Vorticity Advection Research Articles

Intraseasonal variations of precipitation over southern China during boreal winter and their two primary influencing factors

AbstractThis 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.

Quantifying the dynamic and synergistic effects of low and mid-latitudes signals on regional extreme climate events

Unlike previous studies solely focused on the influences of low or mid-latitudes signals on regional extreme events, this paper used the three-pattern decomposition of global atmospheric circulation (3P-DGAC), taking the 2018 hot summer in East Asia for example, to quantitatively reveal the dynamic and synergistic effects of low and mid-latitudes signals on regional extreme events. By analyzing the anomalous three-dimensional structure of atmospheric circulations in 2018 hot summer, we discovered that the local meridional circulation at low latitudes and zonal circulation at mid-latitudes both produced abnormal downdrafts in East Asia, which were consistent with the anomalous anticyclone in this region. Then, we investigated the relative vorticity advection combined with 3P-DGAC to uncover the dominant circulation patterns, and found the horizontal circulation at mid-latitudes and local meridional circulation at low latitudes were the major contributor to the anomalous anticyclone, accounting for 56% and 44% respectively. This result indicated the 2018 hot summer might be influenced by the synergistic effect of low and mid-latitudes signals. Finally, by investigating sea surface temperature anomaly (SSTA) and mid-latitudes wave train, we considered the tripole-like SSTA pattern in the North Atlantic and positive SSTA in Kuroshio and its extension area (K-KE) as the main causes of horizontal circulation anomalies, and the anomalous meridional circulation was related to the extremely late onset of South China Sea summer monsoon (SCSSM). This study provided a novel way to quantitatively study synergistic effects of low and mid-latitudes signals on regional extreme events.

What Controls the Subseasonal Precipitation Reversal Over the Western Tibetan Plateau in Winter?

AbstractThis study reveals a significant subseasonal reversal of precipitation on the western Tibetan Plateau (WTP) from a deficit in December to an increase in January and February (JF). Changes in vertical moisture advection induced by the dynamic effects contribute mostly to the subseasonal precipitation trend reversal. This process involves the reversal of the subseasonal westerly driven uplift, accompanied by the weakened (enhanced) subtropical westerly jet and anticyclonic (cyclonic) anomalies over the WTP in December (JF). Further analysis shows that the North Atlantic Tripolar‐like (NAT) sea surface temperature (SST) modes could regulate the sunseasonal winter precipitation reversal over the WTP. The spatially inconsistent changes in SST can result in subseasonal reversed turbulent heat flux anomalies over Iceland‐Scandinavia in December and JF. In particular, the suppressed turbulent heat flux over the extratropical Northeast Atlantic in December leads to significant descending motion and upper tropospheric convergence. The advection of absolute vorticity induced by convergent winds associated with the NAT favors the generation of Rossby wave sources over Iceland‐Scandinavia, which then enhances the wave activity fluxes propagation. However, there are no significant changes in wave sources over Iceland‐Scandinavia in JF. The discrepancies in wave propagation intensity over Iceland‐Scandinavia determine the changes in the atmospheric pattern over the WTP, with anomalous anticyclone in December and cyclone in JF, and ultimately lead to the precipitation reversal. Furthermore, our results show that the suppressed transient eddies over the Atlantic storm track in JF may also contribute to the weakened wave propagation over Iceland‐Scandinavia.

