Section 1: INTRODUCTION 1.1 Where are the tropics and what makes them special? 1.2 The amount of energy received by the earth 1.3 Moisture in the tropics 1.4 Basic equations

1.1 Where are the tropics and what makes them special? Arbitrary definitions for where they are: Geography: Tropics are the region of the earth bounded by the tropic of Cancer (23.5oN) and the tropic of Capricorn (23.5oS). These are the latitudes where the sun reaches the zenith just once a year at the summer solstices. Equal Halves: The region between 30N and 30S would divide the earth into two equal halves. Defined this way, the tropics would be the source of all the angular momentum of the atmosphere and most of the heat. But this is not meteorologically sensible. Processes: Riehl (1979) chose to define the “meteorological” tropics as those parts of the world where atmospheric processes differ significantly from those in higher latitudes (see next slides). Riehl (1979) Climate and Weather in the Tropics, Academic Press.

Contrasting processes Figure 1.1

Land and ocean contrasts Figure 1.2: Markedly non-uniform distribution of land and ocean areas in the tropics may be expected to have a large influence on the meteorology there

Annual Mean Rainfall Figure 1.3 Precipitation peaks in the tropics

Mean Meridional Circulations Figure 1.4 There are no walls between the tropics and extratropics!

1.2 The amount of energy received by the earth Solar Radiation Received at TOA Figure 1.5 Solar absorbed Outgoing radiation Northward transport of energy Northward transport by atmosphere Figure 1.6

1.2 The amount of energy received by the earth Figure 1.7

1.2 The amount of energy received by the earth Figure 1.8(a)

1.2 The amount of energy received by the earth Figure 1.8(b)

1.2 The amount of energy received by the earth Figure 1.9

1.3 Moisture in the tropics Figure 1.10

1.3 Moisture in the tropics Figure 1.11

1.3 Moisture in the tropics Figure 1.12

1.3 Moisture in the tropics Figure 1.13(a) Figure 1.13(b)

1.3 Moisture in the tropics Figure 1.14

1.4 Basic equations Adiabatic, Frictionless Equations in Pressure Coordinates where