A nonlinear multi-scale theory of atmospheric blocking: Structure and evolution of blocking linked to meridional and vertical structures of storm tracks

2021 ◽  
Author(s):  
Dehai Luo ◽  
Wenqi Zhang
Keyword(s):  
Storm Track ◽  
Interaction Model ◽  
Maximum Amplitude ◽  
Transient Eddy ◽  
Baroclinic Mode ◽  
Upper Troposphere ◽  
Multi Scale ◽  
The North ◽  
Baroclinic Modes ◽  
The Impact

AbstractThis paper examines the impact of the meridional and vertical structures of a preexisting upstream storm track (PUST) organized by preexisting synoptic-scale eddies on eddy-driven blocking in a nonlinear multi-scale interaction model. In this model, the blocking is assumed, based on observations, to be comprised of barotropic and first baroclinic modes, whereas the PUST consists of barotropic, first baroclinic and second baroclinic modes. It is found that the nonlinearity (dispersion) of blocking is intensified (weakened) with increasing amplitude of the first baroclinic mode of the blocking itself. The blocking tends to be long-lived in this case. The lifetime and strength of blocking are significantly influenced by the amplitude of the first baroclinic mode of blocking for given basic westerly winds (BWWs), whereas its spatial pattern and evolution are also affected by the meridional and vertical structures of the PUST.It is shown that the blocking mainly results from the transient eddy forcing induced by the barotropic and first baroclinic modes of PUST, whereas its second baroclinic mode contributes little to the transient eddy forcing. When the PUST shifts northward, eddy-driven blocking shows an asymmetric dipole structure with a strong anticyclone/weak cyclone in a uniform BWW, which induces northward-intensified westerly jet and storm track anomalies mainly on the north side of blocking. However, when the PUST has no meridional shift and is mainly located in the upper troposphere, a north-south anti-symmetric dipole blocking and an intensified split jet with maximum amplitude in the upper troposphere form easily for vertically varying BWWs without meridional shear.

scholarly journals Effect of tropical cyclones on the Stratosphere-Troposphere Exchange observed using satellite observations over north Indian Ocean

2016 ◽  
Author(s):  
M. Venkat Ratnam ◽  
S. Ravindra Babu ◽  
S. S. Das ◽  
Ghouse Basha ◽  
B. V. Krishnamurthy ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Ocean ◽  
Tropical Cyclones ◽  
Lower Stratosphere ◽  
North Indian Ocean ◽  
Satellite Observations ◽  
Upper Troposphere ◽  
North West ◽  
The North ◽  
The Impact

Abstract. Tropical cyclones play an important role in modifying the tropopause structure and dynamics as well as stratosphere-troposphere exchange (STE) process in the Upper Troposphere and Lower Stratosphere (UTLS) region. In the present study, the impact of cyclones that occurred over the North Indian Ocean during 2007–2013 on the STE process is quantified using satellite observations. Tropopause characteristics during cyclones are obtained from the Global Positioning System (GPS) Radio Occultation (RO) measurements and ozone and water vapor concentrations in UTLS region are obtained from Aura-Microwave Limb Sounder (MLS) satellite observations. The effect of cyclones on the tropopause parameters is observed to be more prominent within 500 km from the centre of cyclone. In our earlier study we have observed decrease (increase) in the tropopause altitude (temperature) up to 0.6 km (3 K) and the convective outflow level increased up to 2 km. This change leads to a total increase in the tropical tropopause layer (TTL) thickness of 3 km within the 500 km from the centre of cyclone. Interestingly, an enhancement in the ozone mixing ratio in the upper troposphere is clearly noticed within 500 km from cyclone centre whereas the enhancement in the water vapor in the lower stratosphere is more significant on south-east side extending from 500–1000 km away from the cyclone centre. We estimated the cross-tropopause mass flux for different intensities of cyclones and found that the mean flux from stratosphere to troposphere for cyclonic stroms is 0.05 ± 0.29 × 10−3 kg m−2 and for very severe cyclonic stroms it is 0.5 ± 1.07 × 10−3 kg m−2. More downward flux is noticed in the north-west and south-west side of the cyclone centre. These results indicate that the cyclones have significant impact in effecting the tropopause structure, ozone and water vapour budget and consequentially the STE in the UTLS region.

scholarly journals Impacts of the North Atlantic Warming Hole in Future Climate Projections: Mean Atmospheric Circulation and the North Atlantic Jet