Diverse relationship between the tropical night in South China and the water vapor transport over the South China Sea and the plausible causes

South China (SC) frequently suffers from tropical night (TN), which features extreme high nighttime temperature with abnormal high humidity usually. This study explores the relationship between the TN in SC and the water vapor transport (WVT) over the South China Sea (SCS), an important water vapor source. 64% and 36% of the TN occurs under abnormally increased and decreased SCS WVT (named positive and negative SCS-WVT cases), manifesting their diverse relationship. The positive SCS-WVT cases feature above-normal humidity and subsidence over SC, favoring TN via adiabatic heating, longwave radiation and sensible heat persistently from day to night. The negative SCS-WVT cases feature strong subsiding anomaly over SC, which not only induces adiabatic heating, but also reduces the cloud cover, increases the daytime solar insolation and provides pre heating for TN.The diverse relationship between the TN in SC and SCS WVT is modulated by an anomalous anticyclone over the western North Pacific. For positive SCS-WVT cases, the anticyclone is related to two suppressed convection originating from the southwest and south of the subtropical high and moves westward. The anticyclone is centered east of the SCS on TN onset, inducing anomalous southerly SCS WVT. For negative SCS-WVT cases, the anticyclone is related to a suppressed convection originating from the southwest of the subtropical high and moves northwestward. The anticyclone is centered northwest of the SCS on TN onset, inducing anomalous northerly SCS WVT. SC is dominated by the anomalous subsidence in the northwest (east) of the anticyclone for positive (negative) SCS-WVT cases, and the subsidence is stronger for negative cases due to the vertically upward increase of negative vorticity advection associated with a northward-tilting structure. It is highlighted that different structures of anticyclonic anomaly could result in distinct features of extreme high temperature.

Contribution Assessment of Northern Hemispheric Atmospheric Circulations to Korean Mid-Summer Surface Warming by the Atmospheric Nudging Experiment

Anomalous surface warming in Korea has been explained by the high-pressure anomaly accompanied by the vertical sinking motion and weakening of westerlies at the exit of the East Asian Jet. The large-scale circulations linked to this high pressure over East Asia are characterized by the low pressure over the Arctic (AC) and the high pressure over Western Europe (WE), East Asia, and the North Pacific (NP). To assess the contribution of these circulation anomalies to the hot summer in Korea, the four nudging experiments (AC, NP, AC + NP, and WE) are applied to the simulations with 50 different initial conditions in July. As a result, the most similar patterns on local and hemispheric scales are found in the AC + NP nudging experiment. However, the near-surface response in the AC + NP is still weak, and its center shifts to the north compared to the observed, which is induced by the weaker diabatic contribution for the downward motion in the nudging experiment. Using the quasi-geostrophic omega equation, we find that the simulated radiative feedback process is not sufficient to build up the large-scale subsidence with the short nudging period. Despite this limitation, AC + NP well simulates the coherent sinking motion and high-pressure system near Korea by the vorticity advection associated with the upper-level westerlies. It implies that the contribution of the North Pacific circulation (a downstream region) should also be considered to reasonably simulate the East Asia surface warming along with those in the upstream regions.

A study on some dynamical aspects of Uttarakhand heavy rainfall events

In recent years, heavy rainfall events have been increasing over the Uttarakhand region. Improvement in the prediction of such events crucially dependent on the inclusion of the physical & dynamical processes responsible for such events, in the NWP model. This again, in turn depends on the understanding of such processes. In this study an attempt has been made to understand parts of these processes and some of the dynamical aspects of these heavy rainfall events. For this different important derived NWP products, viz., differential vorticity advection (DVA), differential thermal advection (DTA), Differential moisture advection (DMA), Precipitable water (PW), non-dimensional stability index (NDSI) have been computed using ECMWF high-resolution gridded reanalysis data sets. Heavy rainfall events are defined using IMD high resolution gridded daily rainfall data set. Preliminary analysis revealed that there was a steady increase in DVA, decrease in DTA, increase in PW and decrease in DMA before the heavy rainfall event. An enhanced DVA results in an enhancement in LLC, a decrease in DTA along with a decrease in DMA results in an enhancement of lapse rate. Combined effect of these results in the increase in the low-level convergence at Uttarakhand region along with the rising motion are the major dynamical processes resulted in the heavy rainfall event.

