It has been a weird winter. Extended sunshine, warmer than usual temperatures, weak & loose snow cover, shy rain, and blooming flowers indicating an early Spring arrival; But why is all that?
Let me start by exposing the whole picture about whats happening in the Northern hemisphere:
1-In Europe, many countries have been effected by a series of freezing waves, snow, and ice since December 2009. Great Britain was completely covered with snow. France, Netherlands, Belgium, Germany, Scandinavian countries and Eastern Europe got significant amounts of snow.
2- Northern America also has been and still under the effects of consecutive blizzards, where snow reached historical levels in Washington DC. Just to cite, this winter, All the US states received snow except Hawaii.
3- many areas, including the Middle East, are witnessing decreased rain fall & warmer than usual temperatures.
Throughout my readings, one main common reason was mentioned accross online sources, NASA being one, relating whats happening to the Negative Arctic Oscillation. So, what is the Arctic Oscillation & what does it mean being “negative”?
The image below was taken from NASA’s earth observatory website (http://earthobservatory.nasa.gov). It resembles the temperature margins in the Northern hemisphere during the month of december 2009. The illustrations were added personally in order to simplify and explain.
The Arctic Oscillation is a climate pattern that influences winter weather in the Northern Hemisphere. It is defined by the pressure difference between air at mid-latitudes (around 45 degrees North, about the latitude of Montreal, Canada or Bordeaux, France) and air over the Arctic (http://earthobservatory.nasa.gov/IOTD/view.php?id=42260). It is a natural phenomena where Arctic dense cold polar air sinks towards southern latitudes while warmer air at mid latitudes climb up towards the pole. This oscillation brings changeable weather patterns during the Northern hemisphere winter. During the month of December 2009, the Arctic Oscillation was strongly negative i.e. the pressure difference between the pole and the mid latitudes was small, thus cools air crept into the south gently and cooled the land surface.
During this period, the Middle East, including Lebanon, was witnessing extended periods of sunshine interrupted by few days of stormy rain. The less-frequent weather activity is due to the Negative Arctic Oscillation where low pressure systems form at mid latitudes (Europe) and brought winter storms there, keeping the Eastern Med calm and under High pressure dominance.
Its not that accurate to relate the rain/snow absence in Lebanon to global warming. Although global warming is gradually taking place, but still, as scientists claim, its not still strong enough to drag significant change in the weather.
Years of scarce rain and warmer winters were recorded in the recent past in Lebanon. So to keep it on the optimistic side, lets consider the 2009-2010 winter season another pattern of natural rain scarcity.