18
Compilation of Summaries
lantic in November was accompanied by extremely frequent gales and a massive,
directionally stable inflow of mild maritime air from SW. In December Hurrel’s
NAO index reached a provisional record low at -2.95. These opposing
conditions were in line with, at first, drastically reduced, then, enhanced cooling
of air temperature.
2010 (Page 34 et seq.): (JFM) Hurrel’s NAO index for the DJFM period fell to
a historical low of -2.54, which displayed itself in an unprecedentedly small
number of gales (4). Both, winter air temperature at Norderney and sea temperature
of the GB assumed their lowest levels since 1996. Even so, these
relative minima exceeded those of the winter of 1996 by 2 K. (AMJ) The ANW
general circulation entailed directionally stable cold air transports across the
North Sea on the one hand, and a surplus of global radiation in high pressure
weather on the other. Just as in winter, quarterly means of air and sea temperature
undercut climatological normals no more than slightly, but were at
their lowest levels since 1996 all the same. (JAS) Repercussions of a long-lived
omega block over Belarus in July were limited to the southeastern North Sea.
The North Sea proper firstly governed by SW-erly flow fell under the influence
of the succeeding trough from the 3 rd decade. Consequently, weather type C
not only reached a record frequency of 11 days in August, but also dominated
the monthly sea level pressure distribution, classified as CW. A significant surplus
in global radiation in July made air temperature at Norderney climb to its
3 rd highest level, from which it dropped back to normal in August. (SON) Becoming
increasingly negative in the course of the last quarter, the state of the
NAO culminated at -3.56 in December, thus undercutting the record negative
deflection set exactly one year before. As in the previous winter, the southward
shift of the polar front brought about an abundance of E weather types together
with a dearth of gales (6). Fall temperature at Norderney fell to the record low
of 1993 (5.1 °C). At -5.0 K, the sharp descent in GB temperature from November
to December almost equaled the record cooling rate of 1978 (-5.1 K).
2011 (Page 36 et seq.): (JFM) For the first time in 16 months, the NAO resumed
a steady, positive phase in February. Advection of mild maritime air
from WSW in winter was disrupted but episodically through cold air transports
from NNW and SSE. Air temperature at Norderney, usually assuming its seasonal
minimum in January, returned to normal through an unparalleled ascent
of 3.3 К in this month, thence following climatology until the end of winter.
(AMJ) The sea level pressure distribution in April presented itself as a superposition
of the winter and the summer pattern of the positive mode of the NAO,
thus resembling those of July 2006 and 2013, which went along with extreme
heat waves. At 10.6 °C, air temperature reached its highest level after 2007,
while sea temperature performed an unprecedented jump of 4.1 К to 7.6 °C.
Though vigorous WSW-erly winds caused a marked flattening in further seasonal
ascent, spring temperature was higher at Norderney in 2007, only. (JAS)
The joint frequency for July and August of high pressure weather types (A)
reached a record low of 6 days, while low pressure weather types (C) at 19
days were never more abundant. This spell of unsteady weather came to an
end in September through a vigorous and directionally stable flow from WSW
that took on anticyclonic characteristics past mid-month. Due to substantial
deficits in global radiation in midsummer and, conversely, a strong surplus in
September air temperature evolved sideways, stagnating at the climatological
seasonal mean level of 16.2 °C. (OND) A long-lived (10/22-11/23) blocking episode
caused a directionally stable S-erly flow, delimited from two sustained
