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| Titel |
Upper tropospheric and lower stratospheric ENSO signal derived from GPS radio occultation temperature |
| VerfasserIn |
B. Scherllin-Pirscher, C. Deser, S.-P. Ho, C. Chou, W. Randel, Y.-W. Kuo |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065038
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| Zusammenfassung |
| We use radio occultation (RO) temperature data from CHAMP, GRACE, and
Formosat-3/COSMIC (F3C) to detect the El Niño-Southern Oscillation (ENSO) signal in the
troposphere and lower stratosphere. Merging data of all satellites, we calculate monthly mean
climatologies with a horizontal resolution of 5° latitude and 5° longitude and a vertical
spacing of 100Â m from the surface up to 20Â km. A sufficient number of profiles (>40000
profiles per month) is available since August 2006, when F3C measurements became
available.
The investigation of temperature anomalies (anomalies are obtained from subtracting the
mean annual cycle) in the equatorial region up to 16Â km yields a natural split into
zonal-mean and eddy (deviations from the zonal-mean) ENSO components. EOF1 is
dominated by the zonally-symmetric component where positive sea-surface temperature
anomalies come along with warm tropospheric temperatures. It explains almost 70 %
of total variance. The corresponding PC1 is highly correlated with the Nino 3.4
index (correlation equals 0.85 at a lag of 3Â months). EOF2, which is dominated by
the eddy ENSO signal, explains more than 7 % of total variance. PC2 is almost
perfectly correlated with the Nino 3.4 index (correlation equals 0.95 at a lag of
0Â months). Due to these findings we separate data into zonal-mean and eddy temperature
fields and apply PCA and multiple linear regression analysis separately to both
fields.
Taking advantage of the high vertical resolution of RO data, we show that the node of the
positive and negative zonal-mean ENSO signal occurs around the tropopause. Relative to the
surface ENSO signal, the atmospheric zonal-mean signal is lagged by 3Â months. At low
latitudes equatorwards of about 30°, the eddy ENSO signal is characterized by an
east-west dipole centered slightly westward to the date line. The vertical node to
a reversed east-west dipole occurs at approximately 14.5Â km altitude, which is
well below the tropopause. At tropospheric mid latitudes, the eddy ENSO signal is
out-of-phase with the low latitude signal. The vertical transition of positive/negative ENSO
responses occurs at approximately 11Â km in the southern hemisphere, slightly lower in
the northern hemisphere. These coherent signals are evidence that atmospheric
zonal-mean and eddy ENSO responses are modulated through different physical
mechanisms. |
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