scholarly journals Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010

2011 ◽  
Vol 11 (11) ◽  
pp. 31067-31090 ◽  
Author(s):  
R. D. Hudson
Keyword(s):  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
Hadley Cell ◽  
Jet Streams ◽  
Quasi Biennial Oscillation ◽  
Subtropical Jet ◽  
Direct Radiative Forcing ◽  
Major Factors

Abstract. Previous studies have shown that the mean latitude of the subtropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley. Ferrel, and Polar meridionally overturning circulation cells in the troposphere, each of which has a distinct temperature profile. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1) changes in the Tropical land/ocean temperature, (2) direct radiative forcing from greenhouse gases in the troposphere, (3) changes in the temperature of the lower Tropical stratosphere, (4) the Quasi-Biennial Oscillation, and (5) volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Over the period of study the poleward movement of the subtropical jet streams was 3.7±0.3 degrees in the Northern Hemisphere and 6.5±0.2 degrees in the Southern Hemisphere, with a net expansion of the Tropical belt of 10.2 degrees. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the subtropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns, temperatures, precipitation and the hydrologic cycle.

scholarly journals Measurements of the movement of the jet streams at mid-latitudes, in the Northern and Southern Hemispheres, 1979 to 2010

2012 ◽  
Vol 12 (16) ◽  
pp. 7797-7808 ◽  
Author(s):  
R. D. Hudson
Keyword(s):  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
Hadley Cell ◽  
Jet Streams ◽  
Quasi Biennial Oscillation ◽  
Subtropical Jet ◽  
Direct Radiative Forcing ◽  
Major Factors

Abstract. Previous studies have shown that the mean latitude of the sub-tropical jet streams in both hemispheres have shifted toward the poles over the last few decades. This paper presents a study of the movement of both the subtropical and Polar fronts, the location of the respective jet streams, between 1979 and 2010 at mid-latitudes, using total ozone measurements to identify the sharp horizontal boundary that occurs at the position of the fronts. Previous studies have shown that the two fronts are the boundaries of three distinct regimes in the stratosphere, corresponding to the Hadley, Ferrel, and polar meridionally overturning circulation cells in the troposphere. Over the period of study the horizontal area of the Hadley cell has increased at latitudes between 20 and 60 degrees while the area of the Polar cell has decreased. A linear regression analysis was performed to identify the major factors associated with the movement of the subtropical jet streams. These were: (1) changes in the Tropical land plus ocean temperature, (2) direct radiative forcing from greenhouse gases in the troposphere, (3) changes in the temperature of the lower tropical stratosphere, (4) the Quasi-Biennial Oscillation, and (5) volcanic eruptions. The dominant mechanism was the direct radiative forcing from greenhouse gases. Between 1979 and 2010 the poleward movement of the subtropical jet streams was 3.7 ± 0.3 degrees in the Northern Hemisphere and 6.5 ± 0.2 degrees in the Southern Hemisphere. Previous studies have shown that weather systems tend to follow the jet streams. The observed poleward movement in both hemispheres over the past thirty years represents a significant change in the position of the sub-tropical jet streams, which should lead to significant latitudinal shifts in the global weather patterns and the hydrologic cycle.

scholarly journals Interannual variation patterns of total ozone and lower stratospheric temperature in observations and model simulations

2006 ◽  
Vol 6 (2) ◽  
pp. 349-374 ◽  
Author(s):  
W. Steinbrecht ◽  
B. Haßler ◽  
C. Brühl ◽  
M. Dameris ◽  
M. A. Giorgetta ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Total Ozone ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
The Arctic ◽  
Interannual Variations ◽  
Quasi Biennial Oscillation ◽  
Model Simulations ◽  
Stratospheric Temperature

