Interhemispheric Coupling Mechanisms in the Middle Atmosphere of WACCM6

2019 ◽  
Vol 77 (3) ◽  
pp. 1101-1118
Author(s):  
A. K. Smith ◽  
N. M. Pedatella ◽  
Z. K. Mullen
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Wind ◽  
Wave Activity ◽  
High Latitudes ◽  
Flux Divergence ◽  
Model Version ◽  
Show Evidence ◽  
Summer Hemisphere ◽  
The Tropics

Abstract Simulations with the Community Earth System Model, version 2, using the Whole Atmosphere Community Climate Model version 6 [CESM2(WACCM6)] configuration, show evidence of dynamical coupling from the high latitudes of the winter middle atmosphere to the tropics and the middle and high latitudes of the summer hemisphere. Analysis of monthly and daily output covering 195 simulation years indicates that the response in the summer middle and high latitudes has a weak overall magnitude of a few kelvins or less in temperature but has a repeatable pattern whose structure and phase agree with observational studies. Lag correlation indicates that perturbations in wave activity in the winter stratosphere, as quantified by Eliassen–Palm (EP) flux divergence, are accompanied by perturbations in the transformed Eulerian-mean meridional wind extending into the summer hemisphere. There is not an appreciable correlation with momentum forcing in the summer hemisphere by either resolved waves or parameterized gravity waves. The rapid circulation response and the lack of a wave response in the summer hemisphere suggest that the interhemispheric coupling that is simulated in WACCM6 in both the stratosphere and the mesosphere owes its existence to a circulation that develops to restore balance to the zonally averaged state of the atmosphere. This is an alternative explanation for the coupling from the winter stratosphere to the summer mesosphere; previous studies have assumed a necessary role for wave activity in the summer hemisphere.

scholarly journals Large-Scale Waves in the Mesosphere and Lower Thermosphere Observed by SABER

2005 ◽  
Vol 62 (12) ◽  
pp. 4384-4399 ◽  
Author(s):  
Rolando R. Garcia ◽  
Ruth Lieberman ◽  
James M. Russell ◽  
Martin G. Mlynczak
Keyword(s):  
Large Scale ◽  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Normal Modes ◽  
Zonal Winds ◽  
Broadband Emission ◽  
Summer Hemisphere ◽  
Mean Structure ◽  
Mesosphere And Lower Thermosphere ◽  
The Tropics

Abstract Observations made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board NASA’s Thermosphere–Ionosphere–Mesosphere Energetics and Dynamics (TIMED) satellite have been processed using Salby’s fast Fourier synoptic mapping (FFSM) algorithm. The mapped data provide a first synoptic look at the mean structure and traveling waves of the mesosphere and lower thermosphere (MLT) since the launch of the TIMED satellite in December 2001. The results show the presence of various wave modes in the MLT, which reach largest amplitude above the mesopause and include Kelvin and Rossby–gravity waves, eastward-propagating diurnal oscillations (“non-sun-synchronous tides”), and a set of quasi-normal modes associated with the so-called 2-day wave. The latter exhibits marked seasonal variability, attaining large amplitudes during the solstices and all but disappearing at the equinoxes. SABER data also show a strong quasi-stationary Rossby wave signal throughout the middle atmosphere of the winter hemisphere; the signal extends into the Tropics and even into the summer hemisphere in the MLT, suggesting ducting by westerly background zonal winds. At certain times of the year, the 5-day Rossby normal mode and the 4-day wave associated with instability of the polar night jet are also prominent in SABER data.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (21) ◽  
pp. 6505-6525 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

scholarly journals Influence of Gravity Waves in the Tropical Upwelling: WACCM Simulations

2011 ◽  
Vol 68 (11) ◽  
pp. 2599-2612 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Young-Ha Kim ◽  
Hyun-Joo Choi ◽  
Jung-Yoon Kim
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Zonal Wind ◽  
Annual Cycle ◽  
Climate Model ◽  
Wave Drag ◽  
Flux Divergence ◽  
Relative Contribution ◽  
The Tropics ◽  
Convective Gravity Waves

