Dear MetSoc members:

Please see below for info on a pair of seminars to be held at NIWA
Wellington (Greta Point) on Friday of this week.


Regards,
Jim Renwick
Wellington Vice-President, Met. Society of NZ

-------- Original Message --------
Subject: NIWA Seminar: Friday 12 October

NIWA Seminar


“Temperature and rainfall seasonal anomalies in the Mediterranean and
their connection to the large scale features on the Euro-Atlantic”


Speakers: Dr Marina Baldi and Dr Giovanni Dalu
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).


Dr Giovanni Dalu

Planetary waves and climate and other flows

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.


Friday 12 October 2007
10.30-11.30am

Main Conference Room, Allen Building
NIWA, Greta Point

For further information contact

Jim Renwick
Ext 7343


--
Dr James Renwick, Science Leader, climate variability & change
National Institute of Water & Atmospheric Research
Private Bag 14901, Wellington, NEW ZEALAND
J.Renwick@... Ph: +64-4-3860343 Mob: +64-21-1785550
http://www.niwa.co.nz Fax: +64-4-3862153 or +64-4-3860574