Blocking Highs Research Articles

Relationship between the East Atlantic teleconnection pattern and the spring dust storm in northern China. Part‐I: Impacts of components of the atmospheric circulation over Eurasia on dust storm dynamic power—Spring gales

AbstractSpring gale is a dynamic power for DSs (DSs), which presents a close connection with the DSs of northern China. Both display declining trends during the past 68 years (1954–2021). In this study, the influencing factors of spring gales and DSs around northern China and possible adjustment functions of the East Atlantic (EA) teleconnection pattern have been investigated. It was found that the major systems controlling spring gales include the North Polar vortex (NPV), mid–high‐latitude blocking highs (BHs), air pressure status of the Tibetan Plateau (TP) over the Eurasian continent, India–Burma trough (IBT) and western Pacific subtropical high (WPSH). Under synthetic atmospheric circulation conditions of an enlarged NPV, lower air pressure over the TP, a strong IBT, and a southeastward‐retreated WPSH, spring gales increase, and the frequency of DS occurrence is increased, and vice versa. Additionally, spring gales are also negatively affected by BHs. The most important is the Baikal BH, which has influence not only in previous seasons but also in the contemporary spring. Furthermore, the NPV and IBT have close negative correlation with the EA pattern, whereas the TP and WPSH have positive correlation with the EA pattern both in previous seasons and in the contemporary spring. A high‐pitched EA pattern results in a strong western current north of Lake Baikal, which may prohibit the expansion of the NPV in the sector of northern China. A shrunk NPV means infrequent cold air attacks and decreased gales and DSs.

Circulation system configuration characteristics of four rainfall patterns in summer over the East China

In this study, the simultaneous atmospheric circulation system configuration characteristics of the four rainfall patterns (FRP) over the East China during the period 1951–2015 are analyzed in order to investigate their formation mechanisms. The results confirm that the FRP possess obvious differences in the upper-level, middle-level, and lower-level troposphere. In northern China rainfall pattern (NCP) years, the East Asian subtropical westerly jet stream (EAJS) shows a northward trend, with a higher intensity than normal; the blocking high (BH) in the mid-high latitudes is inactive; and the western Pacific subtropical high (WPSH) tends to be stronger, with a location to the north of its normal position. The East Asian summer monsoon (EASM) is stronger, which promotes vapor transport to northern China, and this leads to increased rainfall. In intermediate rainfall pattern (IRP) years, the EAJS position is close to that in normal years; the BH is inactive; the WPSH tends to be weaker, with a location to the east of its normal position; and the EASM is stronger, which is conducive to increased rainfall over the Huaihe River Basin. In Yangtze River rainfall pattern (YRP) years, the circulations are found to be almost opposite in their features to those in NCP years. In South China rainfall pattern (SCP) years, the circulations are found to be almost opposite in their features to those in IRP years. This leads to increased rainfall over South China. Therefore, the different circulation system configuration characteristics lead to the different rainfall patterns.

Features of Rossby Wave Propagation Associated with the Evolution of Summertime Blocking Highs with Different Configurations over Northeast Asia

Abstract This study categorized blocking high (BH) episodes during the boreal summer in northeast Asia (40°–70°N, 100°–150°E) into four types according to their wave-breaking features at the dynamic tropopause on the initial day: anticyclonic warm, cyclonic warm, anticyclonic cold, and cyclonic cold. Based on the results of a statistical analysis, it was shown that 1) the anticyclonic-warm type tended to occur in eastern Russia (55°–70°N, 127.5°–142.5°E), whereas the other three types preferentially occurred in the vicinity of Lake Baikal; 2) the two cold types generally were more common than the two warm types; and 3) the average life spans of the two anticyclonic types were longer than those of the two cyclonic types. According to a composite analysis, the four BH types were preceded by different wave train–like anomalies over the Eurasian continent over approximately one week. Correspondingly, each BH type was characterized by distinct Rossby wave propagation features. Interestingly, a northeastward propagation of the Rossby waves around the BHs was evident in the two cyclonic types. This feature differs from the quasi-meridional propagation of Rossby waves originating from suppressed convection activity over subtropical regions documented in previous studies. This study also found that every BH type was accompanied by distinct precipitation anomaly patterns over East Asia, highlighting the necessity of classifying BHs.

