7. Additional Material

Chapter 2: Wind driven surface currents

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The Coriolis Effect

Movement in a rotating reference frame, and why winds and currents flow in curves, not straight lines.

Prevailing winds

How the unequal heating of the Earth's surface creates the large scale atmospheric circulation and the prevailing winds.

The Southern Ocean

The windiest, coldest, most inhospitable region on earth plays a vital role in the Earth’s climate system.

Answers

18th century schooner in new york harbour

1. Franklin's question: why the big difference? Why did the mail ships from London to New York take 2 weeks longer to reach America than the merchant ships sailing from Falmouth to Rhode Island?

Answer: The mail ships from London to New York sailed further south than the ships from Falmouth to Rhode Island. Approaching America the mailships sailed against the Gulf Stream, while the ships to Rhode Island avoided this, and may even have had help from the continuation of the cold currents south of Nova Scotia.

2. How can temperature measurements help?

Answer: The difference across the front can be as much as 4 °C. This is easy to detect even with very simple bucket measurements. By knowing the average temperature of Gulf Stream water in a particular season, navigators can determine whether or not they are in the current. If they are sailing to America and want to avoid the Gulf Stream, they can plot a more northerly course. If they are sailing from America they can plot a more southerly course and get some help from the current.