scholarly journals Acceleration of the Brewer–Dobson Circulation due to Increases in Greenhouse Gases

2008 ◽  
Vol 65 (8) ◽  
pp. 2731-2739 ◽  
Author(s):  
Rolando R. Garcia ◽  
William J. Randel
Keyword(s):  
Wave Propagation ◽  
Temperature Distribution ◽  
Greenhouse Gases ◽  
Gravity Waves ◽  
Greenhouse Effect ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Community Climate Model ◽  
Mean Temperature ◽  
Westerly Winds

Abstract The acceleration of the Brewer–Dobson circulation under rising concentrations of greenhouse gases is investigated using the Whole Atmosphere Community Climate Model. The circulation strengthens as a result of increased wave driving in the subtropical lower stratosphere, which in turn occurs because of enhanced propagation and dissipation of waves in this region. Enhanced wave propagation is due to changes in tropospheric and lower-stratospheric zonal-mean winds, which become more westerly. Ultimately, these trends follow from changes in the zonal-mean temperature distribution caused by the greenhouse effect. The circulation in the middle and upper stratosphere also accelerates as a result of filtering of parameterized gravity waves by stronger subtropical westerly winds.

scholarly journals On the Momentum Budget of the Quasi-Biennial Oscillation in the Whole Atmosphere Community Climate Model

2018 ◽  
Vol 76 (1) ◽  
pp. 69-87 ◽  
Author(s):  
Rolando R. Garcia ◽  
Jadwiga H. Richter
Keyword(s):  
Gravity Waves ◽  
Climate Model ◽  
Equatorial Waves ◽  
Quasi Biennial Oscillation ◽  
Community Climate Model ◽  
Westerly Jet ◽  
Momentum Budget ◽  
Zonal Wavenumber ◽  
Biennial Oscillation ◽  
Community Climate

Abstract This study documents the contribution of equatorial waves and mesoscale gravity waves to the momentum budget of the quasi-biennial oscillation (QBO) in a 110-level version of the Whole Atmosphere Community Climate Model. The model has high vertical resolution, 500 m, above the boundary layer and through the lower and middle stratosphere, decreasing gradually to about 1.5 km near the stratopause. Parameterized mesoscale gravity waves and resolved equatorial waves contribute comparable easterly and westerly accelerations near the equator. Westerly acceleration by resolved waves is due mainly to Kelvin waves of zonal wavenumber in the range k = 1–15 and is broadly distributed about the equator. Easterly acceleration near the equator is due mainly to Rossby–gravity (RG) waves with zonal wavenumbers in the range k = 4–12. These RG waves appear to be generated in situ during both the easterly and westerly phases of the QBO, wherever the meridional curvature of the equatorial westerly jet is large enough to produce reversals of the zonal-mean barotropic vorticity gradient, suggesting that they are excited by the instability of the jet. The RG waves produce a characteristic pattern of Eliassen–Palm flux divergence that includes strong easterly acceleration close to the equator and westerly acceleration farther from the equator, suggesting that the role of the RG waves is to redistribute zonal-mean vorticity such as to neutralize the instability of the westerly jet. Insofar as unstable RG waves might be present in the real atmosphere, mixing due to these waves could have important implications for transport in the tropical stratosphere.

scholarly journals A new method to diagnose the contribution of anthropogenic activities to temperature: temperature tagging

2013 ◽  
Vol 6 (2) ◽  
pp. 417-427 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Greenhouse Gases ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Climate Model ◽  
Co2 Concentration ◽  
Base Case ◽  
Atmospheric Absorption ◽  
The Difference ◽  
The Impact ◽  
Longwave Flux

