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Benjamin A. Schenkel (bschenkel@albany), University at Albany, State University of New York,

On the Impacts of Western North Pacific Tropical Cyclones on the Moisture Content of Their Large Scale Tropical Atmospheric Environment. Benjamin A. Schenkel (bschenkel@albany.edu), University at Albany, State University of New York, and Robert E. Hart, The Florida State University

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Benjamin A. Schenkel (bschenkel@albany), University at Albany, State University of New York,

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  1. On the Impacts of Western North Pacific Tropical Cyclones on the Moisture Content of Their Large Scale Tropical Atmospheric Environment Benjamin A. Schenkel (bschenkel@albany.edu), University at Albany, State University of New York, and Robert E. Hart, The Florida State University 38th Northeastern Storms Conference Research Sponsored by NASA Earth and Space Science Fellowship and NSF Grant #ATM–0842618

  2. Background • Motivation • Results • Conclusions Outline • Motivation and previous research • Overview of tropical cyclone (TC) structure • Motivation • Results • Spatial scales of anomalous drying caused by TCs • Processes responsible for drying of environment by TCs • Summary and conclusions Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 2/16

  3. Background • Motivation • Results • Conclusions Outline • Motivation and previous research • Overview of tropical cyclone (TC) structure • Motivation • Results • Spatial scales of anomalous drying caused by TCs • Processes responsible for drying of environment by TCs • Summary and conclusions Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 2/16

  4. Background • Motivation • Results • Conclusions Primary Circulation of TC • Horizontal winds of the TC constitute the “primary circulation” of the TC • Lower tropospheric winds are cyclonic with the strongest winds generally found in the eyewall at the TC center L Large scale response of environment to TC passage similar to TC Yuri Credit: Thomson Higher Education Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 3/16

  5. Background • Motivation • Results • Conclusions Primary Circulation of TC • Wind field of TC is approximately in gradient wind balance • TC is a warm core cyclone meaning that cyclonic winds of TC weaken with height and become anticyclonic in the upper troposphere H L Large scale response of environment to TC passage similar to TC Yuri Credit: Thomson Higher Education Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 3/16

  6. Background • Motivation • Results • Conclusions Secondary Circulation of a TC Credit: http://www.physicalgeography.net/ H L • TC also contains a “secondary circulation” consisting of: • Lower tropospheric inflow towards low pressure at TC center • Ascent in the eyewall • Upper tropospheric outflow away from the anticyclone at the TC center • Adiabatic descent outside the TC circulation Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 4/16

  7. Background • Motivation • Results • Conclusions Secondary Circulation of a TC Credit: http://www.physicalgeography.net/ H L • If the TC is sufficiently strong, some of air that ascends in the eyewall will adiabatically descend in the TC eye serving to lower the pressure of the TC • Secondary circulation results from surface friction which causes air to converge towards TC center primarily in the lower troposphere Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 4/16

  8. Background • Motivation • Results • Conclusions Secondary Circulation of a TC Credit: http://www.physicalgeography.net/ H L • Secondary circulation is significantly weaker than the primary circulation of the TC Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 4/16

  9. Background • Motivation • Results • Conclusions Asymmetric Structure of TCs Middle-to-Upper Tropospheric Water Vapor Imagery and Satellite Derived Winds (kt) for Hurricane Sandy at 1500 UTC 25 October 2012 • TC structure can be very asymmetric particularly in the upper troposphere • Both the magnitude and direction of the radial outflow vary significantly in Hurricane Sandy Dark Light Dry Moist H Large scale response of environment to TC passage similar to TC Yuri Credit: CIMMS-UWM Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 5/16

  10. Background • Motivation • Results • Conclusions Asymmetric Structure of TCs Middle-to-Upper Tropospheric Water Vapor Imagery and Satellite Derived Winds (kt) for Hurricane Sandy at 1500 UTC 25 October 2012 • TC structure can be very asymmetric particularly in the upper troposphere • Both the magnitude and direction of the radial outflow vary significantly in Hurricane Sandy • Subtropical jet to the north enhances outflow on northern side of storm with winds exceeding 120 kts! Dark Light Dry Moist Subtropical Jet H Large scale response of environment to TC passage similar to TC Yuri Focus of the results of this talk will be on the impacts of the asymmetric upper tropospheric structure of TCs on its atmospheric environment Credit: CIMMS-UWM Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 5/16

