Minghao Yang

The mid‐tropospheric winter North Pacific storm track (NPST) underwent an interdecadal transition from weak to strong in the mid‐1980s and exhibited a significant intensification trend. Using climate model outputs, this study investigates the contributions of external forcing and internal variability to the NPST intensification. The result indicates that externally forced NPST trends in historical simulations are not significant. Thus, the dominant cause of the NPST intensification trend is internal variability rather than external forcing. Large‐ensemble simulations reveal that negative‐phase western Pacific (WP)‐like teleconnection patterns are closely linked to the NPST intensification through the acceleration of the mid‐latitude westerlies. In addition, the strengthening NPST is significantly related to a poleward‐shifted Aleutian Low. In contrast, the low‐frequency variability of the East Asian winter monsoon (EAWM) and tropical sea surface temperature anomalies is not significantly related to the NPST intensification.

Employing orographic perturbation experiments from a state‐of‐the‐art climate model, this study investigates the topographic forcing associated with the Tibetan–Iranian Plateau (TIP) in modulating Northern Hemisphere boreal winter blocking frequency. The results show that TIP‐related topographic forcing profoundly impacts blocking frequency, with distinct roles of mechanical and thermal components. The increased hemispheric‐mean blocking under full TIP‐related topographic forcing is dominantly attributed to its mechanical forcing, while localized slight reductions stem from its thermal forcing. In general, the response of Northern Hemisphere winter blocking to TIP‐related topographic forcing is dominated by mechanical forcing. TIP‐related mechanical forcing favors blocking occurrence, particularly over Europe and the Ural region, via strengthened stationary waves and positive geopotential height tendencies induced by weakening synoptic‐scale transient eddies. In addition, decelerating background westerly wind and reducing the meridional gradient of potential vorticity also provide favorable conditions for the formation of blocking. In contrast, TIP‐related thermal forcing mildly suppresses North Pacific blocking, primarily through weakened stationary waves and altered background lower‐level temperatures.

This study investigates the modulation of the Madden‐Julian Oscillation (MJO) by El Niño during decaying springs, using reanalysis data. El Niño events are categorized into fast‐decaying (FD) and slow‐decaying (SD) types based on their decaying rate. In FD El Niño decaying springs, MJO circulation and convection weaken significantly over the central Pacific. In contrast, they are substantially enhanced under SD El Niño conditions. The stronger westerly anomalies, positive moisture anomalies, and anomalous ascending motion over the central Pacific induced by SD El Niño result in a weaker low‐frequency background moisture zonal gradient and a stronger MJO circulation. As a result, both zonal and vertical moisture advection are much stronger under SD El Niño conditions, leading to more pronounced lower‐tropospheric moistening east of the MJO convection center. Thus, MJO activity is enhanced over the central Pacific.

The most active synoptic‐scale disturbances in Eurasia are embedded within the Siberian storm track. This paper investigates the linkage between the winter Siberian storm track (WSST) and the winter precipitation in China and explores the underlying physical processes. The results show that an intensified WSST is associated with a decrease in winter precipitation along the southeast coast of China and in the East China Sea on the interannual scale. The anomalous low‐level northerly winds over eastern China and upper‐level positive vorticity anomalies over the East China Sea, accompanied by the subsidence, exert an inhibitory effect on precipitation. The anomalous moisture flux divergence related to northerly winds reduces the moisture supply. The interaction between WSST and mean flow may sustain the anomalous large‐scale atmospheric circulation and baroclinicity. In addition, synoptic‐scale disturbances originating from the WSST region propagate to the East China Sea, forming cyclonic circulation anomalies that are unfavorable for precipitation.

