Equatorial Zonal Wind in the Middle Atmosphere Derived from Geopotential Height and Temperature Data

Abstract The dominant mode of seasonal variability in the global tropical upper-stratosphere and mesosphere zonal wind is the semiannual oscillation (SAO). However, it is notoriously difficult to measure winds at these heights from satellite or ground-based remote sensing. Here, the balance wind relationship is used to derive monthly and zonally averaged zonal winds in the tropics from satellite retrievals of geopotential height. Data from the Aura Microwave Limb Sounder (MLS) cover about 12.5 yr, and those from the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) cover almost 15 yr. The derived winds agree with direct wind observations below 10 hPa and above 80 km; there are no direct wind observations for validation in the intervening layers of the middle atmosphere. The derived winds show the following prominent peaks associated with the SAO: easterly maxima near the solstices at 1.0 hPa, westerly maxima near the equinoxes at 0.1 hPa, and easterly maxima near the equinoxes at 0.01 hPa. The magnitudes of these three wind maxima are stronger during the first cycle (January at 1.0 hPa and March at 0.1 and 0.01 hPa). The month and pressure level of the wind maxima shift depending on the phase of the quasi-biennial oscillation (QBO) at 10 hPa. During easterly QBO, the westerly maxima are shifted upward, are about 10 m s−1 stronger, and occur approximately 1 month later than those during the westerly QBO phase.

Download Full-text

Characteristics of Stratospheric Winds over Jiuquan (41.1°N, 100.2°E) Using Rocketsonde Data in 1967–2004

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0014.1 ◽

2017 ◽

Vol 34 (3) ◽

pp. 657-667 ◽

Cited By ~ 2

Author(s):

Z. Sheng ◽

J. W. Li ◽

Y. Jiang ◽

S. D. Zhou ◽

W. L. Shi

Keyword(s):

Zonal Wind ◽

Middle Atmosphere ◽

Correlation Coefficients ◽

Meridional Wind ◽

Horizontal Wind ◽

Cycle Period ◽

Observation Data ◽

Wind Fields ◽

Zonal Winds ◽

Model Research

AbstractStratospheric winds play a significant role in middle atmosphere dynamics, model research, and carrier rocket experiments. For the first time, 65 sets of rocket sounding experiments conducted at Jiuquan (41.1°N, 100.2°E), China, from 1967 to 2004 are presented to study horizontal wind fields in the stratosphere. At a fixed height, wind speed obeys the lognormal distribution. Seasonal mean winds are westerly in winter and easterly in summer. In spring and autumn, zonal wind directions change from the upper to the lower stratosphere. The monthly zonal mean winds have an annual cycle period with large amplitudes at high altitudes. The correlation coefficients for zonal winds between observations and the Horizontal Wind Model (HWM) with all datasets are 0.7. The MERRA reanalysis is in good agreement with rocketsonde data according to the zonal winds comparison with a coefficient of 0.98. The sudden stratospheric warming is an important contribution to biases in the HWM, because it changes the zonal wind direction in the midlatitudes. Both the model and the reanalysis show dramatic meridional wind differences with the observation data.

Download Full-text

Winter 2018 major sudden stratospheric warming impact on midlatitude mesosphere from microwave radiometer measurements

10.5194/acp-2018-1361 ◽

2019 ◽

Cited By ~ 2

Author(s):

Yuke Wang ◽

Valery Shulga ◽

Gennadi Milinevsky ◽

Aleksey Patoka ◽

Oleksandr Evtushevsky ◽

...

Keyword(s):

