Transcript Topic 4.1: Variability of Tropical Cyclone Activity

6th International Workshop on Tropical Cyclones
Topic 4.1: Variability of Tropical Cyclone Activity/Intensity on
Intraseasonal and Interannual Scales (Rapporteur: Chang-Hoi Ho)
Joo-Hong Kim (Seoul National University, Korea)
27 November 2006
About Topic 4.1
 Objective: To report current status of understanding on
variability of tropical cyclone [TC] activity on intraseasonal to
interannual timescales.
 This topic partly overlaps with topic 2.1.
 Global and local factors controlling TC activity
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Intraseasonal controlling factors
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Interannual controlling factors
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Madden-Julian oscillation [MJO]
10- to 25-day oscillation (in the western North Pacific)
El Niño-Southern Oscillation [ENSO]
Quasi-Biennial oscillation [QBO]
From intraseasonal to interannual controlling factors
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Annular modes (Arctic oscillation [AO], Antarctic oscillation [AAO]) and/or
North Atlantic Oscillation [NAO] in the North Atlantic
African easterly waves [AEWs] and western Sahel rainfall (in the North
Atlantic)
Local sea level pressure, sea surface temperature [SST], vertical wind shear,
and tropospheric temperature; subtropical high and jets, etc.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Madden-Julian Oscillation [MJO]
 Dominant mode of variability in the tropical circulation and
convection that has characteristic periods of 30-60 days
 Recent publications about its dynamical/physical relationship with
global TC activity
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North Atlantic [NA]: Maloney and Hartmann (2000a), Mo (2000)
Western North Pacific [WNP]: Liebmann et al. (1994), Harr and Elsberry
(1995a, b), Sobel and Maloney (2000), Maloney and Dickinson (2003), etc.
Eastern North Pacific [ENP]: Molinari et al. (1997), Maloney and
Hartmann (2000b), Molinari and Vollaro (2000)
Australia and South Pacific [ASP]: Hall et al. (2001)
Indian Ocean [IO]: Liebmann et al. (1994), Bessafi and Wheeler (2006),
Ho et al. (2006)
“In each basin, composites relative to the storm genesis locations show a similar
phase relationship between the wave (including the MJO) and cyclogenesis,
suggesting consistent forcing mechanisms.” (Frank and Roundy 2006)
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – North Atlantic
 Maloney and Hartmann (2000, Science)
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The MJO is the strongest influencing factor.
Active Phase
 Mo (2000, J. Climate)
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Inactive Phase
Adapted from Maloney and Hartmann (2000)
“Tropical storms are most likely develop and maintain in the Atlantic,
when enhanced convection associated with the tropical intraseasonal
oscillations is located over the Indian Ocean and convection in the
Pacific is suppressed. …”
Remote circulation response to the MJO-related convection alters the
vertical wind shear in the NA.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Western North Pacific
 Liebmann et al. (1994) (J. Meteor. Soc. Japan)
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The TC activity over the WNP tends to be strong during the MJO convective
period.
The ratio of intense systems (TS+TY) to weak systems (TD) seems nearly
constant regardless of the convective and/or dry periods.
 Maloney and Hartmann (2001, J. Atmospheric Sciences)
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During 850-mb MJO westerlies, eddies grow through barotropic eddy kinetic
energy conversion from the mean flow
Conversion terms -u’2∂u/∂x, -u’v’∂u/∂y are important.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Western North Pacific
 Harr and Elsberry (2003, adapted from the PPT presented at
CWB, Taiwan)
Regions of Tropical Cyclone Activity
Jun-Oct 1979-1998, 408 TCs (Distribution
of TC activity stratified according to the
30-60 day zonal wind anomaly in the box
eq.-10oN, 120oE-150oE.
SCS
North of the Monsoon Trough
South China
Monsoon Trough
Sea
East of the
Monsoon
Trough
from Harr and Elsberry (2003)
MT
E-MT N-MT
30-60 d
U>0
Active
MT
28
128*
51
35
242
30-60 d
U<0
Inactive
MT
18
82*
35
31
166
Although the monsoon trough was inactive,
82 TCs formed in the monsoon trough.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Western North Pacific
 Kim et al. (2006, in revision)
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Major TC passages experience an east-west displacement on
intraseasonal timescale according to the phase of the MJO, but not so
dramatic as the impact of ENSO.
