Superposed epoch analysis of coupling mechanisms captured by meteor radars during sudden stratospheric warmings

2021 ◽  
Author(s):  
Benedikt Gast ◽  
Ales Kuchar ◽  
Gunter Stober ◽  
Christoph Jacobi ◽  
Dimitry Pokhotelov ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Lower Thermosphere ◽  
Rio Grande ◽  
Meridional Wind ◽  
Meteorological Conditions ◽  
Special Focus ◽  
Wind Component ◽  
Superposed Epoch Analysis ◽  
Epoch Analysis ◽  
Coupling Mechanisms

<p class="western" align="justify"><span lang="en-GB">Previous studies that analysed the mesosphere and lower thermosphere (MLT) dynamics during sudden stratospheric warmings (SSWs) were limited only to particular SSWs or focused on a particular station representative only for some regions. Here we describe a comprehensive study of the average meteorological conditions during SSWs with a special focus on the general contribution of planetary (PW) and gravity (GW) waves as primary coupling mechanisms between lower and upper atmosphere. The average meteorological conditions in the MLT during SSWs were analyzed using a superposed epoch analysis (Denton et al., 2019) of meteor radar measurements for stations in the northern (NH: Collm, Kiruna, Sodankyla, CMOR) and the southern hemisphere (SH: Rio Grande, Davis, Rothera) for the altitude range of 80–100 km Using the adaptive spectral filtering method (Stober et al., 2021), we study in detail PW and GW characteristics in addition to measured zonal and meridional wind components in a time period from 2000 to 2020.</span></p> <p class="western" align="justify"><span lang="en-GB">In the NH the zonal wind is typically decreasing from around two weeks before the SSW onset, corresponding to an increased PW activity. Around the SSW onset, latitudinal differences in the zonal wind component as well as the PW activity can be seen. In the weeks before the SSW onset, the stations in the NH also show an increased level of GW kinetic energy. The meridional wind at the NH stations fluctuates with a periodicity of about 10 days before and around the onset. In contrast to previous studies (e.g. Yasui et al., 2016), the measurements in the SH are consistent with the inter-hemispheric coupling hypothesis. The expected downward shift of GW drag (Körnich and Becker, 2010) was reproduced by a downward travelling layer of enhanced GW activity at Davis and Rio Grande. Finally, the role of the terdiurnal tide in the GW energy composite is considered.</span></p>

scholarly journals The Temporal Autocorrelation Structure of Sea Surface Winds

2012 ◽  
Vol 25 (19) ◽  
pp. 6684-6700 ◽  
Author(s):  
Adam H. Monahan
Keyword(s):  
Wind Speed ◽  
Zonal Wind ◽  
Large Scale ◽  
Strong Dependence ◽  
Meridional Wind ◽  
Sea Surface ◽  
Small Scale ◽  
Wind Component ◽  
Temporal Autocorrelation ◽  
Vector Wind

Abstract The temporal autocorrelation structures of sea surface vector winds and wind speeds are considered. Analyses of scatterometer and reanalysis wind data demonstrate that the autocorrelation functions (acf) of surface zonal wind, meridional wind, and wind speed generally drop off more rapidly in the midlatitudes than in the low latitudes. Furthermore, the meridional wind component and wind speed generally decorrelate more rapidly than the zonal wind component. The anisotropy in vector wind decorrelation scales is demonstrated to be most pronounced in the storm tracks and near the equator, and to be a feature of winds throughout the depth of the troposphere. The extratropical anisotropy is interpreted in terms of an idealized kinematic eddy model as resulting from differences in the structure of wind anomalies in the directions along and across eddy paths. The tropical anisotropy is interpreted in terms of the kinematics of large-scale equatorial waves and small-scale convection. Modeling the vector wind fluctuations as Gaussian, an explicit expression for the wind speed acf is obtained. This model predicts that the wind speed acf should decay more rapidly than that of at least one component of the vector winds. Furthermore, the model predicts a strong dependence of the wind speed acf on the ratios of the means of vector wind components to their standard deviations. These model results are shown to be broadly consistent with the relationship between the acf of vector wind components and wind speed, despite the presence of non-Gaussian structure in the observed surface vector winds.

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

2004 ◽  
Vol 22 (2) ◽  
pp. 387-404 ◽  
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)

scholarly journals The Effects of Background Zonal and Meridional Winds on ENSO in a Coupled GCM

2020 ◽  
Vol 33 (6) ◽  
pp. 2075-2091 ◽  
Author(s):  
Bowen Zhao ◽  
Alexey Fedorov
Keyword(s):  
Zonal Wind ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Meridional Wind ◽  
Wind Component ◽  
Coupled Models ◽  
Positive Feedbacks ◽  
Zonal Winds ◽  
Meridional Winds

