Interannual Modulation of Northern Hemisphere Winter Storm Tracks by the QBO

Abstract

Storm tracks, defined as the preferred regions of extratropical synoptic‐scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi‐biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity. The North Atlantic storm track varies vertically with a downward shrinking (upward expansion) in easterly (westerly) QBO winters associated with the change of the tropopause height. These results not only fill the knowledge gap of QBO‐storm track relationship but also suggest a potential route to improve the seasonal prediction of extratropical storm activities owing to the high predictability of the QBO.

Progress in Simulating the Quasi‐Biennial Oscillation in CMIP Models

“…Shortcomings in the QBO amplitude below 20 hPa and the inadequate reach into the lowermost stratosphere of the QBOs in CMIP models may have consequences for those QBO teleconnections that have been found to correlate strongly with QBO winds near 50 hPa (Anstey & Shepherd, ; Son et al, ; Wang et al, ; Yoo & Son, ). In addition, if the QBO in zonal mean zonal wind does not reach far down enough, the temperature anomalies associated with the QBO, which are one‐fourth cycle out of phase with the wind anomalies, will likely be weak in the lowermost stratosphere.…”

“…It is only with the generation of ESMs now being run in CMIP6 that “high‐top” atmospheric models are more of a standard feature as faster supercomputers allow increased complexity and vertical resolution, with the latter being crucial for the simulation of the QBO (Geller et al, ; Richter et al, ). Additionally, the importance of stratospheric processes, including the QBO, to credible simulations of Earth system variability and skillful near‐term climate predictions has been demonstrated in numerous studies (Anstey & Shepherd, ; Scaife, Arribas, et al, ; Scaife, Athanassiadou, et al, ; Wang et al, ). Presently, there are sufficient QBO‐simulating ESMs to perform multimodel comparisons within the context of CMIP.…”

“…The QBO effects on the polar vortex manifest themselves in the troposphere as changes in the variability of the North Atlantic Oscillation (NAO), with the QBO West‐East difference resembling the positive phase of the NAO (Anstey & Shepherd, ). The QBO also affects extratropical storm tracks (Wang et al, ) and the Pacific subtropical jet (Garfinkel & Hartmann, ). In the tropics, studies have demonstrated the influence of the QBO on convection (Collimore et al, ; Liess & Geller, ), tropical cyclone tracks in the western North Pacific (Ho et al, ), and recently, several studies have found that in observations, the QBO modulates the amplitude of the Madden‐Julian oscillation (MJO) in boreal winter, and this influence is larger than that from El Niño–Southern Oscillation (ENSO) (Son et al, ; Yoo & Son, ).…”

Modulation of the MJO and North Pacific Storm Track Relationship by the QBO

“…A possible candidate that may be responsible for the observed spatial distribution difference in the NPST is the variation of the seasonal‐mean NPST modulated by the QBO. Over the region where the MJO most strongly modulates the NPST (40°–60°N, 130°E–120°W), the seasonal‐mean NPST is stronger during EQBO winters (Figure S1a in Wang et al, ); hence, there could be a stronger MJO modulation on the NPST. While during WQBO winters, the seasonal‐mean NPST is weaker especially between 180° and 150°W (Figure S1b in Wang et al, ); hence, the MJO modulation may be weaker.…”

“…Over the region where the MJO most strongly modulates the NPST (40°–60°N, 130°E–120°W), the seasonal‐mean NPST is stronger during EQBO winters (Figure S1a in Wang et al, ); hence, there could be a stronger MJO modulation on the NPST. While during WQBO winters, the seasonal‐mean NPST is weaker especially between 180° and 150°W (Figure S1b in Wang et al, ); hence, the MJO modulation may be weaker. This difference may lead to an elongated (separated) intraseasonal EKE distribution in EQBO (WQBO) winters.…”