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Climate Models Still Struggle With Medium-term Climate Forecasts

December 7, 2012
Image Caption: Atmospheric teleconnection patterns influence the weather on a large scale. The pattern of the North Atlantic oscillation plays an important role for the North Atlantic-European area. The North Atlantic oscillation is characterized by fluctuations in atmospheric pressure between the Icelandic Low and the Azores High and occurs in two states: the positive and the negative phase. The negative phase of the North Atlantic oscillation is characterized by lower atmospheric pressure over the Azores and higher atmospheric pressure in the area of the Icelandic Low so that the prevailing westerly wind current is weakened and the wave patterns pronounced. This causes cold polar air to be transported to Europe. Photo: Karsten Reise, Alfred Wegener Institute

April Flowers for redOrbit.com – Your Universe Online

A research team from the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association (AWI) has evaluated 23 current climate models to assess their ability to predict the weather conditions for the coming year or even the next decade. They concluded that there is still a long way to go before reliable regional predictions can be made on these scales, as none of the models assessed is currently able to forecast the weather-determining patterns of high and low pressure areas to the point where a cold winter or a dry summer can be reliably predicted.

Currently, the most important questions being asked in climate research concern the regional and medium term impacts of global climate change. The answers to these questions will most likely play a large part in the next world climate report because societies having to adjust to climatic changes should know which specific changes they must expect. For example, the agricultural or energy sectors would be directly affected if the weather conditions that will prevail in a certain region in the medium term could be reliably predicted, making the quality of current climate models and their ability to predict weather patterns over a period of seasons to decades of great importance.

Large-scale circulation patterns in the atmosphere significantly determine the Earth’s weather. The North Atlantic oscillation, which influences the strength and location of the westerly winds over the North Atlantic, determining the tracks of the low-pressure system over North and Central Europe is one example. Distributed over the entire globe, circulation patterns of this nature, also referred to as “teleconnection,” determine the spatial and temporal distribution of areas of high and low pressure over large distances. Meteorological centers of action determine the weather of an entire region. These are the known weather centers of the “Icelandic Low” and the “Azores High” in the North Atlantic oscillation.

“Short-term weather forecasts are now very reliable. The problems for seasonal and decadal, that is medium-term, predictions refer to the enormous variability and the broad range of feedback effects to which atmospheric circulation is subjected,” explains AWI meteorologist Dörthe Handorf.

To assess the prediction abilities of the 23 climate models, the AWI team investigated how well they were able to reproduce atmospheric teleconnection patterns over the past 50 years. Nine known circulation patterns were investigated retrospectively, four in special detail. The spatial distribution of atmospheric teleconnection patterns is well described by some of these models already, however, none of the 23 was able to reliably reproduce how strong or weak the Icelandic Low, Azores High and other meteorological centers of action were at a particular time over the last 50 years.

“Climate researchers throughout the world are currently working on increasing the resolution of their models and the performance of their climate computers”, says Dörthe Handorf. “But it will not be enough to increase the pure computer power. We must continue to work on understanding the basic processes and interactions in this complicated system called “atmosphere”. Even a high power computer reaches its limits if the mathematical equations of a climate model do not describe the real processes accurately enough.”

As one of the most important drivers of our climate and weather, the Arctic plays a key role in optimizing climate models. The Arctic is also one of the regions in which the climate is currently changing the most. The region is so inhospitable that reliable data is sparse.

The scientists see their research continuing in two directions. They are developing a climate model to resolve the small-scale weather-determining processes in the Arctic. Because improvements in the models are only possible if high quality data records are available, the second direction of the research is a large international field campaign planned for the 2018-2019 Arctic season. Part of this campaign will take place at an Arctic drift station where scientists will drift through the Arctic Ocean with the sea ice during several months of winter.

The results of this study were published in the journal Tellus A.


Source: April Flowers for redOrbit.com - Your Universe Online



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