Variability and changes of the stratospheric large scale circulation and possible consequences for ozone streamer events

2020 ◽  
Author(s):  
Küchelbacher Lisa ◽  
Laux Dominik ◽  
Michael Bittner
Keyword(s):  
Wind Shear ◽  
Large Scale ◽  
Ground Level ◽  
Meridional Wind ◽  
Spectral Model ◽  
Solar Cycles ◽  
Meridional Transport ◽  
Air Masses ◽  
The North ◽  
Mode Decomposition

<p>Planetary waves (PW) dominate the meridional Brewer-Dobson circulation in the stratosphere and therewith, the large-scale mass transport of ozone. As PW break, ozone poor air masses are irreversibly mixed into mid-latitudes. Due to the disproportionate warming of the North Pole, an increase in PW activity (PWA) is expected. This should also have consequences for ozone streamer events.</p><p>We derived the PWA of ERA 5 and Interim Reanalysis temperature from ground level up the mesosphere. We identify Ozone-streamer events with a statistical based approach on the basis of total column concentration measured by GOME-2. We deconvoluted the time series of the PWA and the ozone-streamer events with the empirical mode decomposition method (EMD). Moreover, we developed a simple spectral model of the meridional wind shear on the basis of PW. This model serves as a measure of the atmospheric instability in the stratosphere.</p><p>As we deconvolute the PWA with the EMD we find signatures of QBO, ENSO and solar cycles and quantify their contributions. As PW dominate the circulation in the stratosphere, it appears to be a coherent consequence that ozone streamers are modulated on the same time scales as the PWA.With the spectral model of the meridional wind shear we find regions in the atmosphere, where PW are most likely to break. As a result there is an increased meridional transport of air masses, in particular of ozone. This is why ozone streamers occur most frequently at the transition zones from ocean to continent; strongest from North Atlantic to Europe. Moreover, we find significant long-term trends of the PWA in the stratosphere. Due to the increase of the PWA in the stratosphere, ozone streamer events are likely to occur more often in the future.</p>

scholarly journals Atmospheric Circulation Effects on Wind Speed Variability at Turbine Height

2007 ◽  
Vol 46 (4) ◽  
pp. 445-456 ◽  
Author(s):  
Katherine Klink
Keyword(s):  
Wind Speed ◽  
Pressure Gradient ◽  
Large Scale ◽  
Ground Level ◽  
The Arctic ◽  
Circulation Index ◽  
Regression Equations ◽  
Change Models ◽  
Wind Speeds ◽  
The North

Abstract Mean monthly wind speed at 70 m above ground level is investigated for 11 sites in Minnesota for the period 1995–2003. Wind speeds at these sites show significant spatial and temporal coherence, with prolonged periods of above- and below-normal values that can persist for as long as 12 months. Monthly variation in wind speed primarily is determined by the north–south pressure gradient, which captures between 22% and 47% of the variability (depending on the site). Regression on wind speed residuals (pressure gradient effects removed) shows that an additional 6%–15% of the variation can be related to the Arctic Oscillation (AO) and Niño-3.4 sea surface temperature (SST) anomalies. Wind speeds showed little correspondence with variation in the Pacific–North American (PNA) circulation index. The effect of the strong El Niño of 1997/98 on the wind speed time series was investigated by recomputing the regression equations with this period excluded. The north–south pressure gradient remains the primary determinant of mean monthly 70-m wind speeds, but with 1997/98 removed the influence of the AO increases at nearly all stations while the importance of the Niño-3.4 SSTs generally decreases. Relationships with the PNA remain small. These results suggest that long-term patterns of low-frequency wind speed (and thus wind power) variability can be estimated using large-scale circulation features as represented by large-scale climatic datasets and by climate-change models.

scholarly journals Rapid transport of East Asian pollution to the deep tropics

2015 ◽  
Vol 15 (6) ◽  
pp. 3565-3573 ◽  
Author(s):  
M. J. Ashfold ◽  
J. A. Pyle ◽  
A. D. Robinson ◽  
E. Meneguz ◽  
M. S. M. Nadzir ◽  
...  
Keyword(s):  
East Asia ◽  
East Asian ◽  
Atmospheric Dispersion ◽  
Atmospheric Composition ◽  
Meridional Transport ◽  
Air Masses ◽  
The North ◽  
Westerly Winds ◽  
Modelling Environment ◽  
Cold Surges

