Geoscience Reference
In-Depth Information
-5
0
5
10
15
20°
C
40°
20°W
0°
20°E
40°
40°
20°W
0°
20°E
40°
10˝
H
L
25 cm
L
O
S
D
N
J
Bergen
L
L
8˝
20 cm
A
H
F
D
M
6˝
H
15 cm
N
J
J
H
H
O
F
A
M
A
Westerly
North-Westerly
M
4˝
S
J
10 cm
J
A
Valentia
40°
L
20°W
0°
20°E
40°
40°
20°W
0°
20°E
40°
J
J
M
J
D
S
A
2˝
J
N
5 cm
M
O
A
L
M
F
Berlin
H
0˝
20
0 cm
H
L
30 40 50
Mean monthly temperature
60
70°F
L
Figure 10.3
Hythergraphs for Valentia (Eire),
Bergen and Berlin. Mean temperature and precipi-
tation totals for each month are plotted.
L
Northerly
Easterly
40°
20°W
0°
20°E
40°
40°
20°W
0°
20°E
40°
L
systems are moving. Cyclonic (C) and anti-
cyclonic (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
characteristic 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 condi-
tions and air masses 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 anti-
cyclonic subtypes, it has a 35 percent frequency in
December to January and is almost as frequent in
July to September (
Figure 10.5
). The minimum
occurs in May (15 percent), when northerly and
easterly types reach their maxima (about 10
percent each). Pure cyclonic patterns are most
frequent (13-17 percent) in July to August and
anticyclonic patterns in June and September (20
percent); cyclonic patterns have
L
H
H
L
L
H
Southerly
Cyclonic
40°
20°W
0°
20°E
40°
L
L
H
L
Anticyclonic
Figure 10.4
Synoptic situations over the British Isles
classified according to the primary airflow types of H. H.
Lamb.
Source: Lamb; O'Hare and Sweeney (1993). Copyright © The
Geographical Association and G. O'Hare.
13 percent.
Figure 10.5
illustrates the mean daily
temperature in central England and the mean
daily precipitation over England and Wales for
each type in the mid-season months for
1861-1979.
10 percent
frequency in all months and anticyclonic patterns
