scholarly journals Oceanic moisture sources contributing to wintertime Euro-Atlantic blocking

2021 ◽  
Vol 2 (3) ◽  
pp. 819-840
Author(s):  
Ayako Yamamoto ◽  
Masami Nonaka ◽  
Patrick Martineau ◽  
Akira Yamazaki ◽  
Young-Oh Kwon ◽  
...  
Keyword(s):  
Large Scale ◽  
Dispersion Model ◽  
Reanalysis Data ◽  
Upper Troposphere ◽  
Dry Process ◽  
Maintenance Mechanism ◽  
Moisture Sources ◽  
The Pacific ◽  
Lagrangian Dispersion ◽  
Heat And Moisture

Abstract. Although conventionally attributed to dry dynamics, increasing evidence points to a key role of moist dynamics in the formation and maintenance of blocking events. The source of moisture crucial for these processes, however, remains elusive. In this study, we identify the moisture sources responsible for latent heating associated with the wintertime Euro-Atlantic blocking events detected over 31 years (1979–2010). To this end, we track atmospheric particles backward in time from the blocking centres for a period of 10 d using an offline Lagrangian dispersion model applied to atmospheric reanalysis data. The analysis reveals that 28 %–55 % of particles gain heat and moisture from the ocean over the course of 10 d, with higher percentages for the lower altitudes from which particles are released. Via large-scale ascent, these moist particles transport low-potential-vorticity (PV) air of low-altitude, low-latitude origins into the upper troposphere, where the amplitude of blocking is the most prominent, in agreement with previous studies. The PV of these moist particles remains significantly lower compared to their dry counterparts throughout the course of 10 d, preferentially constituting blocking cores. Further analysis reveals that approximately two-thirds of the moist particles source their moisture locally from the Atlantic, while the remaining one-third of moist particles source it from the Pacific. There is also a small fraction of moist particles that take up moisture from both the Pacific and Atlantic basins, which undergo a large-scale uplift over the Atlantic using moisture picked up over both basins. The Gulf Stream and Kuroshio and their extensions as well as the eastern Pacific northeast of Hawaii not only provide heat and moisture to moist particles but also act as “springboards” for their large-scale, cross-isentropic ascent, where its extent strongly depends on the humidity content at the time of the ascent. While the particles of Atlantic origin swiftly ascend just before their arrival at blocking, those of Pacific origin begin their ascent a few days earlier, after which they carry low-PV air in the upper troposphere while undergoing radiative cooling just as dry particles. A previous study identified a blocking maintenance mechanism, whereby low-PV air is selectively absorbed into blocking systems to prolong blocking lifetime. As they used an isentropic trajectory analysis, this mechanism was regarded as a dry process. We found that these moist particles that are fuelled over the Pacific can also act to maintain blocks in the same manner, revealing that what appears to be a blocking maintenance mechanism governed by dry dynamics alone can, in fact, be of moist origin.

scholarly journals Oceanic origins for wintertime Euro-Atlantic blocking

2020 ◽  
Author(s):  
Ayako Yamamoto ◽  
Masami Nonaka ◽  
Patrick Martineau ◽  
Akira Yamazaki ◽  
Young-Oh Kwon ◽  
...  
Keyword(s):  
Large Scale ◽  
Dispersion Model ◽  
Reanalysis Data ◽  
Low Latitude ◽  
The Pacific ◽  
Atlantic Origin ◽  
Lagrangian Dispersion ◽  
Low Altitude ◽  
Heat And Moisture

Abstract. Although conventionally attributed to dry dynamics, increasing evidence points to a key role of moist dynamics in the formation and maintenance of blocking events. The source of moisture crucial for these processes, however, remains elusive. In this study, we identify the moisture sources responsible for latent heating associated with the wintertime Euro-Atlantic blocking events detected over 31 years (1979–2010). To this end, we track atmospheric particles backward in time from the blocking centres for a period of 10 days, using an offline Lagrangian dispersion model applied to an atmospheric reanalysis data. The analysis reveals that 36–55 % of particles gain a massive amount of heat and moisture from the ocean over the course of 10 days. Via large-scale ascent, these moist particles transport low potential vorticity (PV) air of low-altitude, low-latitude origins to the upper troposphere where the amplitude of blocking is the most prominent, consistent with the previous studies. PV of these moist particles remains significantly lower compared to their dry counterparts throughout the course of 10 days, preferentially constituting blocking cores. Further analysis reveals that approximately two-thirds of the moist particles source their moisture locally from the Atlantic, while the remaining one-third from the Pacific. The Gulf Stream and Kuroshio and their extensions, as well as the eastern Pacific northeast of Hawaii, not only provide heat and moisture to the particles but also act as springboards for their large-scale, cross-isentropic ascent. While the particles of the Atlantic origin swiftly ascend just before their arrival at the blocking, those of the Pacific origin ascend additional few days earlier, after which they carry low PV in the same manner as dry particles. Thus, our study reveals that what may appear to be a blocking maintenance mechanism governed by dry dynamics alone can, in fact, be of moist origin.

