The Effects of Gap Wind Induced Vorticity, the ITCZ, and Monsoon Trough on Tropical Cyclogenesis Heather M. Holbach and Mark A. Bourassa Center for Ocean-Atmospheric Prediction Studies Department of Earth, Ocean & Atmospheric Science The Florida State University Email: hmh06d@my.fsu.edu Funded by NASA OVWST
Objectives How do gap winds over the Gulf of Tehuantepec and Gulf of Papagayo contribute to tropical cyclogenesis in the Eastern Pacific basin? How do the Monsoon Trough and ITCZ interact with the gap winds to influence tropical cyclogenesis in the Eastern Pacific? Observational study Chelton et al., 2000, MWR 2
Example Case 2006 Hurricane John 3
GridSAT IR (2006 Hurricane John) IR Brightness Temperature ( C) 4
2006 Hurricane John 12.5 km JPL L2B Version 2 QSCAT 37.5 km Spacing 5
Surface Vorticity (2006 Hurricane John) 125 km averaging 12Z August 24, 2006-12 -10-8 -6-5 -4-3 -2 2 3 4 5 6 8 10 12 Vorticity (*10-5 s -1 ) 6
Surface Vorticity (2006 Hurricane John) 12Z August 25, 2006-12 -10-8 -6-5 -4-3 -2 2 3 4 5 6 8 10 12 Vorticity (*10-5 s -1 ) 7
Surface Vorticity (2006 Hurricane John) 06Z August 26, 2006-12 -10-8 -6-5 -4-3 -2 2 3 4 5 6 8 10 12 Vorticity (*10-5 s -1 ) 8
Surface Vorticity (2006 Hurricane John) 13Z August 27, 2006-12 -10-8 -6-5 -4-3 -2 2 3 4 5 6 8 10 12 Vorticity (*10-5 s -1 ) 9
Surface Vorticity (2006 Hurricane John) 12Z August 28, 2006-12 -10-8 -6-5 -4-3 -2 2 3 4 5 6 8 10 12 Vorticity (*10-5 s -1 ) 10
CCMP Vorticity Hovmöller (2006 Hurricane John) Averaged over 7-17 N Time Longitude 11
Gap Wind Contribution Categories Large: Gap winds produce the main source of initial surface cyclonic vorticity Medium: Gap winds produce some of the initial surface cyclonic vorticity along with another substantial source not associated with gap winds Small: Gap winds contribute vorticity to an existing region after development begins 12
Summary of Gap Wind Contributions 60 2002-2008 Number of Systems 50 40 30 20 10 Papagayo Tehuantepec 0 Small Medium Large Contribution Tehuantepec gap winds contributed vorticity to 29 out of 118 TCs investigated Papagayo gap winds contributed vorticity to 58 out of 118 TCs investigated 13
Zonal wind Hovmöller (2006 Hurricane John) Averaged over 80-140 W Gulf of Papagayo Gulf of Tehuantepec Time Latitude 14
Number of TCs Summary of Monsoon Trough and ITCZ 50 45 40 35 30 25 20 15 10 5 0 Monsoon Trough Weak Westerlies or ITCZ Gap Wind Contribution Comparison 2002-2008 No Gap Wind Present No Gap Wind Contribution Papagayo Tehuantepec 98 out of 118 (83%) TCs form when the monsoon trough is present. 20 out of 118 (17%) TCs form when weak westerlies or ITCZ is present. When monsoon trough is present, Gulf of Papagayo contributes more often than Gulf of Tehuantepec. 15
Conclusion QSCAT provides observational data needed to complete a study Temporal resolution still presents a problem Rain contamination is an issue Gap winds generate surface cyclonic vorticity that contributes to the development of tropical cyclones. Tehuantepec gap winds contributed to ~25% of TCs investigated Papagayo gap winds contributed to ~49% of TCs investigated Gap winds are not sufficient for cyclogenesis to occur Majority of storms form when the monsoon trough is present. ~76% (44/58) of contributions from Papagayo gap winds occurred while the monsoon trough is present ~69% (20/29) of contributions from Tehuantepec gap winds occurred while the monsoon trough is present 16
Questions? 17
Backup Slides 18
Gap Wind Strengths Nicaragua Nicaragua Weak: 6-8 m/s Moderate: 8-10 m/s Yucatan Yucatan Strong: 10-12 m/s Very Strong: 12 m/s 0 3 4 5 6 7 8 9 10 12 Wind Speed (m/s) 19
Number of Days 700 600 500 400 300 200 100 0 Summer Gap Winds May-November, 2002-2008 None Weak Moderate Strong Very Strong Gap Wind Strength Papagayo Tehuantepec Papagayo: 578 (~55%) Gap wind days Majority moderate and strong Tehuantepec: 758 (~52%) Gap wind days Majority strong and very strong 20
2004 Hurricane Celia 11Z July 11, 2004 12Z July 13, 2004 0 3 4 5 6 7 8 9 10 12 Wind Speed (m/s) Rain Contamination 21
GridSAT IR and Dvorak Fix Archive 12Z July 11, 2004 12Z July 13, 2004 Mexico 00Z July 16, 2004 03Z July 19, 2004 Brightness Temperature (C) GridSAT: Knapp et al., 2011, BAMS Dvorak Fix Archive: Cossuth, 2010, personal communication 22
Vorticity Mechanisms Shear Shear + Curvature Monsoon Trough 23
Area-averaged Surface Relative Vorticity Adapted from Bourassa and McBeth-Ford (2010) Added spline fit for winds 12.5 km 25 km 37.5 km 50 km ζ: Relative Vorticity C: Circulation A: Area : velocity along closed contour : length tangent to contour Averaging over larger area reduces random error and noise in calculation We use a diameter of 125 km 24
Surface Relative Vorticity 11Z July 11, 2004 12Z July 13, 2004 01Z July 16, 2004 02Z July 19, 2004-10 -9-8 -7-6 -5-4 -3-2 2 3 4 5 6 7 8 9 10 Vorticity (*10-5 s -1 ) Vorticity calculation adapted from Bourassa and McBeth-Ford, 2010, J.A.O.T. 25
Gap Wind Contribution Categories Large: Gap winds produce the main source of initial surface cyclonic vorticity Medium: Gap winds produce some of the initial surface cyclonic vorticity along with another substantial source not associated with gap winds Small: Gap winds contribute a small amount of vorticity to initial source or contribute vorticity to an existing region after development begins 26
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