IO phase
-
+
Transition phase
WNP phase
+
-
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Eastern North Pacific
 Molinari et al. (1997, Monthly Weather Review)
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A correspondence between MJO convective heating, strength of the
sign reversal of the meridional potential vorticity gradient in the
Caribbean and eastern Pacific, and eastern Pacific cyclogenesis.
Hypothesis: upstream wave growth (Caribbean Sea), downstream TC
genesis (ENP)
 Maloney and Hartmann (2000, J. Climate)
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Westerly equatorial 850-mb wind anomalies are accompanied by
enhanced convection over the ENP hurricane region.
Equatorial Kelvin waves propagating eastward alter dynamical conditions
over the ENP.
 Molinari and Vollaro (2000, Monthly Weather Review)
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Wave growth within the convectively active MJO envelope.
 Maloney and Hartmann (2001, J. Atmospheric Sciences)
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Barotropic eddy kinetic energy conversion from the mean flow.
Conversion term -u’2∂u/∂x is important.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Australia and South Pacific
 Hall
et
al.
(2001,
Weather Review)
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Monthly
The MJO strongly modulates the TC
activity in the ASP with pronounced
modulation to the northwest of
Australia.
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There are significantly more TCs
formed during the active MJO phase.
This relationship is strengthened
during El Niño periods.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Indian Ocean
- Northern IO
 Liebmann et al. (1994, J. Meteorol. Soc. Japan)
 Goswami et al. (2003, Geophysical Research Letters)
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Including weaker systems (such as lows), they showed the frequency of
occurrence of monsoon low pressure systems is nearly 3.5 times higher
in the active phase of monsoon as compared to the break phase.
From Goswami et al. (2003)
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
MJO – Indian Ocean
Shading: OLR
Contour: vorticity
Vector: TLMW
Grey line: zero line of VWS
- Southern IO
 Bessafi and Wheeler (2006,
Monthly Weather Review)
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The MJO perturbations to both the
vorticity and shear fields rather
than the convection modulates TC
genesis.
 Ho et al. (2006, J. Geophysical
Research)
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Similar conclusions about TC genesis
as those of Bessafi and Wheeler
(2006)
Additionally, TC tracks are analyzed.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
10- to 25-day Oscillation – Western North Pacific
 Northwestward-moving circulation and convection that may be
related to the MJO (Hartmann et al. 1992; Kemball-Cook and
Wang 2001; Fukutomi and Yasunari 1999, 2002; and many
others)
 Its timescale is overlapped by the westward-moving equatorial
Rossby wave.
 Relationship with TC activity
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Hartmann et al. (1992, J. Atmospheric Sciences)
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Harr et al. (from the PPT presented at Taiwan, 11 Dec 2003)
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“Typhoons appear to have a preferred recurrence period of between 15 and
25 days, …”
“The 10-25 day circulations may dominate the MJO to influence TC activity
during inactive MJO phases or to influence the timing of TC activity during
MJO active periods. The source of the 10-25 day mode is linked to wave
activity in the Southern Hemisphere.”
Cross-equatorial influence from the Southern Hemisphere is possibly related
to the AAO (e.g., Ho et al. 2005).
Cyclogenesis related to the equatorial Rossby waves seems to reflect
this variability (Frank and Roundy 2006, Monthly Weather Review).
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability
 Global Factors
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ENSO
QBO
AO, AAO and NAO
 Local Factors
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Vertical wind shear
SST
Subtropical high and jets
Sea level pressure
Tropospheric temperature
Monsoon gyre (in the WNP)
Western Sahel rainfall and AEWs (in the NA)
→ Factors are dynamically correlated each other.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 What we know …
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The western Sahel rainfall is negatively correlated with ENSO events.
The activity of AEWs intensifies (weaker) when the rainfall amount over
the western Sahel region is above (below) normal.
During El Niño years, westerly wind in the upper troposphere increases
over the Caribbean and tropical Atlantic, resulting in an increase of the
vertical wind shear over the NA. Consequently, the number of TCs and
their duration are reduced. Besides, the probability of U.S. hurricane
landfalls becomes lower.
The QBO influence on TC activity is known to be pronounced in the
NA than in other basins. Recently, however, the relationship
disappeared from 1984 to the present (Landsea, personal
communication).
 Recent literatures (after 2000)
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Thorncroft and Hodges (2001, J. Climate), Tang and Neelin (2004,
Geophysical Research Letters), Larson et al. (2005, J. Climate), Xie et al.
