‘Many global weather anomalies this year’


When it rained in the Middle East, the high pressure system moved south eastwards and was positioned close to the Middle East. Photo - Times of Oman

Scientists believe they have discovered the cause of the extreme weather that hit the Middle East. When dry cold air meets warm moist air, a phenomenon called 'occlusion' occurs. This caused the record rainfall in Gulf region last month

Muscat: An unusual weather system called 'occlusion' explains the record rainfall in the Middle East, including Oman, in the third week of November, a senior scientist in Abu Dhabi has claimed.

Scientists believe they have discovered the cause of the extreme weather that hit the Middle East.

Around nine people were killed and 200 others had to be rescued after they were trapped in water currents when heavy rains and thunderstorms lashed across Oman in the third week of November.

Following a heavy downpour in the countries across the Middle East, its causes were investigated by the scientists at the Centre for Prototype Climate Modelling at New York University Abu Dhabi.

Senior Scientist Dr Ajaya Ravindran claimed that during the investigation, they found that 2013 was marked by many global weather anomalies, such as unusual jet stream patterns, strong monsoons, heat waves, intense snowfall over the US and Europe, besides the rains in the Middle East.

"The weather bureaus correctly forecasted and attributed the cause of the last pattern to an atmospheric low pressure system that moved across the Middle East countries. But we wanted to learn more about the origins of this weather event," he told the Times of Oman.

In mid-November, Cyclone Hilde formed off the southern coast of Greenland and brought high winds and rain to Norway, Sweden, and Finland. Around the same time, another cyclone, Cleopatra, formed over the Mediterranean and brought destructive rain and flooding to the Italian island of Sardinia.

Cyclones occur rarely over the Mediterranean Sea. "A wave-like atmospheric flow controls the winter weather of mid-latitudes. These are basically a chain of cyclone-anticyclone circulation patterns propagating from west to east. An anticyclone, which is characterised by a high pressure centre around 55°N and clockwise rotating winds, followed Cleopatra.

"Over the next few days, when the rain over the Middle East occurred, this high pressure system moved south eastwards and was positioned close to the Middle East. Eventually, the cold dry air of the anticyclone met the warm moist air from the Arabian Sea and Africa," he said.

When dry cold air meets warm moist air, a phenomenon called 'occlusion' occurs. "This results in the formation of a low pressure area, followed by clouds, and, finally, rain. The amount of rain is determined by the amount of moisture carried by the warm air. This year, the unusually strong Indian monsoon left a great deal of moisture over the Arabian Sea. (The level of moisture over Arabian Sea in October and November was 15 to 20 per cent higher than normal.)

"During the rains in November, the meeting of the dry cold air from the anticyclone and the warm moist air from the tropics triggered a low over the upper Arabian Gulf, which moved south-east down the Gulf after dumping rain over Kuwait, Bahrain, Eastern Saudi Arabia, Qatar, the UAE and Oman," he said.

Scientists at the centre conducted several "hindcasts" with the Weather Research and Forecasting (WRF) models using the assimilated data obtained from various weather agencies like NCEP GFS (National Centre for Environmental Prediction Global Forecast System).

"With these hindcasts, we were able to simulate the extreme rainfall events over the Middle East, which is an example of the ability of the contemporary weather and climate models in simulating extreme weather events," he added.

However, he said that it is too early to blame it on climate change. "It is too early to attribute this rainfall — or any recent isolated weather event — to climate change. That kind of determination must come from a detailed comparison of the present climate to the past and future (projected) climates. Scientists at our centre are in the process of such an investigation," he added.

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