With a particular focus on the Siberian storm track, this study provides new insights into variations in the warm Arctic–cold Eurasia (WACE) temperature anomaly pattern by using reanalysis data. The results show that the Siberian storm track has a significant out-of-phase relationship with both the WACE pattern and Ural blocking on the interannual time scale. The strengthened WACE pattern can weaken the Siberian storm track through a suppression of the low-level atmospheric baroclinicity over midlatitude Eurasia. The weakened Siberian storm track can contribute to the WACE pattern through feedback forcing from synoptic-scale eddies, which can also create favorable conditions for the development of Ural blocking. Composite temporal evolution reveals that the strongest cold Arctic–warm Eurasia pattern is preceded by the peak of the Siberian storm track. The Ural cyclonic circulation reaches its maximum amplitude on the peak day of the Siberian storm track strength and continues to persist for one day with the maximum amplitude due to the feedback forcing resulting from the Siberian storm track. On the intraseasonal time scale, the occurrence of the Siberian storm track activity can serve as an early indication of the diminished Ural blocking and WACE pattern. Significance Statement: Because of the high impacts of the warm Arctic–cold Eurasia (WACE) pattern on public safety, socioeconomic development, and the economy, it is crucial to enhance our understanding of variations in the WACE pattern. This paper specifically investigates the impact of internal atmospheric variability on the WACE pattern, focusing on a pronounced negative correlation between the Siberian storm track and the WACE pattern. Daily composites also reveal that Siberian storm track activities can promote a strong cold Arctic–warm Eurasia pattern by maintaining the strength of the quasi-stationary Ural cyclonic circulation. As such, paying close attention to Siberian storm track activities may hold the promise to improve the prediction of the strength of the WACE pattern.

This paper utilizes reanalysis data and statistical methods to elucidate the physical mechanisms of intraseasonal variations of precipitation over southern China during the boreal winter, as well as the two primary factors influencing these variations. Anomalous southerly (northerly) wind over southern China will result in the strong moisture convergence (divergence) in enhanced (suppressed) scenarios, and the stronger positive (negative) horizontal advection of absolute vorticity at upper troposphere induces the anomalous ascending (descending) motion in enhanced (suppressed) scenarios. The Madden–Julian oscillation (MJO) in the tropics and a wave train over the North Atlantic and Eurasia with four activity centres in the mid–high latitudes (referred as NAE‐wave train) are the two primary factors that modulate the intraseasoanl precipitation over southern China. The intraseasonal circulation induced by MJO and NAE‐wave train exhibits distinct features, resulting in different physical mechanisms of their influences. The moisture flux divergence anomalies over southern China associated with MJO mainly stem from the meridional moisture convergence, whereas the meridional moisture advection is the first contributor in the influence of NAE‐wave train. The anomalous vorticity advection at upper troposphere associated with MJO is primarily influenced by the meridional advection, but that associated with NAE‐wave train is dominated by the zonal advection. Anomalous precipitation induced by MJO is concentrated mainly over South China, while that caused by NAE‐wave train is primarily located in the mid–lower Yangtze River basin. Therefore, different phases locking of MJO and NAE‐wave train could lead to various precipitation anomalies over southern China.

By employing a state‐of‐the‐art global atmospheric general circulation model from the Global Monsoons Model Inter‐comparison Project, this study investigates the mechanical and thermal impacts of the Tibetan‐Iranian Plateau (TIP) on the North Pacific storm track (NPST). When the TIP‐associated mechanical forcing is removed, the winter NPST strengthens remarkably on the northern flank of its climatological maximum and becomes inconspicuously separated from storm track activities over the Asian continent. The midwinter suppression of the NPST is almost inapparent but still exists. In contrast, when TIP‐associated thermal forcing is absent, the winter NPST amplitudes weaken prominently on the north and west sides, and the midwinter suppression remains obvious. The mechanical and thermal impact of the TIP on the NPST are robust not only in winter but also in other seasons. Without the TIP‐associated mechanical forcing, the intensified winter NPST may be dependent on the weakened and widened upper‐level jet, strengthened atmospheric baroclinicity on the north side of climatological winter upper‐level jet, enhanced baroclinic energy conversion, and attenuated East Asian trough. In contrast, without the TIP‐associated thermal forcing, the weakened winter NPST may be determined by the strengthened and narrowed upper‐level jet, reduced atmospheric baroclinicity on the northern flank of upper‐level jet, decreased baroclinic energy conversion, and intensified East Asian trough.