Interhemispheric atmospheric mass oscillation and its relation to interannual variations of the Asian monsoon in boreal summer

2010 ◽  
Vol 53 (9) ◽  
pp. 1343-1350 ◽  
Author(s):  
ChuHan Lu ◽  
ZhaoYong Guan ◽  
JiaXi Cai
Keyword(s):  
Asian Monsoon ◽  
Boreal Summer ◽  
Interannual Variations ◽  
Atmospheric Mass

A Two-Dimensional Dynamical Model for the Subseasonal Variability of the Asian Monsoon Anticyclone

2018 ◽  
Vol 75 (10) ◽  
pp. 3597-3612 ◽  
Author(s):  
Arata Amemiya ◽  
Kaoru Sato
Keyword(s):  
Spatial Structure ◽  
Shallow Water ◽  
Asian Monsoon ◽  
Dynamical Instability ◽  
Water Model ◽  
Boreal Summer ◽  
Shallow Water Model ◽  
Model Composite ◽  
Characteristic Structure ◽  
Subseasonal Variability

The Asian monsoon anticyclone, which develops in the upper troposphere and lower stratosphere during boreal summer, exhibits significant subseasonal variability with a characteristic spatial structure. The dynamics of this variability is investigated using a nonlinear β-plane shallow-water model. The equivalent depth is estimated using reanalysis data to relate the three-dimensional dynamics in isentropic coordinates to the shallow-water model. Composite analysis reveals the resemblance of the horizontal structures between the Montgomery streamfunction and thickness on the 360-K level. However, the coefficients of the linear regressions between those two variables are strongly dependent on latitude. The estimated equivalent depths of the northern region are more than 2 times greater than those of the southern region. This is attributable to the background thermal structure around the tropopause. Based on this, a latitude-dependent mean depth is incorporated into the shallow-water model to numerically investigate responses to a steady localized forcing in the subtropics. With the inclusion of the latitudinal dependence of the mean depth, the vortex shedding state is able to have a longitudinally confined structure, which differs from the conventional case of constant mean depth. The spatial structure of this numerical solution corresponds to the observed structure, in which low-PV air is largely confined to finite longitudes within the Asian monsoon anticyclone. This suggests the possible role of dynamical instability and the interaction with the subtropical jet in determining the characteristic structure of the Asian monsoon anticyclone.

scholarly journals Horizontal and Vertical Structures of the Northward-Propagating Intraseasonal Oscillation in the South Asian Monsoon Region Simulated by an Intermediate Model*

2007 ◽  
Vol 20 (16) ◽  
pp. 4278-4286 ◽  
Author(s):  
Hae-Kyung Lee Drbohlav ◽  
Bin Wang
Keyword(s):  
Phase Difference ◽  
Rossby Wave ◽  
3D Model ◽  
Asian Monsoon ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Monsoon Region ◽  
Wave Type ◽  
Asian Monsoon Region ◽  
Northward Propagation

Abstract The structures and mechanism of the northward-propagating boreal summer intraseasonal oscillation (BSISO) in the southern Asian monsoon region are simulated and investigated in a three-dimensional intermediate model (3D model). The horizontal structure of the intraseasonal variability in the 3D model depicts the Kelvin–Rossby wave–type disturbance, which may or may not produce the northward-propagating disturbance in the Indian Ocean, depending on the seasonal-mean background winds. Two experiments are conducted in order to identify what characteristic of seasonal-mean background can induce the northwestward-tilted band in the Kelvin–Rossby wave, whose overall eastward movement gives the impression of the northward propagation at a given longitude. When the prescribed boreal summer mean winds are excluded in the first experiment, the phase difference between the barotropic divergence tendency and convection disappears. Consequently, the Rossby wave–type convection forms a zonally elongated band. As a result, the northward propagation of convection at a given longitude disappears. When the easterly vertical shear is introduced in the second experiment, the horizontal and the vertical structures of BSISO become similar to that of the northward-propagating one. The reoccurrence of the northwestward-directed convective band and the phase difference between the barotropic divergence tendency and the convection suggest that the summer mean zonal winds in the boreal Indian summer monsoon region are a critical condition that causes the horizontal and vertical structures of northward-propagating BSISO in the southern Asian monsoon region.