Increased frequency of Eurasian double jets linked to summer heat extremes in Europe

2021 ◽  
Author(s):  
Efi Rousi ◽  
Kai Kornhuber ◽  
Goratz Beobide Arsuaga ◽  
Fei Luo ◽  
Dim Coumou
Keyword(s):  
Zonal Wind ◽  
Large Scale ◽  
Driving Forces ◽  
Linear Regression Analysis ◽  
Reanalysis Data ◽  
Self Organizing Maps ◽  
Upper Troposphere ◽  
The North ◽  
Heat Extremes ◽  
Different Levels

<p>Persistent summer extremes, such as heatwaves and droughts, can have considerable impacts on nature and societies. There is evidence that weather persistence has increased in Europe over the past decades, in association to changes in atmosphere dynamics, but uncertainties remain and the driving forces are not yet well understood. </p><p>Particularly for Europe, the jet stream may affect surface weather significantly by modulating the North Atlantic storm tracks. Here, we examine the hypothesis that high-latitude warming and decreased westerlies in summer result in more double jets, consisting of two distinct maxima of the zonal wind in the upper troposphere, over the Eurasian sector. Previous work has shown that such double jet states are related to persistent blocking-like circulation in the mid-latitudes. </p><p>We adapt a dynamical perspective of heat extreme trends by looking at large scale circulation and in particular, changes in the zonal mean zonal wind in different levels of the upper troposphere. We define clusters of jet states with the use of Self-Organizing Maps and analyze their characteristics. We find an increase in frequency and persistence of a cluster of double jet states for the period 1979-2019 during July-August (in ERA5 reanalysis data). Those states are linked to increased surface temperature and more frequent heatwaves compared to climatology over western, central, and northern Europe. Significant positive double jet anomalies are found to be dominant in the days preceding and/or coinciding with some of the most intense historical heatwaves in Europe, such as those of 2003 and 2018. A linear regression analysis shows that the increase in frequency and persistence of double jet states may explain part of the strong upward trend in heat extremes over these European regions.</p>

Global and hemispheric climate variations affecting the Southern Ocean

2004 ◽  
Vol 16 (4) ◽  
pp. 401-413 ◽  
Author(s):  
IAN SIMMONDS ◽  
JOHN C. KING
Keyword(s):  
Southern Ocean ◽  
Fresh Water ◽  
Large Scale ◽  
Mechanical Energy ◽  
Large Fraction ◽  
World Ocean ◽  
Southern Annular Mode ◽  
Reanalysis Data ◽  
Data Set ◽  
The Pacific

The hemispheric and regional atmospheric circulation influences the Southern Ocean in many and profound ways, including intense air-sea fluxes of momentum, energy, fresh water and dissolved gases. The Southern Ocean ventilates a large fraction of the world ocean and hence these influences are spread globally. We use the NCEP-2 reanalysis data set to diagnose aspects of the large-scale atmospheric structure and variability and explore how these impact on the Southern Ocean. We discuss how the ‘Southern Annular Mode’ and the ‘Pacific-South American’ pattern influence the Southern Ocean, particularly in the eastern Pacific. We review the importance of atmospheric eddies in Southern Ocean climate, and the role they play in the transport of mechanical energy into the ocean. The fluxes of fresh water across the air-sea boundary influence strongly the processes of water mass formation. It is shown that climatological precipitation exceeds evaporation over most of the Southern Ocean. When averaged over the ocean from 50°S to the Antarctic coast the annual mean excess is 0.80 mm day−1. The magnitude of the flux displays only a small measure of seasonality, and its largest value of 0.92 mm day−1 occurs in summer.

