Anomalous precipitation signatures of the Arctic Oscillation in the time-variable gravity field by GRACE

Abstract

The Arctic Oscillation (AO) controls winter climates in the Northern Hemisphere to a large extent. Positive AO brings lower/higher surface temperature and higher/lower precipitation in high/middle latitude regions, and negative AO reverses the situation. In this study, we investigate signals of anomalous precipitations caused by AO using the data of the Gravity Recovery and Climate Experiment (GRACE) satellites. Wintertime mass deviations inferred from GRACE in the high and middle (boundary ∼55N) latitude regions in Eurasia showed highly positive and negative correlations with the AO indices. This possibly reflects the northward and southward shift of the centre of winter precipitation during the positive and negative phases of AO, respectively. Wintertime mass deviations also showed positive and negative correlations with the AO indices in the northern and southern parts of Greenland, respectively, but the boundary was further to the north, say ∼75N. AO redistributes the water mass as much as ∼1000 Gt between high and middle latitude regions in the Northern Hemisphere. Such mass redistribution causes significant surface deformation by loading large enough to be observed by Global Positioning System. This also causes the shift of the Earth's rotation axis especially towards the Greenwich Meridian large enough to be detected with space geodetic techniques. AO signatures are also derived from the empirical orthogonal function (EOF) analysis, as the first leading mode of GRACE data after excluding seasonal, linear and quadratic components. The EOF analysis also demonstrates that though AO is a main contributor to bring anomalous winter precipitation in the Northern Hemisphere as a whole, in North America, however, influence of the El Niño and Southern Oscillation on the winter precipitation anomaly is larger than AO.