Geoscience Reference
In-Depth Information
Figure 10.2
Continentality in Europe.
The indices of Gorczynski (dashes) and
Berg (solid lines) are explained in the
text.
Source
: Partly after Blüthgen (1966).
- referring to the compass directions from which the
airflow and weather systems are moving. Cyclonic (C)
and anticyclonic (A) types denote when a low-pressure
or high-pressure cell, respectively, dominates the
weather map (Figure 10.4).
In principle, each category should produce a char-
acteristic type of weather, depending on the season, and
the term
weather type
is sometimes used to convey this
idea. Statistical studies have been made of the actual
weather conditions occurring in different localities with
specific isobaric patterns - a field of study known as
synoptic climatology
. The general weather conditions
and airmasses that are to be associated with the airflow
types identified by Lamb over the British Isles are
summarized in Table 10.1.
On an annual basis, the most frequent airflow type is
westerly; including cyclonic and anticyclonic subtypes,
it has a 35 per cent frequency in December to January
and is almost as frequent in July to September (Figure
10.5). The minimum occurs in May (15 per cent),
when northerly and easterly types reach their maxima
(about 10 per cent each). Pure cyclonic patterns are
most frequent (13 to 17 per cent) in July to August and
anticyclonic patterns in June and September (20 per
cent); cyclonic patterns have ≥10 per cent frequency in
all months and anticyclonic patterns ≥13 per cent.
Figure 10.3
Hythergraphs for Valentia (Eire), Bergen and Berlin.
Mean temperature and precipitation totals for each month are
plotted.