scholarly journals High-ozone layers in the middle and upper troposphere above Central Europe: potential import from the stratosphere along the subtropical jet stream

2011 ◽  
Vol 11 (17) ◽  
pp. 9343-9366 ◽  
Author(s):  
T. Trickl ◽  
N. Bärtsch-Ritter ◽  
H. Eisele ◽  
M. Furger ◽  
R. Mücke ◽  
...  
Keyword(s):  
Transport Model ◽  
Dispersion Model ◽  
Warm Season ◽  
Particle Dispersion ◽  
Jet Stream ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Subtropical Jet Stream ◽  
Subtropical Jet ◽  
The Pacific

Abstract. Specific very dry high-ozone layers, starting roughly two days after the onset of high-pressure periods during the warm season, have been reproducibly observed in the middle and upper troposphere with the ozone lidar in Garmisch-Partenkirchen (Germany). These episodes, previously not understood, were recently analysed based on extending backward simulations with the FLEXPART particle dispersion model to as many as twenty days and on jet-stream analyses including calculations with the LAGRANTO transport model. In all six cases analysed the model results indicate ozone import from the stratosphere on an extremely long path along the subtropical jet stream over the Pacific Ocean, Asia and, in part, all the way back to the Atlantic Ocean. The analysis suggests that stratospheric influence is the most important factor for the increase in ozone and is related to rather shallow transfer of air from the stratosphere into the upper- and mid-tropospheric air streams observed with the lidar. Contributions from the boundary layers of East Asia and North America are just occasionally present, in one case documented by a very dense aerosol plume from the Asian deserts. The considerable vertical and temporal extent of many of these layers and peak ozone mixing ratios between 80 and 150 ppb suggest that the observations are related to an important mechanism for stratosphere-to-troposphere transport (STT) and also confirm the model predictions of pronounced and persistent STT along the subtropical jet stream.

scholarly journals A 15 year record of high-frequency, in situ measurements of hydrogen at Mace Head, Ireland

2009 ◽  
Vol 9 (5) ◽  
pp. 20195-20227 ◽  
Author(s):  
A. Grant ◽  
C. S. Witham ◽  
P. G. Simmonds ◽  
A. J. Manning ◽  
S. O'Doherty
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Dispersion Model ◽  
Research Station ◽  
Seasonal Cycles ◽  
Air Masses ◽  
Lagrangian Dispersion ◽  
Long Term Trends ◽  
Northern Hemispheric ◽  
Primary Emissions

Abstract. Continuous high-frequency measurements of atmospheric molecular hydrogen have been made at Mace Head atmospheric research station on the west coast of Ireland from March 1994 to December 2008. The presented data provides a wealth of information on long term trends and seasonal cycles of hydrogen in background northern hemispheric air. Individual measurements have been sorted using a Lagrangian dispersion model to separate clean background air from regionally polluted European air masses and those transported from southerly latitudes. No significant trend was observed in background northern hemispheric air over the 15 year record, elevations in yearly means were accounted for from large scale biomass burning events. Seasonal cycles show the expected pattern with maxima in spring and minima in late autumn. The mean hydrogen mole fraction in baseline northern hemispheric air was found to be 500.1 ppb. Air transported from southerly latitudes showed an elevation from baseline mean of 11.0 ppb, reflecting both the latitudinal gradient of hydrogen, with higher concentrations in the southern hemisphere, and the large photochemical source of hydrogen from southerly latitudes. European polluted air masses arriving at Mace Head showed mean elevation of 5.3 ppb from baseline air masses, reflecting hydrogen's source from primary emissions like fossil fuel combustion. Forward modelling of transport of hydrogen to Mace Head suggests that the ratio of hydrogen to carbon monoxide in primary emissions is considerably less in non-traffic sources than traffic sources.

scholarly journals The Interannual Variability of the Tropical Divergence Tilt and Its Connection with the Extratropical Circulation

2021 ◽  
Vol 34 (1) ◽  
pp. 259-275
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Interannual Variability ◽  
Momentum Flux ◽  
Large Scale ◽  
Theoretical Work ◽  
Stationary Wave ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
The Pacific ◽  
Divergence Field ◽  
Two Parameters

