Seasonality of components

Figure 3.8 summarizes the annual cycle in the horizontally and vertically integrated transports across 70° N from TE, TE + SE and TE + SE + MMC. These include the

TE+SE+MMC TE+SE

TE+SE+MMC TE+SE

Figure 3.8 Mean annual cycle of the horizontally and vertically integrated energy transports across 70° N from TE, TE + SE and TE + SE + MMC (from Overland and Turet, 1994, by permission of AGU).

JJA 64-39

JJA 64-89

70'N

1000

JJA 64-39

1000

i t

1 - - MMC

1 ----MMC+SË

1

1 — MMC+SE+TE .

\

P \

i A 1

1000

JJA 64-89

70'N

l - - LH

•1 • ■ ■ ■ LH+SH

1 | 1 t

/ ,-J \

1 \ ï \

NDJFM 64-89

NDJFM 64-89

1000

NDJFM 64-89

i

/

/ ..¿s

il - - MMC

MMC+SE

: \ - MMC+SË+TË ■

* \ \ \ : J

'* /

/

/ i (

1000

Figure 3.9 Vertical profiles of the mean zonally averaged energy flux across 70° N by TE, TE + SE and TE + SE + MMC and the contribution to Fwajl by latent heat, sensible heat geopotential for summer (JJA) and winter (NDJFM) (from Overland and Turet, 1994, by permission of AGU).

fluxes of sensible heat, latent heat and potential energy. This figure, reproduced from Overland and Turet (1994) is based on a longer version (1964-89) of the GFDL data set than used by Nakamura and Oort (1988) and employs slightly different analysis techniques. While comparisons between the total transports and those in Table 3.1 show differences, these do not alter the basic story. Fwall (TE + SE + MMC) is of course stronger in winter than in summer. To obtain the SE component separately in Figure 3.8, subtract the value of TE from TE + SE. To obtain the MMC component, subtract TE + SE from TE + SE + MMC. The total transport is seen to be dominated by the transient eddies and the mean meridional circulation, with the stationary eddies having their greatest impact in winter.

Figure 3.9 provides vertical profiles of the mean zonally averaged energy flux across 70° N by the three components. It also indicates the contribution to Fwall by latent heat, sensible heat and geopotential for winter (taken as November through February) and summer (June through August). To obtain individual terms, one can use the same subtraction procedures as just mentioned. There is considerable vertical structure in winter, with peak transports in the lower to middle troposphere and the lower stratosphere. For winter, transports by transient eddies, both of sensible heat and geopotential, are the major components below 300 hPa. The peak transport at higher levels is more strongly due to the MMC and standing eddies from sensible heat and geopotential. For summer, total transports are largest in the middle and lower troposphere from the MMC and transient eddies of sensible heat and geopotential. While the horizontal latent heat transports are a critical component of the Arctic hydrologic budget, we are led to conclude that, in a direct sense, they play only a secondary role in the basic atmospheric

Figure 3.10 Longitudinal and vertical variation in Fwail. The primary regions of poleward energy transport are near the prime meridian, the date line and 100° W (adapted from Overland and Turet, 1994, by permission of AGU).

energy budget - the dominant terms of Fwan are sensible heat and geopotential. It must be remembered, however, that variations in the latent heat transports can also influence the distribution of cloud cover and snowfall, impacting on the energy budget through effects on albedo.

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