Zonal Wind ◽

Geopotential Height ◽

Microwave Radiometer ◽

Recovery Phase ◽

The Arctic ◽

Stratospheric Warming ◽

Sudden Stratospheric Warming ◽

Easterly Wind ◽

The Impact ◽

Midlatitude Mesosphere

Abstract. The impact of a major sudden stratospheric warming (SSW) in the Arctic in February 2018 on the mid-latitude mesosphere was investigated by performing microwave radiometer measurements of carbon monoxide (CO) and zonal wind above Kharkiv, Ukraine (50.0° N, 36.3° E). The mesospheric peculiarities of this SSW event were observed using recently designed and installed microwave radiometer in East Europe for the first time. The data from the ERA-Interim and NCEP–NCAR reanalyses, as well as the Aura Microwave Limb Sounder measurements, have been also used. Microwave observations of the daily CO profiles in January–March 2018 allowed retrieving mesospheric zonal wind at 70–85 km (below the winter mesopause) over the Kharkiv site. The reverse of the mesospheric westerly from about 10 m s−1 to the easterly wind of about −10 m s−1 around 10 February has been registered. Local microwave observations in the NH midlatitudes combined with reanalysis data show wide ranges of daily variability in CO, zonal wind, temperature and geopotential height in the mesosphere and stratosphere during the SSW 2018. Oscillations in the vertical CO profile, zonal wind, and geopotential height during the SSW, stratopause disappearance after the SSW onset and strong CO and westerly wind peaks at the start of the SSW recovery phase have been observed. The observed CO variability can be explained by vertical and horizontal air mass redistribution due to planetary wave activity with the replacement of the CO-rich air by CO-poor air and vice versa, in agreement with other studies. The results of microwave measurements of CO and zonal wind in the midlatitude mesosphere at 70–85 km altitudes, which still is not adequately covered by ground-based observations, are useful for improving our understanding of the SSW impacts in this region.

Download Full-text

Final Sudden Stratospheric Warmings and the memory of the stratosphere

10.5194/egusphere-egu21-9970 ◽

2021 ◽

Author(s):

Alain Hauchecorne ◽

Chantal Claud ◽

Philippe Keckhut

Keyword(s):

Zonal Wind ◽

Planetary Wave ◽

Middle Atmosphere ◽

Temperature Anomaly ◽

Polar Vortex ◽

Wave Activity ◽

Late Winter ◽

Easterly Wind ◽

Weather Forecasts ◽

Stratospheric Circulation

Sudden Stratospheric Warming (SSW) is the most spectacular dynamic event occurring in the middle atmosphere. It can lead to a warming of the winter polar stratosphere by a few tens of K in one to two weeks and a reversal of the stratospheric circulation from wintertime prevailing westerly winds to easterly winds similar to summer conditions. This strong modification of the stratospheric circulation has consequences for several applications, including the modification of the stratospheric infrasound guide. Depending on the date of the SSW, the westerly circulation can be re-established if the SSW occurs in mid-winter or the summer easterly circulation can be definitively established if the SSW occurs in late winter. In the latter case it is called Final Warming (FW). Each year, it is possible to define the date of the FW as the date of the final inversion of the zonal wind at 60&#176;N - 10 hPa . If the FW is associated with a strong peak of planetary wave activity and a rapid increase in polar temperature, it is classified as dynamic FW. If the transition to the easterly wind is smooth without planetary wave activity, the FW is classified as radiative.The analysis of the ERA5 database, which has recently been extended to 1950 (71 years of data), allowed a statistical analysis of the evolution of the stratosphere in winter. The main conclusions of this study will be presented :- the state of the polar vortex in a given month is anticorrelated with its state 2 to 3 months earlier. The beginning of winter is anticorrelated with mid-winter and mid-winter is anticorrelated with the end of winter;- dynamic FWs occur early in the season (March - early April) and are associated with a strong positive polar temperature anomaly, while radiative FWs occur later (late April - early May) without a polar temperature anomaly;- the summer stratosphere (polar temperature and zonal wind) keeps the memory of its state in April-May at the time of FW at least until July .These results could help to improve medium-range weather forecasts in the Northern Hemisphere due to the strong dynamic coupling between the troposphere and stratosphere during SSW events.

Download Full-text

Sensitivity of middle atmosphere GW forcing to vertical model resolution

10.5194/egusphere-egu2020-20423 ◽

2020 ◽

Author(s):

Andrea Schneidereit ◽

Hauke Schmidt ◽

Claudia Stephan

Keyword(s):

