Spring Dust over the Tibetan Plateau and Connections with North Atlantic SST Variability

2021 ◽  
Author(s):  
Chao Xu ◽  
Yaoming Ma ◽  
Jiehua Ma ◽  
Chao You ◽  
Huijun Wang
Keyword(s):  
North Atlantic ◽  
Tarim Basin ◽  
Wave Train ◽  
Lower Troposphere ◽  
Lower Atmosphere ◽  
The Tibetan Plateau ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic ◽  
Spring Dust

<p>Dust is a major component of atmospheric aerosol worldwide, greatly affecting regional and global climate. A dust belt can be clearly found at altitudes higher than 6 km over the downwind direction of the TP at latitudes of around 30°–40°N, crossing the Pacific Ocean and extending to North America during spring. Dust is uplifted to the midtroposphere over the source regions; then, frequent, deep, dry convection prevailing over the TP during spring can cause convective overshooting that uplifts the dust aerosols to the upper troposphere. The TP thus acts as a channel for transporting dust from the lower atmosphere to the upper troposphere, enabling the long-range zonal transport of dust around the Northern Hemisphere. Estimated spring dust mass flux (DMF) showed a significant declining trend over the TP during 2007-2019. The total spring DMF across the TP was mainly affected by DMFs over the Tarim Basin, while the spring DMF across the TP in the mid-troposphere was also connected with DMFs over the northwest Indian Peninsula and Central Asia. Inter-annual variability of spring DMF across the TP was strongly correlated with the North Atlantic winter sea surface temperature (SST) tripole. The North Atlantic winter SST tripole anomalies persist into the subsequent spring, and induce a corresponding atmosphere response. A strong positive North Atlantic winter SST tripole anomaly strengthens the upper-level westerly jets, enhancing air flow towards the TP mid-troposphere; together, these circulation patterns cause anomalous cyclonic conditions in the lower troposphere, especially over the Tarim Basin, via the eastwards propagation of a Rossby wave train. These atmospheric circulation conditions are likely to increase the frequency of dust occurrence and promote the transport of dust onto the TP.</p>

Spring Dust Mass Flux over the Tibetan Plateau during 2007–19 and Connections with North Atlantic SST Variability

2020 ◽  
Vol 33 (22) ◽  
pp. 9691-9703
Author(s):  
Chao Xu ◽  
Yaoming Ma ◽  
Jiehua Ma ◽  
Chao You ◽  
Huijun Wang
Keyword(s):  
Tibetan Plateau ◽  
North Atlantic ◽  
Tarim Basin ◽  
Mass Flux ◽  
The Tibetan Plateau ◽  
Indian Peninsula ◽  
The North ◽  
Dust Mass ◽  
The North Atlantic ◽  
Spring Dust

AbstractDust is the major aerosol type over the Tibetan Plateau (TP), and the TP plays an important role in forming the spring dust belt across the Northern Hemisphere in the upper troposphere. Estimated spring dust mass flux (DMF) showed a significant declining trend over the TP during 2007–19. The total spring DMF across the TP (TDMFTP) was mainly affected by DMFs over the Tarim Basin, while the spring DMF across the TP in the midtroposphere was also connected with DMFs over the northwest Indian Peninsula and central Asia. Interannual variability of spring TDMFTP was strongly correlated with the North Atlantic winter sea surface temperature (SST) tripole. A cold preceding winter induced by the North Atlantic winter SST tripole over midlatitude Eurasia promotes dust activities in the subsequent spring. The North Atlantic winter SST tripole anomalies persist into the subsequent spring and induce a corresponding atmosphere response. Enhanced atmospheric baroclinicity develops over northwest China and the northern Indian Peninsula during spring, which is attributed to surface thermal forcing induced by the positive winter SST tripole phase. A strong positive North Atlantic winter SST tripole anomaly strengthens the upper-level westerly jets, enhancing airflow toward the TP midtroposphere; together, these circulation patterns cause anomalous cyclonic conditions in the lower troposphere, especially over the Tarim Basin, via the eastward propagation of a Rossby wave train. These atmospheric circulation conditions are likely to increase the frequency of dust occurrence and promote the transport of dust onto the TP.

