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Refining the Climate R ole of Tropical C yclones : Key Constituents of the Summer Hadley Cell ?. 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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slide1

Refining the Climate Role of Tropical Cyclones: Key Constituents of the Summer Hadley Cell?

Benjamin A. Schenkel (bschenkel@albany.edu),

University at Albany, State University of New York,

and Robert E. Hart, The Florida State University

4th International Summit on Hurricanes and Climate Change

Research Sponsored by NASA Earth and Space Science Fellowship

and NSF Grant #ATM–0842618

motivation

Results

  • Conclusions
  • Motivation
  • Background
Motivation

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 2/19

motivation1

Results

  • Conclusions
  • Motivation
  • Background
Motivation

Are TCs, on average, responsible for significant energy transports?

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 2/19

outline

Results

  • Conclusions
  • Motivation
  • Background
Outline
  • Background
    • Review of TC structure
  • Results: Cross-equatorial energy transports by TCs
    • Spatial structure of meridional energy transports
    • Processes responsible for meridional energy transport
  • Summary and conclusions

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 3/19

outline1

Results

  • Conclusions
  • Motivation
  • Background
Outline
  • Background
    • Review of TC structure
  • Results: Cross-equatorial energy transports by TCs
    • Spatial structure of meridional energy transports
    • Processes responsible for meridional energy transport
  • Summary and conclusions

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 4/19

review of the secondary circulation of a tc

Results

  • Conclusions
  • Motivation
  • Background
Review of the Secondary Circulation of a TC
  • Secondary circulation of a TC consists of:
  • Isothermal radial inflow
  • Moist adiabatic ascent and radial outflow
  • Descent caused by radiative cooling
  • Adiabatic descent outside storm core

Vertical Cross Section of TC Secondary Circulation

16

14

12

10

8

Altitude (km)

6

4

2

0

0

100

200

300

400

500

Radius from TC Center (km)

Credit: Emanuel (2006)

Warmer colors: high potential temperature

Colder colors: low potential temperature

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 5/19

review of the secondary circulation of a tc1

Results

  • Conclusions
  • Motivation
  • Background
Review of the Secondary Circulation of a TC
  • Secondary circulation of a TC consists of:
  • Isothermal radial inflow
  • Moist adiabatic ascent and radial outflow
  • Descent caused by radiative cooling
  • Adiabatic descent outside storm core
  • Primary focus of this talk will be on impacts of radial outflow on the atmospheric environment of the TC

Vertical Cross Section of TC Secondary Circulation

16

14

12

10

8

Altitude (km)

6

4

2

0

0

100

200

300

400

500

Radius from TC Center (km)

Credit: Emanuel (2006)

Warmer colors: high potential temperature

Colder colors: low potential temperature

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 5/19

upper tropospheric tc structure

Results

  • Conclusions
  • Motivation
  • Background
Upper-Tropospheric TC Structure
  • Composite of 200 hPa wind speed (m s-1; contours)and streamlines for North Atlantic TCs
  • Clockwise flow aloft due to generation of anticyclone from convective heat release
  • Flow is divergent and asymmetric
  • Strongest divergence found in “outflow jet” to northeast of TC
  • Location of outflow jet can change depending on large-scale environmental flow (e.g., polar jet)

North

South

Credit: Merrill (1988)

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 6/19

motivating questions

Results

  • Conclusions
  • Motivation
  • Background
Motivating Questions
  • Can a TC, on average, yield significant cross-equatorial energy transports in the western North Pacific?
  • How are TCs able to transport energy equatorward?
  • Which factors (e.g., TC intensity, TC size) do cross-equatorial TC energy transports show the most sensitivity to?
  • Do western North Pacific TCs play a salient role in aggregate meridional energy transports?

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 7/19

outline2

Results

  • Conclusions
  • Motivation
  • Background
Outline
  • Background
    • Review of TC structure
  • Results: Cross-equatorial energy transports by TCs
    • Spatial structure of meridional energy transports
    • Processes responsible for meridional energy transport
  • Summary and conclusions

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 8/19

slide11

Results

  • Conclusions
  • Motivation
  • Background

Methodology: Quantifying Cross-Equatorial Energy Transports by TCs

  • Objective: To quantify the mean cross-equatorial energy transports from a single TC in the western North Pacific
  • Evaluation of mean meridional energy transports by TCs utilizes three-dimensional storm-relative composites of atmospheric reanalysis data
      • Composites are constructed using the NCEP Climate Forecast System Reanalysis (Saha et al. 2010) for TCs (maximum 10-m wind speed ≥ 34 kt) in the western North Pacific equatorward of 21°N from 1982 to 2009 (N = 589 TCs)