Diagnosing the relationship between the Madden–Julian Oscillation and United States severe convective weather outbreaks

AbstractThe Madden–Julian Oscillation (MJO) is the leading intraseasonal mode of tropical variability and has been connected to influences in extratropical weather. Recently, the MJO has been gaining traction as a useful teleconnection for extending severe weather outbreak forecast lead time. However, the MJO's intraseasonal, planetary‐scale is far from the meso‐ or micro‐scale severe weather phenomena, making identifying links between the two more difficult. In our study, we use severe weather outbreaks comprising all three main hazards (wind, hail and tornadoes), which are typically linked to a synoptic‐scale system. Outbreaks are devised using kernel density estimation and were used to determine spatial shifts for each of the eight phases of the MJO in each month. A total of 15 months/phases indicated a significant spatial shift. In the spring and summer months (March–August), southerly shifts are more likely to occur in MJO phases 7–8 and 1–3, while northerly shifts are more likely in phases 4–6. In the cool season (September–February), only 3 month/phase groups indicated significant shifts, two shifting west and one north. Composite analysis showed the likely link between the MJO and these outbreak shifts was rooted in Rossby wave breaking and generation of a Rossby wave source induced by the barotropic vorticity advection from the MJO convection. These resulting wave breaks and wave trains led to changes in the storm track (amplitude and location) that resulted in a more favourable synoptic‐scale pattern for severe weather over the United States that deviated from the climatologically favourable region.

Dynamic and Thermodynamic Drivers of Severe Sub-Hourly Precipitation Events in Mainland Portugal

Sub-hourly heavy precipitation events (SHHPs) associated with regional low-pressure (RegL) systems in Portugal are a natural hazard that may have significant socioeconomic implications, namely in agriculture. Therefore, in this paper, their dynamic and thermodynamic drivers are analysed. Three weather stations were used to isolate SHHPs from 2000 to 2022. Higher precipitation variability is found in southern Portugal, with a higher ratio of extreme events on fewer rainy days. This study shows that these SHHP events are associated with low-pressure systems located just to the west of the Iberian Peninsula. These systems exhibit a cold core, particularly strong at mid-levels, and a positive vorticity anomaly, which is stronger in the upper troposphere, extending downward to low levels. These conditions drive differential positive vorticity advection and, therefore, rising motion to the east of the low-pressure systems. Moreover, at low levels, these systems promote moisture advection over western Iberia, also generating instability conditions, which are assessed by instability indices (Convective available potential energy, the Total-Totals index, and the K-index). The combination of these conditions drives heavy precipitation events. Lastly, the total column cloud ice water revealed higher values for the heavier precipitation events, suggesting that it may be a useful predictor of such events.

Subsequent tropical cyclogenesis in the South China Sea induced by the pre-existing tropical cyclone over the western North Pacific: a case study

Mechanisms of tropical cyclogenesis have been studied for decades. A new one in the South China Sea, namely, PTC-STC is proposed. A subsequent tropical cyclone (STC) in the South China Sea can be induced by a pre-existing tropical cyclone (PTC) over the western North Pacific. The observations, reanalysis, and numerical sensitivity experiments suggest that the terrain of the Philippines (especially Luzon) is geographically essential to the tropical cyclogenesis and development of STC, whereas the intensity and track of PTC are conditionally decisive. If the terrain of the Philippines is replaced by sea, no STC forms. The steep mountain range of Luzon provides static blocking effect that can 1) enhance the upward motion; 2) accumulate warm moist air mass from the westerly and PTC; and 3) constrain the advection of vorticity from the PTC. Meanwhile, the northeasterly from the PTC climbs over the terrains, increases the adiabatic heating, and warms the proximity in the leeside of the mountains. These processes show that the interactions between the PTC and the terrain of the Philippines could provide favorable dynamic and thermodynamic conditions for the tropical cyclogenesis of STC in the low-to-mid troposphere of the South China Sea. Whereas, if the PTC is too strong, it could move into the South China Sea, suppressing the standalone favorable conditions for the tropical cyclogenesis of STC in the South China Sea.