Abstract. Anthropogenic emissions from East Asia have increased over recent decades. These increases have led to changes in atmospheric composition as far afield as North America under the prevailing westerly winds. Here we show that, during Northern Hemisphere (NH) winter, pollution originating in East Asia also directly affects atmospheric composition in the deep tropics. We present observations of marked intra-seasonal variability in the anthropogenic tracer perchloroethene (C2Cl4) collected at two locations in Borneo (117.84° E, 4.98° N and 118.00° E, 4.22° N) during the NH winter of 2008/2009. We use trajectories calculated with the Numerical Atmospheric-dispersion Modelling Environment to show that the observed enhancements in C2Cl4 mixing ratio are caused by rapid meridional transport, in the form of "cold surges", from the relatively polluted East Asian land mass. In these events air masses can move from ~35° N to Borneo in 4 days. We then present data from the Monitoring Atmospheric Composition and Climate reanalysis which suggest that air masses high in C2Cl4 may also contain levels of the pollutants carbon monoxide and ozone that are approximately double the typical "background" levels in Borneo. In addition to strengthening the meridional transport from the north, cold surges can enhance convection in Southeast Asia, and further trajectory calculations indicate that the polluted air masses can subsequently be lifted to the tropical upper troposphere. This suggests a potentially important connection between midlatitude pollution sources and the very low stratosphere.

Observations on collecting Parasites of Cacoecia histrionana (Froel.) (Lep., Tortricidae)

1952 ◽  
Vol 43 (1) ◽  
pp. 1-19 ◽  
Author(s):  
Jost M. Franz
Keyword(s):  
Large Scale ◽  
Choristoneura Fumiferana ◽  
Ground Level ◽  
Temperature Limit ◽  
Forest Edge ◽  
Mortality Factor ◽  
The North ◽  
Observation Area ◽  
Three Samples ◽  
Lower Temperature

Cacoecia histrionana Froel. a European relative of the North American spruce budworm, Choristoneura fumiferana Clem., was found in several localities on the north-eastern frontier of Bavaria in 1949, but was not abundant anywhere.Details are given of its biology based upon observations made during large-scale collecting in the summer of 1949, which yielded approximately 2,100 larvae of C. histrionana.An important characteristic of the species is the great variation in the stages of larval development present at any given time, which is apparently caused chiefly by the absence of diapause as a synchronising factor.Approximately 4°C. was found to be the lower temperature limit for movement and feeding of larvae ready for overwintering.Three samples of larvae taken in favourable localities showed that 0-15 to 0-70 larvae were present per metre length of spruce forest edge from ground level to a height of 2 metres. An estimate of the minimum population is made for a limited and well searched area.From 1803 C. histrionana larvae collected in the field, 15 species of primary parasites and four of hyperparasites were bred. Combining the result of three samples taken at different times the minimum reduction of the population after hibernation is calculated to be 66-8 per cent., the parasitism of pupae at least 13-5 per cent. Egg parasitism occurred.Nine of the 20 parasites, known hitherto from C. histrionana, have been bred from other hosts of the same animal community.The most important larval parasite was Meteorus ruficeps Nees which completes 2-3 generations in one generation of C. histrionana. A proportion of the population also overwinters in other Microlepidoptera, concentrating on C. histrionana in summer. Details of its life-history are given.Occasionally some larvae were found that had probably died from disease but disease, as a mortality factor, was of little consequence in the observation area in 1949.Mortality caused by parasites proved to be very important in affecting changes in the population density. This result does not agree with Eidmann's theory that the scarcity of C. histrionana is due to climatic control.

Large-scale flows in the Sun: Characteristics and time variations

2018 ◽  
Vol 13 (S340) ◽  
pp. 3-8
Author(s):  
Sarbani Basu
Keyword(s):  
Large Scale ◽  
Solar Rotation ◽  
Spectral Lines ◽  
Solar Interior ◽  
Data Sets ◽  
Solar Cycles ◽  
Zonal Flows ◽  
The North ◽  
Doppler Shifts ◽  
Time Variations

AbstractThe study of solar rotation has a 150-year history. Early studies were restricted to looking at the movement of sunspots; much later came studies using other tracers such as supergranules, and spectroscopic measurements using Doppler shifts of spectral lines. These studies also found evidence of other large-scale flows, such as the meridional flows in the north-south direction and the zonal flows, or torsional oscillations, parallel to the equator. However, until the 1980s, the study of solar rotation and large-scale flows was restricted to what could be observed on the solar surface. The advent of good helioseismic data changed that and gave us the means to study flows in the solar interior. Instruments like GONG, MDI and HMI have now collected helioseismic data for two solar cycles and these also allow us to study the large scale flows and their variations with time and solar activity. We review what the long data sets tell us about the these flows and discuss some of the differences between solar cycles 23 and 24.