AbstractChanges in background zonal wind in the tropical Pacific are often invoked to explain changes in ENSO properties. However, the sensitivity of ENSO to mean zonal winds has been thoroughly explored only in intermediate coupled models (following Zebiak and Cane), not in coupled GCMs. The role of mean meridional winds has received even less attention. Accordingly, the goal of this study is to examine systematically the effects of both zonal (equatorial) and meridional (cross-equatorial) background winds on ENSO using targeted experiments with a comprehensive climate model (CESM). Changes in the mean winds are generated by imposing heat flux forcing in two confined regions at a sufficient distance north and south of the equator. We find that the strengthening of either wind component reduces ENSO amplitude, especially eastern Pacific SST variability, and inhibits meridional swings of the intertropical convergence zone (ITCZ). The effect of zonal winds is generally stronger than that of meridional winds. A stability analysis reveals that the strengthening of zonal and meridional winds weakens the ENSO key positive feedbacks, specifically the zonal advection and thermocline feedbacks, which explains these changes. Zonal wind enhancement also intensifies mean upwelling and hence dynamical damping, leading to a further weakening of El Niño events. Ultimately, this study argues that the zonal and, to a lesser extent, meridional wind strengthening of the past decades may have contributed to the observed shift of El Niño characteristics after the year 2000.

scholarly journals Is there a direct solar proton impact on lower stratospheric ozone?

2020 ◽  
Author(s):  
Jia Jia ◽  
Antti Kero ◽  
Niilo Kalakoski ◽  
Monika E. Szeląg ◽  
Pekka T. Verronen
Keyword(s):  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Individual Case ◽  
Solar Proton ◽  
Special Focus ◽  
Ozone Level ◽  
Superposed Epoch Analysis ◽  
Potential Case ◽  
Epoch Analysis ◽  
The Individual

Abstract. We investigate Arctic polar atmospheric ozone responses to Solar Proton Events (SPEs) using MLS satellite measurements (2004–now) and WACCM-D simulations (1989–2012). Special focus is on lower stratospheric ozone depletion that has been proposed earlier based on superposed epoch analysis of ozonesonde anomalies (up to 10 % ozone decrease). Superposed Epoch Analysis (SEA) of the satellite dataset provides no evidence of any average SPE impact on the lower stratospheric ozone, although at the mesospheric altitudes a statistically significant ozone depletion is present. In the individual case studies, we find only one potential case (January 2005) in which the lower stratospheric ozone level was significantly decreased after the SPE onset. However, similar decreases could not be identified in other SPEs of similar or larger magnitude. We find a very good overall consistency between SPE-driven ozone anomalies derived from the WACCM-D model simulations and the Aura MLS data. The simulation results before the Aura MLS era indicate no significant effect on the lower stratospheric ozone either. As a conclusion, the SPE has a zero direct impact on the lower stratospheric ozone.

A Climatology of Diurnal and Semidiurnal Surface Wind Variations over the Tropical Pacific Ocean Based on the Tropical Atmosphere Ocean Moored Buoy Array

2008 ◽  
Vol 21 (4) ◽  
pp. 593-607 ◽  
Author(s):  
Rei Ueyama ◽  
Clara Deser
Keyword(s):  
Zonal Wind ◽  
Surface Wind ◽  
Meridional Wind ◽  
Equatorial Pacific ◽  
Wind Component ◽  
Tropical Atmosphere ◽  
Tropical Pacific Ocean ◽  
Southerly Wind ◽  
Eastern Equatorial Pacific ◽  
The Tropical Pacific

Abstract Hourly measurements from 51 moored buoys in the Tropical Atmosphere Ocean array (9°N–8°S, 165°E–95°W) during 1993–2004 are used to document the climatological seasonal and annual mean patterns of diurnal and semidiurnal near-surface wind variability over the tropical Pacific Ocean. In all seasons, the amplitude of the semidiurnal harmonic is approximately twice as large as the diurnal harmonic for the zonal wind component, while the diurnal harmonic is at least 3 times as large as the semidiurnal harmonic for the meridional wind component, both averaged across the buoy array. Except for the eastern equatorial Pacific, the semidiurnal zonal wind harmonic exhibits uniform amplitude (∼0.14 m s−1) and phase [maximum westerly wind anomalies ∼0325/1525 local time (LT)] across the basin in all seasons. This pattern is well explained by atmospheric thermal tidal theory. The semidiurnal zonal wind signal is diminished over the cold surface waters of the eastern equatorial Pacific where it is associated with enhanced boundary layer stability. Diurnal meridional wind variations tend to be out of phase north and south of the equator (maximum southerly wind anomalies ∼0700 LT at 5°N and ∼1900 LT at 5°S), while a noon southerly wind anomaly maximum is observed on the equator in the eastern Pacific particularly during the cold season (June–November). The diurnal meridional wind variations result in enhanced divergence along the equator and convergence along the southern border of the intertropical convergence zone ∼0700 LT (opposite conditions ∼1900 LT); the amplitude of the divergence diurnal cycle is ∼5 × 10−7 s−1. The diurnal meridional wind variations are largely consistent with the diurnal pressure gradient force.

