scholarly journals Interannual Variability of Stratospheric Final Warming in the Southern Hemisphere and its Tropospheric Origin

2021 ◽  
pp. 1-59
Author(s):  
Soichiro Hirano ◽  
Masashi Kohma ◽  
Kaoru Sato
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Reanalysis Data ◽  
Stationary Waves ◽  
High Latitudes ◽  
Wave Source ◽  
Barotropic Model ◽  
Stratospheric Final Warming ◽  
Zonal Wavenumber ◽  
Favorable Conditions

AbstractThe relation between interannual variability of stratospheric final warming (SFW) and tropospheric circulation in the Southern Hemisphere (SH) is explored using reanalysis data and a linear barotropic model. The analysis is focused on quasi-stationary waves with zonal wavenumber 1 (s = 1 QSWs; s is zonal wavenumber), which are the dominant component of the SH extratropical planetary waves.First, interannual variability of SFW is investigated in terms of amplitudes of stratospheric and tropospheric s = 1 QSWs, and wave transmission properties of the mean flow from the late austral winter to spring. Upward Eliassen–Palm flux due to s = 1 QSWs is larger from the stratosphere down to the middle troposphere in early-SFW years than late-SFW years. More favorable conditions for propagation of s = 1 stationary waves into the stratosphere are identified in early-SFW years. These results indicate that the amplification of tropospheric s = 1 QSWs and the favorable conditions for their propagation into the stratosphere lead to the amplification of stratospheric s = 1 QSWs, and hence earlier SFWs.Next, numerical calculations using a linear barotropic model are performed to explore how tropospheric s = 1 QSWs at high latitudes amplifies in early-SFW years. By using tropical Rossby wave source and horizontal winds in the reanalysis data as a source and background field, respectively, differences in s = 1 steady responses between early- and late-SFWs are examined at high latitudes. It is suggested that the larger amplitudes of tropospheric s = 1 QSWs in early-SFW years are attributed to differences in wave propagation characteristics associated with structure of the midlatitude jets in austral spring.

scholarly journals Interannual variability of precipitable water

1996 ◽  
Vol 14 (4) ◽  
pp. 464-467 ◽  
Author(s):  
R. P. Kane
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Precipitable Water ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Zonal Winds ◽  
Low Latitudes ◽  
Linear Trends

Abstract. The 12-month running means of the surface-to-500 mb precipitable water obtained from analysis of radiosonde data at seven selected locations showed three types of variability viz: (1) quasi-biennial oscillations; these were different in nature at different latitudes and also different from the QBO of the stratospheric tropical zonal winds; (2) decadal effects; these were prominent at middle and high latitudes and (3) linear trends; these were prominent at low latitudes, up trends in the Northern Hemisphere and downtrends in the Southern Hemisphere.

scholarly journals The South Atlantic–South Indian Ocean Pattern: a Zonally Oriented Teleconnection along the Southern Hemisphere Westerly Jet in Austral Summer

Atmosphere ◽  
2019 ◽  
Vol 10 (5) ◽  
pp. 259 ◽  
Author(s):  
Zhongda Lin
Keyword(s):  
Indian Ocean ◽  
Interannual Variability ◽  
Southern Hemisphere ◽  
Austral Summer ◽  
South Atlantic ◽  
The South ◽  
South Indian Ocean ◽  
Westerly Jet ◽  
South Indian ◽  
Zonal Wavenumber

Extratropical teleconnections significantly affect the climate in subtropical and mid-latitude regions. Understanding the variability of atmospheric teleconnection in the Southern Hemisphere, however, is still limited in contrast with the well-documented counterpart in the Northern Hemisphere. This study investigates the interannual variability of mid-latitude circulation in the Southern Hemisphere in austral summer based on the ERA-Interim reanalysis dataset during 1980–2016. A stationary mid-latitude teleconnection is revealed along the strong Southern Hemisphere westerly jet over the South Atlantic and South Indian Ocean (SAIO). The zonally oriented SAIO pattern represents the first EOF mode of interannual variability of meridional winds at 200 hPa over the region, with a vertical barotropic structure and a zonal wavenumber of 4. It significantly modulates interannual climate variations in the subtropical Southern Hemisphere in austral summer, especially the opposite change in rainfall and surface air temperature between Northwest and Southeast Australia. The SAIO pattern can be efficiently triggered by divergences over mid-latitude South America and the southwest South Atlantic, near the entrance of the westerly jet, which is probably related to the zonal shift of the South Atlantic Convergence Zone. The triggered wave train is then trapped within the Southern Hemisphere westerly jet waveguide and propagates eastward until it diverts northeastward towards Australia at the jet exit, in addition to portion of which curving equatorward at approximately 50° E towards the southwest Indian Ocean.

