NIWA invite Met Society memberes to a Meteorology seminar being given
by Docters Marina Baldi and giovanni Dalu at 269 Kyber Pass Road,
Newmarket on Thusday 11 October starting at 12:30pm
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Abstracts:

Temperature and rainfall seasonal anomalies in the Mediterranean and
their connection to the large scale features on the Euro-Atlantic
Dr Marina Baldi

National Institute of Water and Atmospheric Research, Auckland, New
Zealand

On leave from: Institute of Biometeorology (IBIMET – CNR), Rome, Italy

ABSTRACT
The climate of the Mediterranean basin (MB) is governed by both mid-
latitude and tropical dynamics, and it is affected by air masses of
different origins and characteristics. In this region, summers are
hot and dry, autumns and winters are wet.
In the cold season the westerly flow is relatively strong, and the MB
is under the direct influence of the Atlantic Ocean. In this season,
important modes are: the North Atlantic Oscillation (NAO), the
Eastern Atlantic pattern (EA), and the Eastern Atlantic/Western
Russia pattern. In the warm season, the large scale flow is generally
weak, with breezes driven by local thermal gradients, with, towards
the end of the season, local extreme precipitation episodes. In the
warm season, the West Mediterranean basin (WMB) is under the
influence of the Azores high, strenghtened by the West African
Monsoon, while the East Mediterranean basin (EMB) is under a ridge
connected to the Asian monsoon through Rossby waves. In this
study, we investigate the role of the Atlantic jet and of the African
jet in relation to the Mediterranean climate.
In the Euro-Atlantic region the westerly jetstream has two branches:
the Atlantic jet, generated by the thermal contrast between the cold
air over the Polar ocean and the relatively warm air over the
Atlantic ocean, crosses this ocean with a north-easterly tilt, and
the African jet, generated by the thermal contrast between the
African warm air and the Euro-Asian relatively cold air, spans from
the west coast of North Africa to the Indian ocean.
Moreover, the Mediterranean climate shows specific trends on
a decadal time scale. Summers were hot in the 1950s, 1980s, and 1990,
and cool from mid 1960s to mid 1970s; cold seasons were very dry in
the 1980s and early 1990s, with an almost monotonic decrease of the
rainfall since the 1960s. Given these strong trends, in order to have
a relatively homogeneous climatic period, we limited our study to the
years 1979 - 2005, analyzing the temperature anomaly in July-August
(JA), and the rainfall anomaly in November-December (ND) in the
Mediterranean basin. Finally, we also analyzed the rainfall behaviour
in the West basin in autumn (SO) and in spring (AM), and in the East
basin in winter (DJF).
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Planetary waves and climate and other flows
Dr Giovanni Dalu

National Institute of Water and Atmospheric Research, Auckland, New
Zealand

On leave from: Institute of Biometeorology (IBIMET – CNR), Rome, Italy

Planetary waves and climate

Planetary waves have a wavelength of thousands of km. They can be
stationary or propagate to east or to the west. They are excited by
topographic features, SSTs, and by changes of snow coverage. There
are important since they act as a wave guide for the perturbations.
We are studying the propagation of these perturbations and their
transition from the tropics into the mid-latitude.


Mesoscale flows induced by landscape variability

We show that landscape variability decreases the temperature in the
surface layer, and generates regions of upward vertical motion and a
sizable amount of available potential energy, and can make the
environment of the lower troposphere more favorable to cloud
formation. This process is enhanced by light ambient wind through
the generation of trapped propagating waves.

Width and depth of mesoscale shallow cells

We evaluate the width of a mesoscale two-layer cell driven by a
diabatic source in an f-plane, using a shallow water approximation in
a dissipative and in a non-dissipative system. We compare the exact
full nonlinear solution with different relevant approximate nonlinear
solutions and discuss the results in the weak temperature gradient
approximation (WTG) and constant temperature gradient approximation
(CTG). In addition we study the behaviour of a cell driven by a
diabatic source in a Boussinesq stratified atmosphere.