scholarly journals Seasonality of the Structure and Propagation Characteristics of the MJO

2016 ◽  
Vol 73 (9) ◽  
pp. 3511-3526 ◽  
Author(s):  
Ángel F. Adames ◽  
John M. Wallace ◽  
Joy M. Monteiro
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Winter Season ◽  
Water Model ◽  
Boreal Winter ◽  
Northwest Pacific ◽  
Monsoon Period ◽  
Asian Summer ◽  
Frictional Convergence

Abstract The seasonality of the Madden–Julian oscillation (MJO) is documented in observational data, and a nonlinear shallow-water model is used to help interpret some of the contrasts in MJO structure between the boreal winter season [November–March (NDJFM)] and the Asian summer monsoon period [June–September (JJAS)]. At upper-tropospheric levels, the flanking Rossby waves remain centered around 28°N/S year-round, but they tend to be stronger in the winter hemisphere, where the climatological-mean jet stream is stronger, rendering the subtropical circulation more sensitive to forcing by a near-equatorial heat source. Amplitudes of the MJO-related deep convection and lower-tropospheric zonal wind are stronger in the summer hemisphere, where the column-integrated water vapor is larger. During NDJFM, the equatorial asymmetry is subtle: as in the annual mean, moisture convergence into swallowtail-shaped regions of enhanced deep convection is an integral part of the equatorial Rossby wave signature, and the eastward propagation is due to moistening of the air to the east of the enhanced convection by poleward moisture advection. During the Asian summer monsoon in JJAS, the convection assumes the form of northward-propagating, west-northwest–east-southeast-oriented rainbands embedded within cyclonic shear lines. These features are maintained by frictional convergence of moisture, and their northward propagation is mainly due to the presence of features in the climatological-mean fields: that is, the west–east moisture gradient over India and the Arabian Sea and the southwesterly low-level monsoon flow over the northwest Pacific.

Annual Cycle of Southeast Asia—Maritime Continent Rainfall and the Asymmetric Monsoon Transition

2005 ◽  
Vol 18 (2) ◽  
pp. 287-301 ◽  
Author(s):  
C-P. Chang ◽  
Zhuo Wang ◽  
John McBride ◽  
Ching-Hwang Liu
Keyword(s):  
Southeast Asia ◽  
Summer Monsoon ◽  
Annual Cycle ◽  
Asian Summer Monsoon ◽  
Small Region ◽  
Winter Monsoon ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Maritime Continent ◽  
Asian Summer

Abstract In general, the Bay of Bengal, Indochina Peninsula, and Philippines are in the Asian summer monsoon regime while the Maritime Continent experiences a wet monsoon during boreal winter and a dry season during boreal summer. However, the complex distribution of land, sea, and terrain results in significant local variations of the annual cycle. This work uses historical station rainfall data to classify the annual cycles of rainfall over land areas, the TRMM rainfall measurements to identify the monsoon regimes of the four seasons in all of Southeast Asia, and the QuikSCAT winds to study the causes of the variations. The annual cycle is dominated largely by interactions between the complex terrain and a simple annual reversal of the surface monsoonal winds throughout all monsoon regions from the Indian Ocean to the South China Sea and the equatorial western Pacific. The semiannual cycle is comparable in magnitude to the annual cycle over parts of the equatorial landmasses, but only a very small region reflects the twice-yearly crossing of the sun. Most of the semiannual cycle appears to be due to the influence of both the summer and the winter monsoon in the western part of the Maritime Continent where the annual cycle maximum occurs in fall. Analysis of the TRMM data reveals a structure whereby the boreal summer and winter monsoon rainfall regimes intertwine across the equator and both are strongly affected by the wind–terrain interaction. In particular, the boreal winter regime extends far northward along the eastern flanks of the major island groups and landmasses. A hypothesis is presented to explain the asymmetric seasonal march in which the maximum convection follows a gradual southeastward progression path from the Asian summer monsoon to the Asian winter monsoon but experiences a sudden transition in the reverse. The hypothesis is based on the redistribution of mass between land and ocean areas during spring and fall that results from different land–ocean thermal memories. This mass redistribution between the two transition seasons produces sea level patterns leading to asymmetric wind–terrain interactions throughout the region, and a low-level divergence asymmetry in the region that promotes the southward march of maximum convection during boreal fall but opposes the northward march during boreal spring.

scholarly journals Dehydration and low ozone in the tropopause layer over the Asian monsoon caused by tropical cyclones: Lagrangian transport calculations using ERA-Interim and ERA5 reanalysis data

