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
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
2/19
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
2/19
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Results
Backgroun
d
Conclusion
s
Review of the Secondary Circulation of a TC
• Secondary circulation of a TC
consists of:
16
Vertical Cross Section of TC Secondary Circulation
14
2. Moist adiabatic ascent and
radial outflow
12
Altitude (km)
1. Isothermal radial inflow
10
3. Descent caused by radiative
cooling
8
6
4. Adiabatic descent outside
storm core
4
2
0
0
100
200
300
400
Radius from TC Center (km)
500
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
Motivation
Results
Backgroun
d
Conclusion
s
Review of the Secondary Circulation of a TC
• Secondary circulation of a TC
consists of:
16
Vertical Cross Section of TC Secondary Circulation
14
2. Moist adiabatic ascent and
radial outflow
12
Altitude (km)
1. Isothermal radial inflow
10
3. Descent caused by radiative
cooling
8
6
4. Adiabatic descent outside
storm core
4
2
0
0
100
200
300
400
Radius from TC Center (km)
500
Credit: Emanuel (2006)
Warmer colors: high potential temperature
Colder colors: low potential temperature
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
• Primary focus of this talk will be
on impacts of radial outflow on
the atmospheric environment of
the TC
University at Albany, SUNY
5/19
Motivation
Backgroun
d
Results
Conclusion
s
Upper-Tropospheric TC Structure
Composite of 200 hPa wind speed (m s-1;
contours) and streamlines for North
Atlantic TCs
North
• 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
South
Credit: Merrill (1988)
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
• Location of outflow
jet can change
depending on largescale environmental
flow (e.g., polar jet)
University at Albany, SUNY
6/19
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Backgroun
d
Results
Conclusion
s
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:
1
Total = v[ (u 2 + v 2 )] + v(L q) + v(gz) + v(c T )
v
p
2
•
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
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
9/19
Motivation
Backgroun
d
Results
Conclusion
s
Lower-Tropospheric Structure of TC and the Environment
• Cyclonic circulation of
TC is dominant feature
in lower and middle
troposphere within
composites
TC
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
10/19
Motivation
Backgroun
d
Results
Conclusion
s
Lower-Tropospheric Transports due to TC and the Environment
• Transports by cyclonic
circulation largely
cancel each other out at
a given latitude band
Blue - Southward transport
Red - Northward transport
• Transports at 925 hPa
typify transports in the
lower and middle
troposphere
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
11/19
Motivation
Results
Backgroun
d
Conclusion
s
Upper-Tropospheric Structure of TC and the Environment
• Convective heat release
yields anticyclonic
circulation in upper
troposphere
Outflow Jet
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
• Equatorward outflow jet
found on southeastern
flank of uppertropospheric anticyclone
University at Albany, SUNY
12/19
Motivation
Backgroun
d
Results
Conclusion
s
Upper-Tropospheric Transports due to TC and the Environment
• Equatorward energy
transports by TC
outflow jet are the
dominant feature in
deep tropics
Blue - Southward transport
Red - Northward transport
• Equatorward outflow jet
of TC, on average,
results in southward
transport of energy into
Southern Hemisphere
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
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Backgroun
d
Results
Conclusion
s
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
1. Cyclonic circulation of
TC
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
14/19
Motivation
Backgroun
d
Results
Conclusion
s
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
1. Cyclonic circulation of
TC
2. Upper-tropospheric
anticyclone of TC and
equatorward outflow jet
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
14/19
Motivation
Backgroun
d
Results
Conclusion
s
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
1. Cyclonic circulation of
TC
2. Upper-tropospheric
anticyclone of TC and
equatorward outflow jet
3. Extratropical cyclone
triggered by interaction
of TC with mid-latitudes
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
14/19
Motivation
Backgroun
d
Results
Conclusion
s
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
1. Cyclonic circulation of
TC
2. Upper-tropospheric
anticyclone of TC and
equatorward outflow jet
3. Extratropical cyclone
triggered by interaction
of TC with mid-latitudes
• Outflow jet will be primary
Next, we will zonally integrate the meridional energy transports
the shaded
focus ofacross
the remainder
of
region to determine the net transports due to TCs across
latitude band…
theeach
study
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
14/19
Motivation
Backgroun
d
Results
Conclusion
s
Climatological Meridional Energy Transports
Energy
Convergence
Energy
Divergence
Energy
Convergence
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
• 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 midlatitudes
University at Albany, SUNY
15/19
Motivation
Results
Backgroun
d
Conclusion
s
Comparison of Transports at Time of TC Passage Versus Climatology
Increased
northward
transports
Increased
southward
transports
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
• 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
University at Albany, SUNY
16/19
Motivation
Backgroun
d
Results
Conclusion
s
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
Cross-Equatorial Energy Transports by TCs
Benjamin A. Schenkel
University at Albany, SUNY
16/19
Motivation
Backgroun
d
Results
Conclusion
s
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
Motivation
Results
Backgroun
d
Conclusion
s
Conceptual Model of TC Impacts on Meridional Energy Transports
p
Adapted from Waliser et al. (1999)
Late Summer Western Pacific Hadley Cell
30°S
Hadley
cell
15°S
Cross-Equatorial Energy Transports by TCs
Hadley
cell
0
Benjamin A. Schenkel
15°N
University at Albany, SUNY
30°N
18/19
Motivation
Results
Backgroun
d
Conclusion
s
Conceptual Model of TC Impacts on Meridional Energy Transports
p
Adapted from Waliser et al. (1999)
Late Summer Western Pacific Hadley Cell with a Low-Latitude TC
30°S
Hadley
cell
15°S
Cross-Equatorial Energy Transports by TCs
TC
0
Benjamin A. Schenkel
Hadley
cell
15°N
University at Albany, SUNY
30°N
18/19
Motivation
Results
Backgroun
d
Conclusion
s
Conceptual Model of TC Impacts on Meridional Energy Transports
p
Adapted from Waliser et al. (1999)
Late Summer Western Pacific Hadley Cell with a Low-Latitude TC
30°S
Hadley
cell
TC
Hadley
cell
Heat and Moisture
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
Motivation
Results
Backgroun
d
Conclusion
s
Conceptual Model of TC Impacts on Meridional Energy Transports
p
Adapted from Waliser et al. (1999)
Late Summer Western Pacific Hadley Cell with a Low-Latitude TC
30°S
Heat and Potential Energy
Hadley
cell
TC
Hadley
cell
Heat and Moisture
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
Motivation
Results
Backgroun
d
Conclusion
s
Conceptual Model of TC Impacts on Meridional Energy Transports
p
Adapted from Waliser et al. (1999)
Late Summer Western Pacific Hadley Cell with a Low-Latitude TC
30°S
Heat and Potential Energy
Hadley
cell
TC
Hadley
cell
Heat and Moisture
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
Motivation
Backgroun
d
Results
Conclusion
s
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