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Climate Variability |
Monitoring Climate Change in the Tropics
The figure below shows the smoothed anomaly time series for three climate variables over the tropical oceans tropics (20 S to 20 N):
sea-surface temperature (SST), lower tropospheric temperature (TLT), and total atmospheric water vapor (WV).
Monthly averages are shown. The seasonal cycle has been removed, and the resulting anomaly time series
smoothed to reveal the interannual variability. In the tropics, SST, TLT, and WV are closely
coupled and exhibit relative scalings of WV/SST = 9.6%/K, W/LTT = 6.9%/K, and LTT/SST = 1.3, in
close agreement with the Clausius-Clapeyron relationship and a moist adiabatic lapse rate, and
predictions made by climate models (ref Mears et al, 2007, Santer et al 2005, 2007). In the figure,
the TLT curve has been scaled down by a factor of 1.3 to reflect this scaling.
The three largest El Niņos during the past 20 years are clearly evident as peaks in the time series
occurring during 1982-1983, 1987-1988, and 1997-1998, with the most recent one being the largest. El
Niņos are often followed by a La Niņa cycle characterized by cooler than normal temperatures. In 2007-2008,
a strong La Niņa event occured without a preceding strong El Niņo leading to reduced temperature and
water vapor.
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