Analysis of Water Vapor Transport and Trigger Mechanisms for Severe Rainstorms Associated with a Northeast China Cold Vortex in 2022

Rainstorms always occur in the southeast and northeast quadrants of the Northeast China Cold Vortex (NCCV), resulting in significant flooding. This study investigated water vapor and trigger mechanisms for rainstorms within these two regions of an NCCV event during 11–14 June 2022 in terms of Lagrangian backward tracking, stratification stability, and upward motion using the ERA5 reanalysis. In the mid-troposphere, a quasi-stationary “ridge-NCCV-ridge” pattern resided over northeastern China, with an “anticyclonic-cyclonic-anticyclonic” airflow in the lower troposphere. As a result, water vapor originated from the Yellow Sea and was transported in an “L” shape toward both two regions. The southeast region was influenced by southwesterly and northwesterly airflows, resulting in the convergence of moist air from the Yangtze River and Lake Baikal and significant vertical shear of positive vorticity advection. This dynamic created deep and pronounced upward currents in the southeast of the NCCV, leading to the development of intensive and extensive rainstorms in situ. In contrast, the northeast region of the NCCV was dominated by southerly airflow. The moist air converged against the lee side of the Great Khingan Mountains and generated shallow, unstable stratification. The upward motion in this area was relatively weaker and thus induced regional rainstorms.

Variations in Key Factors at Different Explosive Development Stages of an Extreme Explosive Cyclone over the Japan Sea

Explosive cyclones (ECs) occur frequently over the Japan Sea. The most rapidly intensifying EC over the Japan Sea during the 44-year period 1979–2022, in the cold season (October–April), was examined to reveal the variations in the key factors at different explosive development stages. The EC deepened at a maximum deepening rate of 3.07 bergerons and explosive development lasted for 15 h. At the initial moment of explosive development, the EC had distinctive low-level baroclinicity, the low-level water vapor convergence was weak, and mid-level cyclonic vorticity advection was far away from the EC’s center. At the moment at which the EC reached the maximum deepening rate, the low-level water vapor convergence and mid-level cyclonic vorticity advection increased distinctly and approached the EC’s center. A diagnostic analysis using the Zwack–Okossi equation showed that the main contributor to the initial explosive development was warm-air advection. Through the evolutionary process of the explosive development, the non-key factors of the cyclonic vorticity advection and diabatic heating at the initial explosive development stage increased quickly and became key factors contributing to the maximum explosive development. The key factors contributing to the explosive development varied with the stage of explosive development. The cross-section and vertical profile of each term suggested that the cyclonic vorticity advection was enhanced in the upper troposphere and diabatic heating increased in the middle troposphere.

Interannual Variations in the Intraseasonal Variability of Spring Precipitation over Southern China and the Possible Mechanisms

Abstract This study first investigates the interannual variations in spring precipitation intraseasonal variability over southern China (SC). The results show that SC spring precipitation exhibits distinct intraseasonal variations with a period of 7–25 days. The first mode of 7–25-day precipitation intraseasonal variability (PIV) displays a monopole pattern over SC, and the PIV magnitude is largely determined by the upward motion intensity during intraseasonal precipitation events. Further analysis suggests that two atmospheric wave trains are observed during intraseasonal precipitation events, which propagate eastward from the North Atlantic along the northern and southern paths. In strong PIV years, the two wave trains can propagate to East Asia and show coordinated influences. The resultant low pressure to the west of SC causes strong upward motion and PIV over SC by bringing strong zonal vorticity and meridional temperature advection. In weak PIV years, the southern wave train can only propagate to the Bay of Bengal; therefore, the northern wave train plays a major role. The resultant low pressure is now over the upper to middle reaches of the Yangtze River, which causes relatively weak upward motion and PIV over SC by bringing weak meridional vorticity and temperature advection. Further analysis indicates that the sea surface temperature (SST) condition over the tropical Indian Ocean and the South China Sea is essential for southern wave train propagation. The warming SST over the regions can intensify westerlies to its north and consequently favors the propagation of the southern wave train to SC, eventually contributing to strong PIV over SC.