2019 ◽  
Vol 32 (10) ◽  
pp. 2673-2689 ◽  
Author(s):  
Melissa Gervais ◽  
Jeffrey Shaman ◽  
Yochanan Kushnir
Keyword(s):  
Atmospheric Circulation ◽  
North Atlantic ◽  
Forced Response ◽  
Future Climate ◽  
Climate Projections ◽  
Transient Eddy ◽  
The North ◽  
Climate Simulations ◽  
The North Atlantic ◽  
The Impact

Abstract In future climate simulations there is a pronounced region of reduced warming in the subpolar gyre of the North Atlantic Ocean known as the North Atlantic warming hole (NAWH). This study investigates the impact of the North Atlantic warming hole on atmospheric circulation and midlatitude jets within the Community Earth System Model (CESM). A series of large-ensemble atmospheric model experiments with prescribed sea surface temperature (SST) and sea ice are conducted, in which the warming hole is either filled or deepened. Two mechanisms through which the NAWH impacts the atmosphere are identified: a linear response characterized by a shallow atmospheric cooling and increase in sea level pressure shifted slightly downstream of the SST changes, and a transient eddy forced response whereby the enhanced SST gradient produced by the NAWH leads to increased transient eddy activity that propagates vertically and enhances the midlatitude jet. The relative contributions of these two mechanisms and the details of the response are strongly dependent on the season, time period, and warming hole strength. Our results indicate that the NAWH plays an important role in midlatitude atmospheric circulation changes in CESM future climate simulations.

scholarly journals The Basic Ingredients of the North Atlantic Storm Track. Part I: Land–Sea Contrast and Orography

2009 ◽  
Vol 66 (9) ◽  
pp. 2539-2558 ◽  
Author(s):  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
North Atlantic ◽  
Rocky Mountains ◽  
Large Scale ◽  
Storm Track ◽  
Storm Tracks ◽  
Cold Pool ◽  
North American Continent ◽  
The North ◽  
The North Atlantic ◽  
The Impact

Abstract Understanding and predicting changes in storm tracks over longer time scales is a challenging problem, particularly in the North Atlantic. This is due in part to the complex range of forcings (land–sea contrast, orography, sea surface temperatures, etc.) that combine to produce the structure of the storm track. The impact of land–sea contrast and midlatitude orography on the North Atlantic storm track is investigated through a hierarchy of GCM simulations using idealized and “semirealistic” boundary conditions in a high-resolution version of the Hadley Centre atmosphere model (HadAM3). This framework captures the large-scale essence of features such as the North and South American continents, Eurasia, and the Rocky Mountains, enabling the results to be applied more directly to realistic modeling situations than was possible with previous idealized studies. The physical processes by which the forcing mechanisms impact the large-scale flow and the midlatitude storm tracks are discussed. The characteristics of the North American continent are found to be very important in generating the structure of the North Atlantic storm track. In particular, the southwest–northeast tilt in the upper tropospheric jet produced by southward deflection of the westerly flow incident on the Rocky Mountains leads to enhanced storm development along an axis close to that of the continent’s eastern coastline. The approximately triangular shape of North America also enables a cold pool of air to develop in the northeast, intensifying the surface temperature contrast across the eastern coastline, consistent with further enhancements of baroclinicity and storm growth along the same axis.

Tropical cloud-radiative changes contribute to robust DJF jet exit strengthening over Europe under global warming

2021 ◽  
Author(s):  
Nicole Albern ◽  
Aiko Voigt ◽  
Joaquim G. Pinto
Keyword(s):  
Climate Change ◽  
North Atlantic ◽  
Storm Track ◽  
Tropical Pacific ◽  
Jet Stream ◽  
The North ◽  
The North Atlantic ◽  
Stream Response ◽  
The Impact ◽  
North Atlantic Jet