Abstract. We report results from a multiple linear regression analysis of long-term total ozone observations (1979 to 2000, by TOMS/SBUV), of temperature reanalyses (1958 to 2000, NCEP), and of two chemistry-climate model simulations (1960 to 1999, by ECHAM4.L39(DLR)/CHEM (=E39/C), and MAECHAM4-CHEM). The model runs are transient experiments, where observed sea surface temperatures, increasing source gas concentrations (CO2, CFCs, CH4, N2O, NOx), 11-year solar cycle, volcanic aerosols and the quasi-biennial oscillation (QBO) are all accounted for. MAECHAM4-CHEM covers the atmosphere from the surface up to 0.01 hPa (≈80 km). For a proper representation of middle atmosphere (MA) dynamics, it includes a parametrization for momentum deposition by dissipating gravity wave spectra. E39/C, on the other hand, has its top layer centered at 10 hPa (≈30 km). It is targeted on processes near the tropopause, and has more levels in this region. Despite some problems, both models generally reproduce the observed amplitudes and much of the observed low-latitude patterns of the various modes of interannual variability in total ozone and lower stratospheric temperature. In most aspects MAECHAM4-CHEM performs slightly better than E39/C. MAECHAM4-CHEM overestimates the long-term decline of total ozone, whereas underestimates the decline over Antarctica and at northern mid-latitudes. The true long-term decline in winter and spring above the Arctic may be underestimated by a lack of TOMS/SBUV observations in winter, particularly in the cold 1990s. Main contributions to the observed interannual variations of total ozone and lower stratospheric temperature at 50 hPa come from a linear trend (up to -10 DU/decade at high northern latitudes, up to -40 DU/decade at high southern latitudes, and around -0.7 K/decade over much of the globe), from the intensity of the polar vortices (more than 40 DU, or 8 K peak to peak), the QBO (up to 20 DU, or 2 K peak to peak), and from tropospheric weather (up to 20 DU, or 2 K peak to peak). Smaller variations are related to the 11-year solar cycle (generally less than 15 DU, or 1 K), or to ENSO (up to 10 DU, or 1 K). These observed variations are replicated well in the simulations. Volcanic eruptions have resulted in sporadic changes (up to -30 DU, or +3 K). At low latitudes, patterns are zonally symmetric. At higher latitudes, however, strong, zonally non-symmetric signals are found close to the Aleutian Islands or south of Australia. Such asymmetric features appear in the model runs as well, but often at different longitudes than in the observations. The results point to a key role of the zonally asymmetric Aleutian (or Australian) stratospheric anti-cyclones for interannual variations at high-latitudes, and for coupling between polar vortex strength, QBO, 11-year solar cycle and ENSO.

scholarly journals Interannual variation patterns of total ozone and temperature in observations and model simulations

2005 ◽  
Vol 5 (5) ◽  
pp. 9207-9248 ◽  
Author(s):  
W. Steinbrecht ◽  
B. Haßler ◽  
C. Brühl ◽  
M. Dameris ◽  
M. A. Giorgetta ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Total Ozone ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Linear Regression Analysis ◽  
Volcanic Eruptions ◽  
Interannual Variations ◽  
Quasi Biennial Oscillation ◽  
Model Simulations ◽  
Stratospheric Temperature

Abstract. We report results from a multiple linear regression analysis of long-term total ozone observations (1979 to 2002, by TOMS/SBUV), of temperature reanalyses (1958 to 2002, NCEP), and of two chemistry-climate model simulations (1960 to 1999, by ECHAM4.L39(DLR)/CHEM (=E39/C), and MAECHAM4-CHEM). The model runs are transient experiments, where observed sea surface temperatures, increasing source gas concentrations (CO2, CFCs, CH4, N2O, NOx), 11-year solar cycle, volcanic aerosols and the quasi-biennial oscillation (QBO) are all accounted for. MAECHAM4-CHEM covers the atmosphere from the surface up to 0.01 hPa (≈80 km). For a proper representation of middle atmosphere (MA) dynamics, it includes a parametrization for momentum deposition by dissipating gravity wave spectra. E39/C, on the other hand, has its top layer centered at 10 hPa (≈30 km). It is targeted on processes near the tropopause, and has more levels in this region. Both models reproduce the observed amplitudes and much of the observed low-latitude patterns of the various modes of interannual variability, MAECHAM4-CHEM somewhat better than E39/C. Total ozone and lower stratospheric temperature show similar patterns. Main contributions to the interannual variations of total ozone and lower stratospheric temperature at 50 hPa come from a linear trend (up to −30 Dobson Units (DU) per decade, or −1.5 K/decade), the QBO (up to 25 DU, or 2.5 K peak to peak), the intensity of the polar vortices (up to 50 DU, or 5 K peak to peak), and from tropospheric weather (up to 30 DU, or 3 K peak to peak). Smaller variations are related to the 11-year solar cycle (generally less than 25 DU, or 2.5 K), and to ENSO (up to 15 DU, or 1.5 K). Volcanic eruptions have resulted in sporadic changes (up to −40 DU, or +3 K). Most stratospheric variations are connected to the troposphere, both in observations and simulations. At low latitudes, patterns are zonally symmetric. At higher latitudes, however, strong, zonally non-symmetric signals are found close to the Aleutian Islands or south of Australia. Such asymmetric features appear in the model runs as well, but often at different longitudes than in the observations. The results point to a key role of the zonally asymmetric Aleutian (or Australian) stratospheric anti-cyclones for interannual variations at high- latitudes, and for coupling between polar vortex strength, QBO, 11-year solar cycle and ENSO.