scholarly journals Dynamical evolution of a minor sudden stratospheric warming in the Southern Hemisphere in 2019

2021 ◽  
Author(s):  
Guangyu Liu ◽  
Toshihiko Hirooka ◽  
Nawo Eguchi ◽  
Kirstin Krüger
Keyword(s):  
Southern Hemisphere ◽  
Vertical Component ◽  
Polar Vortex ◽  
Planetary Waves ◽  
High Latitudes ◽  
Stratospheric Warming ◽  
Sudden Stratospheric Warming ◽  
Zonal Wavenumber ◽  
Westerly Winds ◽  
A Minor

Abstract. This study analyzes the Japanese 55-year Reanalysis (JRA-55) dataset from 2002 to 2019 to examine the sudden stratospheric warming event that occurred in the Southern Hemisphere (SH) in 2019 (hereafter referred to as SSW2019). Strong warming at the polar cap and decelerated westerly winds were observed, but since there was no reversal of westerly winds to easterly winds at 60° S in the middle to lower stratosphere, the SSW2019 is classified as a minor warming event. The results show that quasi-stationary planetary waves of zonal wavenumber 1 developed during the SSW2019. The strong vertical component of the Eliassen–Palm flux with zonal wavenumber 1 is indicative of pronounced propagation of planetary waves to the stratosphere. The wave driving in September 2019 shows that the values are larger than those of the major SSW event in 2002 (hereafter referred to as SSW2002). Since there was no pronounced preconditioning (as in SSW2002) and the polar vortex was already strong before the SSW2019 occurred, a major disturbance of the polar vortex was unlikely to have taken place. The strong wave driving in SSW2019 occurred in high latitudes. Waveguides (i.e., positive values of the refractive index) are found at high latitudes in the upper stratosphere during the warming period, which provided favorable conditions for quasi-stationary planetary waves to propagate upward and poleward.

scholarly journals Interannual Variability and Trends of Extratropical Ozone. Part II: Southern Hemisphere

2008 ◽  
Vol 65 (10) ◽  
pp. 3030-3041 ◽  
Author(s):  
Xun Jiang ◽  
Steven Pawson ◽  
Charles D. Camp ◽  
J. Eric Nielsen ◽  
Run-Lie Shia ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Climate Model ◽  
Observation System ◽  
Stationary Waves ◽  
Quasi Biennial Oscillation ◽  
Total Column Ozone ◽  
The Third ◽  
Column Ozone

A principal component analysis (PCA) is applied to the Southern Hemisphere (SH) total column ozone following the method established for analyzing the data in the Northern Hemisphere (NH) in a companion paper. The interannual variability (IAV) of extratropical O3 in the SH is characterized by four main modes, which account for 75% of the total variance. The first two leading modes are approximately zonally symmetric and relate to the Southern Hemisphere annular mode and the quasi-biennial oscillation. The third and fourth modes exhibit wavenumber-1 structures. Contrary to the Northern Hemisphere, the third and fourth modes are not related to stationary waves. Similar results are obtained for the 30–100-hPa geopotential thickness. The decreasing O3 trend in the SH is captured in the first mode. The largest trend is at the South Pole, with value ∼−2 Dobson Units (DU) yr−1. Both the spatial pattern and trends in the column ozone are captured by the Goddard Earth Observation System chemistry–climate model (GEOS-CCM) in the SH.

scholarly journals Tropical and subtropical forcing of future southern hemisphere stationary wave changes

2021 ◽  
pp. 1-48
Author(s):  
Matthew Patterson ◽  
Tim Woollings ◽  
Thomas J. Bracegirdle
Keyword(s):  
Climate Change ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Regional Climate ◽  
Stationary Wave ◽  
Hadley Cell ◽  
Cmip5 Models ◽  
Wave Source ◽  
Barotropic Model ◽  
Rossby Wave Source