Summer Rainfall Seesaw between Hetao and the Middle and Lower Reaches of the Yangtze River and Its Relationship with the North Atlantic Oscillation

2017 ◽  
Vol 30 (17) ◽  
pp. 6629-6643 ◽  
Author(s):  
Dachao Jin ◽  
Zhaoyong Guan
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Yangtze River ◽  
Lower Troposphere ◽  
Summer Rainfall ◽  
Northern China ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Using the NCEP–NCAR reanalysis and other observational datasets, the authors have investigated the relationship of summer rainfall variations between the Hetao region of northern China and the middle and lower reaches of Yangtze River (MLRYR). The results have demonstrated that rainfall in Hetao varies out of phase with that in MLRYR on the interannual time scales. This phenomenon is referred to as the Hetao–Yangtze rainfall seesaw (HYRS). An HYRS index is defined to reveal both spatial and temporal features of HYRS. It is found that the North Atlantic Oscillation (NAO) affects the HYRS. In years when the NAO is in its positive phase, anomalous divergences in the lower troposphere and anomalous convergences in the upper troposphere are observed in regions of the Mediterranean and eastern Europe. The anomalous convergences in the upper troposphere occur as the positive Rossby wave source excites a circumglobal teleconnection (CGT) in the midlatitudes, exhibiting the eastward propagation of Rossby wave energy along the Asian jet. Meanwhile, the Eurasian–Pacific (EUP) teleconnection also affects the HYRS. Influenced mainly by the CGT pattern, the circulations over Hetao and MLRYR are consequently perturbed. The atmosphere over Hetao converges anomalously in the lower troposphere and diverges anomalously in the upper troposphere, facilitating more than normal rainfall there. At the same time, the atmosphere over MLRYR diverges anomalously in the lower troposphere and converges anomalously in the upper troposphere, resulting in more than normal summer rainfall in MLRYR. In this way, the north–south rainfall seesaw is formed. This NAO-induced rainfall seesaw is potentially useful for summer rainfall predictions in both MLRYR and the Hetao region of northern China.

The AMV phase-dependence of the connection between February NAO and March surface air temperature over the Tibetan Plateau

2021 ◽  
Author(s):  
Jingyi Li ◽  
Fei Li ◽  
Shengping He ◽  
Huijun Wang ◽  
Yvan J Orsolini
Keyword(s):  
Tibetan Plateau ◽  
Air Temperature ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
Surface Air Temperature ◽  
The Tibetan Plateau ◽  
The North ◽  
Rossby Wave Train ◽  
The North Atlantic

<p>The Tibetan Plateau (TP), referred to as the “Asian water tower”, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals a distinct out-of-phase connection between the February North Atlantic Oscillation (NAO) and March TPSAT, which is non-stationary and regulated by the warm phase of the Atlantic Multidecadal Variability (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO does not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO−TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low-frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic−TP connections in late winter−early spring.</p>

Teleconnection between NAO and Climate Downstream of the Tibetan Plateau

2008 ◽  
Vol 21 (18) ◽  
pp. 4680-4690 ◽  
Author(s):  
Jian Li ◽  
Rucong Yu ◽  
Tianjun Zhou
Keyword(s):  
North Atlantic ◽  
Climate Changes ◽  
North China ◽  
Reanalysis Data ◽  
Teleconnection Pattern ◽  
The Tibetan Plateau ◽  
Northeastern Asia ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic

Abstract Analysis of the monthly NCEP–NCAR reanalysis data and station data reveals a teleconnection pattern (NAULEA) that links climate changes over the North Atlantic and Eurasia. The NAULEA pattern has five action centers. It extends from the North Atlantic to northwestern Europe, and then stretches eastward to the Urals, with its eastern end over North China. Certain climate changes over East Asia, such as the cooling changes in both the upper troposphere and surface in the last few decades of the twentieth century, can be attributed to the NAULEA pattern anomalies and traced upstream to the North Atlantic. The NAULEA pattern is suggested to be another NAO-related teleconnection pattern. Compared with the pattern with the Asian jet waveguide path, which leads to temperature anomalies over northeastern Asia, the NAULEA pattern with a high-latitude path exerts stronger influences on the climate of southwestern China.

Characteristics and Possible Sources of the Intraseasonal South Asian Jet Wave Train in Boreal Winter

2020 ◽  
Vol 33 (24) ◽  
pp. 10523-10537
Author(s):  
Sijie Huang ◽  
Xiuzhen Li ◽  
Zhiping Wen
Keyword(s):  
Mediterranean Sea ◽  
South Asian ◽  
North Atlantic ◽  
Wave Train ◽  
Western Mediterranean ◽  
Upper Troposphere ◽  
The North ◽  
Western Mediterranean Sea ◽  
Activity Center ◽  
The North Atlantic