Impact of the Eurasian Wave Train on the Interannual Variability of Autumn Precipitation in the Central Region of China

AbstractAutumn precipitation in the central region of China (APCC) can considerably influence on agricultural production and human livelihood. With reanalysis data from 1979 to 2020, it revealed that APCC is significantly affected by the second mode of the meridional wind field at 200 hPa over the Eurasian continent on the interannual scale, which featured a quasi‐barotropic “+‐+” wave‐like pattern from Europe to China (EC pattern) in extratropical zone. When the EC pattern is in a positive phase, central China lags behind the downstream positive geopotential height (anticyclone) anomaly. In this context, the transport of moisture from the south and east is enhanced and the advancement of the southerly monsoon is blocked, providing sufficient water vapor to support the occurrence of APCC. Further diagnosis revealed that local ascending motion is strengthened owing to the warm advection induced by anomalous southerly and positive vorticity advection associated with the anomalous anticyclone over East Asia. Additionally, wave flux analysis and model simulation suggest that the EC pattern results from the propagation of stationary Rossby wave, which could be excited by dipole sea surface temperature anomalies in the North Atlantic. These discoveries will contribute to improving the predictability of APCC.

Influence of Underlying Topography on Post-Monsoon Cyclonic Systems over the Indian Peninsula

During the post-monsoon cyclone season, the landfalls of westward-moving cyclonic systems often lead to extreme rainfall over the east coast of the Indian peninsula. A stationary cyclonic system over the coast can produce heavy rainfall for several days and cause catastrophic flooding. This study analyzes the dynamics of a propagating and stationary cyclonic system over the east coast, highlighting the possible cause behind the stagnation. The vorticity budgets of these two systems are presented using a reanalysis dataset. Vortex stretching and horizontal vorticity advection were the dominant terms in the budget. Vertical advection and tilting terms were significant over the orography. The horizontal advection of vorticity was positive (negative) on the western (eastern) side of the systems and, thus, favored westward propagation. Vortex stretching was confined to the upstream of orography in the stationary vortex. In the propagating vortex, the vortex stretching occurred over the orography during its passage. Data from the radiosonde soundings over a coastal station showed orographic blocking of the low-level winds in the stationary case. Conversely, the flow crossed the orographic barrier in the propagating case. Thus, the predominance of the upstream orographic convergence over the vortex circulation can be the reason for system stagnation over the coast.

Variability in coastal downwelling circulation in response to high-resolution regional atmospheric forcing off the Pearl River estuary

Abstract. We investigated the variabilities in coastal circulation and dynamics in response to spatiotemporally variable high-resolution atmospheric forcing off the Pearl River estuary during the downwelling wind. Our investigation focused on the dynamics of coastal downwelling circulation in response to variable atmospheric forcing of (1) single-station observation, (2) global reanalysis data, and (3) a high-resolution regional atmospheric model. We found that the high-resolution atmospheric model significantly improved the representations of the near-surface wind and air temperature, and the ocean model driven by the high-resolution and spatially variable atmospheric forcing improved the circulation and associated hydrographic properties in the coastal ocean. Momentum and vorticity analyses further revealed that the cross-isobath water exchange was primarily governed by the along-isobath pressure gradient force (PGF), which was influenced by different components of the atmospheric forcing. The spatial–temporal variability in high-resolution wind forcing determined the strength and structure of coastal circulation and improved estimates of cross-isobath transport and the associated PGF by refining the net stress curl and nonlinear advection of relative vorticity in the simulation. The high-resolution heat forcing can greatly improve the sea surface temperature simulation and adjust the nonlinear advection of relative vorticity, resulting in changes in cross-isobath transport.

