Monsoon !

I'm a bit of a nerd when it comes to geography and related fields, so i've been looking forward to the arrival of monsoon season. I was secretly hoping that monsoon would arrive in a single day, the months of stifling dry season heat suddenly broken by a dramatic thunderstorm and torrential downpour which would be repeated every day at 3pm in the afternoon like clockwork for the next 3 months. The reality of course is a little different. There were some unseasonally early rains in Phnom Penh in April, and it has rained on and off at different times of the day and night for the past few weeks. Out in the provinces things are green and lush, the rice crop has gone in and there is little doubt that the 'wet' season has arrived from a farmers perspective. Anyway, after a few days straight of heavy afternoon rains in Phnom Penh, i'm going to call it - monsoon has arrived !

No doubt I will be proved wrong by the fickle weather, but the regularity and intensity of the rains align with my expectations, and Em's Khmer work colleagues work seem to think we're there too. So, what's it like ? Well, the morning's invariably start out sunny and fine. By midday the cloud is starting to build (isolated Cumulus drifting overhead, towering Cumulo-Nimbus on the horizon to the west) and it's usually hot with high humidity . The sky gets dark around 3pm-4pm as the clouds roll in, the wind suddenly picks up and gusts strongly (a good indicator that it's time to find some cover), the skies open up and sheets of rain come down. It typically lasts for anywhere between 1-3 hrs and can be accompanied by some impressive thunder and lightning. The timing and the warning signs actually make it pretty easy to avoid as long as you don't have to be somewhere at a certain time. In case we do get caught out, Em & I have taken to carrying around these disposable rain coats. Before you collapse on the floor laughing, everyone wears these here, and if you didn't have one the rain would drench you to the skin in seconds. Coincidentally, mine is blue and Em's is yellow. If I get down to the gym to tone up a bit and practise my blue steel pose we might be able to model these for you in person.

Anyway, I wasn't too clear on what causes monsoon and why they are so regular so I did a little internet research. Rather than paraphrasing i'm just going to link to wikipedia, if you're even remotely interested check out the link below. So, that's us for the next 3 months, no need to check the weather forecast I guess - hot and wet. In September, we have the 'cool wet' season to look forward to, apparently it can get as low as a frigid 20c...brrr

http://en.wikipedia.org/wiki/Monsoon
Monsoons are caused by the larger amplitude of the seasonal cycle of land temperature compared to that of nearby oceans. This differential warming happens because heat in the ocean is mixed vertically through a "mixed layer" that may be fifty meters deep, through the action of wind and buoyancy-generated turbulence, whereas the land surface conducts heat slowly, with the seasonal signal penetrating perhaps a meter or so. Additionally, the specific heat capacity of liquid water is significantly higher than that of most materials that make up land. Together, these factors mean that the heat capacity of the layer participating in the seasonal cycle is much larger over the oceans than over land, with the consequence that the air over the land warms faster and reaches a higher temperature than the air over the ocean. Heating of the air over the land reduces the air's density, creating an area of low pressure. This produces a wind blowing toward the land, bringing moist near-surface air from over the ocean. Rainfall is caused by the moist ocean air being lifted upwards by mountains, surface heating, convergence at the surface, divergence aloft, or from storm-produced outflows at the surface. However the lifting occurs, the air cools due to expansion, which in turn produces condensation.