2020 ◽  
Vol 20 (7) ◽  
pp. 4133-4152 ◽  
Author(s):  
Dan Li ◽  
Bärbel Vogel ◽  
Rolf Müller ◽  
Jianchun Bian ◽  
Gebhard Günther ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Water Vapour ◽  
Tropical Cyclones ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Reanalysis Data ◽  
Trajectory Calculations ◽  
Asian Summer ◽  
The Western Pacific

Abstract. Low ozone and high water vapour mixing ratios are common features in the Asian summer monsoon (ASM) anticyclone; however, low ozone and low water vapour values were observed near the tropopause over Kunming, China, within the ASM using balloon-borne measurements performed during the SWOP (sounding water vapour, ozone, and particle) campaign in August 2009 and 2015. Here, we investigate low ozone and water vapour signatures in the upper troposphere and lower stratosphere (UTLS) using FengYun-2D, FengYun-2G, and Aura Microwave Limb Sounder (MLS) satellite measurements and backward trajectory calculations. Trajectories with kinematic and diabatic vertical velocities were calculated using the Chemical Lagrangian Model of the Stratosphere (CLaMS) trajectory module driven by both ERA-Interim and ERA5 reanalysis data. All trajectory calculations show that air parcels with low ozone and low water vapour values in the UTLS over Kunming measured by balloon-borne instruments originate from the western Pacific boundary layer. Deep convection associated with tropical cyclones over the western Pacific transports ozone-poor air from the marine boundary layer to the cold tropopause region. Subsequently, these air parcels are mixed into the strong easterlies on the southern side of the Asian summer monsoon anticyclone. Air parcels are dehydrated when passing the lowest temperature region (< 190 K) at the convective outflow of tropical cyclones. However, trajectory calculations show different vertical transport via deep convection depending on the employed reanalysis data (ERA-Interim, ERA5) and vertical velocities (diabatic, kinematic). Both the kinematic and the diabatic trajectory calculations using ERA5 data show much faster and stronger vertical transport than ERA-Interim primarily because of ERA5's better spatial and temporal resolution, which likely resolves convective events more accurately. Our findings show that the interplay between the ASM anticyclone and tropical cyclones has a significant impact on the chemical composition of the UTLS during summer.

Radiation and aerosol measurements over the Tibetan Plateau during the Asian summer monsoon period

2020 ◽  
Vol 11 (9) ◽  
pp. 1543-1551
Author(s):  
Jinqiang Zhang ◽  
Xiangao Xia ◽  
Hongrong Shi ◽  
Xuemei Zong ◽  
Jun Li
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
The Tibetan Plateau ◽  
Monsoon Period ◽  
Asian Summer

Large Volcanic Aerosol Load in the Stratosphere Linked to Asian Monsoon Transport

Science ◽  
2012 ◽  
Vol 337 (6090) ◽  
pp. 78-81 ◽  
Author(s):  
Adam E. Bourassa ◽  
Alan Robock ◽  
William J. Randel ◽  
Terry Deshler ◽  
Landon A. Rieger ◽  
...  
Keyword(s):  
Sulfur Dioxide ◽  
Summer Monsoon ◽  
Asian Monsoon ◽  
Lower Stratosphere ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Volcanic Eruptions ◽  
Volcanic Aerosol ◽  
Upper Troposphere ◽  
Asian Summer

The Nabro stratovolcano in Eritrea, northeastern Africa, erupted on 13 June 2011, injecting approximately 1.3 teragrams of sulfur dioxide (SO2) to altitudes of 9 to 14 kilometers in the upper troposphere, which resulted in a large aerosol enhancement in the stratosphere. The SO2 was lofted into the lower stratosphere by deep convection and the circulation associated with the Asian summer monsoon while gradually converting to sulfate aerosol. This demonstrates that to affect climate, volcanic eruptions need not be strong enough to inject sulfur directly to the stratosphere.

scholarly journals Stalagmite-inferred abrupt climate change of Asian Summer Monsoon at MIS 5a/4 transition

2017 ◽  
Author(s):  
Xiuyang Jiang ◽  
Yaoqi He ◽  
Xiaoyan Wang ◽  
Jinguo Dong ◽  
Zhizhong Li ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Ice Core ◽  
Precise Determination ◽  
Monsoon Period ◽  
Atmospheric Teleconnection ◽  
The North ◽  
Strong Resemblance ◽  
Asian Summer