Propagation Diversity of Quasi-Biweekly Oscillation of Summer Precipitation in the Middle and Lower Reaches of the Yangtze River

Abstract Summer precipitation in the middle and lower reaches of the Yangtze River (MLYR) has obvious characteristics of intraseasonal oscillation, but there are different inferences about its propagation. Based on observed precipitation and ERA5 data, the propagation diversity of summer quasi-biweekly precipitation in the MLYR is analyzed. The results show that summer precipitation in the MLYR has obvious quasi-biweekly oscillation (QBWO) characteristics, and precipitation QBWO events can be classified into three categories: southward, northward, and local oscillation events. The frequency of southward events is significantly higher than that of northward or local oscillation events. For southward events, a wave train is observed in the mid–high latitudes and propagates southward in East Asia. The northward and local oscillation events are closely related to the QBWO of the northwest Pacific in low latitudes. The meridional asymmetry of quasi-biweekly divergence and background wind is responsible for the diversity of QBWO propagation. Quasi-biweekly convergence is usually located on the south of the quasi-biweekly cyclone, so the convergence interacts with geostrophic vorticity to guide the quasi-biweekly cyclone to move southward; in the southerly basic flow, north of the quasi-biweekly cyclone is positive relative vorticity advection, which leads the quasi-biweekly cyclone to move northward. Therefore, quasi-biweekly disturbances originating from north of the MLYR, with weak basic wind, mainly move southward under the influence of convergence. However, quasi-biweekly disturbances at low latitudes move northward under the guidance of relative vorticity advection due to the strong basic flow. A disturbance originating from the MLYR presents local oscillation under the coaction of quasi-biweekly relative vorticity advection and divergence.

Synoptic meteorological conditions and contributing factors to air quality during the SIJAQ campaign

The Satellite Integrated Joint Monitoring of Air Quality (SIJAQ) field campaign was conducted from October 10 to November 25, 2021, to assess air quality across the Korean Peninsula and validate the results of the Geostationary Environment Monitoring Spectrometer (GEMS) employing remote sensing, modeling, and satellite, aircraft, and ground measurements. To integrate all measurements collected during the campaign, synoptic features across the Korean Peninsula were analyzed. We identified cyclones and anticyclones by tracing weather charts and divided the campaign into five periods (P1 to P5): P1 - Sustained marine stagnation (October 10–28, 2021), P2 - Transitional stagnant high (October 29–November 7, 2021), P3 - Continental migratory low (November 8–14, 2021), P4 - Continental migratory high (November 15–21, 2021), and P5 - Continental migratory low (November 22–25, 2021). The synoptic features, such as the locations of stagnant or migratory cyclones and anticyclones were analyzed during the periods, in association with levels of particulate matter with a diameter of less than 2.5 μm (PM2.5 levels) over the Seoul metropolitan area (SMA). The synoptic characteristics showed that the presence of a high pressure system was well associated with the occurrence of high PM2.5 level over the SMA, and a pattern of near-surface divergence and descending motions originating from the mid-troposphere. In addition, we identified and compared two PM2.5 level peaks caused by local accumulation and transboundary transport process. We also investigated the underlying synoptic meteorological mechanisms of these peaks in terms of large-scale dynamic variables, such as geostrophic wind speed, transient synoptic scale features, vorticity, and vorticity advection at 850 hPa geopotential height, which are responsible for transboundary transport and local accumulation-driven process of PM2.5 in the SMA.