scholarly journals Dominant patterns of interaction between the tropics and mid-latitudes in boreal summer: Causal relationships and the role of time-scales

2020 ◽  
Author(s):  
Giorgia Di Capua ◽  
Jakob Runge ◽  
Reik V. Donner ◽  
Bart van den Hurk ◽  
Andrew G. Turner ◽  
...  
Keyword(s):  
Time Scales ◽  
South Asian ◽  
North Pacific ◽  
Asian Monsoon ◽  
Causal Effect ◽  
Tropical Convection ◽  
Boreal Summer ◽  
Convective Activity ◽  
The Tropics ◽  
Patterns Of Interaction

Abstract. Tropical convective activity represents a source of predictability for mid-latitude weather in the Northern Hemisphere. In winter, the El Niño–Southern Oscillation (ENSO) is the dominant source of predictability in the tropics and extra-tropics, but its role in summer is much less pronounced and the exact teleconnection pathways are not well understood. Here, we assess how tropical convection interacts with mid-latitude summer circulation at different intraseasonal time-scales and how ENSO affects these interactions. First, we apply maximum covariance analysis (MCA) between tropical convective activity and mid-latitude geopotential height fields to identify the dominant modes of interaction. The first MCA mode connects the South Asian monsoon with the mid-latitude circumglobal teleconnection pattern. The second MCA mode connects the western North Pacific summer monsoon in the tropics with a wave-5 pattern centred over the North Pacific High in the mid-latitudes. We show that the MCA patterns are fairly insensitive to the selected intraseasonal time-scale from weekly to 4-weekly data. To study the potential causal interdependencies between these modes and with other atmospheric fields, we apply causal effect networks (CEN) at different time-scales. CENs extend standard correlation analysis by removing the confounding effects of autocorrelation, indirect links and common drivers. In general, there is a two-way causal interaction between the tropics and mid-latitudes but the strength and sometimes sign of the causal link are time-scale dependent. We introduce causal maps that plot the regionally specific causal effect from each MCA mode. Those maps confirm the dominant patterns of interaction and in addition, highlight specific mid-latitude regions that are most strongly connected to tropical convection. In general, the identified causal teleconnection patterns are only mildly affected by ENSO and the tropical-mid-latitude linkages remain similar. Still, La Niña strengthens the South Asian monsoon generating a stronger response in the mid-latitudes, while during El Niño years, the Pacific pattern is reinforced. This study paves the way for process-based validation of boreal summer teleconnections in (sub-)seasonal forecast models and climate models and therefore helps to improve sub-seasonal and climate projections.

scholarly journals Impact of the Asian monsoon on the extratropical lower stratosphere: trace gas observations during TACTS over Europe 2012

2015 ◽  
Vol 15 (23) ◽  
pp. 34765-34812
Author(s):  
S. Müller ◽  
P. Hoor ◽  
H. Bozem ◽  
E. Gute ◽  
B. Vogel ◽  
...  
Keyword(s):  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Trace Gas ◽  
Boreal Summer ◽  
Monsoon Circulation ◽  
Transport Pathway ◽  
Air Masses ◽  
Time Period ◽  
Asian Summer

Abstract. The transport of air masses originating from the Asian monsoon anticyclone into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) above potential temperatures Θ = 380 K was identified during the HALO aircraft mission TACTS in August and September 2012. In-situ measurements of CO, O3 and N2O during TACTS Flight 2 on the 30 August 2012 show the irreversible mixing of aged with younger (originating from the troposphere) stratospheric air masses within the Ex-UTLS. Backward trajectories calculated with the trajetory module of the CLaMS model indicate that these tropospherically affected air masses originate from the Asian monsoon anticyclone. From the monsoon circulation region these air masses are quasi-isentropically transported above Θ = 380 K into the Ex-UTLS where they subsequently mix with stratospheric air masses. The overall trace gas distribution measured during TACTS shows that this transport pathway has a significant impact on the Ex-UTLS during boreal summer and autumn. This leads to an intensification of the tropospheric influence on the Ex-UTLS with ΔΘ > 30 K (relative to the tropopause) within three weeks during the TACTS mission. In the same time period a weakening of the tropospheric influence on the lowermost stratosphere (LMS) is determined. Therefore, the study shows that the transport of air masses originating from the Asian summer monsoon region within the lower stratosphere above Θ = 380 K is of major importance for the change of the chemical composition of the Ex-UTLS from summer to autumn.

