Tropical-extratropical teleconnections and atmospheric drivers of European drought events

Atmospheric dynamics are important in tropical-extratropical teleconnections. Using maximum covariance analysis (MCA), we investigate the leading modes of covariability between the tropical outgoing longwave radiation and the extratropical geopotential height. Using observed data, the leading mode of covariability on the seasonal timescale is associated with the El-Ni~no Southern Oscillation. Using a Met Office climate model (GC3) control run, although the leading tropical mode is still ENSO, the extratropical pattern shows large differences in the North Pacific-American region. GC3 has a large North Pacific jet bias, which according to ray tracing can affect wave propagations from the tropics. Using a barotropic model with the same ENSO tropical forcing but linearized upon the different basic states of reanalysis and GC3, the largest differences in the response are in the North Pacific-American region and agree with the MCA differences. The result is also supported by baroclinic experiments. Our finding may contribute to resolving the signal-tonoise paradox in some climate predictions. Next, we test the mechanism of influence from the tropics to European droughts, to find potential tropical drivers of Rossby waves that are consistent between observations and the idealized models. We identify a northward shift in the tropical Atlantic precipitation and a weakening of the tropical eastern Pacific precipitation, which significantly influence about 60% of European drought events.