Impact of North Indian Atmospheric Diabatic Heating on Summer Precipitation in Central Asia

Abstract The impact of North Indian atmospheric diabatic heating variation on summer rainfall over Central Asia (CA) at an interannual scale during 1960–2019 was investigated from thermal adaptation and water vapor transportation perspective. The results showed that more precipitation in southeastern CA is associated with the southward subtropical westerly jet (SWJ), caused by the ascending motion and weakened water vapor output on the south side. When the SWJ moves southward, the high-level water vapor transportation on the south side changes from outward (−1.9 × 106 kg s−1) to inward (0.6 × 106 kg s−1), and the positive anomalous relative vorticity advections by the basic westerly winds produce ascending anomalies over southeastern CA. The position change in the SWJ was mainly related to atmospheric diabatic heating over northern India (NI). The thermal vorticity adaptation caused by a weakened heating rate over NI leads to an anomalous upper-level cyclone over southeastern CA, and the associated cold temperature advection eventually cools the upper troposphere of southeastern CA and reduces the temperature gradient at mid-to-high latitudes, leading to the southward SWJ. Thermal adaptation of the circulation and temperature anomaly over southeastern CA to the NI thermal forcing were also verified by numerical experiments. Both the abnormal ascending motions and the weakened outward water vapor associated with the southward SWJ, caused by the weakened heating rate over NI, lead to more summer rainfall in southeastern CA. The changes in diabatic heating over NI are closely related to Indian Ocean SST. When the Indian Ocean SST is warmer, the south Asian summer monsoon weakens, causing less precipitation and, thus, a weakened heating rate over NI. Significance Statement This study established that the northern Indian atmospheric diabatic heating anomalies associated with Indian Ocean SST variation play an important role in influencing precipitation in central Asia (CA). The weakening of the atmospheric diabatic heating over the NI would not only cause an abnormal cyclone and cooling over southern CA through thermal adaptation but also lead to southward subtropical westerly jet (SWJ), ascending motions, and decreased outward water vapor on the south side in southeastern CA, eventually resulting in more precipitation in southeastern CA. The results emphasize the influence of tropical SST and atmospheric heat sources on midlatitude climate and are important for understanding summer precipitation change in southeastern CA.

Finite-time blowup for the inviscid vortex stretching equation

In this paper, we will introduce the inviscid vortex stretching equation, which is a model equation for the 3D Euler equation where the advection of vorticity is neglected. We will show that there are smooth solutions of this equation which blowup in finite-time, even when restricting to axisymmetric, swirl-free solutions. This provides further evidence of the role of advection in depleting nonlinear vortex stretching for solutions of the 3D Euler equation.

Synoptic-Scale Effects of Atmospheric Heat Source over Key Areas of the Tibetan Plateau on Its Downstream Rainfall in Summer

Abstract This study demonstrates the synoptic-scale relationship between the atmospheric heat source over the Tibetan Plateau (TP) (TP<Q1>) and summer rainfall in eastern China. The results show that the summer TP<Q1> has three key areas [eastern, western, and northeastern TP (TPE, TPW, TPNE, respectively)] and 3–8-day dominant oscillation periods on the synoptic time scale for each subregion. Analogously, on the synoptic scale, the downstream rainfall of the TP in China has six sensitive regions (zone I to zone VI), each with 3–8-day dominant periods. The TPE<Q1>, TPW<Q1>, and TPNE<Q1> lead rainfall by 4 days with a southeastward propagation pathway, by 5 days with both southeastward and northeastward propagation routes, and by 4 days with an eastward route, respectively. Mechanistically, when TP<Q1> lies in the positive-to-negative transition phase, the rainfall moves off the TP and reaches the maximum in its most inactive phase; the jet cores embedded in the subtropical westerly jet band and the trough from the region of the TP<Q1> lead the eastward movement of the rainfall by the propagation of the divergence center and generalized moist potential vorticity. Besides, the southwest vortex and northwest vortex generated at the southeastern and northeastern flank of the TP are the main cause for the southeastward and northeastward or eastward movement of the precipitation. Further internal atmospheric dynamic structures indicate that both the horizontal moisture advection and generalized moist potential vorticity advection act on the entire propagation processes of the synoptic-scale signals for each TP<Q1> key area. In conclusion, the study has obvious theoretical significance and application value for the development of plateau synoptics.