJF 0203-0405

24. South America: DJF 02-03+03-04 (1mm/d mask)

25. DJF - South America (1mm mask)

27. Diurnal Cycle DJF 02-03

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

29. Seasonal variations of the Diurnal Cycle of Precipitation over the Amazon Basin

30. Time-Longitude Diurnal Cycle EQ DJF 2002-03 +2003-04 Coast Mean diurnal cycle Repeated four times Maximum over the ocean ~ 12Z. Minimum over the ocean ~00Z. Minimum over the land ~ 12Z. Maximum over the land ~00Z.

31. Time-Longitude Diurnal Cycle 10S DJF 2002-03 +2003-04

32. Time-Longitude Diurnal Cycle 20S DJF 2002-03 +2003-04 Coast

33. Time-Longitude Diurnal Cycle 30S DJF 2002-03 +2003-04 Coast Eastward- propagating precipitation systems between the Andes Mts. and southern Brazil.

34. MAM Mean Diurnal Cycle – EQ-5N East Coast West Coast Convective rainfall systems start along east coast on day-1 propagate westward, reaching western Amazon on day-3.

35. Southeast Brazil

36. Southeast Brazil (cont.)

37. Seasonally varying diurnal cycle: 27S, top, and area averaged (2x2 degrees), bottom.

38. Seasonally varying diurnal cycle of preciitation (area averaged 2x2 degrees), 24S (top) and 27S (bottom). 24S 27S

39. Seasonally varying diurnal cycle of preciitation (area averaged 2x2 degrees), 2S. 55W52W49W46W Westward propagating lines occur primarily during February-May.

40. Conclusions CMORPH precipitation analyses are useful in obtaining a detailed description of the diurnal cycle. A pronounced diurnal cycle in precipitation is found in many areas of South America. –Daytime peak over high terrain (e.g., Andes Mts., Brazilian Planalto). –Daytime peak near the coast, especially NE South America, associated with the sea breeze. –Nocturnal peak in the central La Plata Basin, over oceanic regions, and over portions of the Amazon Basin (affected by westward propagating sea breeze-induced convection).

41. Future Work There is a need to document the regional and large-scale atmospheric circulation features that contribute to the formation of westward- propagating lines over the Amazon Basin. Studies should be developed to evaluate the ability of numerical prediction models to simulate and predict the occurrence of these westward- propagating lines.