Abstract The annual cycle of tropical upwelling and contributions by planetary and gravity waves are investigated from climatological simulations using the Whole Atmosphere Community Climate Model (WACCM) including three gravity wave drag (GWD) parameterizations (orographic, nonstationary background, and convective GWD parameterizations). The tropical upwelling is estimated by the residual mean vertical velocity at 100 hPa averaged over 15°S–15°N. This is well matched with an upwelling estimate from the balance of the zonal momentum and the mass continuity. A clear annual cycle of the tropical upwelling is found, with a Northern Hemispheric (NH) wintertime maximum and NH summertime minimum determined primarily by the Eliassen–Palm flux divergence (EPD), along with a secondary contribution from the zonal wind tendency. Gravity waves increase tropical upwelling throughout the year, and of the three sources the contribution by convective gravity wave drag (CGWD) is largest in most months. The relative contribution by all three GWDs to tropical upwelling is not larger than 5%. However, when tropical upwelling is estimated by net upward mass flux between turnaround latitudes where upwelling changes downwelling, annual mean contribution by all three GWDs is up to 19% at 70 hPa by orographic and convective gravity waves with comparable magnitudes. Effects of CGWD on upwelling are investigated by conducting an additional WACCM simulation without CGWD parameterization. It was found that including CGWD parameterization increases tropical upwelling not only directly by adding CGWD forcing, but also indirectly by modulating EPD and zonal wind tendency terms in the tropics.

scholarly journals Chemistry-climate model SOCOL: a validation of the present-day climatology

2005 ◽  
Vol 5 (1) ◽  
pp. 509-555 ◽  
Author(s):  
T. Egorova ◽  
E. Rozanov ◽  
V. Zubov ◽  
E. Manzini ◽  
W. Schmutz ◽  
...  
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Data Sets ◽  
Radiation Heating ◽  
Polar Night ◽  
Temperature Bias ◽  
Significant Temperature ◽  
Higher Temperature ◽  
The Tropics

Abstract. In this paper we document ''SOCOL'', a new chemistry-climate model, which has been ported for regular PCs and shows good wall-clock performance. An extensive validation of the model results against present-day climate obtained from observations and assimilation data sets shows that the model describes the climatological state of the atmosphere for the late 1990s with reasonable accuracy. The model has a significant temperature bias only in the upper stratosphere and near the tropopause in the tropics and high latitudes. The latter is the result of the rather low vertical resolution of the model near the tropopause. The former can be attributed to a crude representation of the radiation heating in the middle atmosphere. A comparison of the simulated and observed link between the tropical stratospheric structure and the strength of the polar vortex shows that in general, both observations and simulations reveal a higher temperature and ozone mixing ratio in the lower tropical stratosphere for the case with stronger Polar night jet (PNJ) as predicted by theoretical studies.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (3) ◽  
pp. 12115-12162 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall on both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affecting mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

scholarly journals Simulation of the climate impact of Mt. Pinatubo eruption using ECHAM5 – Part 2: Sensitivity to the phase of the QBO and ENSO

2009 ◽  
Vol 9 (9) ◽  
pp. 3001-3009 ◽  
Author(s):  
M. A. Thomas ◽  
M. A. Giorgetta ◽  
C. Timmreck ◽  
H.-F. Graf ◽  
G. Stenchikov
Keyword(s):  
General Circulation ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Polar Vortex ◽  
Circulation Model ◽  
Climate Impact ◽  
High Latitudes ◽  
Stratospheric Temperature ◽  
Pinatubo Eruption ◽  
The Tropics

Abstract. The sensitivity of the climate impact of Mt. Pinatubo eruption in the tropics and extratropics to different QBO phases is investigated. Mt. Pinatubo erupted in June 1991 during the easterly phase of the QBO at 30 hPa and the phase change to westerly took place in August 1992. Here, the consequences are analyzed if the QBO phase had been in the opposite phase during the eruption of Mt. Pinatubo. Hence, in this study, simulations are carried out using the middle atmosphere configuration of ECHAM5 general circulation model for two cases – one with the observed QBO phase and the other with the opposite QBO phase. The response of temperature and geopotential height in the lower stratosphere is evaluated for the following cases – (1) when only the effects of the QBO are included and (2) when the effects of aerosols, QBO and SSTs (combined response) are included. The tropical QBO signature in the lower stratospheric temperature is well captured in the pure QBO responses and in the combined (aerosol + ocean + QBO) responses. The response of the extratropical atmosphere to the QBO during the second winter after the eruption is captured realistically in the case of the combined forcing showing a strengthening of the polar vortex when the QBO is in its westerly phase and a warm, weak polar vortex in the easterly QBO phase. The vortex is disturbed during the first winter irrespective of the QBO phases in the combined responses and this may be due to the strong influences of El Niño during the first winters after eruption. However, the pure QBO experiments do not realistically reproduce a strengthening of the polar vortex in the westerly QBO phase, even though below normal temperatures in the high latitudes are seen in October-November-December months when the opposite QBO phase is prescribed instead of the December-January-February winter months used here for averaging.