scholarly journals Tropospheric Double Jets, Meridional Cells, and Eddies: A Case Study and Idealized Simulations

2007 ◽  
Vol 135 (9) ◽  
pp. 3118-3133 ◽  
Author(s):  
Isabella Bordi ◽  
Klaus Fraedrich ◽  
Frank Lunkeit ◽  
Alfonso Sutera
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Baroclinic Instability ◽  
Low Frequency ◽  
Circulation Model ◽  
Hadley Cell ◽  
Zonal Wind Anomaly ◽  
Subtropical Jet ◽  
Low Frequency Variability ◽  
Summer Hemisphere

Abstract The observed low-frequency variability of the zonally averaged atmospheric circulation in the winter hemisphere is found to be amenable to an interpretation where the subtropical jet is flanked by a secondary midlatitude one. Observations also suggest that the link between the stratosphere and the troposphere modulates the variability of the tropospheric double-jet structure. Moreover, the summer hemisphere is characterized by a strong midlatitude jet sided by an intermittent subtropical one and easterly winds in the stratosphere. This work addresses the question about the role of eddies in generating and maintaining these key features of the general circulation by means of a simplified general circulation model. Model solutions for different parameter settings and external radiative forcings in the stratosphere are studied with and without eddies active on the system. The following main findings are noted. 1) Eddy dynamics alone, through the baroclinic instability processes in an atmosphere subjected to radiative forcing and dissipation, may account for the observed meridional variance of the tropospheric jets. 2) The Hadley cell can extend to the pole overlying the Ferrel cell, a feature supported by observations in the summer hemisphere. 3) The meridional temperature gradient reversal in the summer stratosphere contributes to the observed low-frequency variability introducing an intermittent formation of a subtropical jet and the occurrence of easterlies in the tropical stratosphere. 4) Poleward propagation of the zonal wind anomaly is, when it occurs, related to the activity of synoptic eddies.

scholarly journals Stratospheric SO<sub>2</sub> and sulphate aerosol, model simulations and satellite observations

2013 ◽  
Vol 13 (4) ◽  
pp. 11395-11425 ◽  
Author(s):  
C. Brühl ◽  
J. Lelieveld ◽  
M. Höpfner ◽  
H. Tost
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Lower Boundary ◽  
Circulation Model ◽  
Volcanic Eruptions ◽  
Satellite Observations ◽  
Quasi Biennial Oscillation ◽  
Tropospheric Aerosol

Abstract. A multiyear study with the atmospheric chemistry general circulation model EMAC with the aerosol module GMXe at high altitude resolution demonstrates that the sulfur gases COS and SO2, the latter from low-latitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. The model consistently uses the same parameters in the troposphere and stratosphere for 7 aerosol modes applied. Lower boundary conditions for COS and other long-lived trace gases are taken from measurement networks, while estimates of volcanic SO2 emissions are based on satellite observations. We show comparisons with satellite data for aerosol extinction (e.g. SAGE) and SO2 in the middle atmosphere (MIPAS on ENVISAT). This corroborates the interannual variability induced by the Quasi-Biennial Oscillation, which is internally generated by the model. The model also realistically simulates the radiative effects of stratospheric and tropospheric aerosol including the effects on the model dynamics. The medium strength volcanic eruptions of 2005 and 2006 exerted a nonnegligible radiative forcing of up to −0.6 W m−2 in the tropics, while the large Pinatubo eruption caused a maximum though short term tropical forcing of about −10 W m−2. The study also shows that observed upper stratospheric SO2 can be simulated accurately only when a sulphur sink on meteoritic dust is included and the photolysis of gaseous H2SO4 in the near infrared is higher than assumed previously.