  11. Background • Motivation • Results • Conclusions Outline • Motivation and previous research • Overview of tropical cyclone (TC) structure • Motivation • Results • Spatial scales of anomalous drying caused by TCs • Processes responsible for drying of environment by TCs • Summary and conclusions Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 6/16

  12. Background • Motivation • Results • Conclusions Motivation - 1600 km Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 7/16

  13. Background • Motivation • Results • Conclusions Motivation - 1600 km - 1700 km Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 7/16

  14. Background • Motivation • Results • Conclusions Motivation - 1600 km - 1700 km - 1800 km Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 7/16

  15. Background • Motivation • Results • Conclusions Motivation Credit: COMET/UCAR 1200 UTC 29 August 1995 What factors determine the horizontal spacing between TCs when multiple TCs are present? Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 8/16

  16. Background • Motivation • Results • Conclusions Motivating Questions • What is the role of TCs in the tropics? • How do TCs impact their tropical atmospheric environment? • What are the spatial scales over which TCs impact the tropical atmosphere? • Can the impact of TCs upon their tropical atmospheric environment on the aggregate help explain the annual number of TCs? Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 9/16

  17. Background • Motivation • Results • Conclusions Outline • Motivation and previous research • Overview of tropical cyclone (TC) structure • Motivation • Results • Spatial scales of anomalous drying caused by TCs • Processes responsible for drying of environment by TCs • Summary and conclusions Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 10/16

  18. Background • Motivation • Results • Conclusions Methodology: Quantifying the Large Scale Response to TCs • Objective: To examine how Western North Pacific TCs impact the moisture content of their large scale tropical atmospheric environment • Evaluation of mean environmental response will occur using three-dimensional storm-relative composites of normalized and raw anomalies • Composites are constructed using the NCEP Climate Forecast System Reanalysis (Saha et al. 2010) for strong TCs (maximum 10-m winds  64 kt) in the Western North Pacific equatorward of 36°N from 1982 to 2009 (N = 477 TCs) • Reanalysis: A past model simulation that assimilates historical observations providing the most likely atmospheric state at a given time (Thorne and Vose 2010) Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 11/16

  19. Background • Motivation • Results • Conclusions Large Scale Drying in the Tropics Following TC Passage • Precipitable water: measure of depth of liquid water that would result if all the water vapor in the column fell as precipitation • TCs primarily impact their atmospheric environment by anomalously drying within two distinct regions TC Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 12/16

  20. Background • Motivation • Results • Conclusions Large Scale Drying in the Tropics Following TC Passage • Precipitable water: measure of depth of liquid water that would result if all the water vapor in the column fell as precipitation • TCs primarily impact their atmospheric environment by anomalously drying within two distinct regions • West region: stronger drying with area approximately equal to TC TC West region Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 12/16

  21. Background • Motivation • Results • Conclusions Large Scale Drying in the Tropics Following TC Passage • Precipitable water: measure of depth of liquid water that would result if all the water vapor in the column fell as precipitation • TCs primarily impact their atmospheric environment by anomalously drying within two distinct regions • West region: stronger drying with area approximately equal to TC • Southwest region: weaker drying in area over twice as large as TC TC West region Southwest region Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 12/16

  22. Background • Motivation • Results • Conclusions Large Scale Drying in the Tropics Following TC Passage • Although the horizontal scales of the dryingare large, the anomalies do not last long after TC passage TC West region Southwest region Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 12/16

  23. Background • Motivation • Results • Conclusions Large Scale Drying in the Tropics Following TC Passage • Although the horizontal scales of the dryingare large, the anomalies do not last long after TC passage West region Southwest region Large scale response of environment to TC passage similar to TC Yuri The remainder of this talk will focus on the processes responsible for dry anomalies to the southwest of the TC… Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 12/16

  24. Background • Motivation • Results • Conclusions Physical Explanation of Drying in the Southwest Region Outflow Jet H L TC Anticyclone of TC Large scale response of environment to TC passage similar to TC Yuri Outflow Jet Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 13/16

  25. Background • Motivation • Results • Conclusions Physical Explanation of Drying in the Southwest Region • To the north and east of TC, air is forced to rotate clockwise around TC’s anticyclone • Parcels eventually pass through anticyclonically curved outflow jet to the southeast of the TC Outflow Jet H L TC Anticyclone of TC Large scale response of environment to TC passage similar to TC Yuri Outflow Jet Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 13/16