AbstractStationary wave changes play a significant role in the regional climate change response in Southern Hemisphere (SH) winter. In particular, almost all CMIP5 models feature a substantial strengthening of the westerlies to the south of Australia and enhancement of the subtropical jet over the eastern Pacific in winter. In this study we investigate the mechanisms behind these changes, finding that the stationary wave response can largely be explained via reductions in the magnitude of the upper level Rossby wave source over the tropical / subtropical East Pacific. The Rossby wave source changes in this region are robust across the model ensemble and are strongly correlated with changes to low latitude circulation patterns, in particular, the projected southward migration of the Hadley cell and weakening of the Walker circulation. To confirm our mechanism of future changes, we employ a series of barotropic model experiments in which the barotropic model is given a background state identical to a particular CMIP5 model and an anomalous Rossby wave source is imposed. This simple approach is able to capture the primary features of the ensemble mean change, including the cyclonic anomaly south of Australia, and is also able to capture many of the inter-model differences. These findings will help to advance our understanding of the mechanisms underpinning SH extratropical circulation changes under climate change.

Temperature Trend Patterns in Southern Hemisphere High Latitudes: Novel Indicators of Stratospheric Change

2009 ◽  
Vol 22 (23) ◽  
pp. 6325-6341 ◽  
Author(s):  
Pu Lin ◽  
Qiang Fu ◽  
Susan Solomon ◽  
John M. Wallace
Keyword(s):  
Southern Hemisphere ◽  
General Circulation ◽  
Circulation Model ◽  
Temperature Trend ◽  
Radiative Cooling ◽  
High Latitudes ◽  
Intergovernmental Panel ◽  
Temperature Changes ◽  
Zonal Wavenumber ◽  
Simulated Temperature

Abstract Robust stratospheric temperature trend patterns are suggested in the winter and spring seasons in the Southern Hemisphere high latitudes from the satellite-borne Microwave Sounding Unit (MSU) measurement for 1979–2007. These patterns serve as indicators of key processes governing temperature and ozone changes in the Antarctic. The observed patterns are characterized by cooling and warming regions of comparable magnitudes, with the strongest local trends occurring in September and October. In September, ozone depletion induces radiative cooling, and strengthening of the Brewer–Dobson circulation (BDC) induces dynamical warming. Because the trends induced by these two processes are centered in different locations in September, they do not cancel each other, but rather produce a wavelike structure. In contrast, during October, the ozone-induced radiative cooling and the BDC-induced warming exhibit a more zonally symmetric structure than in September, and hence largely cancel each other. However, the October quasi-stationary planetary wavenumber 1 has shifted eastward from 1979 to 2007, producing a zonal wavenumber-1 trend structure, which dominates the observed temperature trend pattern. Simulated temperature changes for 1979–2007 from coupled atmosphere–ocean general circulation model (AOGCM) experiments run for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) are compared with the observations. In general, the simulated temperature changes are dominated by zonally symmetric ozone-induced radiative cooling. The models fail to simulate the warming in the southern polar stratosphere, implying a lack of the BDC strengthening in these models. They also fail to simulate the quasi-stationary planetary wave changes observed in October and November.

scholarly journals The Zonal Asymmetry of the Southern Hemisphere Winter Storm Track

2004 ◽  
Vol 17 (24) ◽  
pp. 4882-4892 ◽  
Author(s):  
Masaru Inatsu ◽  
Brian J. Hoskins
Keyword(s):  
Indian Ocean ◽  
Southern Hemisphere ◽  
General Circulation ◽  
Storm Track ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Stationary Waves ◽  
Winter Storm ◽  
Wave Source ◽  
Zonal Asymmetry

Abstract Atmospheric general circulation model experiments have been performed to investigate how the significant zonal asymmetry in the Southern Hemisphere (SH) winter storm track is forced by sea surface temperature (SST) and orography. An experiment with zonally symmetric tropical SSTs expands the SH upper-tropospheric storm track poleward and eastward and destroys its spiral structure. Diagnosis suggests that these aspects of the observed storm track result from Rossby wave propagation from a wave source in the Indian Ocean region associated with the monsoon there. The lower-tropospheric storm track is not sensitive to this forcing. However, an experiment with zonally symmetric midlatitude SSTs exhibits a marked reduction in the magnitude of the maximum intensity of the lower-tropospheric storm track associated with reduced SST gradients in the western Indian Ocean. Experiments without the elevation of the South African Plateau or the Andes show reductions in the intensity of the major storm track downstream of them due to reduced cyclogenesis associated with the topography. These results suggest that the zonal asymmetry of the SH winter storm track is mainly established by stationary waves excited by zonal asymmetry in tropical SST in the upper troposphere and by local SST gradients in the lower troposphere, and that it is modified through cyclogenesis associated with the topography of South Africa and South America.

