benjamin a. schenkel ([email protected]), university at albany, state university of new york,

Benjamin A. Schenkel ([email protected]), University at Albany, State University of New York,

and Robert E. Hart, The Florida State University

4th International Summit on Hurricanes and Climate Change

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

Research Sponsored by NASA Earth and Space Science Fellowshipand NSF Grant #ATM–0842618

Motivation

Cross-Equatorial Energy Transports by TCs Benjamin A. Schenkel University at Albany, SUNY2/19

Backgroun

dResults Conclusion

sMotivation

Motivation

Backgroun

dResults Conclusion

sMotivation

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


• 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

Outline

Backgroun

dResults Conclusion

sMotivation


• Background






Outline

Backgroun

dResults Conclusion

sMotivation


Review of the Secondary Circulation of a TC

Credit: Emanuel (2006)

Alti

tude

(km

)

0

10

16

8

12

6

4

2

14

0 100 200 300 400 500Radius from TC Center (km)

Vertical Cross Section of TC Secondary Circulation

• Secondary circulation of a TC consists of:

1. Isothermal radial inflow

2. Moist adiabatic ascent and radial outflow

3. Descent caused by radiative cooling

4. Adiabatic descent outside storm core

Warmer colors: high potential temperatureColder colors: low potential temperature

Backgroun

dResults Conclusion

sMotivation


Review of the Secondary Circulation of a TC

Credit: Emanuel (2006)

Alti

tude

(km

)

0

10

16

8

12

6

4

2

14

0 100 200 300 400 500Radius from TC Center (km)

Vertical Cross Section of TC Secondary Circulation

• Secondary circulation of a TC consists of:

1. Isothermal radial inflow

2. Moist adiabatic ascent and radial outflow

3. Descent caused by radiative cooling

4. Adiabatic descent outside storm core

• Primary focus of this talk will be on impacts of radial outflow on the atmospheric environment of the TCWarmer colors: high potential temperature

Colder colors: low potential temperature

Backgroun

dResults Conclusion

sMotivation


Upper-Tropospheric TC Structure

Credit: Merrill (1988)

• 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)

Composite of 200 hPa wind speed (m s-1; contours) and streamlines for North

Atlantic TCs

North

South

Backgroun

dResults Conclusion

sMotivation


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?

Backgroun

dResults Conclusion

sMotivation


• Background






Outline

Motivation Backgroun

dConclusions

Results


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)


dConclusions

Results


• 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

Methodology: Quantifying Cross-Equatorial Energy Transports by TCs

Total


dConclusions

Results


Lower-Tropospheric Structure of TC and the Environment

TC


dConclusions

Results

• Cyclonic circulation of TC is dominant feature in lower and middle troposphere within composites

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

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 and middle troposphere

Blue - Southward transportRed - Northward transport


dConclusions

Results


Upper-Tropospheric Structure of TC and the Environment

Outflow JetH

• Convective heat release yields anticyclonic circulation in upper troposphere

• Equatorward outflow jet found on southeastern flank of upper-tropospheric anticyclone

Conclusions


dConclusions

Results


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

H

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…


dConclusions

Results

Blue - Southward transportRed - Northward transport


Vertically Integrated Meridional Energy Transports due to TCs


dConclusions

Results

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


Blue/Dashed - Southward transportRed/Solid - Northward transport



dConclusions

Results


1. Cyclonic circulation of TC





dConclusions

Results



2. Upper-tropospheric anticyclone of TC and equatorward outflow jet

H




H

L


dConclusions

Results




3. Extratropical cyclone triggered by interaction of TC with mid-latitudes





dConclusions

Results




3. Extratropical cyclone triggered by interaction of TC with mid-latitudes

• Outflow jet will be primary focus of the remainder of the study

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…



Climatological Meridional Energy Transports

Energy Divergence

Energy Convergence

• 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


dConclusions

Results


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


dConclusions

Results

Increased northward transports

Increased southward transports


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 equatorward TC outflow jet


dConclusions

Results


• Background






Outline


dResults Conclusion

s


Conceptual Model of TC Impacts on Meridional Energy Transports

Hadley cell

Hadley cellp

30°N15°S 0 15°N30°S

Ada

pted

from

Wal

iser

et a

l. (1

999)

Late Summer Western Pacific Hadley Cell


dResults Conclusion

s



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

Hadley cell

Hadley cellp

30°N15°S 0

TC

15°N30°S

Ada

pted

from

Wal

iser

et a

l. (1

999)


dResults Conclusion

s



Hadley cellp

30°N15°S 0 15°N30°S

Ada

pted

from

Wal

iser

et a

l. (1

999)

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


dResults Conclusion

s


Hadleycell

TC

Heat and Moisture



Hadley cellp

30°N15°S 0 15°N30°S

Ada

pted

from

Wal

iser

et a

l. (1

999)


dResults Conclusion

s


Hadleycell

TC

Heat and Moisture

Heat and Potential Energy

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



Hadley cellp

30°N15°S 0 15°N30°S

Ada

pted

from

Wal

iser

et a

l. (1

999)


dResults Conclusion

s


Hadleycell

TC

Heat and Moisture

Heat and Potential Energy

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


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?


dResults Conclusion

s


benjamin a. schenkel ([email protected]), university at albany, state university of new york,

Documents

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impacts of radial outflow

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