Impacts of Western North Pacific Tropical
Cyclones on the Atmospheric Moisture Content of
Their Large-Scale Environment
Benjamin A. Schenkel (bschenkel@albany.edu),
University at Albany, State University of New York,
and Robert E. Hart, The Florida State University
6th Northeast Tropical Workshop
Research Sponsored by NASA Earth and Space Science Fellowship
and NSF Grant #ATM–0842618
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
- 1600 km
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
2/18
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
- 1600 km
- 1700 km
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
2/18
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
- 1600 km
- 1700 km
- 1800 km
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
2/18
Motivatio
n
Backgroun
d
Results
Conclusion
s
Motivation
1200 UTC 29 August 1995
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
Credit: COMET/UCAR
University at Albany, SUNY
3/18
Motivation
Backgroun
d
Results
Conclusion
s
Outline
• Background and previous research
– Overview of tropical cyclone (TC) structure
• 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
4/18
Motivation
Backgroun
d
Results
Conclusion
s
Outline
• Background and previous research
– Overview of tropical cyclone (TC) structure
• 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
4/18
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
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
5/18
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
Impact of TCs on Environmental Moisture Content
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
5/18
Motivation
Backgroun
d
Results
Conclusion
s
Upper Level Structure of the TC
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
North
TC
South
Credit: Merrill (1988)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
6/18
Motivation
Backgroun
d
Results
Conclusion
s
Upper Level Structure of the TC
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 generally
very asymmetric
• Strongest divergence found in
“outflow jet” well away from TC
• Location of outflow jet can change
depending on large-scale
environment (e.g., tropical uppertropospheric troughs, subtropical
jet)
TC
South
Credit: Merrill (1988)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
6/18
Motivation
Backgroun
d
Results
Conclusion
s
Motivating Questions
• What impact do TCs have upon their large-scale tropical
atmospheric environment?
• What are the spatial and temporal scales over which TCs alter
their atmospheric environment?
• Is the response of the atmospheric environment sensitive to the
size or intensity of the TC?
• Can the aggregate impact of TCs upon their atmospheric and
oceanic environment help explain the annual number of TCs?
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
7/18
Motivation
Backgroun
d
Results
Conclusion
s
Outline
• Background and previous research
– Overview of tropical cyclone (TC) structure
• 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
8/18
Motivation
Backgroun
d
Results
Conclusion
s
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 to TC passage will utilize threedimensional 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 wind speed ≥ 64 kt) in the
western North Pacific equatorward of 36°N from 1982 to 2009 (N = 477 TCs)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
9/18
Motivation
Results
Backgroun
d
Conclusion
s
Large-Scale Drying in the Tropics Following TC Passage
0.1σ ≈ 1 kg m-2
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
• TCs primarily impact their
atmospheric environment
by anomalously drying
within two distinct regions
University at Albany, SUNY
10/18
Motivation
Results
Backgroun
d
Conclusion
s
Large-Scale Drying in the Tropics Following TC Passage
0.1σ ≈ 1 kg m-2
• TCs primarily impact their
atmospheric environment
by anomalously drying
within two distinct regions
• West region: stronger
drying with area
approximately equal to TC
West
region
• Southwest region: weaker
drying in area over twice
as large as TC
Southwes
t
region
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
• Although the horizontal
scales of the drying are
large, the anomalies do not
last long after TC passage
University at Albany, SUNY
10/18
Motivation
Results
Backgroun
d
Conclusion
s
Large-Scale Drying in the Tropics Following TC Passage
0.1σ ≈ 1 kg m-2
• 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
Southwes
t
region
• Although the horizontal
scales of the drying are
large, the anomalies do not
The remainder of this talk will focus on the processes responsible for dry anomalies to the
last long after TC passage
southwest of the TC…
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
10/18
Motivation
Results
Backgroun
d
Conclusion
s
Upper-Tropospheric Forcing of Dry Anomalies in the Southwest Region
Outflow Jet
TC
Anticyclone
of TC
Outflow Jet
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
11/18
Motivation
Results
Backgroun
d
Conclusion
s
Upper-Tropospheric Forcing of Dry Anomalies in the Southwest Region
• To the north and east of
TC, air is forced to
rotate clockwise around
TC’s anticyclone
Outflow Jet
TC
Anticyclone
of TC
• Parcels eventually pass
through anticyclonically
curved outflow jet to the
southeast of the TC
• Upon exiting the jet,
these parcels will
converge and subside…
Outflow Jet
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
11/18
Motivation
Results
Backgroun