Zonal Wind ◽

Middle Atmosphere ◽

Wave Spectrum ◽

Austral Summer ◽

Vertical Gradient ◽

Summer Season ◽

Grid Spacing ◽

Flux Divergence ◽

The Mean ◽

Horizontal Grid

Several current general atmospheric circulation models provide sufficiently high resolutions to resolve important parts of the internal gravity wave spectrum allowing for numerical experiments without GW drag parameterizations. GWs start to be well resolved from horizontal wavelengths of about 7 times the horizontal grid spacing. How much does the resolved wave spectrum and its forcing on the mean circulation depend on the vertical resolution?&#8722;1,The middle atmosphere summer hemisphere provides a suitable background to investigate this question. The mean stratospheric and mesospheric circulation is characterised by prevailing easterlies which prevent planetary wave propagation upwards and represents a mean state driven by IGWs. The sensitivity of the forcing by IGWs is analysed on the basis of the Eliassen-Palm (EP) flux divergence, which describes the forcing on the circulation by resolved eddies. Model simulations are performed using the upper atmosphere version of the ICON (ICOsahedral Nonhydrostatic) general circulation model, UA-ICON (Borchert et al. 2019, GMD). The simulations start in October and run for an extended austral summer season until March with a horizontal grid spacing of roughly 20 km. The top of the model atmosphere is located at 150 km. Three different model configurations are used with 90, 180, and 360 vertical model layers. The mean vertical grid spacing ranges from roughly 1300 m (90 layers) to 320 m (360 layers) at stratospheric levels, and from roughly 2300 m to 500 m at mesospheric levels. Gravity wave drag parameterizations (orographic and non-orographic) are turned off. The resolved forcing on the mean state due to the EP flux divergence is decomposed into contributions of different scales with respect to horizontal wave numbers. For contributions of IGWs wave numbers above 20 are considered.The stratospheric and mesospheric easterlies appear stronger in the lower resolution from October to the end of the austral summer season. Westerlies occur above the mesopause. This strong vertical gradient in the zonal mean zonal wind amplifies in the lower resolution. At the beginning of the simulation period, differences between the mean states are weak, of the order of 5 ms&#8722;1 , and strengthen during the summer season. The forcing due to internal GWs appears stronger in the lower resolution at higher altitudes and amplifies in the region of the strong vertical gradient of the zonal mean zonal wind. Furthermore, wave spectra are discussed. In accordance with previous studies, an increased vertical resolution results in a reduction of the IGW forcing close to strong zonal mean zonal wind gradients in the upper mesosphere/lower thermosphere.

Download Full-text

Is Missing Orographic Gravity Wave Drag near 60°S the Cause of the Stratospheric Zonal Wind Biases in Chemistry–Climate Models?

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0159.1 ◽

2012 ◽

Vol 69 (3) ◽

pp. 802-818 ◽

Cited By ~ 97

Author(s):

Charles McLandress ◽

Theodore G. Shepherd ◽

Saroja Polavarapu ◽

Stephen R. Beagley

Keyword(s):

Gravity Wave ◽

Zonal Wind ◽

Climate Models ◽

Middle Atmosphere ◽

Wave Drag ◽

Early Summer ◽

Systematic Bias ◽

Stratospheric Polar Vortex ◽

Column Ozone ◽

The Impact

Abstract Nearly all chemistry–climate models (CCMs) have a systematic bias of a delayed springtime breakdown of the Southern Hemisphere (SH) stratospheric polar vortex, implying insufficient stratospheric wave drag. In this study the Canadian Middle Atmosphere Model (CMAM) and the CMAM Data Assimilation System (CMAM-DAS) are used to investigate the cause of this bias. Zonal wind analysis increments from CMAM-DAS reveal systematic negative values in the stratosphere near 60°S in winter and early spring. These are interpreted as indicating a bias in the model physics, namely, missing gravity wave drag (GWD). The negative analysis increments remain at a nearly constant height during winter and descend as the vortex weakens, much like orographic GWD. This region is also where current orographic GWD parameterizations have a gap in wave drag, which is suggested to be unrealistic because of missing effects in those parameterizations. These findings motivate a pair of free-running CMAM simulations to assess the impact of extra orographic GWD at 60°S. The control simulation exhibits the cold-pole bias and delayed vortex breakdown seen in the CCMs. In the simulation with extra GWD, the cold-pole bias is significantly reduced and the vortex breaks down earlier. Changes in resolved wave drag in the stratosphere also occur in response to the extra GWD, which reduce stratospheric SH polar-cap temperature biases in late spring and early summer. Reducing the dynamical biases, however, results in degraded Antarctic column ozone. This suggests that CCMs that obtain realistic column ozone in the presence of an overly strong and persistent vortex may be doing so through compensating errors.

Download Full-text

Meteor radar observations of atmospheric waves in the equatorial mesosphere/lower thermosphere over Ascension Island

Annales Geophysicae ◽

10.5194/angeo-22-387-2004 ◽

2004 ◽

Vol 22 (2) ◽

pp. 387-404 ◽

Cited By ~ 43

Author(s):

D. Pancheva ◽

N. J. Mitchell ◽

P. T. Younger

Keyword(s):