AbstractThe characteristics and possible energy sources of the South Asian jet wave train in winter are analyzed, with the intraseasonal signal emphasized. The wave train is equivalently barotropic and strongest in the upper troposphere, with its daily evolution dominated by the intraseasonal (10–30 day) time scale. Along the wave train, the propagation of disturbances from the North Atlantic to the western North Pacific takes around 8 days, which is much faster than the eastward migration of activity centers. The energy sources of the intraseasonal wave train are complicated and can be separated into three categories depending on the role of the North Atlantic Oscillation (NAO). When NAO− precedes the wave train, it is northwest–southeast oriented. The energy is rooted in the lower troposphere over the high-latitude North Atlantic, and excites the Rossby wave source (RWS) over the western Mediterranean Sea via vortex stretching by abnormal divergence. When NAO+ precedes the wave train, it is southwest–northeast oriented. The energy rooted in the northeastern activity center excites RWS over the eastern Mediterranean Sea. Additionally, disturbances from the western North Atlantic and southwestern activity center of NAO+ excite the RWS over the western Mediterranean Sea. Hence, both NAO− and NAO+ can excite the same wave train, but with different orientation and via different paths. Without the NAO, the wave train can also be stimulated by enhanced disturbances over the midlatitude central North Atlantic. The signal lies mainly in the middle-upper troposphere, which might be related to atmospheric internal dynamic processes, such as kinetic energy conversion from synoptic disturbances.

scholarly journals The Atlantic Multidecadal Variability phase-dependence of teleconnection between the North Atlantic Oscillation in February and the Tibetan Plateau in March

2021 ◽  
pp. 1-40
Author(s):  
Jingyi Li ◽  
Fei Li ◽  
Shengping He ◽  
Huijun Wang ◽  
Yvan J Orsolini
Keyword(s):  
Tibetan Plateau ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
The Tibetan Plateau ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
The North ◽  
Rossby Wave Train ◽  
The North Atlantic

AbstractThe Tibetan Plateau (TP), referred to as the “Asian water tower”, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals that the relationship between the February North Atlantic Oscillation (NAO) and March TPSAT is unstable with time and regulated by the phase of the Atlantic Multidecadal Variability (AMV). The significant out-of-phase connection occurs only during the warm phase of AMV (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO can not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO−TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic−TP connection in late winter−early spring.

scholarly journals Composite analysis of the tropopause inversion layer in extratropical baroclinic waves

2019 ◽  
Vol 19 (10) ◽  
pp. 6621-6636 ◽  
Author(s):  
Thorsten Kaluza ◽  
Daniel Kunkel ◽  
Peter Hoor
Keyword(s):  
Sea Level ◽  
North Atlantic ◽  
Inversion Layer ◽  
Static Stability ◽  
Composite Analysis ◽  
Sea Level Pressure ◽  
Air Masses ◽  
Upper Troposphere ◽  
The North ◽  
The North Atlantic

Abstract. The evolution of the tropopause inversion layer (TIL) during cyclogenesis in the North Atlantic storm track is investigated using operational meteorological analysis data (Integrated Forecast System from the European Centre for Medium-Range Weather Forecasts). For this a total of 130 cyclones have been analysed during the months August through October between 2010 and 2014 over the North Atlantic. Their paths of migration along with associated flow features in the upper troposphere and lower stratosphere (UTLS) have been tracked based on the mean sea level pressure field. Subsets of the 130 cyclones have been used for composite analysis using minimum sea level pressure to filter the cyclones based on their strength. The composite structure of the TIL strength distribution in connection with the overall UTLS flow strongly resembles the structure of the individual cyclones. Key results are that a strong dipole in TIL strength forms in regions of cyclonic wrap-up of UTLS air masses of different origin and isentropic potential vorticity. These air masses are associated with the cyclonic rotation of the underlying cyclones. The maximum values of enhanced static stability above the tropopause occur north and northeast of the cyclone centre, vertically aligned with outflow regions of strong updraft and cloud formation up to the tropopause, which are situated in anticyclonic flow patterns in the upper troposphere. These regions are co-located with a maximum of vertical shear of the horizontal wind. The strong wind shear within the TIL results in a local minimum of Richardson numbers, representing the possibility for turbulent instability and potential mixing (or air mass exchange) within regions of enhanced static stability in the lowermost stratosphere.

A Unified Nonlinear Multiscale Interaction Model of Pacific–North American Teleconnection Patterns

2020 ◽  
Vol 77 (4) ◽  
pp. 1387-1414
Author(s):  
Dehai Luo ◽  
Yao Ge ◽  
Wenqi Zhang ◽  
Aiguo Dai
Keyword(s):  
North Atlantic ◽  
North American ◽  
Wave Train ◽  
Interaction Model ◽  
Energy Dispersion ◽  
Pacific North American ◽  
The North ◽  
The North Atlantic ◽  
The Difference ◽  
Multiscale Interaction