scholarly journals Modelled thermal and dynamical responses of the middle atmosphere to EPP-induced ozone changes

2015 ◽  
Vol 15 (22) ◽  
pp. 33283-33329 ◽  
Author(s):  
K. Karami ◽  
P. Braesicke ◽  
M. Kunze ◽  
U. Langematz ◽  
M. Sinnhuber ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Ozone Depletion ◽  
Rossby Waves ◽  
Lower Stratosphere ◽  
Middle Atmosphere ◽  
Wave Activity ◽  
Flux Divergence ◽  
Starting Point ◽  
Wide Range ◽  
The Impact

Abstract. Energetic particles including protons, electrons and heavier ions, enter the Earth's atmosphere over the polar regions of both hemispheres, where they can greatly disturb the chemical composition of the upper and middle atmosphere and contribute to ozone depletion in the stratosphere and mesosphere. The chemistry–climate general circulation model EMAC is used to investigate the impact of changed ozone concentration due to Energetic Particle Precipitation (EPP) on temperature and wind fields. The results of our simulations show that ozone perturbation is a starting point for a chain of processes resulting in temperature and circulation changes over a wide range of latitudes and altitudes. In both hemispheres, as winter progresses the temperature and wind anomalies move downward with time from the mesosphere/upper stratosphere to the lower stratosphere. In the Northern Hemisphere (NH), once anomalies of temperature and zonal wind reach the lower stratosphere, another signal develops in mesospheric heights and moves downward. Analyses of Eliassen and Palm (EP) flux divergence show that accelerating or decelerating of the stratospheric zonal flow is in harmony with positive and negative anomalies of the EP flux divergences, respectively. This results suggest that the oscillatory mode in the downwelling signal of temperature and zonal wind in our simulations are the consequence of interaction between the resolved waves in the model and the mean stratospheric flow. Therefore, any changes in the EP flux divergence lead to anomalies in the zonal mean zonal wind which in turn feed back on the propagation of Rossby waves from the troposphere to higher altitudes. The analyses of Rossby waves refractive index show that the EPP-induced ozone anomalies are capable of altering the propagation condition of the planetary-scale Rossby waves in both hemispheres. It is also found that while ozone depletion was confined to mesospheric and stratospheric heights, but it is capable to alter Rossby wave propagation down to tropospheric heights. In response to an accelerated polar vortex in the Southern Hemisphere (SH) late wintertime, we found almost two weeks delay in the occurrence of mean dates of Stratospheric Final Warming (SFW). These results suggest that the stratosphere is not merely a passive sink of wave activity from below, but it plays an active role in determining its own budget of wave activity.

scholarly journals Large-scale emergence of regional changes in year-to-year temperature variability by the end of the 21st century

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Dirk Olonscheck ◽  
Andrew P. Schurer ◽  
Lucie Lücke ◽  
Gabriele C. Hegerl
Keyword(s):  
Global Warming ◽  
Large Scale ◽  
Climate Model ◽  
Climate Extremes ◽  
Temperature Variability ◽  
High Latitudes ◽  
Large Ensembles ◽  
Proxy Reconstructions ◽  
Instrumental Records ◽  
The Tropics

AbstractGlobal warming is expected to not only impact mean temperatures but also temperature variability, substantially altering climate extremes. Here we show that human-caused changes in internal year-to-year temperature variability are expected to emerge from the unforced range by the end of the 21st century across climate model initial-condition large ensembles forced with a strong global warming scenario. Different simulated changes in globally averaged regional temperature variability between models can be explained by a trade-off between strong increases in variability on tropical land and substantial decreases in high latitudes, both shown by most models. This latitudinal pattern of temperature variability change is consistent with loss of sea ice in high latitudes and changes in vegetation cover in the tropics. Instrumental records are broadly in line with this emerging pattern, but have data gaps in key regions. Paleoclimate proxy reconstructions support the simulated magnitude and distribution of temperature variability. Our findings strengthen the need for urgent mitigation to avoid unprecedented changes in temperature variability.

