Consider the following statements:
1. Jet streams occur in the Northern Hemisphere only.
2. Only some cyclones develop an eye.
3. The temperature inside the eye of a cyclone is nearly 10°C less than that of the surroundings.
Which of the statements given above is/are correct?
(a) 1 only
(b) 2 and 3 only
(c) 2 only
(d) 1 and 3 only
7. Ans: c
Explanation:
There are several different jet streams, or jets, around the globe. The polar jet is located between the 50°-60° latitude lines in both the northern and southern hemispheres. The subtropical jet is located around the 30° latitude line. Jet streams vary in height of four to eight miles and can reach speeds of more than 275 mph (239 kts / 442 km/h). Jet streams occur in both the Northern and Southern Hemispheres.
Hence, statement 1 is incorrect.
The “eye” is a roughly circular area of comparatively light winds and fair weather found at the center of a severe tropical cyclone.
The eye is the region of lowest surface pressure and warmest temperatures aloft – the eye temperature may be 10°C [18°F] warmer or more at an altitude of 12 km [8 mi] than the surrounding environment, but only 0-2°C [0-3°F] warmer at the surface in the tropical cyclone. Eyes range in size from 8 km [5 mi] to over 200 km [120 mi] across, but most are in the range 30-60 km [20-40 mi] in diameter.
The eye is surrounded by the “eyewall”, the roughly circular ring of deep convection which is the area of highest surface winds in the tropical cyclone. The eye is composed of air that is slowly sinking and the eyewall has a net upward flow as a result of many moderate – occasionally strong – updrafts and downdrafts. The eye’s warm temperatures are due to compressional warming of the subsiding air. Most soundings taken within the eye show a low-level layer which is relatively moist, with an inversion above – suggesting that the sinking in the eye typically does not reach the ocean surface, but instead only gets to around 1-3 km [1-2 mi] of the surface.
The formation of the eyewall is related to the convergence of air in a shallow layer some 500 m to 1 km deep adjacent to the sea surface. This layer is referred to as the boundary layer, or friction layer. Above this layer, the swirling winds are approximately in gradient wind balance , that is, the inward-directed pressure gradient force is approximately balanced by the sum of the outward-directed centrifugal and Coriolis forces.
Hence, statement 2 is correct & statement 3 is incorrect.
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