Talk presented at Davidson College March 10, 2011. Comprises an introduction to and summary of my thesis research.

1. Satellite Observations of Rainfall and Water Vapor Kelly Howell with Tom Vonder Haar and Stan Kidder Cooperative Institute for Research in the Atmosphere March 10, 2011

3. September 5, 2008 at 00 UTC Areas with elevated TPW are often associated with instances of rainfall. Hurricane Ike

5. Global Circulation and Rain Production

6. General Circulation Patterns (a) Tropical atmosphere expands, polar atmosphere contracts, causing air to flow poleward at the upper levels (b) Redistribution of mass causes high pressure at poles, low pressure in tropics, causing equatorward flow at the surface (c) Coriolis force imparts a westward component to the equatorward flow and an eastward component to the poleward flow (d) Spontaneous instability imparts a wave-like character to the eastward flow in the midlatitudes Source: Wallace, J. M. and P. V. Hobbs, 2006: Atmospheric Science: An Introductory Survey. Elsevier Inc. , 483 pp.

7. Angular Momentum When an air parcel moves closer to the axis of rotation (i.e., poleward), the relative eastward velocity must increase to conserve angular momentum When an air parcel moves farther from the axis of rotation (i.e., equatorward), the relative westward velocity must increase to conserve angular momentum

9. September 5, 2008 at 00 UTC Oceanic Deserts Midlatitudes Subtropics Tropics Subtropics Midlatitudes West Pacific Warm Pool SPCZ ITCZ

14. Data

20. Radiation Along a Path Material absorbs radiation Material emits radiation Other radiation is scattered into path Material scatters radiation out of path

24. Total Precipitable Water and Rainfall Climatology

25. Annual Mean TPW The global mean TPW is 24.94 mm, with a maximum of approximately 45 mm just north of the equator.

26. Seasonal Mean TPW The seasonal TPW distributions are similar to previous findings, with the SPCZ extending its farthest eastward during DJF and TPW highs around southeast Asia during the JJA monsoon period. The presence of a double ITCZ can be detected in the eastern tropical Pacific during MAM.

27. Annual Mean RR in mm day -1 Source: Xie, P., and P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc. , 78 , 2539-2558. Surface Type (CMORPH) RR [mm day -1 ] Ocean 2.68 Land 2.57 All Surfaces 2.63 Surface Type (CMAP) RR [mm day -1 ] Ocean 3.02 Land 1.86 Globe 2.69

28. Annual Mean RR in mm year -1 The zonal mean RR distribution over land is fairly symmetric, while the oceanic distribution peaks in the tropics and has secondary peaks in the midlatitudes. Latitude (degrees N)

29. Annual Mean Rainfall Frequency The zonal distributions of rainfall frequency are analogous to the zonal distributions of rainfall. Overall, the oceans receive rain more frequently than land surfaces, but land surfaces receive heavy rain more frequently than ocean surfaces. Latitude (degrees N) Rainfall frequency = 100× 0.07 % 0.03 % 10.0 mm hr -1 0.34 % 0.27 % 5.0 mm hr -1 RR Threshold 8.58 % 11.04 % 0.1 mm hr -1 Land Ocean Surface Type

30. Seasonal Mean RR in mm month -1 Seasonal mean rainfall estimates from CMORPH are similar to previous findings (Ferraro et al. 1996). The NH and SH land areas show large changes between DJF and JJA: the winter hemisphere’s land areas receive very little rainfall.

31. Seasonal Mean Rainfall Frequency Rainfall frequency maximizes in the expected areas: the ITCZ, SPCZ, and eastern storm tracks. Rain falls infrequently in desert regions. Using the 0.1 mm hr -1 threshold, quasi-global frequencies hover around 10%. Season 0.1 mm hr -1 0.5 mm hr -1 1.0 mm hr -1 DJF 10.31 % 4.88 % 2.76 % MAM 10.30 % 4.79 % 2.76 % JJA 10.17 % 5.00 % 2.92 % SON 10.09 % 4.95 % 2.88 %

32. Regional Studies

33. TPW Threshold for Rainfall? Time series of (a) RR in mm hr -1 , (b) TPW in mm, and (c) global solar radiation at the Koto Tabang GPS station on Sumatra Island during JJA 2001. Rainfall does not tend to occur at times with relatively low TPW. Source: Wu, P., J.-I. Hamada, S. Mori, Y. I. Tauhid, M. D. Yamanaka, and F. Kimura, 2003: Diurnal variation of precipitable water over a mountainous area of Sumatra Island. J. Appl. Meteorol. , 42 , 1107-1115.

34. Regional Studies The following plots were constructed using the data at each of these grid points analyzed over all 35 months. Location Longitude Latitude East of Florida 70 o W 30 o N Indian Ocean 75 o E 8 o S East of Japan 142 o E 35 o N South of Panama 83 o W 4 o N South Atlantic Ocean 22 o W 45 o S North Atlantic Ocean 30 o W 50 o N West Pacific 155 o E 6 o N Southeastern Pacific 120 o W 8 o S SPCZ 170 o E 10 o S

35. TPW Distributions Annual mean TPW is highly variable in the midlatitude location, relatively high in the tropical location, and relatively low in the oceanic desert location. TPW (mm) Location Mean TPW East of Florida 30.66 mm West Pacific 54.28 mm Southeastern Pacific 29.62 mm

36. RR Distributions Equation of exponential decay. A more negative slope indicates a faster rate of decay (i.e., there are relatively few heavy rain events). More negative slopes tend to be associated with lower rainfall frequencies. RR [mm hr -1 ] Location Slope of Fit Rainfall Frequency East of Florida -0.58 11.11 % West Pacific -0.516 31.20 % Southeastern Pacific -1.556 2.29 %

37. RR vs TPW The shapes of these distributions approximate the TPW distributions. In general, the higher RRs occur at the more frequently occurring TPW values. However, this is not the case in the southeastern Pacific, where the highest RRs occur at higher TPW values. TPW (mm)

38. Probability of Rainfall RR ≥ 0.1 mm hr -1 RR ≥ 3.0 mm hr -1 Higher-intensity rainfall is less likely at lower TPW values. TPW (mm)

39. Global RR Distributions by TPW Range

40. RR Distribution by TPW Range At higher TPW values, rainfall is more probable and there is a higher proportion of heavier rainfall. RR [mm hr -1 ] TPW Range Probability of Rainfall 0-15 mm 2.34 % 15-30 mm 7.64 % 30-45 mm 16.59 % 45-60 mm 29.89 % 60-75 mm 45.89 %

41. RR Distribution by TPW Range The RR distributions are not strictly exponential, but an exponential fit is a consistent representation of the distribution. Steeper slopes are associated with drier environments. RR [mm hr -1 ] TPW Range Slope of RR Distribution 0-15 mm -1.01 15-30 mm -0.90 30-45 mm -0.70 45-60 mm -0.59 60-75 mm -0.49

44. Questions?