Zonal Wind ◽

Middle Atmosphere ◽

Lower Thermosphere ◽

Meridional Wind ◽

Kelvin Wave ◽

Vertical Wavelength ◽

Period Range ◽

Meridional Component ◽

Ascension Island ◽

Waves And Tides

Abstract. Some preliminary results about the planetary wave characteristics observed during the first seven months (October 2001-April 2002) of observations over Ascension Island (7.9°S, 14.4°W) are reported in this study. The zonal wind is dominated by the 3–7-day waves, while the meridional component – by the quasi-2-day wave. Two wave events in the zonal wind are studied in detail: a 3–4-day wave observed in the end of October/November and the 3–6-day wave in January/February. The moderate 3- and 3.2-day waves are interpreted as an ultra-fast Kelvin wave, while for the strong 4-day wave we are not able to make a firm decision. The 6-day wave is interpreted as a Doppler-shifted 5-day normal mode, due to its very large vertical wavelength (79km). The quasi-2-day wave seems to be present almost continuously in the meridional wind, but the strongest bursts are observed mainly in December and January. The observed period range is large, from 34 to 68h, with some clustering around 43–44 and 50h. The estimated vertical wavelengths indicate shorter lengths during the equinoxes, in the range of 25-30km, and longer ones, ∼40–50km, in January/February, when the 48-h wave is strongest. Key words. Meteorology and atmospheric dynamics middle atmosphere dynamics, waves and tides)

Download Full-text

Effect of latitudinally displaced gravity wave forcing in the lower stratosphere on the polar vortex stability

10.5194/angeo-2019-15 ◽

2019 ◽

Cited By ~ 1

Author(s):

Nadja Samtleben ◽

Christoph Jacobi ◽

Petr Pišoft ◽

Petr Šácha ◽

Aleš Kuchař

Keyword(s):

Refractive Index ◽

Gravity Wave ◽

Zonal Wind ◽

Polar Region ◽

Middle Atmosphere ◽

Negative Refractive Index ◽

Baroclinic Instability ◽

Polar Vortex ◽

Circulation Model ◽

The Impact

Abstract. In order to investigate the impact of a locally confined gravity wave (GW) hotspot, a sensitivity study based on simulations of the middle atmosphere circulation during northern winter was performed with a nonlinear, mechanistic, global circulation model. To this end, for the hotspot region we selected a fixed longitude range in the East Asian region (120° E–170° E) and a latitude range from 22.5° N–52.5° N between 18 km and 30 km, which was then shifted northward in steps of 5°. For the southernmost hotspots, we observe a decreased stationary planetary wave (SPW) 1 activity in the upper stratosphere/lower mesosphere, i.e. less SPWs 1 are propagating upwards. These GW hotspots are leading to a negative refractive index inhibiting SPW propagation at midlatitudes. The decreased SPW 1 activity is connected with an increased zonal mean zonal wind at lower latitudes. This in turn decreases the meridional potential vorticity gradient (qy) from midlatitudes towards the polar region. A reversed qy indicates local baroclinic instability which generates SPWs 1 in the polar region, where we observe a strong positive Eliassen-Palm (EP) divergence. Thus, the EP flux is increasing towards the polar stratosphere (corresponding to enhanced SPW 1 amplitudes) where the SPWs 1 are breaking and the zonal mean zonal wind is decreasing. Thus, the local GW forcing is leading to a displacement of the polar vortex towards lower latitudes. The effect of the local baroclinic instability indicated by the reversed qy also produces SPWs 1 in the lower mesosphere. The effect on the dynamics in the middle atmosphere by GW hotspots which are located northward of 50° N is negligible because the refractive index of the atmosphere is strongly negative in the polar region. Thus, any changes in the SPW activity due to the local GW forcing are quite ineffective.

Download Full-text

Vertical and interhemispheric links in the stratosphere-mesosphere as revealed by the day-to-day variability of Aura-MLS temperature data

Annales Geophysicae ◽

10.5194/angeo-27-3387-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3387-3409 ◽

Cited By ~ 27

Author(s):

X. Xu ◽

A. H. Manson ◽

C. E. Meek ◽

T. Chshyolkova ◽

J. R. Drummond ◽

...

Keyword(s):