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 9/19

slide12

Results

  • Conclusions
  • Motivation
  • Background

Methodology: Quantifying Cross-Equatorial Energy Transports by TCs

  • Meridional energy transports will be calculated to quantify the role of TCs in transporting energy out of the tropics:
  • Term 1: Meridional kinetic energy transports
  • Term 2: Meridional latent energy transports
  • Term 3: Meridional potential energy transports
  • Term 4: Meridional sensible heat transports
  • Any future reference to meridional energy transports will be referring to meridional transports of TOTAL energy
  • Total

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 9/19

lower tropospheric structure of tc and the environment

Results

  • Conclusions
  • Motivation
  • Background
Lower-Tropospheric Structure of TC and the Environment
  • Cyclonic circulation of TC is dominant feature in lower and middle troposphere within composites

TC

large-scale response of environment to TC passage similar to TC Yuri

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 10/19

lower tropospheric transports due to tc and the environment

Results

  • Conclusions
  • Motivation
  • Background
Lower-Tropospheric Transports due to TC and the Environment
  • Transports by cyclonic circulation largely cancel each other out at a given latitude band
  • Transports at 925 hPa typify transports in the lower andmiddletroposphere

Blue - Southward transport

Red - Northward transport

large-scale response of environment to TC passage similar to TC Yuri

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 11/19

upper tropospheric structure of tc and the environment

Results

  • Conclusions
  • Conclusions
  • Motivation
  • Background
Upper-Tropospheric Structure of TC and the Environment
  • Convective heat release yields anticyclonic circulation in upper troposphere
  • Equatorward outflow jet found on southeastern flank of upper-tropospheric anticyclone

H

Outflow Jet

large-scale response of environment to TC passage similar to TC Yuri

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 12/19

upper tropospheric transports due to tc and the environment

Results

  • Conclusions
  • Motivation
  • Background
Upper-Tropospheric Transports due to TC and the Environment
  • Equatorward energy transports by TC outflow jet are the dominant feature in deep tropics
  • Equatorward outflow jet of TC, on average, results in southward transport of energy into Southern Hemisphere

Blue - Southward transport

Red - Northward transport

H

large-scale response of environment to TC passage similar to TC Yuri

  • Next, we will vertically integrate the meridional energy transport anomalies from the surface to 50 hPa to obtain the net contribution of TCs in the troposphere…

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 13/19

slide17

Results

  • Conclusions
  • Motivation
  • Background

Vertically Integrated Meridional Energy Transports due to TCs

  • Meridional energy transports by TC are caused by three features:

Blue/Dashed - Southward transport

Red/Solid - Northward transport

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 14/19

slide18

Results

  • Conclusions
  • Motivation
  • Background

Vertically Integrated Meridional Energy Transports due to TCs

  • Meridional energy transports by TC are caused by three features:
  • Cyclonic circulation of TC

Blue/Dashed - Southward transport

Red/Solid - Northward transport

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 14/19

slide19

Results

  • Conclusions
  • Motivation
  • Background

Vertically Integrated Meridional Energy Transports due to TCs

  • Meridional energy transports by TC are caused by three features:
  • Cyclonic circulation of TC
  • Upper-tropospheric anticyclone of TC and equatorward outflow jet

Blue/Dashed - Southward transport

Red/Solid - Northward transport

H

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 14/19

slide20

Results

  • Conclusions
  • Motivation
  • Background

Vertically Integrated Meridional Energy Transports due to TCs

  • Meridional energy transports by TC are caused by three features:
  • Cyclonic circulation of TC
  • Upper-tropospheric anticyclone of TC and equatorward outflow jet
  • Extratropical cyclone triggered by interaction of TC with mid-latitudes

Blue/Dashed - Southward transport

Red/Solid - Northward transport

L

H

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 14/19

slide21

Results

  • Conclusions
  • Motivation
  • Background

Vertically Integrated Meridional Energy Transports due to TCs

  • Meridional energy transports by TC are caused by three features:
  • Cyclonic circulation of TC
  • Upper-tropospheric anticyclone of TC and equatorward outflow jet
  • Extratropical cyclone triggered by interaction of TC with mid-latitudes
  • Outflow jet will be primary focus of the remainder of the study

Blue/Dashed - Southward transport

Red/Solid - Northward transport

  • Next, we will zonally integrate the meridional energy transports across the shaded region to determine the net transports due to TCs across each latitude band…