(2005, J. Climate), Bell and Chelliah (2006, J. Climate), etc.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 Thorncroft and Hodges (2001, J.
Climate)
“The 850-hPa easterly wave at the
West African coast between about
10°N and 15°N is highly correlated
to NA TC activity. The NA TC
activity may be influenced by the
number of AEWs leaving the West
African coast, and not simply by
the total number of AEWs.”
Atlantic
6th International Workshop on Tropical Cyclones
Africa
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 Tang and Neelin (2004, Geophysical
Research Letters)
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The tropospheric warming spread
eastward from the Pacific by
equatorial wave dynamics disfavors
the TC development by affecting
column stability relative to equilibrium
with NA SST.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
AO (or NAO) – North Atlantic
 Larson et al. (2006, J. Climate)
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The AO (and/or NAO) has a strong
influence on the intraseasonal and
interannual variability of NA TC
activity.
“During La Niña (El Niño) conditions,
atmospheric circulation appears more
(less) conductive to TC activity in the
main developing region [MDR] during
AO-positive (negative) conditions
than during AO negative (positive)
ones.”
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An enhanced (decreased) TC activity
during the positive (negative) phase
of the AO. During the positive phase
of the AO,
The subtropical ridge in the NA is
enhanced.
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The westerly wind shear weakens over
the MDR.
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The tropical easterly jet intensifies
over Africa.
→ provide favorable conditions for TC
development.
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6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 Larson et al. (2005, J. Climate)
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The impact of ENSO and the AO is greater together than apart.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 Xie et al. (2005, J. Climate)
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In addition to ENSO and vertical wind shear, hurricane tracks are
strongly modulated by the dipole mode of Atlantic SST (SSTDM) as well
as the NAO and AO.
<EOFs of Hurricane Track Density Function (defined by Anderson and Gyakum 1989)>
1
VWS (Aug-Oct), SSTDM (Jun-Jul)
2
3
NAO&AO (Jan-Jun), SSTDM
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SSTDM
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – North Atlantic
 Bell and Chelliah (2006, J. Climate)
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The ENSO teleconnections and impacts on Atlantic hurricane activity
can be substantially masked or accentuated by the leading multidecadal
modes (1971-1994 inactive decades versus 1995-2004 active decade).
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 What we know …
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The active genesis region of the TC moves both eastward and toward the equator,
the life span and probability of the intense TC increase, and TCs recurve more
often and tend to recurve farther eastward during the warm phase of ENSO.
The northward steering flows increase in the WNP.
There is a notable frequency reduction in TC formation in the summer following of
the El Niño year, corresponding to a longitudinal shift of the Walker circulation.
The westerly phase of the QBO corresponds to a larger number of TCs. However,
this relationship do not hold true during ENSO years.
The vertical shear equatorward of 18°N over the eastern portion of the WNP is
substantially reduced during El Niño periods.
 Recent literatures (since 2002)
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ENSO: Wang and Chan (2002, J. Climate), Elsner and Liu (2003, Climate Research),
Camargo et al. (2004, AMS conference), Wu et al. (2004, J. Climate), Camargo and
Sobel (2005, J. Climate), etc.
More factors: Chia and Ropelewski (2002, J. Climate), Chen et al. (2004, J. Climate),
Ho et al. (2005, J. Geophysical Research), Kim et al. (2005, J. Climate), Xie et al.
(2005, Geophysical Research Letters), etc.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 Sobel and Camargo (2005, J. Atmospheric Sciences)
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Possibility of a two-way positive feedback between ENSO and TC activity
ACE leads
SST leads
SST (5.5°N-5.5°S)
6th International Workshop on Tropical Cyclones
Equatorial surface zonal wind (5.5°N-5.5°S)
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 Chen et al. (2004, Wea. Forecasting)
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Approximately 70% of WNP TC/TD genesis/development is linked to the
monsoon gyre.
The interannual variation of TC/TD genesis/development related to the
monsoon gyre is highly correlated with that of the monsoon gyre activity
(which is out of phase with that of the Nino-3 SSTs).
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 Ho et al. (2005, J. Geophysical Research)
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Cross-equatorial influence from the Southern Hemisphere (i.e., AAO) is
comparable to that of ENSO. Main region of influence is different.
Magnitude of composite difference of TC activity over the East China
Sea toward west Japan with respect to the AAO phase is much larger
than that related to ENSO phase.
