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General

Blocked jet stream to blame for weather catastrophe

media A storm cloud forming along the jet stream above the Norwegian coast Reuters

Meteorologists have linked the floods in Pakistan with the extreme heat in Russia. The clue lies in the jet stream, a current of strong winds circulating 10 kilometres above the Earth's surface, which are blocked.

The northern hemisphere jet stream normally circles the globe, shifting the air and transforming the weather.

But scientists say that it has been blocked for the past two weeks, and is to blame for unchanging weather over Russian and Pakistani territories.

Interview: meteorologist Andy Turner, University of Reading 15/08/2010 - by Sarah Elzas Listen

So while heat-stricken Russia desperately waits for rain, Pakistan is stuck in a seemingly perpetual monsoon season.

Andy Turner, a scientist at meteorology department of the University of Reading, told RFI the jet stream has “meanders” or turns, and over Russia it has turned to the north and created what is called a “blocking high”.

He said that during the summer months, they are associated with very high temperatures, and low cloud cover.

“But what is interesting is that because you have this northward meander in the jet stream going up over Russia, you then have a subsequent southward meander, which actually causes what is known a trough, or a low-pressure region,” Turner said.

WikiMedia Commons

“And especially in the last week of July, this has been situated over the northern regions of Pakistan, and at the same time there’s also been a monsoon depression, which has come up from the Bay of Bengal.”

Turner said the trough of low pressure has intensified Pakistan’s normal monsoon rainfall for this time of year.

But is global warming responsible for the anomalous jet stream, or “stationary wave pattern”? Turner says it’s too early to tell.

“The climate change models that we use aren’t really good enough to tell us about what is going to happen to the changes in blocking or stationary wave patterns at the moment,” he said.

“We can’t say at the moment that this particular event relates to climate change. We don’t know if, under climate change, things like blocking events will become more common.

“But what we do know is that, in general, the normal monsoon that happens over south Asia will get slightly more intense, and we also know that rainfall will tend to happen in heavier bursts.”
 

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