  26. Background • Motivation • Results • Conclusions Physical Explanation of Drying in the Southwest Region • Anomalous dry air to the southwest of the TC is immediately downstream of the TC outflow jet • Location of the anomalous drying suggests that the upper tropospheric convergence caused by the outflow jet is the cause of the drying Outflow Jet H L TC Anticyclone of TC Large scale response of environment to TC passage similar to TC Yuri Outflow Jet Area of significant dry precipitable water anomalies Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 13/16

  27. Background • Motivation • Results • Conclusions Review of Divergence Induced by Anticyclonically Curved Jet • Convergence downstream and to the right of the jet axis is due to acceleration associated with the jet streak and the curvature of the flow • According to the four quadrant jet streak model, a jet streak is associated with the following divergence pattern due to acceleration of the flow Convergence due to jet streak Divergence due to jet streak Credit: Beebe and Bates (1965) Divergence due to jet streak Convergence due to jet streak Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 14/16

  28. Background • Motivation • Results • Conclusions Review of Divergence Induced by Anticyclonically Curved Jet • Curvature of the flow will also induce divergence upstream and convergence downstream of the anticyclonically curved jet Convergence due to jet streak Divergence due to jet streak Credit: Beebe and Bates (1965) Divergence due to jet streak Convergence due to jet streak Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 14/16

  29. Background • Motivation • Results • Conclusions Review of Divergence Induced by Anticyclonically Curved Jet • Curvature of the flow will also induce divergence upstream and convergence downstream of the anticyclonically curved jet Divergence due to flow curvature Convergence due to flow curvature Credit: Beebe and Bates (1965) Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 14/16

  30. Background • Motivation • Results • Conclusions Review of Divergence Induced by Anticyclonically Curved Jet • Curvature of the flow will also induce divergence upstream and convergence downstream of the anticyclonically curved jet • Added together, the contributions from the jet streak and curvature of the flow lead to strong divergence and convergence to the right of the jet axis and cancel each other to the left of jet axis Divergence due to flow curvature Convergence due to flow curvature Credit: Beebe and Bates (1965) Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 14/16

  31. Background • Motivation • Results • Conclusions Review of Divergence Induced by Anticyclonically Curved Jet • Curvature of the flow will also induce divergence upstream and convergence downstream of the anticyclonically curved jet • Added together, the contributions from the jet streak and curvature of the flow lead to strong divergence and convergence to the right of the jet axis and cancel each other to the left of jet axis Credit: Beebe and Bates (1965) Divergence Convergence Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 14/16

  32. Background • Motivation • Results • Conclusions Physical Explanation of Drying in the Southwest Region Blue: Convergence Red: Divergence Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 15/16

  33. Background • Motivation • Results • Conclusions Physical Explanation of Drying in the Southwest Region • Upper tropospheric convergence in right exit region of the equatorward outflow jet yields anomalous subsidence and drying throughout the column • Equatorward outflow jet results from interaction of the TC with its environment Blue: Convergence Red: Divergence Large scale response of environment to TC passage similar to TC Yuri Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 15/16

  34. Background • Motivation • Results • Conclusions Conceptual Model of Drying Induced by TCs Tropopause 45°N TC Height Latitude Longitude 0 Sfc. Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 16/16

  35. Background • Motivation • Results • Conclusions Conceptual Model of Drying Induced by TCs Moist Tropopause 45°N Height Latitude Longitude 0 Sfc. Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 16/16

  36. Background • Motivation • Results • Conclusions Conceptual Model of Drying Induced by TCs Right exit region of TC outflow jet yields upper tropospheric convergence, subsidence, and lower tropospheric divergence to southwest of TC H Moist Outflow Jet Convergence Tropopause 45°N Subsidence Height Latitude Divergence Longitude 0 Sfc. Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 16/16

  37. Background • Motivation • Results • Conclusions Conceptual Model of Drying Induced by TCs H Moist Dry Outflow Jet Tropopause 45°N Height Latitude TC outflow jet induces an anomalous drying Longitude 0 Sfc. Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 16/16

  38. Background • Motivation • Results • Conclusions Conceptual Model of Drying Induced by TCs H Moist Dry Outflow Jet Tropopause 45°N Height Latitude The drying of the environment by Western North Pacific TCs may explain the 1700 km spacing between TCs during multiple TC events Longitude 0 Sfc. Impact of TCs on Environmental Moisture Content Benjamin A. Schenkel University at Albany, SUNY 16/16

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