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 14/19

climatological meridional energy transports

Results

  • Conclusions
  • Motivation
  • Background
Climatological Meridional Energy Transports
  • Climatology consists of transports due to all phenomena (e.g., Hadley cell, Asian monsoon, TCs) primarily during the summer and fall
  • Energy is exported out of the Northern Hemisphere tropics
  • Energy is imported into the Southern Hemisphere tropics, Northern Hemisphere subtropics, and mid-latitudes
  • Energy Convergence
  • Energy Divergence

large-scale response of environment to TC passage similar to TC Yuri

  • Energy Convergence

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 15/19

comparison of transports at time of tc passage versus climatology

Results

  • Conclusions
  • Motivation
  • Background
Comparison of Transports at Time of TC Passage Versus Climatology
  • Blue line comprised of meridional transports by all phenomena (e.g., TCs, Hadley cell, MJO) at time of TC passage
  • TCs generally strengthen Hadley cell circulation
  • Peak transports in the tropics are highly anomalous compared to the subtropics and mid-latitudes
  • Increased northward transports
  • Increased southward transports

large-scale response of environment to TC passage similar to TC Yuri

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 16/19

comparison of transports at time of tc passage versus climatology1

Results

  • Conclusions
  • Motivation
  • Background
Comparison of Transports at Time of TC Passage Versus Climatology
  • Southward transports of energy from the Northern Hemisphere tropics to the Southern Hemisphere tropics are primarily due to equatorwardTC outflow jet

large-scale response of environment to TC passage similar to TC Yuri

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 16/19

outline3

Results

  • Conclusions
  • Motivation
  • Background
Outline
  • Background
    • Review of TC structure
  • Results: Cross-equatorial energy transports by TCs
    • Spatial structure of meridional energy transports
    • Processes responsible for meridional energy transport
  • Summary and conclusions

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 17/19

conceptual model of tc impacts on meridional energy transports

Results

  • Conclusions
  • Motivation
  • Background
Conceptual Model of TC Impacts on Meridional Energy Transports

Late Summer Western Pacific Hadley Cell

Hadley cell

Hadley cell

Adapted from Waliser et al. (1999)

p

30°S

15°S

0

15°N

30°N

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 18/19

conceptual model of tc impacts on meridional energy transports1

Results

  • Conclusions
  • Motivation
  • Background
Conceptual Model of TC Impacts on Meridional Energy Transports

Late Summer Western Pacific Hadley Cell with a Low-Latitude TC

TC

Hadley cell

Hadley cell

Adapted from Waliser et al. (1999)

p

30°S

15°S

0

15°N

30°N

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 18/19

conceptual model of tc impacts on meridional energy transports2

Results

  • Conclusions
  • Motivation
  • Background
Conceptual Model of TC Impacts on Meridional Energy Transports

Late Summer Western Pacific Hadley Cell with a Low-Latitude TC

TC

Hadley cell

Hadley

cell

Adapted from Waliser et al. (1999)

p

Heat and Moisture

30°S

15°S

0

15°N

30°N

  • TCs are associated with anomalous lower-tropospheric imports of heat and moisture from Southern Hemisphere into Northern Hemisphere

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 18/19

conceptual model of tc impacts on meridional energy transports3

Results

  • Conclusions
  • Motivation
  • Background
Conceptual Model of TC Impacts on Meridional Energy Transports

Late Summer Western Pacific Hadley Cell with a Low-Latitude TC

TC

Heat and Potential Energy

Hadley cell

Hadley

cell

Adapted from Waliser et al. (1999)

p

Heat and Moisture

30°S

15°S

0

15°N

30°N

  • TC are also responsible for anomalous upper-tropospheric imports of heat and potential energy from Northern Hemisphere into Southern Hemisphere

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 18/19

conceptual model of tc impacts on meridional energy transports4

Results

  • Conclusions
  • Motivation
  • Background
Conceptual Model of TC Impacts on Meridional Energy Transports

Late Summer Western Pacific Hadley Cell with a Low-Latitude TC

TC

Heat and Potential Energy

Hadley cell

Hadley

cell

Adapted from Waliser et al. (1999)

p

Heat and Moisture

30°S

15°S

0

15°N

30°N

  • Net transport of energy from Northern Hemisphere to Southern Hemisphere suggests that TCs may be responsible for locally accelerating the Hadley cell

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 18/19

slide31

Results

  • Conclusions
  • Motivation
  • Background

Questions Raised

  • Can the average annual frequency of western North Pacific TCs be partially explained by the role of TCs in transporting energy from the Northern Hemisphere into the Southern Hemisphere during the late summer and early fall?
  • Can cross-equatorial energy transports by TCs help explain the inter-compensation in TC activity that exists between some basins (e.g., North Atlantic and eastern North Pacific; Maue 2009)?
  • Is the fidelity of general circulation model simulations of future climates potentially impacted if the model is unable to reasonably simulate cross-equatorial energy transports associated with TCs?

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY 19/19