AbstractPrevious theoretical work has suggested that the strength of the divergent eddy momentum flux in the deep tropics, due to correlations between rotational zonal velocities and divergent meridional velocities, increases with the meridional tilt of the large-scale divergence field. To test that idea, this work investigates the interannual variability of the divergent eddy momentum flux in reanalysis data. Consistent with the theory, it is found that the eddy momentum flux variability is driven by two main parameters: the amplitude of the tropical stationary wave and the tilt of the divergence field. Together, these two parameters account for 80% (90%) of the interannual eddy momentum flux variance during boreal (austral) winter. The interannual variability of these parameters is governed by the internal atmospheric dynamics. During boreal winter, interannual changes in MJO variability explain nearly half of the interannual variance in the stationary wave amplitude, depending on whether on average MJO anomalies interfere constructively or destructively with the stationary wave. The interannual variability of the divergence phase tilt is modulated by tropical–extratropical interactions in the Pacific. The tilt increases during the negative phase of the west Pacific Oscillation associated with a dipole of upper-level divergence (convergence) on the northern (southern) side of the Pacific jet exit region.

scholarly journals High-ozone layers in the middle and upper troposphere above Central Europe: strong import from the stratosphere over the Pacific Ocean

2009 ◽  
Vol 9 (1) ◽  
pp. 3113-3166 ◽  
Author(s):  
T. Trickl ◽  
N. Bärtsch-Ritter ◽  
H. Eisele ◽  
M. Furger ◽  
R. Mücke ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Dispersion Model ◽  
Warm Season ◽  
Particle Dispersion ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Trajectory Calculations ◽  
The Pacific ◽  
The Pacific Ocean ◽  
Air Streams

Abstract. Very dry high-ozone layers have been repeatedly observed with the ozone lidar in Garmisch-Partenkirchen (Germany) starting one or two days after the onset of high-pressure periods during the warm season. These episodes have been analysed by trajectory calculations and extended simulations with the FLEXPART particle dispersion model. Mixed contributions from the stratosphere over the Pacific Ocean and the boundary layers of East Asia and North America were found. The stratospheric influence is mostly dominating and caused by a rather shallow transfer from the stratosphere into these rapid upper- and mid-tropospheric air streams. The considerable vertical extent of these layers and peak ozone mixing ratios between 80 and 150 ppb suggest an important mechanism for stratosphere-to-troposphere transport.

A coupled heat and moisture tracking framework to assess water cycle changes in a warming climate

2020 ◽  
Author(s):  
Jessica Keune ◽  
Dominik L. Schumacher ◽  
Diego G. Miralles
Keyword(s):  
Water Cycle ◽  
Dispersion Model ◽  
Reanalysis Data ◽  
Particle Dispersion ◽  
Warming Climate ◽  
Numerical Noise ◽  
Spatial Dependencies ◽  
Energy Conserving ◽  
Coupled Heat And Moisture ◽  
Heat And Moisture

<p>The expected intensification of the global water cycle in a warming climate comes along with an increase in the frequency and intensity of extreme events, such as droughts and floods. From a drought perspective, local limitations of terrestrial evaporation can cause a reduction of water vapor in the atmosphere and thus further induce local and remote precipitation deficits. Despite the existing myriad of tools and models to assess the origin of precipitation, trends and uncertainties in such source–sink relationships remain largely unexplored. The main reason is the scarcity of observations to explore these relationships and validate moisture-tracking models, which are commonly subject to assumptions that limit their reliability and applicability. Lagrangian models, for example, typically establish source–sink relationships based on moisture changes along air parcel trajectories, yet tend to be heavily affected by numerical noise. Moreover, they do not assess the plausibility of a given moisture change by considering the increasing saturation point of air with increasing temperatures, which hampers reliable assessments of trends under global warming. </p><p>Here, we present a holistic framework for the process-based evaluation of atmospheric trajectories to infer source–sink relationships of moisture. Building upon previous process-based evaluations of trajectories, we extend the analysis to a coupled heat and moisture diagnosis that includes physics-based limits for the detection of evaporation and precipitation from humidity changes along each trajectory. The framework comprises three steps: (i) the coupled moisture and heat diagnosis of fluxes from Lagrangian trajectories using multi-objective criteria, (ii) the attribution of sources following a mass- and energy-conserving algorithm, and (iii) the bias correction of diagnosed fluxes and the corresponding source–sink relationship. Applying this framework to simulations from the Lagrangian particle dispersion model FLEXPART, driven with ERA-Interim reanalysis data, allows us to quantify errors and uncertainties associated with the resulting source–sink relationships. A comparison to alternative methodologies illustrates the benefit of our coupled heat and moisture tracking approach. Moreover, the multivariate character of this framework paves the way for a cohesive assessment of the spatial dependencies that cause water cycle changes in a warming climate.</p>

scholarly journals A 15 year record of high-frequency, in situ measurements of hydrogen at Mace Head, Ireland

