The weather and climate of the tropics Part 1 – Setting the scene

In this series, I will describe various aspects of tropical weather and climate as it is understood today. The series will cover these topics: the sub-tropical jet streams; synoptic-scale weather systems; forecasting significant cloud and associated weather; dry environments; the development and maintenance of monsoon systems; tropical revolving storms; and mesoscale convective complexes. Each part will include a description of the effects of tropical weather. This series is not intended to be a detailed mathematical description of tropical weather. A number of very good texts are available for those who wish to go into greater depth; in particular, I recommend Hastenrath (1991) and Riehl (1979). Much of what we know about the weather has been focused on mid-latitude weather systems: first, because most early researchers came from Western Europe and eastern North America; and second, because of the risks and consequences of weather systems prevalent in these zones. However, although there are simple nonscientific descriptions of weather events from the tropics going back hundreds of years, it is only since the late 1960s that much scientific research has been carried out within the tropical zone. What we know of the weather (and, to some extent, the climate) of the tropics remains limited and has typically focused on severe weather events, such as tropical revolving storms (e.g. Emanuel, 2005), or data from a limited range of observing stations. However, many factors of the day-to-day weather are important in the tropics, not least for aviation and public safety. For instance, the primary purposes of forecasting for aircraft operations in the tropics are safety and maximization of efficiency for the benefit of passengers and aircraft operators. The most accurate and appropriate forecasts will achieve this goal, using a mixture of numerical weather prediction products, observed data and good forecasting knowledge. It is the effects of the weather, in other words its outcomes, which must be considered. The research carried out as part of the World Climate Research Programme since the early 1970s is very important in allowing us to understand many of the processes and associated weather of the tropical zone (Gates and Newson, 2006). Knowledge continues to grow through more recent research programmes, such as TOGA, which investigates the important links between the tropical ocean and the global atmosphere (Fleming, 1986). It is clear that the tropics have an important effect on weather systems throughout the globe, providing much of their energy.