<p>During boreal winter (December to February, DJF), the North Atlantic jet stream and storm track are expected to extend eastward over Europe in response to climate change. This will affect future weather and climate over Europe, for example by steering storms which are associated with strong winds and heavy precipitation towards Europe. The jet stream and storm track responses over Europe are robust across coupled climate models of phases 3, 5, and 6 of the Coupled Model Intercomparison Project (CMIP; Harvey et al., 2020, JGR-A, https://doi.org/10.1029/2020JD032701). We show that the jet stream response is further robust across CMIP5 models of varying complexity ranging from coupled climate models to atmosphere-only General Circulation Models (GCMs) with prescribed sea-surface temperatures (SSTs) and sea-ice cover. In contrast to the jet stream response over Europe, the jet stream response over the North Atlantic is not robust in the coupled climate models and the atmosphere-only GCMs.</p><p>In addition to the CMIP5 simulations, we investigate Amip-like simulations with the atmospheric components of ICON-NWP, and the CMIP5 models MPI-ESM-LR and IPSL-CM5A-LR that apply the cloud-locking method to break the cloud-radiation-circulation coupling and to diagnose the contribution of cloud-radiative changes on the jet stream response to climate change. In the simulations, SSTs are prescribed to isolate the impact of cloud-radiative changes via the atmospheric pathway, i.e., via changes in atmospheric cloud-radiative heating, and global warming is mimicked by a uniform 4K SST increase (cf. Albern et al., 2019, JAMES, https://doi.org/10.1029/2018MS001592 and Voigt et al., 2019, J. Climate, https://doi.org/10.1175/JCLI-D-18-0810.1). In all three models, cloud-radiative changes contribute significantly and robustly to the eastward extension of the North Atlantic jet stream towards Europe. At the same time, cloud-radiative changes contribute to the model uncertainty over the North Atlantic. In addition to the jet stream response, we investigate the impact of cloud-radiative changes on the storm track response in ICON-NWP and discuss similarities and differences between the jet stream and storm track responses over the North Atlantic-European region.</p><p>In ICON-NWP, the impact of cloud-radiative changes on the jet stream response is dominated by tropical cloud-radiative changes while midlatitude and polar cloud-radiative changes have a minor impact. A further division of the tropics into four smaller tropical regions that cover the western tropical Pacific, the eastern tropical Pacific, the tropical Atlantic, and the Indian Ocean shows that cloud-radiative changes over the western tropical Pacific, eastern tropical Pacific, and Indian Ocean all contribute about equally to the eastward extension of the North Atlantic jet stream towards Europe because these regions exhibit substantial upper-tropospheric cloud-radiative heating in response to climate change. At the same time, cloud-radiative changes over the tropical Atlantic hardly contribute to the jet response over Europe because changes in atmospheric cloud-radiative heating under climate change are small in this region. As for the impact of global cloud-radiative changes, we also discuss the impact of the regional cloud-radiative changes on the storm track response over the North Atlantic-European region to climate change.</p>

The impact of baroclinity on tidal ranges in the North Sea

2020 ◽  
Author(s):  
Wenguo Li ◽  
Bernhard Mayer ◽  
Thomas Pohlmann
Keyword(s):  
Sea Level ◽  
North Sea ◽  
Tide Gauge ◽  
Tidal Range ◽  
Baroclinic Mode ◽  
Kelvin Wave ◽  
Ocean Stratification ◽  
The North ◽  
The North Sea ◽  
The Impact

<p>Tidal range is one of significant contributors of coastal inundation. Therefore, it is very important to investigate the dynamics of tidal range variations over different time scales. The baroclinity has the potential to modulate surface tides through ocean stratification on seasonal scale. In order to better understand the impact of ocean stratification on tidal ranges in the North Sea, the numerical simulations were carried out in baroclinic and barotropic modes covering the period from 1948 to 2014, using the regional 3D hydrodynamic prognostic Hamburg Shelf Ocean Model (HAMSOM). In the barotropic mode, the river forcing was also included, which only increases the local sea level without any influence on the density. The tidal range difference between baroclinic and barotropic modes in winter (less stratification) and summer (strong stratification) are compared at 22 tide-gauge stations, where the simulated sea surface elevations agree well with observations from 1950 to 2014. The statistical analysis generally shows that the difference at 19 stations (86% of total stations) in summer is much larger than that in winter during more than 32 years (50% of the analysis period). This suggests that the stratification decouples the surface and bottom layers weakening the damping effects of bottom friction, which is visible even at the coastal tide-gauge stations, where the ocean water is well-mixed. Obviously, the signal induced by stratification is propagated by the tidal Kelvin wave through the North Sea. Additionally, the spatial distribution of tidal range differences indicate that the amphidromic points in the North Sea moved westward in the baroclinic mode. Regarding the seasonal mean sea level at the stations, the results show that the coastal sea level could be increased by baroclinity itself, since the river runoff freshens the coastal water in the baroclinic mode, and thus the local sea level increases due to steric effect. Consequently, the increased sea level could further weaken the damping effect. However, this is a relatively minor impact on the tidal range.</p>

scholarly journals The Basic Ingredients of the North Atlantic Storm Track. Part II: Sea Surface Temperatures