Abstract. This study presents a new methodology, called temperature tagging. It keeps track of the contributions of individual processes to temperature within a climate model simulation. As a first step and as a test bed, a simple box climate model is regarded. The model consists of an atmosphere, which absorbs and emits radiation, and of a surface, which reflects, absorbs and emits radiation. The tagging methodology is used to investigate the impact of the atmosphere on surface temperature. Four processes are investigated in more detail and their contribution to the surface temperature quantified: (i) shortwave influx and shortwave atmospheric absorption ("sw"), (ii) longwave atmospheric absorption due to non-CO2 greenhouse gases ("nC"), (iii) due to a base case CO2 concentration ("bC"), and (iv) due to an enhanced CO2 concentration ("eC"). The differential equation for the temperature in the box climate model is decomposed into four equations for the tagged temperatures. This method is applied to investigate the contribution of longwave absorption to the surface temperature (greenhouse effect), which is calculated to be 68 K. This estimate contrasts an alternative calculation of the greenhouse effect of slightly more than 30 K based on the difference of the surface temperature with and without an atmosphere. The difference of the two estimates is due to a shortwave cooling effect and a reduced contribution of the shortwave to the total downward flux: the shortwave absorption of the atmosphere results in a reduced net shortwave flux at the surface of 192 W m−2, leading to a cooling of the surface by 14 K. Introducing an atmosphere results in a downward longwave flux at the surface due to atmospheric absorption of 189 W m−2, which roughly equals the net shortwave flux of 192 W m−2. This longwave flux is a result of both the radiation due to atmospheric temperatures and its longwave absorption. Hence the longwave absorption roughly accounts for 91 W m−2 out of a total of 381 W m−2 (roughly 25%) and therefore accounts for a temperature change of 68 K. In a second experiment, the CO2 concentration is doubled, which leads to an increase in surface temperature of 1.2 K, resulting from a temperature increase due to CO2 of 1.9 K, due to non-CO2 greenhouse gases of 0.6 K and a cooling of 1.3 K due to a reduced importance of the solar heating for the surface and atmospheric temperatures. These two experiments show the feasibility of temperature tagging and its potential as a diagnostic for climate simulations.

Observational validation of parameterized gravity waves from tropical convection in the Whole Atmosphere Community Climate Model (WACCM)

2020 ◽  
Author(s):  
M. Joan Alexander ◽  
Chuntao Liu ◽  
Julio T. Bacmeister ◽  
Martina Bramberger ◽  
Albert Hertzog ◽  
...  
Keyword(s):  
Gravity Waves ◽  
Climate Model ◽  
Tropical Convection ◽  
Community Climate Model ◽  
Community Climate

scholarly journals Carbon Dioxide Emission Pathways Avoiding Dangerous Ocean Impacts

2012 ◽  
Vol 4 (3) ◽  
pp. 212-229 ◽  
Author(s):  
K. Kvale ◽  
K. Zickfeld ◽  
T. Bruckner ◽  
K. J. Meissner ◽  
K. Tanaka ◽  
...  
Keyword(s):  
Greenhouse Gases ◽  
Ocean Acidification ◽  
Sea Level Rise ◽  
Sea Level ◽  
Co2 Emissions ◽  
Climate Model ◽  
Ice Sheet ◽  
Global Mean Temperature ◽  
Mean Temperature ◽  
Global Mean

Abstract Anthropogenic emissions of greenhouse gases could lead to undesirable effects on oceans in coming centuries. Drawing on recommendations published by the German Advisory Council on Global Change, levels of unacceptable global marine change (so-called guardrails) are defined in terms of global mean temperature, sea level rise, and ocean acidification. A global-mean climate model [the Aggregated Carbon Cycle, Atmospheric Chemistry and Climate Model (ACC2)] is coupled with an economic module [taken from the Dynamic Integrated Climate–Economy Model (DICE)] to conduct a cost-effectiveness analysis to derive CO2 emission pathways that both minimize abatement costs and are compatible with these guardrails. Additionally, the “tolerable windows approach” is used to calculate a range of CO2 emissions paths that obey the guardrails as well as a restriction on mitigation rate. Prospects of meeting the global mean temperature change guardrail (2° and 0.2°C decade−1 relative to preindustrial) depend strongly on assumed values for climate sensitivity: at climate sensitivities >3°C the guardrail cannot be attained under any CO2 emissions reduction strategy without mitigation of non-CO2 greenhouse gases. The ocean acidification guardrail (0.2 unit pH decline relative to preindustrial) is less restrictive than the absolute temperature guardrail at climate sensitivities >2.5°C but becomes more constraining at lower climate sensitivities. The sea level rise and rate of rise guardrails (1 m and 5 cm decade−1) are substantially less stringent for ice sheet sensitivities derived in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report, but they may already be committed to violation if ice sheet sensitivities consistent with semiempirical sea level rise projections are assumed.

scholarly journals Gravity waves simulated by high-resolution Whole Atmosphere Community Climate Model