Middle Atmosphere ◽

Chemical Constituents ◽

Polar Vortex ◽

Temperature Data ◽

The Arctic ◽

Time Lags ◽

Research Activity ◽

Mean Temperature ◽

The Antarctic ◽

Coupling Processes

Abstract. The coupling processes in the middle atmosphere have been a subject of intense research activity because of their effects on atmospheric circulation, structure, variability, and the distribution of chemical constituents. In this study, the day-to-day variability of Aura-MLS (Microwave Limb Sounder) temperature data are used to reveal the vertical and interhemispheric coupling processes in the stratosphere-mesosphere during four Northern Hemisphere winters (2004/2005–2007/2008). The UKMO (United Kingdom Meteorological Office) assimilated data and mesospheric winds from MF (medium frequency) radars are also applied to help highlight the coupling processes. In this study, a clear vertical link can be seen between the stratosphere and mesosphere during winter months. The coolings and reversals of northward meridional winds in the polar winter mesosphere are often observed in relation to warming events (Sudden Stratospheric Warming, SSW for short) and the associated changes in zonal winds in the polar winter stratosphere. An upper-mesospheric cooling usually precedes the beginning of the warming in the stratosphere by 1–2 days. Inter-hemispheric coupling has been identified initially by a correlation analysis using the year-to-year monthly zonal mean temperature. Then the correlation analyses are performed based upon the daily zonal mean temperature. From the original time sequences, significant positive (negative) correlations are generally found between zonal mean temperatures at the Antarctic summer mesopause and in the Arctic winter stratosphere (mesosphere) during northern mid-winters, although these correlations are dominated by the low frequency variability (i.e. the seasonal trend). Using the short-term oscillations (less than 15 days), the statistical result, by looking for the largest magnitude of correlation within a range of time-lags (0 to 10 days; positive lags mean that the Antarctic summer mesopause is lagging), indicates that the temporal variability of zonal mean temperature at the Antarctic summer mesopause is also positively (negatively) correlated with the polar winter stratosphere (mesosphere) during three (2004/2005, 2005/2006, and 2007/2008) out of the four winters. The highest value of the correlation coefficient is over 0.7 in the winter-stratosphere for the three winters. The remaining winter (2006/2007) has more complex correlations structures; correspondingly the polar vortex was distinguished this winter. The time-lags obtained for 2004/2005 and 2006/2007 are distinct from 2005/2006 and 2007/2008 where a 6-day lag dominates for the coupling between the winter stratosphere and the summer mesopause. The correlations are also provided using temperatures in northern longitudinal sectors in a comparison with the Antarctic-mesopause zonal mean temperature. For northern mid-high latitudes (~50–70° N), temperatures in Scandinavia-Eastern Europe and in the Pacific-Western Canada longitudinal sectors often have opposite signs of correlations with zonal mean temperatures near the Antarctic summer mesopause during northern mid-winters. The statistical results are shown to be associated with the Northern Hemisphere's polar vortex characteristics.

Download Full-text

Observed and simulated zonally asymmetric zonal wind patterns under NAO conditions

10.5194/egusphere-egu21-7743 ◽

2021 ◽

Author(s):

Aslı İlhan ◽

Deniz Demirhan ◽

Yurdanur Ünal

Keyword(s):

Zonal Wind ◽

Impact Analysis ◽

Middle Atmosphere ◽

Incident Radiation ◽

Extreme Weather Events ◽

Winter Climate ◽

Weather Patterns ◽

Zonal Winds ◽

Funding Program ◽

Wind Patterns

The North Atlantic Oscillation (NAO), coexistent meridional oscillation of subpolar Icelandic low and the subtropical Azores high dominates the Northern Hemispheric winter climate. Variability in the circulation of NAO may activate the extreme weather events, such as the enhanced zonal winds, in northeast America, Atlantic and Eurasia. On the other hand variability in the zonal wind patterns effects the position of the NAO events. It is more relevant to investigate the interaction between NAO and the weather patterns during the winter time since NAO is powerful during winter. Hence the wintertime weather systems are highly altered by such an impact. Analysis indicate that negative and positive phases of NAO mainly modulate the local cyclonic and anticyclonic wave characteristics and hence the zonally asymmetric circulation of the middle atmosphere. Zonal asymmetries in the weather patterns originate from ocean-continent temperature gradients and topographical contrasts after all solar incident radiation is almost uniform over the longitudes. Thus zonally asymmetric patterns for certain variables such as zonal winds show strong seasonal dependence and highly correlate with the climatological position of the NAO mainly in the winter hemisphere. In this study longitudinal differences in the zonal wind is analyzed in order to observe its strong influence on the evolution of NAO. Zonal asymmetries of zonal wind is examined by evaluating the deviation from zonal mean of the long term annual average of both winter and spring months from December to April. Zonal winds up to 100km for winter and spring is examined between 2006-2100 using CMIP5 MPI-ESM-MR RCP4.5 scenario for the extratropical and the polar latitudes. Additionally ERA5 reanalysis data is used to identify the ability of CMIP5 Reference Period (RP) data to capture the observed patterns for the years from 1979 to 2005.Acknowledgements: This study is supported by TUB&#304;TAK (The Scientific and Technology Research Council of Turkey), The Scientific and Technological Research Projects Funding Program, 1001. The projects number is 117Y327.

Download Full-text