Thermodynamic and dynamic influences in the Far East‐Okhotsk region on stagnant Meiyu‐Baiu

Abstract

Westerly perturbation is enlarged over the Far East‐Okhotsk region in late June and early July and is associated with the largest land‐sea heating contrast surrounding the Sea of Okhotsk. The corresponding characteristics in the lower troposphere are southward deepening of the cold low over northeastern China, and intensification of the Okhotsk high. Coincidentally, the Meiyu‐Baiu coupled with the western North Pacific (WNP) subtropical high is nearly stagnant during this period. By simulations using a global climate model with an intensified Okhotsk surface high in response to cooling Sea of Okhotsk, it is suggested that the enhanced thermal contrast over the Far East‐Okhotsk region can generate an obstacle to Meiyu‐Baiu poleward migration. Corresponding to the intensified Okhotsk high, the WNP subtropical high is strengthened by the high ridge over Taiwan. The East Asian midlatitude westerly jet stream in the northern flank of the WNP subtropical high also strengthens; the consequently enhanced midtropospheric warm temperature advection can regulate the latitude position of the Meiyu‐Baiu. The wave source generated in the upper troposphere is located over the midlatitude WNP (anomalous cyclone) bordering the Sea of Okhotsk, whereas that in the lower troposphere is related to the strengthened westerly in the northern WNP subtropical high. The wave activity propagation consistently indicates the strengthening and equatorward confinement of the westerly jet. Therefore, the intensified Okhotsk high and enlarged westerly perturbation beginning in late June are suggested as an inherently geographic limit of the Far East‐Okhotsk region in regard to Meiyu‐Baiu migration.

Persistent precipitation extremes in the Yangtze River Valley prolonged by opportune configuration among atmospheric teleconnections

“…The confrontation between these air masses of opposite natures substantially sharpens the meridional gradient of equivalent potential temperature (shadings in Figure b,c), facilitating the formation of a typical Mei‐Yu front there (Ding and Chan, ). Sandwiched between the WPSH and the Okhotsk high, this front is forced to stay nearly put around the YRV (Figure b–d, also see Wu ()). In this context, continuous elevation of abundant moisture by this quasi‐stationary front leads to PPEs in the YRV.…”

Role of Indochina Peninsula Topography in Precipitation Seasonality over East Asia

“…In the early summer monsoon over South Asia (May-June, 50 • E-100 • E), the northward advancement of the lower tropospheric monsoonal westerly (color shadings, Figure 3a) competes with the mid-to-upper tropospheric westerly (contour lines, Figure 3a) over the southern Tibetan Plateau; the latter westerly weakens with the onset of the former westerly (over the latitude around 25 • N), which corresponds with the beginning of the summer monsoon. By contrast, in the East Asia-WNP (110 Figure 3b), the vertical westerly coupling (i.e., lower-level westerly along the northern flank of the WNP high and upper-level westerly jet stream) is a control factor of the Meiyu-Baiu [29,38]. In both South Asia (Figure 3a) and the East Asia-WNP (Figure 3b), the mid-to-upper tropospheric easterly reaches its northern end in late July (contour line u = 0), thereafter retreating, with an approximately symmetric seasonal variation.…”