. Compendium of meteorology. Meteorology. ISOmb 200 300 t= 400 500 600 fe-— "x"^^-- 0»-700 35»N eoo 900 1000 700 800 ^="—i290r-900 ,»'000 40» I 3? 10" sec' Fig. 7.—Meridional profiles through a model of straight westerlies with quasi-stationary polar front (Palmen and Newton [24]). Left: Dashed lines show isotherms (degrees centigrade), and solid lines isovels (m see"') of zonal geostrophic wind. Right: Dashed lines show the field of dry-isentropes (degrees absolute), and the saturation-isentrope of 281° in the frontal zone. Solid lines represent the quantity 2^2 —
. Compendium of meteorology. Meteorology. ISOmb 200 300 t= 400 500 600 fe-— "x"^^-- 0»-700 35»N eoo 900 1000 700 800 ^="—i290r-900 ,»'000 40» I 3? 10" sec' Fig. 7.—Meridional profiles through a model of straight westerlies with quasi-stationary polar front (Palmen and Newton [24]). Left: Dashed lines show isotherms (degrees centigrade), and solid lines isovels (m see"') of zonal geostrophic wind. Right: Dashed lines show the field of dry-isentropes (degrees absolute), and the saturation-isentrope of 281° in the frontal zone. Solid lines represent the quantity 2^2 — dvg/dti in units of 10"^ sec"'.. -^ii . J I I 150 mb ^4===/=-200 300 400 500 600 values, as far as the lower troposphere is concerned, will be found in the frontal zone where 2U^ — dvg/dr) is at a minimum. As shown in Fig. 7, the warm air over the lower and intermediate portion of the polar-front surface has anticyclonic isentropic shear, increasing to great values in the upper troposphere, whereas the air above the upper part of the frontal surface has cyclonic shear, likewise increasing to high values in the upper tropo- sphere. The dividing line between anticyclonic and cyclonic shear runs almost vertically through the maxi- mum of west-wind velocity, which in the average con- dition represented by Fig. 7 is located above the place where the frontal surface intersects the 500-mb level. Isentropic upgliding or downgliding as defined by equa- tion (11) will reach larger values south of the velocity maximum than north of it. It is likely that this differ- ence in V, values north and south of the velocity maxi- mum does give rise to important horizontal divergence effects because the Tj-component represents a nongeo- strophic part of the total wind. The y,-divergence effect in the jet-stream region should work out as shown sche- matically in Fig. 8. Where there is "confluence" of the winds into the western beginning of a "jet stream,"
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