Investigating Daily Summertime Circulation and Precipitation Over West Africa with the WRF Model: A Regional Climate Model Adaptation Study

Size: px

Start display at page:

Download "Investigating Daily Summertime Circulation and Precipitation Over West Africa with the WRF Model: A Regional Climate Model Adaptation Study"

Rosemary Phelps
5 years ago
Views:

University of Colorado, Boulder CU Scholar Environmental Studies Graduate Theses & Dissertations Environmental Studies Spring 1-1-2014 Investigating Daily Summertime Circulation and Precipitation

1 University of Colorado, Boulder CU Scholar Environmental Studies Graduate Theses & Dissertations Environmental Studies Spring Investigating Daily Summertime Circulation and Precipitation Over West Africa with the WRF Model: A Regional Climate Model Adaptation Study Erik Ulysses Noble University of Colorado Boulder, erik.u.noble@gmail.com Follow this and additional works at: Part of the Atmospheric Sciences Commons, Climate Commons, Environmental Monitoring Commons, and the Environmental Studies Commons Recommended Citation Noble, Erik Ulysses, "Investigating Daily Summertime Circulation and Precipitation Over West Africa with the WRF Model: A Regional Climate Model Adaptation Study" (2014). Environmental Studies Graduate Theses & Dissertations This Dissertation is brought to you for free and open access by Environmental Studies at CU Scholar. It has been accepted for inclusion in Environmental Studies Graduate Theses & Dissertations by an authorized administrator of CU Scholar. For more information, please contact cuscholaradmin@colorado.edu.

9 υ

12 υ

13 υ

30 Praia! Cape Verde! Kawsara,' Senegal' ζ υ

33 ..

34 Δ Δ..

35 υ υ υ υ υ υ υ υ υ

36 υ υ

38 Source MERRA NCEP2 NAMMA Radiosonde: Kawsara, Senegal NAMMA Radiosonde: Praia, Cape-Verde Regional Model v.3 (RM3) Diagnostic Zonal Wind (U) Meridional Wind (υ) Relative Vorticity (ζ) Zonal Wind (U) Meridional Wind (υ) Relative Vorticity (ζ) Meridional Wind (V) Meridional Wind (υ) Zonal Wind (U) Meridional Wind (υ) Relative Vorticity (ζ) Spatial Resolution Temporal resolution hourly hourly hourly hourly hourly hourly 0-6 x daily 0-6 x daily hourly hourly hourly Period of Record 2-13 SEP SEP SEP SEP SEP SEP SEP SEP SEP SEP SEP 2006 Reference a/gridded/data.ncep.reanalysis2. html nasa.gov/namma nasa.gov/namma Druyan et al. (2006) Data Source Diagnostic Spatial Resolution Temporal Resolution Period of Record Reference GPCP Precipitation 0.25 Daily 2-13 SEP daily_choice.html TRMM 3B42 Precipitation hourly 2-13 SEP ta.html CMORPH Precipitation hourly 2-13 SEP 2006 cts/janowiak/cmorph_description.ht ml PERSIANN Precipitation hourly 2-13 SEP MERRA Precipitation hourly 2-13 SEP Precipitation hourly 2-13 SEP 2006 NCPR2 Precipitation hourly 2-13 SEP dded/data.ncep.reanalysis2.html Precipitation hourly 2-13 SEP 2006 NAMMA Senegal Rainguage Network Precipitation Minute 2-13 SEP

39 υ

40 υ υ υ

42 υ ζ = δυδ

43 29 Hodges (2001) that neglects the background contribution of δ u δ y 1. Figure 3.1 depicts a series of wave troughs and ridges, represented by 700-hPa ζ ( ζ 7) maxima and minima, on three consecutive days. It compares MERRA (top three plots) and WRF27 (bottom three plots) 700-hPa total wind (V 7) vectors superimposed over horizontal distributions of ζ 7 at 0000 UTC September 2006, during which three of the four AEWs, designated as AEW2, AEW3 and AEW4 in subsequent ﬁgures, traversed the region. AEW1 is not shown. Figure 3.1: A comparison between NASA MERRA (Top three panels) and WRF27 (bottom three panels) at 0000 UTC on each day, September ζ 7 maxima (blue-red contours) represent AEW troughcenters ζ 7 maxima indicate the positions of inverted troughs, and thus the axis of each AEW, while the V7vectors outline the shape of each 700-hPa trough. WRF27 is shown here because it achieves relatively high validation scores for vorticity (see below) and precipitation (not shown). Figure 3.1a identiﬁes the MERRA AEW2 ζ 7 maximum and its V 7-vector trough-axis at 25 W, and a corresponding WRF27 shallower trough is shown in Figure 3.1b. e MERRA AEW3 propagates westward from 7 N, 7 W (Figure 6c) to 10 N, 20 W (Figure 3.1e), and the corresponding WRF27 AEW3 shows a similar track in Figures 3.1d-f except for a slight northward displacement. A noticeable diﬀerence between WRF and MERRA is that the intensity of the AEW3 trough decreases with time in the simulation, while it increases in MERRA. AEW4 is near 18 E on 10 September, eventually reaching 5 E by 12 September, while the WRF27 AEW4 lags by several degrees to the northeast. In this example, WRF27 generates the

