Oral or Poster

IAMAS

M05 - Advances in Dynamic Meteorology

Observed changes of atmospheric fluctuations with different time scales in extratropical boreal winter

As an important link between the Arctic and the mid-latitudes, atmospheric fluctuations on different timescales show distinct spatiotemporal structures and different energy distributions. The interactions between multiscale disturbances and the background flow can cause persistent anomalies on global and reginal scales. In this study, we decompose the eddy components into low-frequency (LF: 30-90 days), intermediate- frequency (IF: 10-30 days), and high-frequency (HF: <10 days) parts and study the variations in characteristics of atmospheric fluctuations in boreal winter before and after the 1990s. Our work finds that IF and LF fluctuations are the dominant time scales of the changes. The zonal part of the fluctuations in the East Asia-North Pacific (EA-NP) region has weakened, whereas the dipole fluctuations in the Eastern North America- North Atlantic (ENA-NA) region and the wave-train patterns in the Norwegian Sea- Ural Mountains (NS-UM) region both enhanced. The speed of the LF waves has decelerated obviously, but the eastward propagation of the IF in the NS-UM region has accelerated. In vertical direction, the downstream propagation to the stratosphere of IF and LF with zonal structure have strengthened (weakened) with the enhancement (reduction) of the westward tilt. We further investigate that the increase in the background flow favors the maintenance and propagation of zonal structure of LF fluctuations; whereas an increase in zonal wind is detrimental to the maintenance of north-south type dipole structures.