2014 ◽  
Vol 41 (24) ◽  
pp. 9106-9112 ◽  
Author(s):  
H.-L. Liu ◽  
J. M. McInerney ◽  
S. Santos ◽  
P. H. Lauritzen ◽  
M. A. Taylor ◽  
...  
Keyword(s):  
High Resolution ◽  
Gravity Waves ◽  
Climate Model ◽  
Community Climate Model ◽  
Community Climate

scholarly journals A new method to diagnose the contribution of anthropogenic activities to temperature: temperature tagging

2012 ◽  
Vol 5 (4) ◽  
pp. 3183-3215 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Greenhouse Gases ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Climate Model ◽  
Co2 Concentration ◽  
Base Case ◽  
Atmospheric Absorption ◽  
The Difference ◽  
The Impact ◽  
Longwave Flux

Abstract. This study presents a new methodology, called temperature tagging. It keeps track of the contributions of individual processes to temperature within a climate model simulation. As a first step and as a test bed a simple box climate model is regarded. The model consists of an atmosphere, which absorbs and emits radiation and of a surface, which reflects, absorbs and emits radiation. The tagging methodology is used to investigate the impact of the atmosphere on surface temperature. Four processes are investigated in more detail and their contribution to the surface temperature quantified: (i) shortwave influx and shortwave atmospheric absorption ("sw"), (ii) longwave atmospheric absorption due to non-CO2 greenhouse gases ("nC"), (iii) due to a base case CO2 concentration ("bC"), and (iv) due to an enhanced CO2 concentration ("eC"). The differential equation for the temperature in the box climate model is decomposed into four equations for the tagged temperatures. This method is applied to investigate the contribution of longwave absorption to the surface temperature (greenhouse effect), which is calculated to be 68 K. This estimate contrasts an alternative calculation of the greenhouse effect of slightly more than 30 K based on the difference of the surface temperature with and without an atmosphere. The difference of the two estimates is due to a shortwave cooling effect and a reduced contribution of the shortwave to the total downward flux: The shortwave absorption of the atmosphere results in a reduced net shortwave flux at the surface of 192 W m−2, leading to a cooling of the surface by 14 K. Introducing an atmosphere results in a downward longwave flux at the surface due to atmospheric absorption of 189 W m−2, which roughly equals the net shortwave flux of 192 W m−2. This longwave flux is a result of both, the radiation due to atmospheric temperatures and its longwave absorption. Hence the longwave absorption roughly accounts for 91 W m−2 out of a total of 381 W m−2 (roughly 25%) and therefore accounts for a temperature of 68 K. In a second experiment, the CO2 concentration is doubled, which leads to an increase in surface temperature of 1.2 K, resulting from an temperature increase due to CO2 of 1.9 K, due to non-CO2 greenhouse gases of 0.6 K and a cooling of 1.3 K due to a reduced importance of the solar heating for the surface and atmospheric temperatures. These two experiments show the feasibility of temperature tagging and its potential as a diagnostic for climate simulations.

scholarly journals Dynamically Forced Increase of Tropical Upwelling in the Lower Stratosphere

2011 ◽  
Vol 68 (6) ◽  
pp. 1214-1233 ◽  
Author(s):  
Hella Garny ◽  
Martin Dameris ◽  
William Randel ◽  
Greg E. Bodeker ◽  
Rudolf Deckert
Keyword(s):  
Wave Propagation ◽  
Annual Cycle ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Deep Convection ◽  
Positive Trend ◽  
Wave Forcing ◽  
Upward Shift ◽  
Wave Flux ◽  
Subtropical Jets

Abstract Drivers of upwelling in the tropical lower stratosphere are investigated using the E39C-A chemistry–climate model. The climatological annual cycle in upwelling and its wave forcing are compared to the interim ECMWF Re-Analysis (ERA-Interim). The strength in tropical upwelling and its annual cycle can be largely explained by local resolved wave forcing. The climatological mean forcing is due to both stationary planetary-scale waves that originate in the tropics and extratropical transient synoptic-scale waves that are refracted equatorward. Increases in atmospheric greenhouse gas (GHG) concentrations to 2050 force a year-round positive trend in tropical upwelling, which maximizes in the lowermost stratosphere. Tropical ascent is balanced by downwelling between 20° and 40°. Strengthening of tropical upwelling can be explained by stronger local forcing by resolved wave flux convergence, which is driven in turn by processes initiated by increases in tropical sea surface temperatures (SSTs). Higher tropical SSTs cause a strengthening of the subtropical jets and modification of deep convection affecting latent heat release. While the former can modify wave propagation and dissipation, the latter affects tropical wave generation. The dominant mechanism leading to enhanced vertical wave propagation into the lower stratosphere is an upward shift of the easterly shear zone due to the strengthening and upward shift of the subtropical jets.

