SAJC Cluster 2 Lecture 3 Notes (Rainfall Patterns in The Tropics)

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2_Lecture 3_2024/pg1 Lecture 3 Tropical Climates (IIb): Rainfall Patterns in the Tropics KEY QUESTIONS: How does global atmospheric circulation affect rainfall in the tropics? How does synoptic scale circulation affect rainfall in the tropics? With the completion of this lecture, attached readings and tutorial, you should be able to understand the: • Influence of atmospheric circulation in the Hadley cells on rainfall patterns in the tropics • Influence of seasonal migration of the Hadley cells on rainfall patterns in the tropics • Influence of distribution of heat over land and sea on summer and winter monsoon circulations in humid tropical Asia, and the resultant effects on rainfall patterns Lecture Outline 3.1 Introduction: Rainfall and the Tropics 3.2 Some basics to Understanding Rain Formation 3.2.1 Atmospheric Stability and Instability 3.2.2 Condensation, Clouds and Rain Box 1: Latent Heat 3.3 Influence of Hadley cells on Rainfall Patterns in the Tropics 3.3.1 Influence of Hadley cells on rainfall patterns of Af climates 3.3.2 Influence of Hadley cells on rainfall patterns of BWh and BSh climates 3.3.3 Influence of seasonal migration of Hadley cells on rainfall patterns of Am/Aw climates 3.4 Influence of distribution of heat over land and sea in humid tropical climates 3.5 Summary All these photographs are of places in the tropics. Why are some places in the tropics so wet all year round ( top left ), some dry all year round ( right), and others seasonally wet and dry (bottom left)?

St Andrew’s Junior College H2 Cluster 2: Tropical Environments H2_Cluster 2_Lecture 3_2024/pg2 3.1 Introduction: Rainfall and the Tropics • Recall from Lect 1 that the Tropics may be described as… A climatic region of solar radiation surplus delimited by boundaries fluctuating between 30 ˚ and 35 ˚ north and south latitudes. Common to all areas in this region (at sea level) is high temperature. Significant variations in the amount and pattern of rainfall differentiate these areas into different tropical climate zones, primarily the humid tropics and the arid tropics. • While mean annual temperature in the Tropics is generally high everywhere (as we saw in Lect 1 and 2), the definition provided above reminds us that rainfall in the Tropics is not as simple to explain. Indeed, as we shall see in thus lecture , the Tropics can be further categorised into different climatic regions, by virtue of how much rainfall they receive and how that varies over time and space. • In this lecture, we first focus on the basic conditions for rainfall to occur so that we can understand the role of Hadley Cells in influen