Unraveling the Teleconnection Mechanisms that Induce Wintertime Temperature Anomalies over the Northern Hemisphere Continents in Response to the MJO

Abstract

Significant extratropical surface air temperature variations arise as a result of teleconnections induced by the Madden–Julian oscillation (MJO). The authors elucidate the detailed physical processes responsible for the development of temperature anomalies over Northern Hemisphere continents in response to MJO-induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique. A quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating Rossby wave train. Over East Asia, a local Hadley circulation causes adiabatic subsidence following MJO phase 3 to be a main driver for the warming. Meanwhile, for North America and eastern Europe, horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling. A ray-tracing analysis illustrates that Rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over North America and a faster wavenumber 4 affects surface temperature over eastern Europe. Although recent studies demonstrate the impacts of the Arctic Oscillation, Arctic sea ice melting, and Eurasian snow cover variations on extremely cold wintertime episodes over the NH extratropics, the weather and climate there are still considerably modulated through teleconnections induced by the tropical heat forcing. In addition, the authors show that the MJO is a real source of predictability for strong warm/cold events over these continents, suggesting a higher possibility of making a skillful forecast of temperature extremes with over 1 month of lead time.

Quantifying Regional Sensitivities to Periodic Events: Application to the MJO

“…This is expected: The remote MJO must communicate its signal to North America through a control on larger‐scale circulations in order to influence weather at the surface. Seo et al () show that low‐level horizontal advection is the dominant process through which the MJO influences temperatures over this region. Figure c shows the 2‐D composite for TMAX area averaged (as in McKinnon et al, ) over the region enclosed by the magenta box in Figures a and b.…”

“…Warm anomalies over this region occur around 10 days after MJO Phase 3. When this occurs, Seo et al () show that the circulation pattern characterized by an anomalous low over Alaska and high over the Atlantic encourages warm air advection over eastern North America, which is situated between the two circulation anomalies. Figure e, which shows the diagonal means of the 2‐D composites for TMAX and 500‐hPa geopotential height (Figure d) for the boxed eastern North America region, shows this pattern.…”

A Cautionary Note on the Long‐term Trend in Activity of the Madden‐Julian Oscillation During the Past Decades

“…The Authors. The increased frequency of active MJO phases over the MC and WP in the recent decades, therefore, could promote more frequent occurrence of positive Pacific North America patterns and thus lead to Arctic warming Seo et al, 2016;Yoo et al, 2011;Yoo et al, 2012), featuring a so-called tropically excited Arctic warming mechanism to interpret the recent Arctic amplification (e.g., Lee, 2014). large portion of the Arctic (e.g., Yoo et al, 2011).…”

Intra‐seasonal characteristics of wintertime extreme cold events over South Korea

“…The wave‐like pattern is found around East Asia and the North Pacific. It looks like the Rossby wave propagation induced by enhanced local Hadley circulation initiated from a convection over the Indian Ocean for MJO phases 2–3 (Seo et al ). The upper‐tropospheric trough of the propagating Rossby wave is located on Korea aloft.…”