Stalagmites as useful barometers of precipitation The annual see-saw of the tropical rain belt. The NAO is a numeric index: if it is positive, both the Icelandic low and the Azores high are very strong, which generally causes wet weather and strong westerly winds in central Europe, or in extreme cases winter storms and hurricanes, such as the violent Lothar storm in 1999. This phenomenon dictates the weather in western and central Europe, and is the result of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high over the North Atlantic. The scientists also found that the climates in the tropical rain belt and the mid-latitudes are interconnected through the North Atlantic Oscillation (NAO). The migration of the tropical rain belt also caused substantial changes in the tropical and subtropical climate during this time, affecting the areas of drought and heavy rainfall. The latest climate reconstructions show that the average temperatures during this period were around 0.4 degrees Celsius lower than before and after the Little Ice Age. "This migration is linked to the lower global temperatures during this time," explains Lechleitner. The ETH researcher and her colleagues have now managed to demonstrate how the tropical weather system shifted a good way south between 14, a period known as the Little Ice Age. "So far, however, scientists have not investigated the past two millennia on a global scale, when temperature changes have been far less pronounced," explains the climate geologist. In the past, scientists have only studied the migration of the tropical rain belt over very long timespans, such as glacial and interglacial cycles over tens of thousands of years, with correspondingly sizeable temperature differences of several degrees. The team's findings have been published in the journal Scientific Reports, where they present the most comprehensive reconstruction of rainfall patterns within the Intertropical Convergence Zone for the past 2000 years. An international team of researchers led by Franziska Lechleitner from the Geological Institute at ETH Zurich has proven for the first time that the migration of the tropical rain belt is quite sensitive to even small changes in global temperatures.
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