Transport processes in the lowermost stratosphere - interhemispheric differences from trace gas observations during WISE and SouthTRAC

2020 ◽  
Author(s):  
Vera Bense ◽  
Peter Hoor ◽  
Björn Kluschat ◽  
Heiko Bozem ◽  
Daniel Kunkel ◽  
...  
Keyword(s):  
Large Scale ◽  
Trace Gases ◽  
Potential Temperature ◽  
Chemical Species ◽  
Transport Processes ◽  
Spatial And Temporal Variability ◽  
Remarkable Change ◽  
Transport Pathways ◽  
Air Masses ◽  
The North

<p><span>The lowermost stratosphere (LMS) plays an important role in determining the Earth's energy budget. </span><span>The chemical species that absorb and re-emit radiation in the LMS have a large spatial and temporal variability, which is controlled by mixing and transport processes. </span><span>T</span><span>he troposphere </span><span>and</span><span> middle stratosphere </span><span>affect the </span><span>LMS through large scale isentropic transport across the tropopause or downwelling from higher altitudes.</span></p><p><span>The data presented </span><span>in this study</span><span> originates from two HALO measurement campaigns that allow an interhemispheric comparison of the composition of the lower stratosphere: First the WISE campaign which took place in September and October 2017 over Europe and the North Atlantic, and second the mission SouthTRAC (September and November 2019) where measurements focused on South America and the region around the Antarctic Peninsula.</span></p><p><span>We use high resolution in-situ measurements of different trace gases (N<sub>2</sub>O, O<sub>3</sub>, CO<sub>2</sub>, CO, </span><span>SF<sub>6</sub></span><span>) in order to quantify transport time scales, to estimate tracer fluxes and to examine the prevalent transport pathways. Particularly correlations of trace gases of different lifetime can </span><span>provide</span><span> insight in the origin of air masses in the lower stratos</span><span>p</span><span>here and their transport histories.</span></p><p><span>During WISE a remarkable change of the N<sub>2</sub>O-O<sub>3</sub> correlation at the 380 K potential temperature isentrope indicates a surprisingly strong distinction between the lowermost stratosphere and the stratosphere, suggesting two mixing regimes. Above 380 K, isentropic mixing occurs between stratospheric air masses from the tropics to</span><span>wards</span><span> high latitudes leading to a slope flattening effect. In the lowermost stratosphere isentropic mixing connects the stratosphere with the tropical tropopause layer (TTL). Based on CO observations we quantify the contribution of air from the TTL to reach 60 % - 80 % in the LMS. Using CO<sub>2</sub> measurements we estimate a typical time scale of less than 30 days for transport from the TTL into the LMS. </span></p><p><span>These methods are applied to the observations during SouthTRAC as well. </span><span>Preliminary CO budget calculations suggest a smaller contribution of TTL air to the LMS in the order of 50 %. This analysis along with correlation s</span><span>lope s</span><span>tudies</span><span> allow for an interhemispheric and interseasonal comparison of the transport processes that were observed during the two measurement periods.</span></p>

Examining the Relationship between Tropopause Polar Vortices and Tornado Outbreaks

2021 ◽  
Author(s):  
Matthew T. Bray ◽  
Steven M. Cavallo ◽  
Howard B. Bluestein
Keyword(s):  
Wind Shear ◽  
Large Scale ◽  
Gulf Of Alaska ◽  
Static Stability ◽  
The Arctic ◽  
The North ◽  
Jet Streaks ◽  
Significant Patterns ◽  
Tornado Outbreaks ◽  
Jet Streak

