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Vol.:(0123456789)
1 3
Clim Dyn (2018) 50:705–715
DOI 10.1007/s00382-017-3636-7
Is thepoleward migration oftropical cyclone maximum intensity
associated withapoleward migration oftropical cyclone genesis?
AnneSophieDaloz1 · SuzanaJ.Camargo2
Received: 29 November 2016 / Accepted: 16 March 2017 / Published online: 3 April 2017
© Springer-Verlag Berlin Heidelberg 2017
1 Introduction
Kossin et al. (2014) showed that in the past few dec-
ades (1982–2009) the large-scale environment of tropi-
cal cyclones has evolved over the tropics and subtropics.
Indeed, favorable conditions for the development of tropical
cyclones have migrated towards higher latitudes (vertical
wind shear and potential intensity), moving from the trop-
ics closer to the subtropics. With a globally homogenized
record of intensity (Kossin etal. 2013) and a global best-
track archive (Knapp et al. 2010), they also demonstrated
that the location where observed tropical cyclones reach
their maximum intensity has been migrating towards higher
latitudes. More recently, Kossin etal. (2016) used observa-
tions and simulations to examine the changes in lifetime-
maximum intensity and tropical cyclone exposure for the
present and future climates over the western North Pacific
Ocean. The projections of tropical cyclones were simu-
lated by, and downscaled from, an ensemble of numerical
Coupled Model Intercomparison Project Phase 5 (CMIP5)
models (Taylor et al. 2012). They showed a poleward
migration of lifetime-maximum intensity (LMI) latitude in
the present century and continuing into the future using one
of the representative concentration pathways (RCP8.5). A
possible mechanism responsible for these global and local
changes is the expansion of the tropics (Lucas etal. 2014),
however this link has not been proved yet.
The current study expands on the findings by Kossin
etal. (2014, 2016) by analyzing the possible origin of the
poleward migration of the LMI latitude. More precisely, we
would like to answer the following question: Is the pole-
ward migration of tropical cyclones’ LMI location related
to a poleward migration in tropical cyclone genesis loca-
tion? Tropical cyclones are very sensitive to the large-scale
environment both during their genesis and development
Abstract A recent study showed that the global average
latitude where tropical cyclones achieve their lifetime-
maximum intensity has been migrating poleward at a rate
of about one-half degree of latitude per decade over the last
30years in each hemisphere. However, it does not answer
a critical question: is the poleward migration of tropical
cyclone lifetime-maximum intensity associated with a pole-
ward migration of tropical cyclone genesis? In this study
we will examine this question. First we analyze changes
in the environmental variables associated with tropical
cyclone genesis, namely entropy deficit, potential intensity,
vertical wind shear, vorticity, skin temperature and specific
humidity at 500 hPa in reanalysis datasets between 1980
and 2013. Then, a selection of these variables is combined
into two tropical cyclone genesis indices that empirically
relate tropical cyclone genesis to large-scale variables. We
find a shift toward greater (smaller) average potential num-
ber of genesis at higher (lower) latitudes over most regions
of the Pacific Ocean, which is consistent with a migration
of tropical cyclone genesis towards higher latitudes. We
then examine the global best track archive and find coher-
ent and significant poleward shifts in mean genesis position
over the Pacific Ocean basins.
Keywords Tropical cyclone genesis· Poleward
migration· Tropical cyclone genesis index· Observations
* Anne Sophie Daloz
adaloz@wisc.edu
1 Space andScience Engineering Center, University
ofWisconsin-Madison, 1225 West Dayton Street, Madison,
WI53706, USA
2 Lamont-Doherty Earth Observatory, Columbia University,
Palisades, NY, USA
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