scholarly journals Dynamical Mechanism for the Increase in Tropical Upwelling in the Lowermost Tropical Stratosphere during Warm ENSO Events

2010 ◽  
Vol 67 (7) ◽  
pp. 2331-2340 ◽  
Author(s):  
N. Calvo ◽  
R. R. Garcia ◽  
W. J. Randel ◽  
D. R. Marsh
Keyword(s):  
Gravity Waves ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Southern Oscillation ◽  
Dynamical Mechanism ◽  
Wind Pattern ◽  
Upper Troposphere ◽  
Enso Events ◽  
Anomalous Wind ◽  
Recent Version

Abstract The Brewer–Dobson circulation strengthens in the lowermost tropical stratosphere during warm El Niño–Southern Oscillation (ENSO) events. Dynamical analyses using the most recent version of the Whole Atmosphere Community Climate Model show that this is due mainly to anomalous forcing by orographic gravity waves, which maximizes in the Northern Hemisphere subtropics between 18 and 22 km, especially during the strongest warm ENSO episodes. Anomalies in the meridional gradient of temperature in the upper troposphere and lower stratosphere (UTLS) are produced during warm ENSO events, accompanied by anomalies in the location and intensity of the subtropical jets. This anomalous wind pattern alters the propagation and dissipation of the parameterized gravity waves, which ultimately force increases in tropical upwelling in the lowermost stratosphere. During cold ENSO events a similar signal, but of opposite sign, is present in the model simulations. The signals in ozone and water vapor produced by ENSO events in the UTLS are also investigated.

scholarly journals Attribution of recent ozone changes in the Southern Hemisphere mid-latitudes using statistical analysis and chemistry-climate model simulations

2017 ◽  
Author(s):  
Guang Zeng ◽  
Olaf Morgenstern ◽  
Hisako Shiona ◽  
Alan J. Thomas ◽  
Richard R. Querel ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Greenhouse Gases ◽  
Southern Hemisphere ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Lower Troposphere ◽  
Positive Trend ◽  
Tropopause Height ◽  
Significant Positive Trend ◽  
Tropopause Region

Abstract. Ozone (O3) trends and variability from a 28-year (1987–2014) ozonesonde record at Lauder, New Zealand, have been analysed and interpreted using a statistical model and a global chemistry-climate model (CCM). Lauder is a clean rural measurement site often representative of the Southern Hemisphere (SH) mid-latitude background atmosphere. O3 trends over this period at this location are characterised by a significant positive trend below 6 km, a significant negative trend in the tropopause region and the lower stratosphere between 9 to 15 km, and no significant trend in the free troposphere (6–9 km) and the stratosphere above 15 km. We find that significant positive trends in lower tropospheric ozone are correlated with increasing temperature and decreasing relative humidity at the surface over this period, whereas significant negative trends in the upper troposphere and the lower stratosphere appear to be strongly linked to an upward trend of the tropopause height, associated with increasing greenhouse gases. Relative humidity and the tropopause height also dominate O3 variability at Lauder in the lower troposphere and the tropopause region, respectively. We perform an attribution of these trends to anthropogenic forcings including O3 precursors, greenhouse gases (GHGs), and O3 depleting substances (ODSs), using CCM simulations. Results indicate that changes in anthropogenic O3 precursors contribute significantly to stratospheric O3 reduction, changes in ODSs contribute significantly to tropospheric O3 reduction, and increased GHGs contribute significantly to stratospheric O3 increases at Lauder. Methane (CH4) likely contributes positively to O3 trends in both the troposphere and the stratosphere, but the contribution is not significant at the 95 % confidence level over this period. An extended analysis of CCM results covering 1960–2010 (i.e. starting well before the observations) reveals significant contributions from all forcings to O3 trends at Lauder, i.e., increases of GHGs and the increase of CH4 alone all contribute significantly to O3 increases, net increases of ODSs lead to O3 reduction, and increases of non-methane O3 precursors cause O3 increases in the troposphere and reductions in the stratosphere. This study suggests that a long-term ozonesonde record obtained at a SH mid-latitude background site (corroborated by a surface O3 record at a nearby SH mid-latitude site, Baring Head, which also shows a significant positive trend) is a useful indicator for detecting atmospheric composition and climate change associated with human activities.

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