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The rainiest places on earth: how does eastern NC/VA rank? & PRECIPITATION EXTREMES IN THE CAROLINAS: SATELLITES V

Scott Curtis Sol Wuensch Applied Atmospheric Science Program Craven County, NC GIS Dept. Geography East Carolina University. The rainiest places on earth: how does eastern NC/VA rank? & PRECIPITATION EXTREMES IN THE CAROLINAS: SATELLITES V.s. GAUGES. Satellite precipitation.

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The rainiest places on earth: how does eastern NC/VA rank? & PRECIPITATION EXTREMES IN THE CAROLINAS: SATELLITES V

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  1. Scott Curtis Sol Wuensch Applied Atmospheric Science Program Craven County, NC GIS Dept. Geography East Carolina University The rainiest places on earth: how does eastern NC/VA rank?&PRECIPITATION EXTREMES IN THE CAROLINAS:SATELLITES V.s. GAUGES

  2. Satellite precipitation • Global Precipitation Climatology Project • 1979-2009; 2.5 degree; pentad (5-day) • Recently released version 2.1 of the monthly data set corrected for a jump discontinuity at the boundary between two gauge data sets (Huffman et al. 2009) • However, the introduction of satellites leads to temporal inhomogeneities in second order statistics

  3. Precipitation distribution changes Eastern NC/VA % mm/day

  4. Spatial Rank “Percentile” • Temporal inhomogeneities require extremes be assessed at each time step individually • Spatial percentile compares the precipitation at a particular grid box with the rest of the global population. What is the rank? • A trend towards a higher (lower) rank would indicate that a location is contributing more (less) to global extreme weather

  5. 144 x 72 = 10,368

  6. H. Gloria (#5) Summer, non-tropical (#13) H. Floyd (#4) H. Ernesto (#2) 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 • Eastern NC/VA average percentile is 0.615 (rank #3128) when rain is present • No obvious trend or discontinuity • Interesting 7-year return interval for the biggest events (labeled) • 20 > 0.99 percentile: 9 tropical cyclones

  7. Seasonality

  8. Strong correlation between occurrences in excess of the 90thand 95thpercentiles (r = 0.84), but time series of 99th percentile is unrelated • Downward trends in numbers of pentads that exceed the 90th and 95th percentiles (p = 0.065 and 0.113, respectively)

  9. Conclusions I • Eastern NC/VA has contributed less to the global distribution of extreme rainfall (90th and 95th percentiles) from 1979 to 2007. • 50% of the time when eastern NC/VA is ranked high (> 99th percentile) it is due to tropical cyclones. However, an extreme pentad has occurred in all months of the year, except December.

  10. Can Satellites Properly Classify Extreme Precipitation Events? • North Carolina / South Carolina from 1998 to 2006 • Tropical Rainfall Measuring Mission • 0.25 degree, daily • Gauges • Daily quality controlled, 83 COOP, 11 first order • 1-year return interval • Synoptic classification • Wuensch and Curtis, accepted in Southeastern Geographer

  11. East = • Central = x West = +

  12. EAST Percent of extreme precipitation days

  13. Manual synoptic classification decision tree

  14. Synoptic • Mid-latitude cyclones produce more extreme rainfall according to TRMM • Convective thunderstorms produce more extreme rainfall according to gauge

  15. Conclusions II • Gauge results agree with previous studies on extremes in the Carolinas carried out over longer time periods (Changnon 1994, Keim 1996, Gamble and Meentemeyer 1997, etc.) • Differences between TRMM and gauge in the west are due to the landscape - rapidly changing elevation leading to large spatial variations in rainfall (orographic enhancement / rain shadow) • In the east TRMM and gauge handle tropical cyclones equally well • The differences in synoptic attribution are due to polygon versus point measurements • TRMM observes large footprints of intense rainfall (e.g. Mid-latitude cyclones) and gauge attributes more extremes to small-scale features (e.g. convective thunderstorms)

  16. Differences in seasonality are consistent with Ebert et al. (2007) who found that in the U.S. infrared satellite techniques overestimated mean winter precipitation by 50-100%, and summer precipitation was underestimated by 50% GAUGE TRMM

  17. Thank you! QUESTIONS?

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