Considerable differences of the interannual variations for the tropical cyclone landfall over north and south East Asia in summer

2020 ◽  
Author(s):  
Jufen Lai ◽  
Chaofan Li ◽  
Riyu Lu
Keyword(s):  
Tropical Cyclone ◽  
East Asia ◽  
The Philippines ◽  
Boreal Summer ◽  
South East Asia ◽  
Interannual Variations ◽  
Seasonal Forecasts ◽  
The South ◽  
North East ◽  
North And South

<p>Interannual variation of tropical cyclone (TC) landfall frequency is not consistent along the coast of East Asia, with large contrast of north and south East Asia coast regions in boreal summer. This study examines interannual variations of TC landfall frequency over north and south East Asia and identifies roles of the western North Pacific subtropical high (WNPSH) and TC genesis frequency associated with these variations. Although the total number of landing TC of north and south East Asia is similar, interannual variations of TC landfall frequency are relatively independent to each other, with the corresponding correlation coefficient north and south of 25°N is only –0.024 from 1979 to 2017. TC landfall over north East Asia is largely modulated by the circulation related to the WNPSH, while TC landfall in the south has no significant relationship with the WNPSH or other remote large-scale circulations. The WNPSH effectively regulates TC landfall in the north by modulating TC genesis east of the Philippines and steering flows. Nonetheless, the two factors have weak contradictory effects on TC landing in the south region. The frequency of TC genesis around the South China Sea directly connects to the TC landfall over south East Asia, which is modulated by the surrounding genesis environment, including relative humidity and relative vorticity. This work favors for a better understanding of the seasonal forecasts of TC landfall frequency and the subsequent climate service over East Asia.</p>

scholarly journals How Does El Niño Affect the Interannual Variability of the Boreal Summer Hadley Circulation?

2014 ◽  
Vol 27 (7) ◽  
pp. 2622-2642 ◽  
Author(s):  
Yong Sun ◽  
Tianjun Zhou
Keyword(s):  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Asian Summer Monsoon ◽  
Hadley Circulation ◽  
Department Of Energy ◽  
Hadley Cell ◽  
Boreal Summer ◽  
Interannual Variations ◽  
Sst Forcing

Abstract Analyses of 30-yr four reanalysis datasets [NCEP–NCAR reanalysis (NCEP1), NCEP–Department of Energy reanalysis (NCEP2), Japanese 25-year Reanalysis Project (JRA-25), and Interim ECMWF Re-Analysis (ERA-Interim)] reveal remarkably interannual variability of the Hadley circulation (HC) in boreal summer (June–August). The two leading modes of interannual variability of boreal summer HC are obtained by performing empirical orthogonal function (EOF) analysis on the mass streamfunction. A general intensification of boreal summer HC is seen in EOF-1 mode among NCEP1, NCEP2, and JRA-25 but the corresponding EOF-2 mode in ERA-Interim, while a weakened northern Hadley cell and remarkable regional variation of a southern Hadley cell are captured by the EOF-2 mode (from NCEP1, NCEP2, and JRA-25) and EOF-1 mode (from ERA-Interim), as evidenced by the enhanced (decreased) southern Hadley cell in the southern tropics (the northern tropics and southern subtropics). Both modes are driven by El Niño–like SST forcing in boreal summer, but are relevant to different phases of El Niño events. The EOF-1 (or EOF-2 derived from ERA-Interim) [EOF-2 (or EOF-1 derived from ERA-Interim)] mode is driven by SST anomalies in developing (decaying) El Niño summers. The interannual variations of the northern Hadley cell in both modes are driven by El Niño through modulating the interannual variations of the East Asian summer monsoon, while anomalous local Hadley circulation (LHC) in the regions 30°S–20°N, 110°E–180° and 30°S–20°N, 160°E–120°W in response to El Niño forcing largely determine the interannual variations of southern Hadley cell in both modes, respectively. The different behaviors of the southern Hadley cell between two leading modes can be well explained by the southward shift of the tropical heating center from north of 10°N in developing El Niño summers to south of 10°N in decaying El Niño summers.

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