d
Conclusion
s
Upper-Tropospheric Forcing of Dry Anomalies in the Southwest Region
• Anomalous dry air to
the southwest of the TC
is immediately
downstream of the TC
outflow jet
Outflow Jet
TC
Anticyclone
of TC
Outflow Jet
Area of statistically significant
dry precipitable water anomalies
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
11/18
Motivation
Backgroun
d
Results
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
• Location of dry
anomalies relative to the
anticyclonically curved
jet can vary with latitude
Adapted from Beebe and Bates (1955)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
12/18
Motivation
Results
Backgroun
d
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Tropical Environment
• Location of dry
anomalies relative to the
anticyclonically curved
jet can vary with latitude
• TC outflow jet in tropical
latitudes has
convergence throughout
exit region
Divergence
• Divergence patterns
induced by
acceleration/deceleration
of flow in presence of
weak Coriolis and
pressure gradient forces
Adapted from Beebe and Bates (1955)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
12/18
Motivation
Backgroun
d
Results
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Subtropical Environment
• Divergence pattern
induced by two factors:
1. Ageostrophic wind
due to change in
pressure gradient
relative to Coriolis
force as parcels move
through jet (four
quadrant model)
Adapted from Beebe and Bates (1955)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
13/18
Motivation
Results
Backgroun
d
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Subtropical Environment
Divergence
• Divergence pattern
induced by two factors:
1. Ageostrophic wind
due to change in
pressure gradient
relative to Coriolis
force as parcels move
through jet (four
quadrant model)
2. Ageostrophic wind
due to curvature of
the flow
Adapted from Beebe and Bates (1955)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
13/18
Motivation
Backgroun
d
Results
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Subtropical Environment
• Divergence pattern
induced by two factors:
1. Ageostrophic wind
due to change in
pressure gradient
relative to Coriolis
force as parcels move
through jet (four
quadrant model)
2. Ageostrophic wind
due to curvature of
the flow
• Net impact of two factors
yields convergence in
right exit region of TC
outflow jet
Adapted from Beebe and Bates (1955)
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
13/18
Motivation
Backgroun
d
Results
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Tropical Environment
Subtropical Environment
Div.
• Upper-tropospheric convergence in jet exit region is hybrid of tropical and
subtropical environment in composites due to varying latitude of TCs
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
14/18
Motivation
Backgroun
d
Results
Conclusion
s
Linking the TC Outflow Jet to the Dry Anomalies
Composite TC Outflow Jet
• Upper-tropospheric convergence in jet exit region is hybrid of tropical and
subtropical environment in composites due to varying latitude of TCs
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
15/18
Motivation
Backgroun
d
Results
Conclusion
s
Location of Upper-Tropospheric Convergence Relative to Outflow Jet in Composites
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
16/18
Motivation
Backgroun
d
Results
Conclusion
s
Location of Upper-Tropospheric Convergence Relative to Outflow Jet in Composites
• Upper tropospheric
convergence in exit
region of the
equatorward outflow jet
yields anomalous
subsidence and dry
anomalies
• Upper-tropospheric
convergence favored
slightly to right of jet
axis
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
16/18
Motivation
Backgroun
d
Results
Conclusion
s
Conceptual Model of Drying Induced by TCs
Tropopause
Height
45°N
Sfc.
Impact of TCs on Environmental Moisture Content
Longitude
Benjamin A. Schenkel
0
University at Albany, SUNY
17/18
Motivation
Backgroun
d
Results
Conclusion
s
Conceptual Model of Drying Induced by TCs
Tropopause
Height
45°N
Sfc.
Impact of TCs on Environmental Moisture Content
Longitude
Benjamin A. Schenkel
0
University at Albany, SUNY
17/18
Motivation
Backgroun
d
Results
Conclusion
s
Conceptual Model of Drying Induced by TCs
Dry anomalies located to the west and southwest of TC
Tropopause
Height
45°N
Sfc.
Impact of TCs on Environmental Moisture Content
Longitude
Benjamin A. Schenkel
0
University at Albany, SUNY
17/18
Motivation
Backgroun
d
Results
Conclusion
s
Conceptual Model of Drying Induced by TCs
Exit region of TC outflow jet yields upper-tropospheric convergence,
subsidence, and lower-tropospheric divergence to southwest of TC
Tropopause
Height
45°N
Sfc.
Impact of TCs on Environmental Moisture Content
Longitude
Benjamin A. Schenkel
0
University at Albany, SUNY
17/18
Motivation
Backgroun
d
Results
Conclusion
s
Conceptual Model of Drying Induced by TCs
Why do we observe approximately 1700 km spacing between WPAC TCs?
Tropopause
Height
45°N
Sfc.
Impact of TCs on Environmental Moisture Content
Longitude
Benjamin A. Schenkel
0
University at Albany, SUNY
17/18
Motivation
Results
Backgroun
d
Conclusion
s
Concluding Thoughts
Anomalous drying
~2000 km
~1800 km
1800 km
TC?
~3800
km
TC?
Anomalous vertical wind shear
Perhaps TCs may control the spacing between TCs during multiple TC
events…
Impact of TCs on Environmental Moisture Content
Benjamin A. Schenkel
University at Albany, SUNY
18/18