2011 ◽  
Vol 68 (8) ◽  
pp. 1784-1805 ◽  
Author(s):  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Storm Track ◽  
Horizontal Wind ◽  
Near Surface ◽  
Continental Scale ◽  
The North ◽  
The North Atlantic ◽  
The Impact ◽  
Sst Gradient

Abstract The impact of North Atlantic SST patterns on the storm track is investigated using a hierarchy of GCM simulations using idealized (aquaplanet) and “semirealistic” boundary conditions in the atmospheric component (HadAM3) of the third climate configuration of the Met Office Unified Model (HadCM3). This framework enables the mechanisms determining the tropospheric response to North Atlantic SST patterns to be examined, both in isolation and in combination with continental-scale landmasses and orography. In isolation, a “Gulf Stream” SST pattern acts to strengthen the downstream storm track while a “North Atlantic Drift” SST pattern weakens it. These changes are consistent with changes in the extratropical SST gradient and near-surface baroclinicity, and each storm-track response is associated with a consistent change in the tropospheric jet structure. Locally enhanced near-surface horizontal wind convergence is found over the warm side of strengthened SST gradients associated with ascending air and increased precipitation, consistent with previous studies. When the combined SST pattern is introduced into the semirealistic framework (including the “North American” continent and the “Rocky Mountains”), the results suggest that the topographically generated southwest–northeast tilt in the North Atlantic storm track is enhanced. In particular, the Gulf Stream shifts the storm track south in the western Atlantic whereas the strong high-latitude SST gradient in the northeastern Atlantic enhances the storm track there.

scholarly journals Further Investigation of the Impact of Idealized Continents and SST Distributions on the Northern Hemisphere Storm Tracks

2012 ◽  
Vol 69 (3) ◽  
pp. 840-856 ◽  
Author(s):  
Jérôme Saulière ◽  
David James Brayshaw ◽  
Brian Hoskins ◽  
Michael Blackburn
Keyword(s):  
Boundary Conditions ◽  
North Atlantic ◽  
North Pacific ◽  
Rossby Waves ◽  
Storm Track ◽  
Storm Tracks ◽  
The North ◽  
The Pacific ◽  
The North Atlantic ◽  
The Impact

Abstract Building on previous studies of the basic ingredients of the North Atlantic storm track (examining land–sea contrast, orography, and SST), this article investigates the impact of Eurasian topography and Pacific SST anomalies on North Pacific and Atlantic storm tracks through a hierarchy of atmospheric GCM simulations using idealized boundary conditions in the Hadley Centre HadGAM1 atmospheric circulation model. The Himalaya–Tibet mountain complex is found to play a crucial role in shaping the North Pacific storm track. The northward deflection of the westerly flow around northern Tibet generates an extensive pool of very cold air in the northeastern tip of the Asian continent, which strengthens the meridional temperature gradient and favors baroclinic growth in the western Pacific. The Kuroshio SST front is also instrumental in strengthening the Pacific storm track through its impact on near-surface baroclinicity, while the warm waters around Indonesia tend to weaken it through the impact on baroclinicity of stationary Rossby waves propagating poleward from the convective heating regions. Three mechanisms by which the Atlantic storm track may be affected by changes in the boundary conditions upstream of the Rockies are discussed. In the model configuration used here, stationary Rossby waves emanating from Tibet appear to weaken the North Atlantic storm track substantially, whereas those generated over the cold waters off Peru appear to strengthen it. Changes in eddy-driven surface winds over the Pacific generally appear to modify the flow over the Rocky Mountains, leading to consistent modifications in the Atlantic storm track. The evidence for each of these mechanisms is, however, ultimately equivocal in these simulations.

scholarly journals Geographical Dependence of Upper-Level Blocking Formation Associated with Intraseasonal Amplification of the Siberian High

2005 ◽  
Vol 62 (12) ◽  
pp. 4441-4449 ◽  
Author(s):  
Koutarou Takaya ◽  
Hisashi Nakamura
Keyword(s):  
Wave Train ◽  
Grid Point ◽  
Far East ◽  
Storm Track ◽  
The Tibetan Plateau ◽  
Cold Air ◽  
Upper Troposphere ◽  
Siberian High ◽  
The North ◽  
Upper Level

Abstract Intraseasonal amplification events of the surface Siberian high in winter are generally associated with blocking ridge formation in the upper troposphere. Composite analysis applied to the 20 strongest intraseasonal events of upper-level anticyclonic anomalies at every grid point over Siberia reveals that the blocking formation differs fundamentally between the east and west of the climatological upper-level trough over the Far East. To the west, what can be called “wave-train (Atlantic-origin)” type is common, where a blocking ridge develops from anomalies as a component of a quasi-stationary Rossby wave train propagating across the Eurasian continent under modest feedback forcing from transient eddies. To the east of the trough, what can be called “Pacific-origin” type dominates, where a blocking ridge forms in association with westward development of anticyclonic anomalies from the North Pacific under stronger feedback forcing from the Pacific storm track. Regardless of a particular type of blocking formation in the upper troposphere, a cold air outbreak tends to occur once anomalously cold air reaches the northeastern slope of the Tibetan Plateau.

