Diurnal cycle of precipitation based on cmorph
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Diurnal Cycle of Precipitation Based on CMORPH. Vernon E. Kousky, John E. Janowiak and Robert Joyce Climate Prediction Center, NOAA. CMORPH (CPC Morphing technique).

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Diurnal Cycle of Precipitation Based on CMORPH

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Diurnal Cycle of Precipitation Based on CMORPH

Vernon E. Kousky, John E. Janowiak


Robert Joyce

Climate Prediction Center, NOAA

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.


  • 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


  • 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

    For more information about CMORPH:


Comparison: CMORPH and Gridded Analyses (DJF 0203+0304)



CMORPH over estimates precipitation by 40-50% over Brazil.

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

DJF - South America (1mm mask)

DJF - South America (1mm mask)

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

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

Percent Total Precipitation: Diurnal Cycle DJF 2002-03




La Plata Basin




Daytime maximum

Nighttime maximum







Diurnal Cycle DJF 02-03 + 03-04

Time-Longitude Diurnal Cycle EQ DJF 2002-03 +2003-04

Rainfall develops along coast during the day and propagates westward through the night and into the next day.

Early morning maximum in rainfall over tropical Atlantic.

MAM Mean Diurnal Cycle – EQ-5N

Convective rainfall systems start along east coast on day-1 propagate westward, reaching western Amazon on day-3.

West Coast

East Coast

Time-Longitude Diurnal Cycle 30S DJF 2002-03 +2003-04

Rainfall develops over Andes Mts. During late afternoon, then shifts eastward during the night and following day.


East Coast SA


  • 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 sea breeze.

    • Nocturnal peak in the central La Plata Basin, and inland areas affected by westward propagating sea breeze-induced convection (Amazon Basin).

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