Geography Reference
In-Depth Information
180¡
580
556
532
508
524
548
588
572
JANUARY
500 hPa
Fig. 6.3
Mean 500-hPa contours in January in the Northern Hemisphere. Heights shown in tens of
meters. (After Palmen and Newton, 1969.)
The large departure of the northern winter climatological jetstream from zonal
symmetry can also be readily inferred from examination of Fig. 6.3, which shows
the mean 500-hPa geopotential contours for January in the Northern Hemisphere.
Even after averaging the height field for a month, very striking departures from
zonal symmetry remain. These are clearly linked to the distributions of continents
and oceans. The most prominent asymmetries are the troughs to the east of the
American and Asian continents. Referring back to Fig. 6.2, we see that the intense
jet at 35˚N and 140˚E is a result of the semipermanent trough in that region. Thus,
it is apparent that the mean flow in which synoptic systems are embedded should
really be regarded as a longitude-dependent time-averaged flow.
In addition to its longitudinal dependence, the planetary scale flow also varies
from day to day due to its interactions with transient synoptic-scale disturbances.
