Why do we have Monsoons in Asia?
For the first 21 years of my life I lived in New Zealand, where the most common question to ask someone up on meeting is “what do you think of the weather?”. In New Zealand the weather seems to dictate our daily lives, our actions, our moods and our conversations. Maybe one of the reasons for weather being such a ‘hot’ topic in New Zealand is the fact it is extreme, it changes fast and can be very difficult to predict.
When I moved to Singapore at the age of 22, I found it strange that people thought I was strange when I asked them about the weather! Here the topic of conversation on everyone’s lips revolves around food – “Have you taken your breakfast yet?”. I soon realised that the weather in Singapore is generally very predictable, and can be described in two ways:
- hot and muggy
- VERY hot and muggy
After living here for 19 years I also learned there were two main wind patterns that affected Singapore and the south-east-asian region.
- The north east monsoon: December through to March
- The south west monsoon: June through to September.
As the names suggest for each monsoon seasons the winds blow predictably in these directions during these periods.
The times in between these monsoons are typically called ‘inter-monsoon periods’. These are characterized by light and variable winds and are often the times of the most intense thunder and electrical storms. Singapore has over 180 ‘lightning days’ per year (days when lightning is recorded somewhere in the country). Every year a handful of people die from lightning strikes in Singapore such as this poor chap here, making it one of the lightning capitals of the world. Indeed being caught out, especially in a small boat in a major electrical storm (as I have on occasions) is an unnerving experience.
After 19 years of living in Singapore and whilst researching the Rowing from Home to Home expedition – I finally learnt the reason why we have monsoon winds in Singapore. The answer is very straightforward and can be explained in three steps:
Step One – pressure differences
All of the weather on the earth is fundamentally caused – believe it or not, by the sun. The sun warms certain part of the earth, while other parts in the shadow or further from the sun are cooled. When the earth is heated, warmer air rises causing lower air pressure close to the earths surface.
Consequently where land or sea is cooler – the air sinks and stays lower. This means more air, more dense and more pressure, making high pressure areas close to the earths surface. Air always tries to travel from areas of high pressure to areas of low pressure. It tries to even out the air pressure all over the world. This movement causes winds.
Step Two – The asian continent cools
During winter in the northern hemisphere, the enormous land mass of Asia cools. This is from November through to March. As it cools, (as described above) the air is heavier and more dense close to the surface making area of HIGH pressure. Over the equator where Singapore is located – it is hot and there is LOW pressure. Hence the air travels from the HIGH pressure to the LOW pressure – down from the Asian continent towards and over the equator. Initially it travels as a north-easterly wind (remember when describing winds the direction is where the wind comes from NOT where the wind is going – so a north-easterly wind is in fact heading in the opposite direction i.e. south-west) direction until it hits the equator, then it turns to a north-westerly wind down towards Australia.
Click this LINK to see an animation of north-east monsoon winds on the 19 January 2015.
I was often confused when people talked about the monsoons as they used the terms ‘north-east’ or ‘north-west’ monsoon and I wondered which is which? Until I finally understood that they are the same phenomenon, it just depends whether you stand north of the equator where you would call it the north-east monsoon, or south of the equator where it would be the north-west monsoon.
Step Three – The asian continent warms
During summer in the northern hemisphere, the asian land mass warms and the opposite occurs. The air rises and creates a LOW pressure region over the Asian continent, lower in pressure even than the air at the equator and further south. Consequently the air travels towards the low pressure region in Asia making the winds south-easterly (below the equator) and south-westerly above the equator.
Click this LINK here to see an animation of winds during the south-east monsoon on 19 June 2015.
Why is this important to Rowing from Home to Home?
Wind strength and direction is extremely important to sailors and mariners for obvious reasons. Now we are travelling by human power so will NOT be using sails of my kind, however the wind still influences our vessel enormously, either aiding our progress or restricting it. It can even push us backwards or worse still into dangerous areas/objects where we do not want to be. We cannot really make headway against wind speed more than 15 knots and the higher the wind speed the rougher the sea state becomes, to a point when we cannot row safely.
So judging the best time of the year to make this expedition is something that I have been studying for a very long time. As know one has even tried to travel from Singapore to Australia by human power in a rowing boat – I need to research and make the decisions without the benefit of others experience. Based on the information given above it would seem the north-east monsoon is the logical time to attempt the expedition?
But wait! There is one more factor to consider.
A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane , typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone. (source Wikipedia)
Unfortunately the period of the north-east monsoon is also cyclone season. As you can see from the image above of cyclone tracks recorded over time, our rowing route from Indonesian across to Darwin in Australia passes right through ‘cyclone alley’. Being caught in a cyclone is something we will need to be very careful to try to avoid. These are massive storms, with very rough sea states and bad enough for large vessels let alone small little rowing boats. But as with most things in life of value, you have to make compromises and take risks to achieve them. We need the north-easterly/westerly winds therefore the risk of cyclones is something we will have to manage.