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Phil Arkin, ESSIC University of Maryland With thanks to:

Describing the Diurnal Cycle of Precipitation Using Satellite Observations. Phil Arkin, ESSIC University of Maryland With thanks to: Pingping Xie, John Janowiak, and Bob Joyce Climate Prediction Center/NOAA.

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Phil Arkin, ESSIC University of Maryland With thanks to:

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  1. Describing the Diurnal Cycle of Precipitation Using Satellite Observations Phil Arkin, ESSIC University of Maryland With thanks to: Pingping Xie, John Janowiak, and Bob Joyce Climate Prediction Center/NOAA

  2. The diurnal cycle in precipitation remains a very difficult challenge for global and regional models of the atmosphere • Observations from which the diurnal cycle of precipitation can be inferred have been limited until recently • radar and some gauges over land • inferences from geostationary imagery over oceans • Newly available high resolution precipitation products (CMORPH, TRMM RT, PERSIANN, others) make more detailed description of many phenomena possible • CMORPH is composite product using all available passive microwave-derived estimates with interpolation by advection inferred from geostationary IR (Joyce et al., 2004, J. Hydrometeorology) • Basic dataset is 30 minute/8 km – 3 hour totals for 0.25ºx 0.25º areas used for the most part

  3. Seasonal mean diurnal cycle – IR(top), radar(bottom) JJA 2000 JJA 2002 JJA 2003 • Seasonal mean diurnal cycles in deep convective cloud (<215K) and radar rainfall are similar • Interannual changes also similar • Amounts, phases can’t be compared effectively

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

  5. 215K 215K 215K LAND ONLY Climatology of diurnal cycle of cloudiness (pentads for full year) OCEAN ONLY Mean diurnal cycle in fractional coverage (87-97) at 215K averaged over the NAME region (upper left), and over land (upper right) and ocean (lower left) subregions. 0000 UTC at bottom (4-6pm local), time increasing upward.

  6. 1987 1988 1989 LAND – 215K 1992 1990 1991 1993 1994 1995

  7. 1987 1988 1989 OCEAN – 215K 1992 1990 1991 1993 1994 1995

  8. 2004 2003 May June July

  9. Diurnal cycle prominent during May – September when averaged over whole region • Huge differences between land and water • Begins in late June in both (northern/western subset of full domain) • Over land, clouds begin to increase in mid-afternoon and peak around 7-8pm; seasonal peak mid-July – mid-August • Over water, diurnal cycle much weaker but still clear – peaks around 4-6am; seasonal peak later – August – September • Much more intraseasonal variability in 11-year average over water • Interannual variations more in amplitude than phase over both land and ocean • CMORPH allows us to visualize details of the influence of the terrain of the diurnal cycle of precipitation that may never have been seen before • Precipitation dies away quickly to the west of the Sierra Madre Occidental • Seasonal cycles in 2003 and 2004 are similar, but some differences are evident

  10. Difference between largest and smallest values in mean diurnal cycle (left) and time of maximum value (right). Index value of 1 corresponds to 0115 UTC, roughly 10pm local on average. Mean precipitation through lifetime of Isabel

  11. Isabel exhibited substantial mean diurnal cycle in precipitation during its lifetime • Peak values found on northeast side of eye near local midnight • Maximum values about 50% greater than minimum • Ivan, Jeanne and Karl also show substantial diurnal (also some semidiurnal) variability averaged over their lifetime • Not clear whether the (local) time of maximum is the same for each • Mechanisms? • Solar forcing? • Inertial oscillation? • Dynamic oscillation that aliases to 24 hour period?

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

  13. Day 1 Day 2 Day 3 Day 4 W. Coast E. Coast Sea breeze induced convection near the coast on Day 1 propagates westward reaching the western Amazon Basin on Day 3.

  14. Syntheses of available satellite data make it possible to describe diurnal cycle of precipitation (as well as other variations) in much greater detail than in the past • CMORPH, PERSIANN, TRMM/RT, Osaka Pref. U., NRL/Turk, … • Have to see if Regional Reanalysis capable of providing circulation details (global reanalyses so far cannot) • Details still have to be validated • CMORPH, radar and IR give similar results over U.S. • Many other high resolution precipitation products have been developed (PERSIANN, TRMM RT, NESDIS Autoestimator, …) • All provide interesting and provocative detail • Some validation is available (CPC for US, BoM for Australia) • But a thorough evaluation and intercomparison is badly needed (more discussion tomorrow)

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