Abstract In this paper, reanalysis data are first analyzed to reveal that the individual negative (positive)-phase Pacific–North American pattern (PNA) or PNA− (PNA+) has a lifetime of 10–20 days, is characterized by strong (weak) westerly jet stream meanders, and exhibits clear wave train structures, whereas the PNA− with rapid retrogression tends to have longer lifetime and larger amplitude than the PNA+ with slow retrogression. In contrast, the wave train structure of the North Atlantic Oscillation (NAO) is less distinct, and the positive (negative)-phase NAO shows eastward (westward) movement around a higher latitude than the PNA. Moreover, it is found that the PNA wave train occurs under a larger background meridional potential vorticity gradient (PVy) over the North Pacific than that over the North Atlantic for the NAO. A unified nonlinear multiscale interaction (UNMI) model is then developed to explain why the PNA as a nonlinear wave packet has such characteristics and its large difference from the NAO. The model results reveal that the larger background PVy for the PNA (due to its location at lower latitudes) leads to its larger energy dispersion and weaker nonlinearity than the NAO, thus explaining why the PNA (NAO) is largely a linear (nonlinear) process with a strong (weak) wave train structure, though it is regarded as a nonlinear initial-value problem. The smaller PVy for the PNA− than for the PNA+ leads to lower energy dispersion and stronger nonlinearity for PNA−, which allows it to maintain larger amplitude and have a longer lifetime than the PNA+. Thus, the difference in the background PVy is responsible for the asymmetry between the two phases of PNA and the difference between the PNA and NAO.

Why Is There an Early Spring Cooling Shift Downstream of the Tibetan Plateau?

2005 ◽  
Vol 18 (22) ◽  
pp. 4660-4668 ◽  
Author(s):  
Jian Li ◽  
Rucong Yu ◽  
Tianjun Zhou ◽  
Bin Wang
Keyword(s):  
Tibetan Plateau ◽  
North Africa ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Temperature Shift ◽  
Early Spring ◽  
Climate Feedback ◽  
The Tibetan Plateau ◽  
The North ◽  
The North Atlantic

Abstract The temperature shift over the eastern flank of the Tibetan Plateau is examined using the last 50 yr of Chinese surface station observations. It was found that a strong cooling shift occurs in early spring (March and April) and late summer (July, August, and September) in contrast to the warming shift in other seasons. The cause of the March–April (MA) cooling is investigated in this study. The MA cooling shift on the lee side of the Tibetan Plateau is found to be not a local phenomenon, but rather it is associated with an eastward extension of a cooling signal originating from North Africa that is related to the North Atlantic Oscillation (NAO) in the previous winter. The midtropospheric westerlies over the North Atlantic and North Africa tend to intensify during positive NAO phases. The enhanced westerlies, after passing over the Tibetan Plateau, result in strengthened ascending motion against the lee side of the plateau, which favors the formation of midlevel stratiform clouds. The increased amount of stratus clouds induces a negative net cloud–radiative forcing, which thereby cools the surface air and triggers a positive cloud–temperature feedback. In this way, the cooling signal from the upstream could “jump” over the Tibetan Plateau and leave a footprint on its lee side. The continental stratiform cloud–climate feedback plays a significant role in the amplification of the cooling shift downstream of the Tibetan Plateau.

Atmospheric Teleconnections of Tropical Atlantic Variability: Interhemispheric, Tropical–Extratropical, and Cross-Basin Interactions

2007 ◽  
Vol 20 (5) ◽  
pp. 856-870 ◽  
Author(s):  
Lixin Wu ◽  
Feng He ◽  
Zhengyu Liu ◽  
Chun Li
Keyword(s):  
North Atlantic ◽  
Southern Oscillation ◽  
Wave Train ◽  
Seasonal Migration ◽  
Atmospheric Response ◽  
Tropical Atlantic ◽  
The North ◽  
Atmospheric Teleconnections ◽  
Ocean Atmosphere ◽  
The North Atlantic

Abstract In this paper, the atmospheric teleconnections of the tropical Atlantic SST variability are investigated in a series of coupled ocean–atmosphere modeling experiments. It is found that the tropical Atlantic climate not only displays an apparent interhemispheric link, but also significantly influences the North Atlantic Oscillation (NAO) and the El Niño–Southern Oscillation (ENSO). In spring, the tropical Atlantic SST exhibits an interhemispheric seesaw controlled by the wind–evaporation–SST (WES) feedback that subsequently decays through the mediation of the seasonal migration of the ITCZ. Over the North Atlantic, the tropical Atlantic SST can force a significant coupled NAO–dipole SST response in spring that changes to a coupled wave train–horseshoe SST response in the following summer and fall, and a recurrence of the NAO in the next winter. The seasonal changes of the atmospheric response as well as the recurrence of the next winter’s NAO are driven predominantly by the tropical Atlantic SST itself, while the resulting extratropical SST can enhance the atmospheric response, but it is not a necessary bridge of the winter-to-winter NAO persistency. Over the Pacific, the model demonstrates that the north tropical Atlantic (NTA) SST can also organize an interhemispheric SST seesaw in spring in the eastern equatorial Pacific that subsequently evolves into an ENSO-like pattern in the tropical Pacific through mediation of the ITCZ and equatorial coupled ocean–atmosphere feedback.

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