Some physical drivers of changes in the winter storm tracks over the North Atlantic and Mediterranean during the Holocene

2010 ◽  
Vol 368 (1931) ◽  
pp. 5185-5223 ◽  
Author(s):  
David James Brayshaw ◽  
Brian Hoskins ◽  
Emily Black
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Storm Track ◽  
Storm Tracks ◽  
The Holocene ◽  
The North ◽  
The North Atlantic ◽  
The Mediterranean ◽  
The Impact ◽  
Holocene Period

The winter climate of Europe and the Mediterranean is dominated by the weather systems of the mid-latitude storm tracks. The behaviour of the storm tracks is highly variable, particularly in the eastern North Atlantic, and has a profound impact on the hydroclimate of the Mediterranean region. A deeper understanding of the storm tracks and the factors that drive them is therefore crucial for interpreting past changes in Mediterranean climate and the civilizations it has supported over the last 12 000 years (broadly the Holocene period). This paper presents a discussion of how changes in climate forcing (e.g. orbital variations, greenhouse gases, ice sheet cover) may have impacted on the ‘basic ingredients’ controlling the mid-latitude storm tracks over the North Atlantic and the Mediterranean on intermillennial time scales. Idealized simulations using the HadAM3 atmospheric general circulation model (GCM) are used to explore the basic processes, while a series of timeslice simulations from a similar atmospheric GCM coupled to a thermodynamic slab ocean (HadSM3) are examined to identify the impact these drivers have on the storm track during the Holocene. The results suggest that the North Atlantic storm track has moved northward and strengthened with time since the Early to Mid-Holocene. In contrast, the Mediterranean storm track may have weakened over the same period. It is, however, emphasized that much remains still to be understood about the evolution of the North Atlantic and Mediterranean storm tracks during the Holocene period.

scholarly journals The Role of Tropical, Midlatitude, and Polar Cloud-Radiative Changes for the Midlatitude Circulation Response to Global Warming

2020 ◽  
Vol 33 (18) ◽  
pp. 7927-7943 ◽  
Author(s):  
Nicole Albern ◽  
Aiko Voigt ◽  
David W. J. Thompson ◽  
Joaquim G. Pinto
Keyword(s):  
Global Warming ◽  
Storm Track ◽  
Radiative Heating ◽  
Sea Surface ◽  
Relative Importance ◽  
Upper Troposphere ◽  
The Mean ◽  
The Impact ◽  
Circulation Changes

AbstractPrevious studies showed that global cloud-radiative changes contribute half or more to the midlatitude atmospheric circulation response to global warming. Here, we investigate the relative importance of tropical, midlatitude, and polar cloud-radiative changes for the annual-mean, wintertime, and summertime circulation response across regions in AMIP-like simulations. To this end, we study global warming simulations from the ICON model run with the cloud-locking method and prescribed sea surface temperatures, which isolate the impact of changes in atmospheric cloud-radiative heating. Tropical cloud changes dominate the global cloud impact on the 850 hPa zonal wind, jet strength, and storm track responses across most seasons and regions. For the jet shift, a more diverse picture is found. In the annual mean and DJF, tropical and midlatitude cloud changes contribute substantially to the poleward jet shift in all regions. The poleward jet shift is further supported by polar cloud changes across the Northern Hemisphere but not in the Southern Hemisphere. In JJA, the impact of regional cloud changes on the jet position is small, consistent with an overall small jet shift during this season. The jet shift can be largely understood via the anomalous atmospheric cloud-radiative heating in the tropical and midlatitude upper troposphere. The circulation changes are broadly consistent with the influence of cloud-radiative changes on upper-tropospheric baroclinicity and thus the mean potential energy available for conversion into eddy kinetic energy. Our results help to explain the jet response to global warming and highlight the importance of tropical and midlatitude cloud-radiative changes for this response.

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