| On the heels of E1 , its opposite, La may soon arrive. In a Weekly Update, scientists
at the NOAA Climate Prediction Center reported that as the 2006-2007 E1 faded, surface and subsurface ocean temperatures
have rapidly decreased. Recently, cooler-than-normal water temperatures have
developed at the surface in the east-central equatorial Pacific, indicating a
possible transition to La conditions.
Typically, during the U.S. spring and summer months, La conditions do not significantly impact overall inland temperature and precipitation (雨水的降落) patterns, however, La episodes often do have an effect on Atlantic and Pacific hurricane activity. "Although other scientific factors affect the hurricanes, there tends to be a greater-than-nor-mal number of Atlantic hurricanes and fewer-than-normal number of eastern Pacific hurricanes during La events," said retired Navy Vice Adm. Conrad C. Lautenbacher, Ph.D., under secretary of commerce for oceans and atmosphere and NOAA administrator. "During the winter, usual La impacts include drier and warmer-than-average conditions over the southern United States." "NOAA's ability to detect and monitor the formation, duration and strength of E1 and La events is enhanced by continuous improvements in satellite and buoy observations in the equatorial Pacific," Lautenbacher added. "These observing systems include the TAO/TRITON moored and Argo drift buoys, as well as NOAA's polar orbiting satellites." La conditions occur when ocean surface temperatures in the central and east-central equatorial Pacific become cooler than normal. These changes affect tropical rainfall patterns and atmospheric winds over the Pacific Ocean, which influence the patterns of rainfall and temperatures in many areas worldwide. "La events sometimes follow on the heels of E1 conditions," said Vernon Kousky, research meteorologist at the NOAA Climate Prediction Center. "It is a naturally occurring phenomenon that can last up to three years. La episodes tend to develop during March-June, reach peak intensity during December-February, and then weaken during the following March-May." "The last lengthy La event was 1998-2001, which contributed to serious drought conditions in many sections of the western United States," said Douglas Lecomte, drought specialist at the NOAA Climate Prediction Center. NOAA will issue the U.S. Spring Outlook on March 15, and its Atlantic Hurricane Season Outlook in May. Both outlooks will reflect the most current La forecast. "While the status of E1 /La is of vital importance to our seasonal forecasts, it is but one measure we use when making actual temperature and precipitation forecasts," said Kousky. |