scholarly journals ITCZ shift and extratropical teleconnections drive ENSO response to volcanic eruptions

2020 ◽  
Author(s):  
Francesco S.R. Pausata ◽  
Davide Zanchettin ◽  
Christina Karamperidou ◽  
Rodrigo Caballero ◽  
David S. Battisti
Keyword(s):  
Radiative Forcing ◽  
Initial Conditions ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
Ensemble Simulations ◽  
Direct Radiative Forcing ◽  
Volcanic Aerosols ◽  
And Shifts ◽  
The Tropics ◽  
Extratropical Circulation

&lt;p&gt;The mechanisms through which volcanic eruptions impact the El Ni&amp;#241;o-Southern Oscillation (ENSO) state are still controversial. Previous studies have invoked direct radiative forcing, an ocean dynamical thermostat (ODT) mechanism and shifts of the Intertropical Convergence Zone (ITCZ), among others, to explain the ENSO response to tropical eruptions. Here, these mechanisms are tested using ensemble simulations with an Earth System Model in which volcanic aerosols from a Tambora-like eruption are confined either in the Northern or the Southern Hemisphere. We show that the primary drivers of the ENSO response are the shifts of the ITCZ together with extratropical circulation changes, which affect the tropics; the ODT mechanism does not operate in our simulations. Our study highlights the importance of initial conditions in the ENSO response to tropical volcanic eruptions and provides explanations for the predominance of post-eruption El Ni&amp;#241;o events and for the occasional post-eruption La Ni&amp;#241;a in observations and reconstructions.&lt;/p&gt;

scholarly journals Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO<sub>2</sub>injection studied with the LMDZ-S3A model

2018 ◽  
Vol 18 (4) ◽  
pp. 2769-2786 ◽  
Author(s):  
Christoph Kleinschmitt ◽  
Olivier Boucher ◽  
Ulrich Platt
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Quasi Biennial Oscillation ◽  
Detailed Model ◽  
Mass Unit ◽  
Modelling Studies ◽  
Injection Rates

Abstract. The enhancement of the stratospheric sulfate aerosol layer has been proposed as a method of geoengineering to abate global warming. Previous modelling studies found that stratospheric aerosol geoengineering (SAG) could effectively compensate for the warming by greenhouse gases on the global scale, but also that the achievable cooling effect per sulfur mass unit, i.e. the forcing efficiency, decreases with increasing injection rate. In this study we use the atmospheric general circulation model LMDZ with the sectional aerosol module S3A to determine how the forcing efficiency depends on the injected amount of SO2, the injection height, and the spatio-temporal pattern of injection. We find that the forcing efficiency may decrease more drastically for larger SO2 injections than previously estimated. As a result, the net instantaneous radiative forcing does not exceed the limit of –2 W m−2 for continuous equatorial SO2 injections and it decreases (in absolute value) for injection rates larger than 20 Tg S yr−1. In contrast to other studies, the net radiative forcing in our experiments is fairly constant with injection height (in a range 17 to 23 km) for a given amount of SO2 injected. Also, spreading the SO2 injections between 30∘ S and 30∘ N or injecting only seasonally from varying latitudes does not result in a significantly larger (i.e. more negative) radiative forcing. Other key characteristics of our simulations include a consequent stratospheric heating, caused by the absorption of solar and infrared radiation by the aerosol, and changes in stratospheric dynamics, with a collapse of the quasi-biennial oscillation at larger injection rates, which has impacts on the resulting spatial aerosol distribution, size, and optical properties. But it has to be noted that the complexity and uncertainty of stratospheric processes cause considerable disagreement among different modelling studies of stratospheric aerosol geoengineering. This may be addressed through detailed model intercomparison activities, as observations to constrain the simulations of stratospheric aerosol geoengineering are not available and analogues (such as volcanic eruptions) are imperfect.

scholarly journals The role of carbonyl sulphide as a source of stratospheric sulphate aerosol and its impact on climate