AbstractMid-latitude jet streaks are known to produce conditions broadly supportive of tornado outbreaks, including forcing for large-scale ascent, increased wind shear, and decreased static stability. Although many processes may initiate a jet streak, we focus here on the development of jet maxima by interactions between the polar jet and tropopause polar vortices (TPVs). Originating from the Arctic, TPVs are long-lived circulations on the tropopause, which can be advected into the mid-latitudes. We hypothesize that when these vortices interact with the jet, they may contribute supplemental forcing for ascent and shear to tornado outbreaks, assuming other environmental conditions supportive of tornado development exist. Using a case set of significant tornado outbreak days from three states—Oklahoma, Illinois, and Alabama—we show that a vortex-jet streak structure is present (within 1250 km) in around two-thirds of tornado outbreaks. These vortices are commonly Arctic in origin (i.e., are TPVs) and are advected through a consistent path of entry into the mid-latitudes in the week before the outbreak, moving across the Northern Pacific and into the Gulf of Alaska before turning equatorward along the North American coast. These vortices are shown to be more intense and longer-lived than average. We further demonstrate that statistically significant patterns of wind shear, quasi-geostrophic forcing for ascent, and low static stability are present over the outbreak regions on the synoptic scale. In addition, we find that TPVs associated with tornadic events occur most often in the spring and are associated with greater low-level moisture when compared to non-tornadic TPV cases.

scholarly journals Impact of the North Atlantic Oscillation on the variations of aerosol ground levels through local processes over Europe

2013 ◽  
Vol 13 (5) ◽  
pp. 13889-13914 ◽  
Author(s):  
S. Jerez ◽  
P. Jimenez-Guerrero ◽  
J. P. Montávez ◽  
R. M. Trigo
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Large Scale ◽  
Ground Level ◽  
Oxidative Capacity ◽  
Radiation Balance ◽  
Potential Predictability ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract. This contribution assesses non-antropogenic variations in ground-level aerosol concentrations over Europe associated to changes in the phase of the North Atlantic Oscillation (NAO). The NAO controls a large amount of the European climate variability with asymmetric impacts in both time and space. Based on simulated data and focusing on how the local atmospheric processes (without considering large-scale mechanisms) governed by the NAO affect the levels of various aerosol species, this study highlights that positive NAO phases favor increased aerosols levels in southern (northern) regions in winter (summer), while negative NAO phases enhance them in northern (southern) regions in winter (summer). Variations are up to and over 100% for most aerosols, being clearly related to the NAO-impact on precipitation and wind, as they act to clean the atmosphere through removal and dispersion processes, and to the NAO-impact on the radiation balance (i.e. cloudiness) as it rebounds on the biogenic emitting activity and on the oxidative capacity of the atmosphere. Beyond deepening on the understanding of fundamental interactions between climate and air quality, these results provide a basis for improving the potential predictability of this later since much work is being done in order to gain accuracy in the NAO predictions.

scholarly journals Semi-Adiabatic Model of the Deep Stratification and Meridional Overturning

2011 ◽  
Vol 41 (4) ◽  
pp. 757-780 ◽  
Author(s):  
Timour Radko ◽  
Igor Kamenkovich
Keyword(s):  
Large Scale ◽  
Formation Rate ◽  
Three Dimensional ◽  
Meridional Overturning Circulation ◽  
Small Scale ◽  
Western Boundary ◽  
Meridional Transport ◽  
The North ◽  
Meridional Overturning ◽  
Circumpolar Current

An analytical model of the Atlantic deep stratification and meridional overturning circulation is presented that illustrates the dynamic coupling between the Southern Ocean and the midlatitude gyres. The model, expressed here in terms of the two-and-a-half-layer framework, predicts the stratification and meridional transport as a function of the mechanical and thermodynamic forcing at the sea surface. The approach is based on the classical elements of large-scale circulation theory—ideal thermocline, inertial western boundary currents, and eddy-controlled Antarctic Circumpolar Current (ACC) models—which are combined to produce a consistent three-dimensional view of the global overturning. The analytical tractability is achieved by assuming and subsequently verifying that the pattern of circulation in the model is largely controlled by adiabatic processes: the time-mean and eddy-induced isopycnal advection of buoyancy. The mean stratification of the lower thermocline is determined by the surface forcing in the ACC and, to a lesser extent, by the North Atlantic Deep Water formation rate. Although the vertical small-scale mixing and the diapycnal eddy-flux components can substantially influence the magnitude of overturning, their effect on the net stratification of the midlatitude ocean is surprisingly limited. The analysis in this paper suggests the interpretation of the ACC as an active lateral boundary layer that does not passively adjust to the prescribed large-scale solution but instead forcefully controls the interior pattern.

