Abstract
Abstract. We used a global long-term (1995–2015) data set of total column water vapour (TCWV) derived from satellite observations to quantify to which extent the temporal patterns of various teleconnections can be identified in this data set. To our knowledge, such a comprehensive global TCWV data set was rarely used for teleconnection studies. One important property of the TCWV data set is that it is purely based on observational data. We developed a new empirical method to decide whether a teleconnection index is significantly detected in the global data set. We compared our new method to well-established hypothesis tests and found good agreement with the results of our approach. Based on our empirical method more than 40 teleconnection indices were significantly detected in the global TCWV data set derived from satellite observations. In addition to the satellite data we also applied our method to other global data sets derived from ERA-Interim. One important finding is that the spatial patterns obtained for the ERA TCWV data are very similar to the observational TCWV data set indicating a high consistency between the satellite and ERA data. Moreover, similar results are also found for two selections of ERA data (either all data or mainly clear-sky data). This finding indicates that the clear-sky bias of the satellite data set is negligible for the results of this study. However, for some indices, also systematic differences in the spatial patterns between the satellite and model data set were found probably indicating possible shortcomings in the model data. For most “traditional” teleconnection data sets (surface temperature, surface pressure, geopotential heights and meridional winds at different altitudes) a smaller number of significant teleconnection indices was found than for the TCWV data sets, while for zonal winds at different altitudes, the number of significant teleconnection indices (up to > 50) was higher. The strongest teleconnection signals were found in the data sets of tropospheric geopotential heights and surface pressure. In all global data sets, no “other indices” (solar variability, stratospheric AOD or hurricane frequency) were significantly detected. Since many teleconnection indices are strongly correlated, we also applied our method to a set of orthogonalised indices, which represent the dominant independent temporal teleconnection patterns. The number of significantly detected orthogonalised indices (20) was found to be much smaller than for the original indices (42). Based on the orthogonalised indices we derived the global spatial distribution of the cumulative effect of teleconnections. The strongest effect on the TCWV is found in the tropics and high latitudes.
Highlights
It has been known for a long time that weather at one location can be linked to weather at a far distant location (Walker and Bliss, 1932; Bjerknes, 1966, 1969; Wallace and Gutzler, 1981; Nigam and Baxter, 2015; Feldstein and Frantzke, 2017, and references therein)
We investigated if and how strong the temporal patterns of a large set of teleconnection indices can be identified in the spatio-temporal variability of a global data set of the total column water vapour (TCWV) from 1995–2015 derived from satellite observations
Another important achievement of this study is the development of a new empirical method to decide whether a teleconnection index is significantly detected in the global data set
Summary
It has been known for a long time that weather at one location can be linked to weather at a far distant location (Walker and Bliss, 1932; Bjerknes, 1966, 1969; Wallace and Gutzler, 1981; Nigam and Baxter, 2015; Feldstein and Frantzke, 2017, and references therein). More details about these and further methods can be found in Horel (1981), Wallace and Gutzler (1981), Barnston and Livezey (1987), Thompson and Wallace (1998), Feldstein and Frantzke (2017) and references therein If these methods are applied, the derived teleconnection time series and spatial patterns depend on the selected region of the globe. Most of such studies use pressure or geopotential heights and are confined to midlatitude and Arctic regions in the Northern Hemisphere because of the barotropic conditions in the tropical latitudes.
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