Remote impact of blocking highs on the sudden track reversal of tropical cyclones

Previous work showed that some tropical cyclones (TCs) in the western Pacific Ocean undergo sudden track reversal, and the onset, maintenance and decay of blocking highs (BHs) coexisted with 19 of the studied TCs with sudden track reversal. In these cases, the phase relations between the BH, the continental high (CH), the subtropical high (SH) and the suddenly reversed TCs could be classified into types A, B, C and D. Types C and D were the focal point of this follow-up study, in which Typhoon Pabuk (2007) and Lupit (2009) were employed to conduct numerical simulations. The results showed that the reversed tracks of Pabuk (2007) and Lupit (2009) could have been affected by the BH, particularly in terms of the turning location and the trend of movement after turning. Specifically, the two main features for Pabuk (2007) in the BH perturbations were the deflection of its turning point and a distinct anticlockwise rotation. Lupit (2009) deviated to the southwest and finally made landfall in the Philippines, or experienced further eastward movement, in the perturbed BH. The impact mechanisms can be attributed to the change in the vorticity field transported from the BH, leading to an intensity variation of midlatitude systems. BHs may have a positive feedback effect on the strength of the westerly trough (TR), as indicated by a weakened and strengthened TR corresponding to negative and positive BH perturbations, respectively.

The Relevance of the Location of Blocking Highs for Stratospheric Variability in a Changing Climate

Abstract Previous research shows that blocking highs (BHs) influence wintertime polar stratospheric variability through the modulation of the climatological planetary waves (PWs) depending on the BH location. BHs over the Euro-Atlantic sector tend to enhance the upward PW propagation, and those over the northwestern Pacific Ocean tend to reduce it. Future changes are examined in the response of the wave activity flux to the BH location and their relationship with wintertime stratospheric variability in transient simulations of ECHAM/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC). After it is verified that EMAC can reproduce qualitatively well the geographical dependence of the BH influence on PW activity injection, it is shown that this dependence does not change in the future. However, an eastward shift of the pattern of the BH influence on PW propagation over the Pacific, a farther eastward extension of the pattern over the Atlantic Ocean, and an intensification of the wavenumber-1 component of the interaction between climatological and anomalous waves are detected. Changes in the upper-tropospheric jet and an intensification of the wavenumber-1 climatological wave due to a strengthening of the Aleutian low agree with these variations. The spatial distribution of future BHs preceding extreme polar vortex events is also affected by the slight modifications in the wave activity pattern. Hence, future BHs preceding strong vortex events tend to be more concentrated over the Pacific than in the past, where BHs interfere negatively with wavenumber-1 climatological waves. Future BHs prior to major stratospheric warmings are located in a broader area than in the past, predominantly over an extended Euro-Atlantic sector.

Geographical Dependence Observed in Blocking High Influence on the Stratospheric Variability through Enhancement and Suppression of Upward Planetary-Wave Propagation

Abstract Previous studies have suggested the importance of blocking high (BH) development for the occurrence of stratospheric sudden warming (SSW), while there is a recent study that failed to identify their statistical linkage. Through composite analysis applied to high-amplitude anticyclonic anomaly events observed around every grid point over the extratropical Northern Hemisphere, the present study reveals a distinct geographical dependence of BH influence on the upward propagation of planetary waves (PWs) into the stratosphere. Tropospheric BHs that develop over the Euro-Atlantic sector tend to enhance upward PW propagation, leading to the warming in the polar stratosphere and, in some cases, to major SSW events. In contrast, the upward PW propagation tends to be suppressed by BHs developing over the western Pacific and the Far East, resulting in the polar stratospheric cooling. This dependence is found to arise mainly from the sensitivity of the interference between the climatological PWs and upward-propagating Rossby wave packets emanating from BHs to their geographical locations. This study also reveals that whether a BH over the eastern Pacific and Alaska can enhance or reduce the upward PW propagation is case dependent. It is suggested that BHs that induce the stratospheric cooling can weaken the statistical relationship between BHs and SSWs.