ATM OCN (Meteorology) 100 - Lecture 3

Answers for Homework 6

Fall 1997

The total maximum points were 40.

PLANETARY ATMOSPHERIC CIRCULATION

1. Suppose that in 1849 you would have wanted to join the California Gold Rush and you would have booked passage from New York City to San Francisco on a 19th century Clipper sailing ship that went around Cape Horn. Briefly describe in a paragraph the sequence of weather events that you would have probably experienced leaving New York in October and traveling south to Cape Horn across the North and South Atlantic Oceans. Relate these weather features to the prevailing wind regimes and the semipermanent pressure features of the general atmospheric circulation. (You may want to consult an atlas!)

[20 pts.]

A paragraph (with reasonably good grammar) should have included the fact that leaving New York, one is in the prevailing westerlies with some possible storms. Nearing the Florida coast, one would have reached the horse latitudes, with fair skies and weak winds, under the subtropical high pressure in the western Atlantic. Farther south, the northeast trades can be found with a persistent northeast wind and some cumuliform clouds. Near the equator, the doldrums also known as the Intertropical Convergence Zone, would have been reached, with hot, humid and cloudy conditions, with abundant rainshowers or thunderstorms. Sailing into the Southern Hemisphere, the southeast trades would be encountered first, then the subtropical highs of the South Atlantic (near southern Brazil and northern Argentina) then as one approaches Cape Horn, the prevailing westerlies would have dominated. The passage around the Cape would have probably been stormy in with migratory cyclones moving eastward across the Southern Oceans.

2. Using the January and July sea-level pressure charts found on page 229 of your textbook, answer the following:

a. Locate the high pressure feature situated over the North Pacific Ocean near Hawaii.
What is its average central pressure in January? [1pt.]

and in July? [1pt.]

How has its position changed between January and July? [2pts.]

b. Inspect the corresponding subtropical high pressure cells in the other ocean basins. What general statement can be made concerning the seasonal variation in the location and intensity of these features? [4pts.]

c. Locate the low pressure feature located over the North Atlantic Ocean near Iceland.
What is its average central pressure in January? [1pt.]

and in July? [1pt.]

How has its position changed between January and July? [2pts.]

d. Use the major pressure features over the North American and the Eurasian continents to make a statement as to the seasonal (winter versus summer) variations in the air pressure over the continents. [4pts.]

During winter, the continents are dominated by large high pressure cells, with relatively lower pressure over the oceans, while in summer the continents have lower pressure than over the oceans.

3. From Figure 10.8 on page 234 of your textbook, describe how the Intertropical Convergence Zone shifts geographically with season. [4 pts.]

The Intertropical Convergence Zone moves with the sun, shifting northward of the equator during the Northern Hemisphere's "high sun" season by July (especially over the continents) and toward the geographic equator during the "low sun" season in January.

Last revision 20 November 1997