Abstract. The Greenland Interstadial 21 (GIS 21), one of the longest warm events during the last glacial, occurred in conjunction with the transition from marine isotope stages (MIS) 5a to 4. Precise determination of the timing and duration of this event can improve our understanding of hydroclimatic connection between low and high latitudes over this MIS boundary. Facilitated by a robust chronology with closely spaced U-Th ages, replicated sub-decadal-resolved δ18O records of two stalagmites from Sanxing Cave, Southwest China, express Asian Summer Monsoon (ASM) history from 79.0 ± 0.2 to 75.7 ± 0.2 thousand years before present (kyr BP, before AD 1950) to reveal detailed structure of MIS 5a/4 transition and Chinese Interstadial (CIS) 21. The composited Sanxing record is characterized with three centennial-scale strong monsoon peaks and a 700-yr-long weak monsoon period within the CIS 21 rebound-type event, concurrent with its counterpart of Greenland Interstadial 21 (GIS 21). This strong resemblance suggests a rapid atmospheric teleconnection between the North Atlantic and the ASM regions. The transition at the termination of the Chinese Interstadial (CIS) 21 is determined to be from 77.0 ± 0.2 to 76.6 ± 0.2 kyr BP with a mid-point at 76.8 ± 0.2 kyr BP, which is 0.5–1.0 kyr younger than the correspondent of the end of GIS 21 on GICC05modelext and AICC2012 timescales. Given its high accuracy, our Sanxing Cave chronology can become one of the potential references for chronological refinement for ice-core records.

scholarly journals A PV-based determination of the transport barrier in the Asian summer monsoon anticyclone

2015 ◽  
Vol 15 (7) ◽  
pp. 10593-10628 ◽  
Author(s):  
F. Ploeger ◽  
C. Gottschling ◽  
S. Griessbach ◽  
J.-U. Grooß ◽  
G. Günther ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Large Scale ◽  
Lower Stratosphere ◽  
Transport Model ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Polar Vortex ◽  
Time Averaging ◽  
Transport Barrier ◽  
Asian Summer

Abstract. The Asian summer monsoon provides an important pathway of tropospheric source gases and pollution into the lower stratosphere. This transport is characterized by deep convection and steady upwelling, combined with confinement inside a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS). In this paper, we show that a barrier to horizontal transport along the 380 K isentrope in the monsoon anticyclone can be determined from the potential vorticity (PV) field, following the polar vortex criterion by Nash et al. (1996). Due to large dynamic variability of the anticyclone, the corresponding maximum in the PV gradient is weak and additional constraints are needed (e.g., time averaging). Notwithstanding, PV contours in the monsoon anticyclone agree well with contours of trace gas mixing ratios (CO, O3) and mean age from model simulations with a Lagrangian chemistry transport model (CLaMS) and MLS satellite observations. Hence, the PV-based transport barrier reflects the separation between air inside the anticyclone core and the background atmosphere well. For the summer season 2011 we find an average PV value of 3.6 PVU for the transport barrier in the anticyclone on the 380 K isentrope.

scholarly journals Enhancement of aerosols in UTLS over the Tibetan Plateau induced by deep convection during the Asian summer monsoon

2014 ◽  
Vol 14 (2) ◽  
pp. 3169-3191 ◽  
Author(s):  
Q. S. He ◽  
C. C. Li ◽  
J. Z. Ma ◽  
H. Q. Wang ◽  
X. L. Yan ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Temporal Variations ◽  
Aerosol Layer ◽  
The Tibetan Plateau ◽  
Aerosol Extinction ◽  
Extinction Coefficients ◽  
Asian Summer

Abstract. Vertical profiles of aerosol extinction coefficients were measured by an Micro Pulse Lidar at Naqu (31.5° N, 92.1° E, 4508 m a.m.s.l.), a meteorological station located on the central part of the Tibetan Plateau during summer 2011. Observations show a persistent maximum in aerosol extinction coefficients in the upper troposphere–lower stratosphere (UTLS) within an anticyclone during the Asian summer monsoon. These aerosol layers were generally located at an altitude of 18–19 km m.s.l., 1–2 km higher than the tropopause, with broad layer depth ranging approximately 3–4 km. Variations in these aerosols are found to be closely related to the intensity of underlying deep convection. Efficient vertical transport resulting from the most intensive convection is considered to be most important for the enhancement of aerosols observed near the tropopause. Temporal variations in aerosol layer in UTLS over the Plateau show a significant peak at midnight. This further indicates that deep convection plays an important role in the accumulation of aerosols in UTLS over the Tibetan Plateau.

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