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Benjamin A. Schenkel ([email protected]) and Robert E. Hart
AMS Tropical Conference 2012
Department of Earth, Ocean, and Atmospheric Science
The Florida State University
Assessing the Climate Footprint of Tropical Cyclones: Pertinent Players or
Irrelevant Pawns?
Research Sponsored by NASA Earth and Space Science Fellowshipand NSF Grant #ATM-0842618
Motivation
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 2/13
Introduction Methodology Large Scale Impacts of TCs
Motivation
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 2/13
Introduction Methodology Large Scale Impacts of TCs
Motivation
???
How do tropical cyclones (TCs) impact the large scale circulation?
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 3/13
Introduction Methodology Large Scale Impacts of TCs
HighEnergy
Polar Jet
SST Cold WakeCooler and Drier
Atmospheric Response to TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 4/13
0
45°N
Sfc.
Tropopause
TC
Polar Jet
L H
Does the tropical environmental response extend beyond the SST cold wake?
Significant heat and moisture transports
Excitation of Rossby wave train
Introduction Methodology Large Scale Impacts of TCs
LowEnergy
Significant reduction in meridional energy gradient
Methodology: Quantifying the Large Scale Response to TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 5/13
• Objective: To analyze the response of the tropical atmospheric
environment to TC passage
• Evaluation of mean environmental response will occur using four-
dimensional storm-relative composites of normalized anomalies
• Composites are constructed using the NCEP Climate Forecast System
Reanalysis (Saha et al. 2011) for category 3 to 5 Best-Track TCs in the
Western North Pacific from 1982-2009 (N=257 TCs)
• Space-time spectral analysis (Wheeler and Kiladis 1999) used to
determine which equatorial waves are responsible for anomalies at
tropical latitudes
Introduction Methodology Large Scale Impacts of TCs
Large Scale Pressure Anomalies in the Tropics Following TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 6/13
Introduction Methodology Large Scale Impacts of TCs
Large Scale Pressure Anomalies in the Tropics Following TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 6/13
Introduction Methodology Large Scale Impacts of TCs
• Large scale response similar to TC Tip with significant anomalies through day 11
• Anomalies are significant (0.2σ) over an area extending over one-quarter of the circumference of the globe
• Reduced need for the Hadley cell to do work
Large Scale Pressure Anomalies in the Tropics Following TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 7/13
Introduction Methodology Large Scale Impacts of TCs
Large Scale Pressure Anomalies in the Tropics Following TC Passage
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 7/13
Introduction Methodology Large Scale Impacts of TCs
Vertical cross-sections will be presented next through the domain center
• Large scale response similar to TC Tip with significant anomalies through day 11
• Anomalies are significant (0.2σ) over an area extending over one-quarter of the circumference of the globe
• Reduced need for the Hadley cell to do work
Physical Processes Responsible for Cooling and Drying of Equator
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 8/13
Introduction Methodology Large Scale Impacts of TCs
• Weakening of Hadley cell following TC passageConvergence
Divergence
Subsidence
NorthSouth
Physical Processes Responsible for Cooling and Drying of Equator
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 9/13
Introduction Methodology Large Scale Impacts of TCs
• Weakening of zonal mean circulation following TC passage
• Cooling and drying in lower troposphere due to reduction in low level convergence of heat and moisture into ITCZ
• Anomalous diabatic cooling from reduction in deep convection
NorthSouthNext, we will examine the role of equatorial waves in generating these anomalies
Attributing Physical Processes to Equatorial Waves
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 10/13
• Normalized mean sea level pressure anomalies averaged for points within five degrees of the equator
• Negative sea level pressure anomaly associated with TC
• Positive sea level pressure anomaly at equator
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: MJO
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 11/13
• Normalized mean sea level pressure anomalies averaged for points within five degrees of the equator
• Negative sea level pressure anomaly associated with TC
• Positive sea level pressure anomaly at equator
• Dashed black contours: convectively active MJO
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: MJO
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 11/13
• Normalized mean sea level pressure anomalies averaged for points within five degrees of the equator
• Negative sea level pressure anomaly associated with TC
• Positive sea level pressure anomaly at equator
• Dashed black contours: convectively active MJO
• Solid black contours: convectively suppressed MJO
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: MJO
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 11/13
• MJO amplitude is maximized at time of TC passage although its magnitude is not significant according to Wheeler and Hendon (2004)
• Magnitude and relative location of positive pressure anomalies is beyond what can be attributed solely to MJO suggesting that TCs may also have an impact
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: Kelvin Waves
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 12/13
• Dashed orange contours: convectively active Kelvin wave
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: Kelvin Waves
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 12/13
• Dashed orange contours: convectively active Kelvin wave
• Solid orange contours: convectively suppressed Kelvin wave
• Triggering of convectively suppressed Kelvin wave is stronger and further east than expected for MJO event
Introduction Methodology Large Scale Impacts of TCs
EastWest
Attributing Physical Processes to Equatorial Waves: Kelvin Waves
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 12/13
• Timing and magnitude of the anomalies may suggest that TCs modulate and possibly initiate Kelvin waves potentially due to the following processes:
1. Suppression of deep convection by the subsident secondary circulation outside the TC inner core
2. TCs “steal” heat and moisture rich air at low levels from their environment
Introduction Methodology Large Scale Impacts of TCs
EastWest
Conclusion: A Conceptual Model
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 13/13
0
45°N
Sfc.
Tropopause
Polar Jet
Introduction Methodology Large Scale Impacts of TCs
Convectively Suppressed MJO
Convectively Suppressed MJO
Convectively Active MJO
Conclusion: A Conceptual Model
0
45°N
Sfc.
Anomalous flux of heat and moisture converging into TC at expense of environment
Tropopause
Suppression of precipitation yields cold anomalies due to reduction in diabatic heat release
Polar Jet
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 13/13
Introduction Methodology Large Scale Impacts of TCs
Suppressed PrecipitationPositive pressure
anomalyConvectively Suppressed Kelvin Wave
Modulation of MJO or ENSO???
Significant positive pressure anomalies occur across the entire basin
TC
Reduction in future TC activity???
What is the aggregate impact of anomalous TC activity over an entire season?
Time Series of Sensible Heat Tendency Term Anomalies
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 30/13
Introduction Introduction Methodology Large Scale Impacts of TCs
Vertical Structure of Moisture Anomalies
Assessing the TC Climate Footprint Benjamin A. Schenkel and Robert E. Hart The Florida State University 20/13
• Moistening of upper troposphere due to TC
• Drying of boundary layer due to reduction in sea surface fluxes from cold SST wake from TC
• Anomalous drying of troposphere following TC passage in region in which TC did not directly pass through
Introduction Methodology Large Scale Impacts of TCs