Geoscience Reference
In-Depth Information
(Wernli et al., 2002) and “Martin” in 1999. The heaviest damages occurred in southern
France where millions of homes and commercial properties experienced power cuts and
heavy damages due to falling trees. In Northern Spain and Southwestern France some of
the most productive European forests have been profoundly impacted by the storm and
will likely take decades to recover. In the French Landes department for instance, one
estimates that 70 % of the pine forest - this forest, the largest of this kind in Europe, was
accounting for about one third of France's lumber production - has been completely
wiped in just a few hours.
Fig. 3. (a) Surface analysis and satellite imagery over Western Europe valid 24 January 2009
at 6 UTC. The black square in (a) shows the area where wind retrieval is performed.
Klaus formed west of the Azores islands on 23 January 2009 near 00 UTC and made landfall
about 30 hours later after crossing the Atlantic Ocean at a mean speed of 27 m.s
-1
. The life
cycle of this system approximately follows the conceptual model proposed by Shapiro and
Keyser (SK, 1990). It is characterized by an explosive intensification period, during which
the sea level pressure (SLP) at the cyclone center deepened by ~ 36 hPa in 24 hours, ending
up with a warm seclusion phase and a rapid decay. The SLP minimum (964 hPa) was
reached at 00 UTC, 24 January, as the low-level vortex was located ~ 400 kilometers off the
French coasts. Klaus made landfall slightly before 6 UTC on 24 January near Bordeaux,
France (Fig. 3) with a minimum pressure of ~ 967 hPa (Fig. 4). The corresponding surface
analysis (Fig. 3a) shows a warm frontal zone to the North of the cyclone center and a cold
front extending far southward across the Pyrenees and Northern Spain. According to
satellite images (Fig. 3b) the storm was elongated in the west-east direction along the warm
front, which is in good agreement with the SK model theory (Schultz et al. 1998). After
landfall, the system progressed eastward at a mean speed of about 15 m.s
-1
and reached Italy
near 18UTC (Fig. 4). At this time the associated minimum pressure has already increased to
988 hPa. Maximum surface winds occurred in a region located approximately 300 to 350 km
south of the cyclone center, along a 100 km swath oriented in a direction almost parallel to
the cyclone trajectory. In France, wind gusts peaked at ~ 184 km.h
-1
near Opoul (Fig. 1), a
value corresponding to category 3 hurricane winds on the Saffir-Simpson scale. The
situation was even more impressive in Northern Spain where surface wind gusts over 200
km.h
-1
have been recorded at several locations.
