Posts Tagged ‘Weather’

The Watchers Tweet Tweet Arctic has been experiencing a shift in the general patterns of high and low pressures recently, as well as the direction and speed of the winds. These changes may explain some of the dramatic sea ice loss experienced in the Arctic regions. Wind speed and direction are driven by differences in atmospheric pressure. Generally, air moves from areas of high to low pressure – the greater the pressure difference between two areas, the faster...

    Arctic has been experiencing a shift in the general patterns of high and low pressures recently, as well as the direction and speed of the winds. These changes may explain some of the dramatic sea ice loss experienced in the Arctic regions. Wind speed and direction are driven by differences in atmospheric pressure. Generally, air moves from areas of high to low pressure – the greater the pressure difference between two areas, the faster the air moves.

    According to a new NOAA-led study published on October 10,2012 in Geophysical Research Letters, changes in summer Arctic wind patterns contribute not only to an unprecedented loss of Arctic sea ice, but could also bring  shifts in North American and European weather. As Arctic warms at twice the global rate, scientists expect more extreme weather events like heatwaves, floodings or heavy snowfall across the temperate latitudes of the northern hemisphere, where billions of people live.

    Comparison of the atmospheric pressure (geopotential height at 700 mb) experienced during June of 2007-2012 compared to the longer term average for June from 1980-2010. Much higher pressure is found directly over the Arctic Ocean and Greenland. This difference in pressure has resulted in a change in the wind patterns. Orange arrows indicate the relative direction and strength (indicated by the arrow length) or winds during the 2007-2012 periods, whereas the white arrows are the 1980-2010 average. The most pronounced changes in winds can be seen over the Chuchki Sea, just northeast of Alaska and also east of Greenland. (NCEP Reanalysis data provided by NOAA/ESRL/PSD)

    A research team led by a NOAA research oceanographer James Overland, Ph.D., of NOAA’s Pacific Marine Environmental Laboratory in Seattle, Washington, uncovered a change in the summer Arctic wind pattern over the past six years. They point that this shift demonstrates a physical connection between reduced Arctic sea ice in the summer, loss of Greenland ice, and potentially, weather in North American and Europe.

    The team examined the wind patterns in the subarctic in the early summer between 2007 and 2012 as compared to the average for 1981 to 2010. The new study show that the previously normal west-to-east flowing upper-level winds have been replaced by a north-south undulating wave-like pattern. This new wind pattern transports warmer air into the Arctic and pushes Arctic air farther south. This may influence persistent weather conditions in the mid-latitudes. Higher pressure over the North American continent and Greenland is driving these changes in the early summer wind patterns.

    Warmer air and sea temperatures caused by global warming are rapidly changing Arctic environment but this new shift provides additional evidence that changes in the Arctic are also part of an “Arctic amplification” through which multiple specific physical processes interact to accelerate temperature change, ice variability, and ecological impacts. The effects of Arctic amplification will increase as more summer ice retreats over coming decades. Enhanced warming of the Arctic affects the jet stream by slowing its west-to-east winds and by promoting larger north-south meanders in the flow.

    Sea ice in the Chukchi Sea, on July 20, 2011. Sea ice in the Arctic has shrunk to the lowest levels ever recorded (Credit: Jeremy Potter NOAA/OAR/OER)

    Since 2007, the summer winds were found to blow through the Bering Strait, across the North Pole, more consistently from the south, out toward the Atlantic Ocean. These winds transfer additional heat from the south toward the North Pole and push sea ice across the Arctic and out into the Atlantic Ocean, contributing to record losses of summer sea ice. The 2012 Arctic summer sea ice minimum is the lowest on record.

    The study, entitled “The Recent Shift in Early Summer Arctic Atmospheric Circulation,” was co-authored by scientists from Rutgers University in New Jersey,  the University of Sheffield in the United Kingdom, and the Joint Institute for the Study of the Atmosphere and Ocean, a partnership of NOAA and the University of Washington. It can be found online.

    Sources: NOAA ClimateWatch, NNVL

    Featured image credit: (NASA/Kathryn Hansen)

    By chillymanjaro – October 24, 2012

    UK experiences ‘weirdest’ weather

    Posted: October 19, 2012 by phaedrap1 in News
    Tags: ,

    Rain showers in Portsmouth

    The UK has experienced its “weirdest” weather on record in the past few months, scientists say. The driest spring for over a century gave way to the wettest recorded April to June in a dramatic turnaround never documented before.

    The scientists said there was no evidence that the weather changes were a result of Man-made climate change. But experts from three bodies warned the UK must plan for periodic swings of drought conditions and flooding. The warning came from the Environment Agency, Met Office and Centre for Ecology & Hydrology (CEH) at a joint briefing in London. Terry Marsh, from the CEH, said there was no close modern precedent for the extraordinary switch in river flows. The nearest comparison was 1903 but this year was, he said, truly remarkable. What was also remarkable – and also fortunate – was that more people did not suffer from flooding. Indeed, one major message of the briefing was that society has been steadily increasing its resilience to floods. Paul Mustow, head of flood management at the Environment Agency, told BBC News that 4,500 properties had been flooded this year. “But if you look back to 2007 when over 55,000 properties were flooded, we were relatively lucky – if lucky is the right word – for the impacts we saw this summer,” he said. “The rainfall patterns affected different areas – and also there were periods of respite between the rain which lessened the impact.” Fast moving He said 53,000 properties would have been flooded this year without flood defences. In total, he said, 190,000 properties had received flood protection in recent years. Mr Mustow claimed that flood defences repaid their investment by a factor of 8-1 but admitted that continuing to invest would be a “challenge”, after government cuts to planned projects. But he said that new streams of joint funding from local authorities and private developers had allowed 60 schemes to happen that otherwise would not have gone ahead. He said: “We have to get our heads round the possibility now that we’re going to have to move very quickly from drought to flood – with river levels very high and very low over a short period of time. “We used to say we had a traditional flood season in winter – now often it’s in summer. This is an integrated problem – there’s no one thing that’s going to solve it. The situation is changing all the time.” But scientists present from the Met Office and CEH said not much could be read into the weird weather. Terry Marsh from CEH said: “Rainfall charts show no compelling long-term trend – the annual precipitation table shows lots of variability.” Sarah Jackson from the Met Office confirmed that it did not discern any pattern that suggested Man-made climate change was at play in UK rainfall – although if temperatures rise as projected in future, that would lead to warmer air being able to carry more moisture to fall as rain. She said that this year’s conditions were partly caused by a move to a negative phase of the North Atlantic Oscillation which would be likely to lead to more frequent cold, drier winters – like the 1960s – and also wetter summers for 10-20 years. “Longer term we will see a trend to drier summers but superimposed on that we will always see natural variability,” she said. Whatever happens with the weather, the Environment Agency expects that more and more people will be protected from floods and droughts thanks to water sharing between farmers, water transfer between water companies, and better management of leaks and demand. But Mr Mustow admitted that much more needed to be done to ensure that farmers did not increase flood risk with land drainage schemes and that developers and builders ensured that new developments allowed water to drain into the soil rather than flushing into the sewers.

    BBC

    By Roger Harrabin

    Environmental Analyst