Unit 2 Reading: Observing Climate Variability

Have you ever noticed that some places tend to experience a drought one year and a devastating flood the next? Or that there might be several unusually cold winters followed by several very warm winters?

Climate variability can wreak havoc around the world every year. Dramatic year-to-year shifts in weather can have unanticipated consequences for human activities. For example, in summer 2002, torrential rains in Europe left many cities and villages under water and caused millions in damage. The following summer, a heat wave parched southern European crops. How might we better understand these short-term climate changes? Ideally, a better understanding of how frequently things change might provide us clues as to how to prepare for future climate variability.

We can identify patterns of climate variability by examining data recorded from year to year, and comparing data from a given year with a long-term average.

This is how we find climate anomalies. An anomaly is the difference between a long-term average and the value of a meteorological field (pressure, precipitation, or temperature, for example) at a given time. For example, to identify patterns of climate variability in the South Pacific, scientists examine data depicting cyclic changes in temperature, precipitation, or pressure recorded from an array of 70 moored (anchored) buoys that stretch across the Pacific from the Galapagos to New Guinea. They compare these data to the long-term average. Scientists and students have been using this array, called the TAO/TRITON array, for the past 25 years to gather information about climate variability. TAO/TRITON covers a relatively inaccessible part of the world, where there are few islands and land masses to support terrestrial weather stations. The buoys transmit weather data via satellite each day. The 15 buoys on the western end of the array are maintained by Japan; these are the TRITON buoys (which stands for Triangle Trans-Ocean Buoy Network). The other 55 buoys are TAO buoys (Tropical Atmosphere Ocean) and are maintained by the National Buoy Data Center at the U.S. National Oceanic and Atmospheric Administration (NOAA).

If you want to see the data collected yesterday, go to http://www.pmel.noaa.gov/tao/jsdisplay/. The figure below and to the right shows a map of buoy data that you will find when you click on the link. In this map, you are looking at an average of data from January 2001 (rather than current data, which you would find if you click on the link). This map shows average temperature and wind (top panel) and temperature and wind anomalies (bottom panel). Notice that the maps show only data for the tropical Pacific. The arrows on each map represent the wind data. In the top panel, the arrow shows the direction of prevailing wind during January 2001. The longer the arrow, the stronger the wind. In the bottom panel, the arrows tell us how the wind is different from normal. So, for example, if the arrows are very small, it indicates that the wind in January 2001 was very close to average.
If you see an arrow that is long, it indicates that the wind in this month is quite different than normal. If the arrow in the second panel is long and pointed in the same direction as the arrow in the same place in the top panel, that would suggest that the average wind speeds are in the same direction but faster than normal. If the arrow in the second panel is long but pointed in the opposite direction as the arrow in the same place in the top panel, it would suggest that the average wind is much slower (or, perhaps, in the opposite direction) than normal.

If we wanted to examine how frequently the anomalies cycle between warm and cold, we could look at maps similar to this one, showing monthly average data over many years. The Unit 2 study guide will give you more practice looking at these types of maps.