44 ζ +. ζ ζ υ ζ υ ζ

45 a) b) c) d)

46 υ υ υ ζ υ ζ υ υ υ ζ ζ υ ζ ζ σ σ ζ

47 a) b) c) d) e) f) υ υ ζ

48 σ σ ζ ζ σ σ ζ σ σ >. ζ σ σ

49 ζ σ σ

50 ζ ζ ζ ζ

51 ζ ζ

52 φ

53 φ

54 ζ ζ

55 φ ζ

57 ζ

58 ζ

62 48 Figure 3.10: Precipitation totals (ptot ) units (mm), for the 2-13 September 2006 period, (a) GPCP (b) TRMM (c) WRF2, the default conﬁguration (d) WRF27 (e) WRF32 (f) WRF59 (g) WRF60 (h) WRF64 and (i) RM3. e plot for GPCP shows the Sahel region in red, and the tropical rain-band region in black.

64 σ σ σ σ σ σ υ υ υ υ

65 σ σ

66 υ υ υ υ υ υ υ υ υ υ υ

67 υ υ υ υ υ

70 σ σ =. σ σ σ

71 σ

72 σ σ σ

73 . < <.

76 =.

79 Δ Δ. Δ Δ

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131 Meteorol Atmos Phys (2009) 105: DOI /s ORIGINAL PAPER Regional climate model simulation of the AMMA Special Observing Period #3 and the pre-helene easterly wave Leonard M. Druyan Æ Matthew Fulakeza Æ Patrick Lonergan Æ Erik Noble Received: 6 April 2009 / Accepted: 21 August 2009 / Published online: 10 September 2009 Ó Springer-Verlag 2009 Abstract The study examines results of dynamic downscaling of two global analyses: the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis II and the Global Forecast System final analysis (FNL). Downscaling to a 0.5 grid over West Africa and the adjacent Atlantic Ocean is accomplished by each of two regional models, the Regional Model, version 3 (RM3) of the Center for Climate Systems Research and the Weather, Research and Forecasting model (WRF). Simulations are for September 2006, the African Monsoon Multidisciplinary Analysis (AMMA) Special Observing Period #3 (SOP-3). The aim of this study is to exploit the increased spatial detail in the simulations and representations of climate fields by the regional models to analyze meteorological systems within the SOP-3 area of interest and time frame. In particular, the paper focuses on the regional models representations of the structure and movement of a prominent easterly wave during September 10 13th, the precursor of Tropical Storm/Hurricane Helene. It describes the RM3 simulated structure of the developing storm in terms of circulation, precipitation, vertical motion, cumulus heating rates, and cross-sections of wind and geopotential height anomalies. Simulated cumulus heating rates within the wave s main precipitation area imply a lowering of the bases of active cumulus in the transition from the African continent to the L. M. Druyan (&) M. Fulakeza P. Lonergan NASA/Goddard Institute for Space Studies, NYC and Center for Climate Systems Research, Columbia University, New York, USA LDruyan@giss.nasa.gov; ld12@columbia.edu E. Noble University of Colorado, Boulder, CO, USA Atlantic, indicating that the ocean environment promotes greater upward latent heat flux that in turn intensifies overlying storms. RM3 circulation, precipitation patterns, and storm trajectory are reasonably consistent with observational evidence. Experiments show that precipitation rates near 6 N over the eastern North Atlantic are sensitive to vertical thermal stability, such that they are enhanced by warmer in situ sea-surface temperatures (SSTs) and diminished by colder SSTs. However, prescribing colder SST causes increases in precipitation north of 9 N within areas of large scale upward vertical motion where rainfall rates are less sensitive to in situ SSTs. The evaluation of WRF indicates that its storm propagation is too fast over West Africa, where associated WRF precipitation rates are exaggerated, but its performance is improved over the Atlantic. 1 Introduction The African Monsoon Multidisciplinary Analysis (AMMA) is a concerted effort to improve our understanding of the climate of West Africa, especially the variability of precipitation systems (Redelsperger et al. 2006). The goal is for this increased understanding to improve techniques of seasonal prediction of rainfall anomalies, including droughts and floods, which have a devastating socio-economic impact on very vulnerable populations of the Sahel. In addition, there is special interest in studying disturbances entering the North Atlantic from West Africa, since they are often precursors of tropical storms. The NASA African Monsoon Multidisciplinary Analysis (NAMMA) contribution to the broader AMMA campaign focuses on the downstream or oceanic evolution of precipitating convective systems. To this end, NAMMA sponsored a field 123

132

133

Four- dimensional climate data sets of the AMMA Special Observing Period #3

Four- dimensional climate data sets of the AMMA Special Observing Period #3 Leonard M. Druyan 1, Matthew Fulakeza 1, Patrick Lonergan 1 and Erik Noble 2 NASA/Goddard Institute for Space Studies, NYC and