Atmospheric temperature is one of the most
important climate variables. This observational study presents
detailed descriptions of the temperature variability
imprinted in the 9-year brightness temperature data
acquired by the Advanced Microwave Sounding Unit-
Instrument A (AMSU-A) aboard Aqua since September
2002 over tropical oceans. A non-linear, adaptive method
called the Ensemble Joint Multiple Extraction has been
employed to extract the principal modes of variability in
the AMSU-A/Aqua data. The semi-annual, annual, quasibiennial
oscillation (QBO) modes and QBO–annual beat in
the troposphere and the stratosphere have been successfully
recovered. The modulation by the El Nin˜o/Southern
oscillation (ENSO) in the troposphere was found and correlates
well with the Multivariate ENSO Index. The longterm
variations during 2002–2011 reveal a cooling trend
(-0.5 K/decade at 10 hPa) in the tropical stratosphere; the
trend below the tropical tropopause is not statistically
significant due to the length of our data. A new tropospheric
near-annual mode (period *1.6 years) was also
revealed in the troposphere, whose existence was confirmed
using National Centers for Environmental Prediction
Reanalysis air temperature data. The near-annual
mode in the troposphere is found to prevail in the eastern
Pacific region and is coherent with a near-annual mode in
the observed sea surface temperature over the Warm Pool
region that has previously been reported. It remains a
challenge for climate models to simulate the trends and
principal modes of natural variability reported in this work.