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thus delaying the mature phase and reducing the amplitude of the convective precipitation
diurnal cycle over the land. In addition, they also found changes in the temporal variability
of daily mean precipitation and the partitioning of stratiform and convective rainfall in the
model. Stratton and Stirling (
2011
) made a similar attempt by changing the deep con-
vective parametrisation over land in the MetUM to make the entrainment vary with the
height of the lifting condensation level. This reduced the depth of the convection early in
the day and delayed the development of deep convection by around 2 h, thereby improving
the timing of maximum precipitation. The amplitude of the diurnal harmonic of precipi-
tation was also improved. However, although the amount of precipitation in the evening
was increased, Stratton and Stirling (
2011
) noted that further improvements are required
for the decay phase of the diurnal cycle.
2.3.1.3 Precipitation in Mid-latitude Cyclones Mid-latitude cyclones are the primary
means of transporting energy and moisture poleward at mid-latitudes and can bring severe
weather in terms of heavy rain, leading to flooding, and damaging strong winds to major
population centres. Therefore, determining whether the physical parametrisation of clouds
and cloud properties used in models are providing realistic representations of these phe-
nomena is important. Recent studies have shown a response of the storm tracks in climate
change experiments, with the storm track moving poleward in some models (e.g., Meehl
et al.
2007
). This seems to be accompanied by a consistent poleward shift of mid-latitude
precipitation (e.g., Held and Soden
2006
). However, the poleward shift in the storm track is
not seen in all models or in all locations. Also, the change in the distribution of the
intensity of cyclones under climate change is not consistent across models, and the
mechanisms causing these changes are still unclear.
A good simulation of mid-latitude cyclones is a prerequisite to capturing the main
characteristics of extreme events in the present-day climate and to having confidence in the
response of cyclones to climate change. Field et al. (
2011
) assessed how well the cloud and
precipitation is predicted in the MetUM by physical parametrisations in the presence of an
accurate thermodynamic and dynamic representation of the atmosphere. The main dif-
ferences seen between the model and the satellite data were a lack of cloud above 2 km in
the model associated with the main precipitation region.
Representing mid-level layer cloud is a challenge for global models (e.g., Webb et al.
2001
). One significant obstacle is that the thickness of model levels at altitudes of *15 km
is typically around 600 m, which is similar to the thickness of altostratus/cumulus layers
(Field et al.
2011
). The second challenge is that even if thin mid-level supercooled liquid
cloud can be produced by a model, it will be efficiently transformed to ice by the ice
nucleation scheme and fall out. This formation of ice reduces both the lifetime and radi-
ative effect of these clouds. This has possible implications for the radiative effect of mid-
latitude cyclones on the climate system (Field et al.
2011
). Increased vertical resolution is
now being implemented in many models, and studies such as Field et al. (
2011
) are
informing the development of microphysical parametrisation schemes.
2.3.2 Land-Atmosphere Interactions
The land surface is an important component of the climate system. It controls the parti-
tioning of available energy at the surface between sensible and latent heat, and the par-
titioning of available water between evaporation and runoff. The state of the land surface
has the potential to influence large-scale circulations (Taylor
2008
). Variations in rainfall