scholarly journals Stratospheric sudden warming effects on winds and temperature in the middle atmosphere at middle and low latitudes: a study using WACCM

2014 ◽  
Vol 32 (7) ◽  
pp. 859-874 ◽  
Author(s):  
A. Chandran ◽  
R. L. Collins
Keyword(s):  
Climate Model ◽  
Middle Atmosphere ◽  
Planetary Waves ◽  
Lower Latitude ◽  
High Latitudes ◽  
Mean Flow ◽  
Low Latitude ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Sudden Warming ◽  
Low Latitudes

Abstract. A stratospheric sudden warming (SSW) is a dynamical phenomenon of the wintertime stratosphere caused by the interaction between planetary Rossby waves propagating from the troposphere and the stratospheric zonal-mean flow. While the effects of SSW events are seen predominantly in high latitudes, they can also produce significant changes in middle and low latitude temperature and winds. In this study we quantify the middle and low latitude effects of SSW events on temperature and zonal-mean winds using a composite of SSW events between 1988 and 2010 simulated with the specified dynamics version of the Whole Atmosphere Community Climate Model (WACCM). The temperature and wind responses seen in the tropics also extend into the low latitudes in the other hemisphere. There is variability in observed zonal-mean winds and temperature depending on the observing location within the displaced or split polar vortex and propagation direction of the planetary waves. The propagation of planetary waves show that they originate in mid–high latitudes and propagate upward and equatorward into the mid-latitude middle atmosphere where they produce westward forcing reaching peak values of ~ 60–70 m s−1 day−1. These propagation paths in the lower latitude stratosphere appear to depend on the phase of the quasi-biennial oscillation (QBO). During the easterly phase of the QBO, waves originating at high latitudes propagate across the equator, while in the westerly phase of the QBO, the planetary waves break at ~ 20–25° N and there is no propagation across the equator. The propagation of planetary waves across the equator during the easterly phase of the QBO reduces the tropical upwelling and poleward flow in the upper stratosphere.

The Tropospheric Jet Response to Prescribed Zonal Forcing in an Idealized Atmospheric Model

2008 ◽  
Vol 65 (7) ◽  
pp. 2254-2271 ◽  
Author(s):  
Gang Chen ◽  
Pablo Zurita-Gotor
Keyword(s):  
Zonal Wind ◽  
Climate Model ◽  
Propagation Speed ◽  
Atmospheric Model ◽  
Wave Drag ◽  
Wave Activity ◽  
Zonal Winds ◽  
Wind Response ◽  
Poleward Shift ◽  
The Tropics

Abstract This paper explores the tropospheric jet shift to a prescribed zonal torque in an idealized dry atmospheric model with high stratospheric resolution. The jet moves in opposite directions for torques on the jet’s equatorward and poleward flanks in the troposphere. This can be explained by considering how the critical latitudes for wave activity absorption change, where the eastward propagation speed of eddies equals the background zonal mean zonal wind. While the increased zonal winds in the subtropics allow the midlatitude eddies to propagate farther into the tropics and result in the equatorward shift in the critical latitudes, the increased winds in the midlatitudes accelerate the eastward eddy phase speeds and lead to the poleward shift in the critical latitudes. In contrast, the jet moves poleward when a westerly torque is placed in the extratropical stratosphere irrespective of the forcing latitude. The downward penetration of zonal winds to the troposphere displays a poleward slope for the subtropical torque, an equatorward slope for the high-latitude torque, and less tilting for the midlatitude torques. The stratospheric eddies play a key role in transferring zonal wind anomalies downward into the troposphere. It is argued that these stratospheric zonal wind anomalies can affect the tropospheric jet by altering the eastward propagation of tropospheric eddies. Additionally, the zonal wind response to a subtropical zonal torque in this idealized model is of value in understanding the tropospheric jet sensitivity to the orographic gravity wave drag parameterization in a realistic climate model.

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