scholarly journals Assessment of Modes of Interannual Variability of Southern Hemisphere Atmospheric Circulation in CMIP5 Models

2014 ◽  
Vol 27 (21) ◽  
pp. 8107-8125 ◽  
Author(s):  
Simon Grainger ◽  
Carsten S. Frederiksen ◽  
Xiaogu Zheng
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Slow Component ◽  
Coupled Model ◽  
Reanalysis Data ◽  
Cmip5 Models ◽  
Noise Component ◽  
Modes Of Variability ◽  
Multimodel Ensembles

Abstract An assessment is made of the modes of interannual variability in the seasonal mean summer and winter Southern Hemisphere (SH) 500-hPa geopotential height in the twentieth century in models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) dataset. Modes of variability of both the slow (signal) and intraseasonal (noise) components in the CMIP5 models are evaluated against those estimated from reanalysis data. There is general improvement in the leading modes of the slow (signal) component in CMIP5 models compared with the CMIP phase 3 (CMIP3) dataset. The largest improvement is in the spatial structures of the modes related to El Niño–Southern Oscillation variability in SH summer. An overall score metric is significantly higher for CMIP5 over CMIP3 in both seasons. The leading modes in the intraseasonal noise component are generally well reproduced in CMIP5 models, and there are few differences from CMIP3. A new total overall score metric is used to rank the CMIP5 models over both seasons. Weighting the seasons by the relative spread of overall scores is shown to be suitable for generating multimodel ensembles for further analysis of interannual variability. In multimodel ensembles, it is found that an ensemble of size 5 or 6 is sufficient in SH summer to reproduce well the dominant modes. In contrast, about 13 models are typically are required in SH winter. It is shown that it is necessary that the selected models individually reproduce well the leading modes of the slow component.

scholarly journals Aura MLS observations of the westward-propagating <i>s</i>=1, 16-day planetary wave in the middle atmosphere: climatology and cross-equatorial propagation

2010 ◽  
Vol 10 (10) ◽  
pp. 23197-23227 ◽  
Author(s):  
K. A. Day ◽  
R. E. Hibbins ◽  
N. J. Mitchell
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Wave Amplitude ◽  
Planetary Wave ◽  
High Latitudes ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Significant Wave ◽  
Zonal Wavenumber ◽  
Summer Time

Abstract. The Microwave Limb Sounder (MLS) on the Aura satellite has been used to measure temperatures in the stratosphere, mesosphere and lower thermosphere (MLT). The data used here are from August 2004 to June 2010 and latitudes 75° S to 75° N. The temperature data reveal the persistent presence of a westward propagating 16-day planetary wave with zonal wavenumber 1. The wave amplitude maximises in winter in the stratosphere and MLT at middle to high latitudes, where monthly-mean amplitudes can be as large as ~8 K. Significant wave amplitudes are observed in the summer-time MLT and at lower stratospheric heights of up to ~20 km at middle to high latitudes. Wave amplitudes in the Northern Hemisphere approach values twice as large as those in the Southern Hemisphere. Wave amplitudes are also closely related to climatological zonal winds and are largest in regions of strongest eastward flow. There is a~reduction in wave amplitudes at the stratopause. No significant wave amplitude is observed near the equator or in the strongly westward background winds of the atmosphere in summer. This behaviour is interpreted as a consequence of wave/mean-flow interactions. It has been suggested that the summer-time 16-day wave in the MLT is ducted across the equator from the winter hemisphere and that this ducting is modulated by the equatorial Quasi-Biennial Oscillation (QBO) in the westerly phase. Here we observe that the QBO modulates the 16-day wave in the polar summer-time MLT in the Northern Hemisphere as previously observed, but this modulation is not seen in the Southern Hemisphere.

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