2010 ◽  
Vol 10 (3) ◽  
pp. 1203-1214 ◽  
Author(s):  
A. Grant ◽  
C. S. Witham ◽  
P. G. Simmonds ◽  
A. J. Manning ◽  
S. O'Doherty
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Dispersion Model ◽  
Research Station ◽  
Seasonal Cycles ◽  
Air Masses ◽  
Northern Latitudes ◽  
Lagrangian Dispersion ◽  
Northern Hemispheric ◽  
Primary Emissions

Abstract. Continuous high-frequency measurements of atmospheric molecular hydrogen have been made at Mace Head atmospheric research station on the west coast of Ireland from March 1994 to December 2008. The presented data provides information on long term trends and seasonal cycles of hydrogen in background northern hemispheric air. Individual measurements have been sorted using a Lagrangian dispersion model to separate clean background air from regionally polluted European air masses and those transported from southerly latitudes. No significant trend was observed in background northern hemispheric air over the 15 year record, elevations in yearly means were accounted for from large scale biomass burning events. Seasonal cycles show the expected pattern with maxima in spring and minima in late autumn. The mean hydrogen mole fraction in baseline northern hemispheric air was found to be 500.1 ppb. Air transported from southerly latitudes showed an elevation from baseline mean of 11.0 ppb, reflecting both the latitudinal gradient of hydrogen, with higher concentrations in the Southern Hemisphere, and the photochemical source of hydrogen from low northern latitudes. European polluted air masses arriving at Mace Head showed mean elevation of 5.3 ppb from baseline air masses, reflecting hydrogen's source from primary emissions like fossil fuel combustion. Forward modelling of transport of hydrogen to Mace Head suggests that the ratio of hydrogen to carbon monoxide in primary emissions is considerably less in non-traffic sources than traffic sources.

scholarly journals Blocking and Rossby Wave Breaking on the Dynamical Tropopause in the Southern Hemisphere

2007 ◽  
Vol 64 (8) ◽  
pp. 2881-2898 ◽  
Author(s):  
P. Berrisford ◽  
B. J. Hoskins ◽  
E. Tyrlis
Keyword(s):  
New Zealand ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Potential Temperature ◽  
Upper Troposphere ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Westerly Flow

Rossby wave breaking on the dynamical tropopause in the Southern Hemisphere (the −2-PVU surface) is investigated using the ERA-40 dataset. The indication of wave breaking is based on reversal in the meridional gradient of potential temperature, and persistent large-scale wave breaking is taken as a strong indication that blocking may be present. Blocking in the midlatitudes is found to occur predominantly during wintertime in the Pacific and is most vigorous in the east Pacific, while during summertime, the frequency of blocking weakens and its extent becomes confined to the west Pacific. The interannual variability of blocking is found to be high. Wave breaking occurs most frequently on the poleward side of the polar jet and has some, but not all, of the signatures of blocking, so it is referred to as high-latitude blocking. In general, cyclonic wave breaking occurs on the poleward side of the polar jet, otherwise anticyclonic breaking occurs. However, at least in wintertime, wave breaking in the New Zealand/west to mid-Pacific sector between the polar and subtropical jets is a mixture between cyclonic and anticyclonic types. Together, episodes of wave breaking and enhanced westerly flow describe much of the variability in the seasonal Antarctic Oscillation (AnO) index and give a synoptic manifestation of it with a focus on the date line and Indian Ocean that is in agreement with the centers of action for the AnO. During summertime, anticyclonic wave breaking in the upper troposphere is also to be found near 30°S in both the Pacific and Atlantic, and appears to be associated with Rossby waves propagating into the subtropics from the New Zealand region.

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