However, they didn’t consider the coupled variability.
Normal ENSO conditions only
El Niño minus La Niña
TC passage numbers (#/year)
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 Kim et al. (2005, J. Climate)
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Over the midlatitude East Asia, dominant interannual variability here is
the dipole oscillation between south of Korea and southeast of Japan.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Western North Pacific
 Xie et al. (2005, Geophysical Research Letters)
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The annual frequency of WNP typhoons and the number of landfall in
China are negatively correlated with the Tibetan Plateau snow cover
during the preceding winter and spring.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Eastern and Central North Pacific
 ENP
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Elsner and Kara (1999)
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Irwin and Davis (1999, Geophysical Research Letters), Kimberlain (1999,
preprints)
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TC activity in the ENP tends to be opposite to that in the NA.
During El Niño years, changes in the warm SST regions lead to the westward
shift in the genesis location of TCs in the ENP, resulting in the propagation of
TCs father west into the central Pacific. Also, the lifetimes are longer during
El Niño years relative to La Niña years.
Collins and Mason (2000, Geophysical Research Letters)
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pointed out the need to study the ENP by subregions because environmental
parameters affecting TC activity are different east and west of 116°W.
 CNP
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Chu and Wang (1997, J. Climate), Chu (2005)
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The vertical shear decreases over the tropical CNP during El Niño years,
providing favorable conditions for TC development.
In the non-El Niño years, most TCs follow a westward or northwestward track.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – Australia and South Pacific
 TC activity in the Australian region is higher during La Niña
years and below normal average during El Niño years.
 Nicholls (1979, Monthly Weather Review)
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The ENSO-TC relation is obtained from a strong correlation between
the sea level pressure at Darwin, Australia, and TC days around the
Australian region.
 Evans and Allan (1992, International J. Climatology)
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TC frequency near the date line increases during El Niño years. TC
tracks in the tropical southwestern Pacific (west of the date line)
became more zonal during El Niño years. In contrast, TCs tracked close
to the coase of Queensland, Australia, and persisted southward with
enhanced risk for coastal crossings during La Niña years.
 Basher and Zheng (1995, J. Climate)
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The incidence of TCs in the Coral Sea (west of 170°E) is influenced by
local SST and east of 170°E the dominant control is not local SST but
the eastward extent of ENSO-dependent atmospheric conditions (i.e.,
the monsoon trough).
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Interannual Variability – South Indian Ocean
 Jury (1993, Meteorol. Atmos. Phys.)
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The frequency of TC genesis in the Southwest IO increases during the
east phase of QBO, but the impact of ENSO is not significant because
of increased upper westerly shear, in spite of convection being enhanced
during El Niño summers.
 Jury et al. (1999, J. Climate)
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The QBO is in phase with ENSO approximately every 4 years with the
QBO leading every 4 months. The QBO periodically exerts a similar
influence on the TC activity in the Southwest IO.
 Kuleshov and de Hoedt (2003, Bull.Aust. Meteorol. Ocean. Soc.)
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TC numbers are increased between 85°E and 105°E during La Niña years
compared to El Niño years.
 Ho et al. (2006, J. Geophysical Research)
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During El Niño periods, TC genesis shifts westward, enhancing the TC
formation west of 75°E and reducing east of 75°E.
TC passages show a significant decrease in the southeast of Madagascar
but a moderate increase in the central midlatitude South IO, indicating
TCs move farther east during El Niño years.
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales
Recommendations
 We need more understandings about the coupled variability between the
Northern (Southern) Hemisphere annular modes, ENSO and the MJO,
and the variability related to the QBO.
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What is the coupled impact of the MJO and ENSO on TC activity? (Kim et al., in
revision)
Why does the QBO influence on NA hurricane activity weaken recent decades?
Consideration of the annular modes and ENSO together may improve the skill of
seasonal prediction of genesis, track, and landfall.
 Although ENSO is dominant factor on the interannual variability of
basinwide-scale TC activity, its impact is variable by sub-basin regions.
 Need to verify the new hypothesis on the relationship, ENSO-TC,
TPSC-TC.
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DEQ-PC hypothesis (Tang and Neelin 2004)
Two-way interaction between TC and ENSO (Sobel and Camargo 2005)
Role of Tibetan Plateau on TC activity (Xie et al. 2005)
6th International Workshop on Tropical Cyclones
Topic 4.1. Intraseasonal to Interannual Timescales