2012 ◽  
Vol 12 (3) ◽  
pp. 1239-1253 ◽  
Author(s):  
C. Brühl ◽  
J. Lelieveld ◽  
P. J. Crutzen ◽  
H. Tost
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Ice Core ◽  
Stratospheric Aerosol ◽  
Quasi Biennial Oscillation ◽  
Direct Radiative Forcing ◽  
Upward Transport ◽  
Carbonyl Sulphide ◽  
Aerosol Module

Abstract. Globally, carbonyl sulphide (COS) is the most abundant sulphur gas in the atmosphere. Our chemistry-climate model (CCM) of the lower and middle atmosphere with aerosol module realistically simulates the background stratospheric sulphur cycle, as observed by satellites in volcanically quiescent periods. The model results indicate that upward transport of COS from the troposphere largely controls the sulphur budget and the aerosol loading of the background stratosphere. This differs from most previous studies which indicated that short-lived sulphur gases are also important. The model realistically simulates the modulation of the particulate and gaseous sulphur abundance in the stratosphere by the quasi-biennial oscillation (QBO). In the lowermost stratosphere organic carbon aerosol contributes significantly to extinction. Further, using a chemical radiative convective model and recent spectra, we compute that the direct radiative forcing efficiency by 1 kg of COS is 724 times that of 1 kg CO2. Considering an anthropogenic fraction of 30% (derived from ice core data), this translates into an overall direct radiative forcing by COS of 0.003 W m−2. The direct global warming potentials of COS over time horizons of 20 and 100 yr are GWP(20 yr) = 97 and GWP(100 yr) = 27, respectively (by mass). Furthermore, stratospheric aerosol particles produced by the photolysis of COS (chemical feedback) contribute to a negative direct solar radiative forcing, which in the CCM amounts to −0.007 W m−2 at the top of the atmosphere for the anthropogenic fraction, more than two times the direct warming forcing of COS. Considering that the lifetime of COS is twice that of stratospheric aerosols the warming and cooling tendencies approximately cancel.

scholarly journals Size-Resolved Stratospheric Aerosol Distributions after Pinatubo Derived from a Coupled Aerosol-Chemistry-Climate Model

2018 ◽  
Author(s):  
Timofei Sukhodolov ◽  
Jian-Xiong Sheng ◽  
Aryeh Feinberg ◽  
Bei-Ping Luo ◽  
Thomas Peter ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Radiative Forcing ◽  
Climate Model ◽  
Reference Model ◽  
Volcanic Eruptions ◽  
Stratospheric Aerosol ◽  
Aerosol Layer ◽  
Aerosol Chemistry ◽  
Quasi Biennial Oscillation ◽  
Aerosol Parameters

Abstract. We evaluate how the coupled aerosol-chemistry-climate model SOCOL-AER represents the influence of the 1991 eruption of Mt. Pinatubo on stratospheric aerosol loading, aerosol microphysical processes, radiative effects, and atmospheric chemistry. The aerosol module includes comprehensive sulfur chemistry and microphysics, in which the particle size distribution is represented by 40 size bins spanning radii from 0.39 nm to 3.2 μm. Radiative forcing is computed online using aerosol optical properties calculated according to Mie theory. SOCOL-AER simulations are compared with satellite and in situ measurements of aerosol parameters, temperature reanalyses, and ozone observations. In addition to the reference model configuration, we performed a series of sensitivity experiments looking at different processes affecting the aerosol layer. An accurate sedimentation scheme is found to be essential to prevent particles diffusing too rapidly to high and low altitudes. The aerosol radiative feedback and the use of a nudged quasi-biennial oscillation help to keep aerosol in the tropics and significantly affect the evolution of the stratospheric aerosol burden, which improves the agreement with observed aerosol mass distributions. Changes in the aerosol distribution affected by an inclusion of Van der Waals forces to the particle coagulation scheme suggest improvements in particle effective radius, although other parameters (such as aerosol longevity) deteriorate. Modification of the Pinatubo emission rate also improves some aerosol parameters, while worsens others compared to observations. Observations themselves are highly uncertain and render it difficult to conclusively judge the necessity of further model reconfiguration. In conclusion, our results show that SOCOL-AER is capable of predicting the most important global-scale atmospheric and climate effects following volcanic eruptions, which is also a prerequisite for improved understanding of anthropogenic effects from sulfur emissions.

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