Evolution of idealized vortices in monsoon-like shears: application to monsoon depressions

2021 ◽  
Author(s):  
Michael Diaz ◽  
William R. Boos
Keyword(s):  
South Asian ◽  
Wind Shear ◽  
Asian Monsoon ◽  
Meridional Wind ◽  
Monsoon Depression ◽  
Moist Convection ◽  
Low Level ◽  
The North ◽  
Monsoon Depressions ◽  
Static Energy

AbstractThis study examines processes fundamental to the development of South Asian monsoon depressions using an array of integrations of an idealized convection-permitting numerical model. In each integration, a wave of initially small amplitude is subjected to a different amount of vertical and meridional wind shear, with temperature and moisture fields constructed according to realistic constraints. Based on the evolution of this disturbance into monsoon depression-like vortices, two features of the background environment emerge as important: the low-level gradient of moist static energy (MSE) and the low-level meridional shear. As the low-level MSE gradient steepens, the disturbance becomes stronger and produces more rain. This strengthening results from the interaction of the vortex with latent heat release by convection that is in turn organized by positive MSE advection in the northerly flow west of the vortex. In this region of advection, moister air from the north ascends along upward sloping isentropes, driving moist convection. The disturbance also becomes stronger with increasing meridional shear, which makes the environment more barotropically unstable. The absence of either of these two features of the background environment prevents substantial growth of the disturbance. Our results suggest that monsoon depression growth in South Asia is fostered by the coexistence of a strong low-level MSE gradient with strong meridional wind shear associated with the monsoon trough.

scholarly journals Do CGCMs Simulate the North American Monsoon Precipitation Seasonal–Interannual Variability?

2008 ◽  
Vol 21 (17) ◽  
pp. 4424-4448 ◽  
Author(s):  
Xin-Zhong Liang ◽  
Jinhong Zhu ◽  
Kenneth E. Kunkel ◽  
Mingfang Ting ◽  
Julian X. L. Wang
Keyword(s):  
Interannual Variability ◽  
Great Plains ◽  
Large Scale ◽  
Meridional Wind ◽  
Monsoon Onset ◽  
North American Monsoon ◽  
Interannual Variations ◽  
The Core ◽  
The North ◽  
Anomaly Pattern

Abstract This study uses the most recent simulations from all available fully coupled atmosphere–ocean general circulation models (CGCMs) to investigate whether the North American monsoon (NAM) precipitation seasonal–interannual variations are simulated and, if so, whether the key underlying physical mechanisms are correctly represented. This is facilitated by first identifying key centers where observed large-scale circulation fields and sea surface temperatures (SSTs) are significantly correlated with the NAM precipitation averages over the core region (central–northwest Mexico) and then examining if the modeled and observed patterns agree. Two new findings result from the analysis of observed NAM interannual variations. First, precipitation exhibits significantly high positive (negative) correlations with 200-hPa meridional wind centered to the northwest (southeast) of the core region in June and September (July and August). As such, wet conditions are associated with strong anomalous southerly upper-level flow on the northwest flank during the monsoon onset and retreat, but with anomalous northerly flow on the southeast flank, during the peak of the monsoon. They are often identified with a cyclonic circulation anomaly pattern over the central Great Plains for the July–August peak monsoon and, reversely, an anticyclonic anomaly pattern centered over the northern (southern) Great Plains for the June (September) transition. Second, wet NAM conditions in June and July are also connected with a SST pattern of positive anomalies in the eastern Pacific and negative anomalies in the Gulf of Mexico, acting to reduce the climatological mean gradient between the two oceans. This pattern suggests a possible surface gradient forcing that favors a westward extension of the North Atlantic subtropical ridge. These two observed features connected to the NAM serve as the metric for quantitative evaluation of the model performance in simulating the important NAM precipitation mechanisms. Out of 17 CGCMs, only the Meteorological Research Institute (MRI) model with a medium resolution consistently captures the observed NAM precipitation annual cycle (having a realistic amplitude and no phase shift) as well as interannual covariations with the planetary circulation patterns (having the correct sign and comparably high magnitude of correlation) throughout the summer. For the metric of correlations with 200-hPa meridional wind, there is general agreement among all CGCMs with observations for June and September. This may indicate that large-scale forcings dominate interannual variability for the monsoon onset and retreat, while variability of the peak of the monsoon in July and August may be largely influenced by local processes that are more challenging for CGCMs to resolve. For the metric of correlations with SSTs, good agreement is found only in June. These results suggest that the NAM precipitation interannual variability may likely be determined by large-scale circulation anomalies, while its predictability based on remote signals such as SSTs may not be sufficiently robust to be well captured by current CGCMs, with the exception of the June monsoon onset which is potentially more predictable.

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