Sensitivity of idealised baroclinic waves to mean atmospheric
temperature and meridional temperature gradient changes
· Jouni Räisänen
· Victoria A. Sinclair
· Heikki Järvinen
Received: 27 November 2017 / Accepted: 29 May 2018
© Springer-Verlag GmbH Germany, part of Springer Nature 2018
The sensitivity of idealised baroclinic waves to diﬀerent atmospheric temperature changes is studied. The temperature changes
are based on those which are expected to occur in the Northern Hemisphere with climate change: (1) uniform temperature
increase, (2) decrease of the lower level meridional temperature gradient, and (3) increase of the upper level temperature
gradient. Three sets of experiments are performed, ﬁrst without atmospheric moisture, thus seeking to identify the underlying
adiabatic mechanisms which drive the response of extra-tropical storms to changes in the environmental temperature. Then,
similar experiments are performed in a more realistic, moist environment, using ﬁxed initial relative humidity distribution.
Warming the atmosphere uniformly tends to decrease the kinetic energy of the cyclone, which is linked both to a weaker
capability of the storm to exploit the available potential energy of the zonal mean ﬂow, and less eﬃcient production of
eddy kinetic energy in the wave. Unsurprisingly, the decrease of the lower level temperature gradient weakens the resulting
cyclone regardless of the presence of moisture. The increase of the temperature gradient in the upper troposphere has a more
complicated inﬂuence on the storm dynamics: in the dry atmosphere the maximum eddy kinetic energy decreases, whereas
in the moist case it increases. Our analysis suggests that the slightly unexpected decrease of eddy kinetic energy in the dry
case with an increased upper tropospheric temperature gradient originates from the weakening of the meridional heat ﬂux
by the eddy. However, in the more realistic moist case, the diabatic heating enhances the interaction between upper- and
low-level potential vorticity anomalies and hence helps the surface cyclone to exploit the increased upper level baroclinicity.
Keywords WRF model · Idealised simulation · Extratropical cyclone · Energy conversion
Extra-tropical cyclones are ubiquitous in the mid-latitude
atmosphere, occurring most frequently during the winter
season. They aﬀect our everyday life by inducing variations
and extremes of weather, sometimes with severe impacts
to the society (e.g., Wernli et al. 2002; Fink et al. 2009).
Extra-tropical cyclones also transport large amounts of heat
and momentum, and are thus an important component of the
atmospheric general circulation.
A large number of previous studies have investigated the
changes in the intensity (e.g., Bengtsson et al. 2009), fre-
quency (e.g., Lambert and Fyfe 2006; Zappa et al. 2013),
and tracks (e.g., Yin 2005; Bengtsson et al. 2006) of extra-
tropical cyclones in a warmer climate. All of these changes
in cyclone characteristics partly result from the diﬀerent
atmospheric temperature distribution in the future climate.
For example, climate change projections made with General
Circulation Models (GCM) suggest that in mid-latitudes,
the meridional low-level temperature gradient will decrease
whereas the gradient at upper levels will increase (Woollings
2008; Catto et al. 2011).
One widely used method for studying the dynamics of
extra-tropical cyclones is idealised simulations (e.g., Fantini
2004; Boutle et al. 2010, 2011; Booth et al. 2013; Blázquez
et al. 2013; Kirshbaum et al. 2018). One speciﬁc example
is the baroclinic lifecycle simulation, in which only one low
pressure system is simulated. This technique allows one
to explore the changes in extra-tropical cyclone dynamics
Electronic supplementary material The online version of this
article (https ://doi.org/10.1007/s0038 2-018-4283-3) contains
supplementary material, which is available to authorized users.
* Mika Rantanen
Institute for Atmospheric and Earth System Research/
Physics, University of Helsinki, P.O. Box 64, Gustaf
Hällströmin katu 2a, 00014 Helsinki, Finland