scholarly journals Analisa Angin Zonal dan Meridional Dalam Menentukan Awal Musim Hujan di Kota Jambi

2020 ◽  
Vol 8 (1) ◽  
pp. 43-50
Author(s):  
Presli Panusunan Simanjuntak ◽  
◽  
Agus Safril ◽  
Keyword(s):  
Wind Speed ◽  
Zonal Wind ◽  
El Niño ◽  
Rainy Season ◽  
Prediction Models ◽  
El Nino ◽  
Meridional Wind ◽  
Wind Component ◽  
Meridional Winds ◽  
The City

In Indonesia, prediction models for the beginning of the rainy season have not developed intensively. Jambi City is the capital of Jambi Province as it has quite extensive rainfed gardens / fields and rice fields and contributes significantly to the economy of Jambi Province. Jambi City really needs an accurate prediction of the start of the rainy season to support the economic continuity through agriculture and plantations. This study aims to analyze the zonal and meridional wind components in the 1000 mb layer in determining the start of the rainy season in the city of Jambi. The prediction of the beginning of the season using zonal and meridional winds will be divided into 2 conditions, namely when the normal conditions of monthly rainfall in 1997-2017 and when the El Nino conditions are strong in 1997/1998 and 2015/2016. Based on data processing for 1997-2017, it shows that the beginning of the rainy season is December when the zonal wind speed is highest. In this study, the zonal wind component is more dominant than the meridional wind component in determining the start of the rainy season. However, when conditions are el nino, the zonal wind component is not good to become

scholarly journals Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

Solar Physics ◽  
2021 ◽  
Vol 296 (3) ◽  
Author(s):  
Ryan O. Milligan
Keyword(s):  
Solar Flares ◽  
Solar Spectrum ◽  
Neutral Hydrogen ◽  
Solar Limb ◽  
High Background ◽  
Superposed Epoch Analysis ◽  
Lyman Alpha ◽  
Alpha Emission ◽  
Epoch Analysis ◽  
Very High

AbstractAs the Lyman-alpha (Ly$\upalpha $ α ) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Ly$\upalpha $ α of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Ly$\upalpha $ α emission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Ly$\upalpha $ α irradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Ly$\upalpha $ α emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Ly$\upalpha $ α at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Ly$\upalpha $ α of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

scholarly journals High lightning activity in maritime clouds near Mexico

2012 ◽  
Vol 12 (17) ◽  
pp. 8055-8072 ◽  
Author(s):  
B. Kucienska ◽  
G. B. Raga ◽  
R. Romero-Centeno
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Cloud Condensation Nuclei ◽  
Meridional Wind ◽  
Lightning Activity ◽  
Wind Component ◽  
Inter Tropical Convergence Zone ◽  
High Rainfall ◽  
Wind Variability ◽  
Monthly Distribution

Abstract. Lightning activity detected by the World Wide Lightning Location Network (WWLLN) over oceanic regions adjacent to Mexico is often as high as that observed over the continent. In order to explore the possible causes of the observed high flash density over those regions, the relationships between lightning, rainfall, vertical hydrometeor profiles, latent heating, wind variability and aerosol optical depth are analyzed. The characteristics of lightning and precipitation over four oceanic zones adjacent to Mexican coastlines are contrasted against those over the continent. The number of flashes per rainfall over some coastal maritime regions is found to be higher than over the continent. The largest number of flashes per rainfall is observed during the biomass burning season. In addition, we compare two smaller areas of the Tropical Pacific Ocean: one located within the Inter-Tropical Convergence Zone and characterized by high rainfall and weak lightning activity and the other one influenced by a continental wind jet and characterized by high rainfall and strong lightning activity. During the rainy season, the monthly distribution of lightning within the region influenced by the continental wind jet is contrary to that of rainfall. Moreover, the monthly variability of lightning is very similar to the variability of the meridional wind component and it is also related to the variability of aerosol optical depth. The analysis suggests that the high lightning activity observed over coastal Pacific region is linked to the continental cloud condensation nuclei advected over the ocean. Analysis of daily observations indicates that the greatest lightning density is observed for moderate values of the aerosol optical depth, between 0.2 and 0.35.

scholarly journals Solar influence on Earth's climate

2015 ◽  
Vol 11 (A29A) ◽  
pp. 372-376
Author(s):  
Rémi Thiéblemont ◽  
Katja Matthes
Keyword(s):  
Solar Variability ◽  
Special Focus ◽  
Solar Forcing ◽  
Top Down ◽  
Natural Climate Variability ◽  
System A ◽  
Earth’S Climate ◽  
Natural Climate ◽  
Solar Influence ◽  
Coupling Mechanisms

AbstractUnderstanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar-terrestrial interactions and observations, as well as mechanisms determining the response of the Earth's climate system. A summary of our current understanding from observational and modeling studies is presented with special focus on the “top-down” stratospheric UV and the “bottom-up” air-sea coupling mechanisms linking solar forcing and natural climate variability.

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