It's easy to get confused with the tropical meteorology terminology. What's the difference between monsoon, monsoon trough and monsoon "pulse" as an example.
Monsoon is a season, we often refer to it as the wet season. And it goes from November to April. (1)
During the monsoon we see monsoon events like cyclones and tropical storms that often form on what is called the monsoon trough. "The monsoon trough is an area of low pressure along which broad-scale convergence and convection occurs." (1)
The dashed red line shows where the monsoon trough is, and it may move a little as weather systems move across the continent. On a normal synoptic chart it is marked as dot dash dot dash.
We use a tool called the Madden-Julian Oscillation (MJO) to determine when we are likely to experience monsoonal events. (2) We can also use it to tell when the monsoon will begin.
Essentially the chart has a circle that indicates when the monsoon is relatively inactive. When it is out of the circle this is where the majority of cloud and rain exists along the equator. The pulse moves from west to east roughly taking 30 to 60 days per full revolution. The numbers in each triangle represent the position on the equator. The distance is relative position from the equator. The current position of the monsoon pulse for Dec 30 is Phase 2. The Phases are shown below, blue showing the most intense location of the pulse for each Phase.
So, we can use the MJO to determine when a monsoon is likely to start, and when monsoon events are likely to occur.
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