scholarly journals Planetary wave activity in the lower ionosphere during CRISTA I campaign in autumn 1994 (October−November)

1998 ◽  
Vol 16 (8) ◽  
pp. 1014-1023 ◽  
Author(s):  
D. Pancheva ◽  
J. Laštovička
Keyword(s):  
Planetary Wave ◽  
Middle Atmosphere ◽  
Lower Ionosphere ◽  
Wave Activity ◽  
Atmospheric Dynamics ◽  
Planetary Scale ◽  
Meteorology And Atmospheric Dynamics ◽  
Wave Numbers ◽  
Dominant Period ◽  
Waves And Tides

Abstract. On the basis of MEM spectrum analysis, the main planetary scale fluctuations formed in the lower ionosphere are studied over a period of 3–25 days during the CRISTA campaign (October-November 1994). Three dominant period bands are found: 3–5, 6–8 and 15–23 (mainly 16–18) days. For 7–8 and 16–18 day fluctuations, propagation was eastward with wave numbers K = 3 and K = 1, respectively. The magnitude of planetary wave activity in the mid-latitudes of the Northern Hemisphere during the CRISTA campaign seems to be fairly consistent with the expected undisturbed normal/climatological state of the atmosphere at altitudes of 80–100 km.Key words. Ionosphere (ionosphere-atmosphere interactions) · Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Unexpectedly small semidiurnal tidal wind amplitudes in the mid-latitudemesopause region during September 2002

2004 ◽  
Vol 22 (2) ◽  
pp. 701-704 ◽  
Author(s):  
D. Kürschner ◽  
Ch. Jacobi
Keyword(s):  
Phase Transition ◽  
Key Words ◽  
Central Europe ◽  
Annual Cycle ◽  
Middle Atmosphere ◽  
Atmospheric Dynamics ◽  
Mesopause Region ◽  
Meteorology And Atmospheric Dynamics ◽  
Middle Atmosphere Dynamics ◽  
Waves And Tides

Abstract. The mesopause region monthly mean winds and semidiurnal tidal amplitudes and phases over Central Europe have been measured at Collm Observatory since September 1982. The regular annual cycle of the semidiurnal tidal amplitudes show maximum values during late August and September. In contrast to that, in autumn 2002 no enhancement of the tidal amplitudes was measured, while the autumn tidal phase transition occurred unusually early. Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides; climatology)

Final Sudden Stratospheric Warmings and the memory of the stratosphere

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

<p>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°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.</p><p>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 :</p><p>- 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;</p><p>- 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;</p><p>- 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 .</p><p>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.</p>

scholarly journals A new approach to momentum flux determinations using SKiYMET meteor radars

2005 ◽  
Vol 23 (7) ◽  
pp. 2433-2439 ◽  
Author(s):  
W. K. Hocking
Keyword(s):  
New Mexico ◽  
Momentum Flux ◽  
Middle Atmosphere ◽  
Beam Forming ◽  
New Approach ◽  
Meteorology And Atmospheric Dynamics ◽  
Momentum Fluxes ◽  
Waves And Tides ◽  
Resolute Bay

Abstract. The current primary radar method for determination of atmospheric momentum fluxes relies on multiple beam studies, usually using oppositely directed coplanar beams. Generally VHF and MF radars are used, and meteor radars have never been successfully employed. In this paper we introduce a new procedure that can be used for determination of gravity wave fluxes down to time scales of 2-3h, using the SKiYMET meteor radars. The method avoids the need for beam forming, and allows simultaneous determination of the three components of the wind averaged over the radar volume, as well as the variance and flux components , where refers to the fluctuating eastward wind, refers to the fluctuating northward wind, and refers to the fluctuating vertical wind. Data from radars in New Mexico and Resolute Bay are used to illustrate the data quality, and demonstrate theoretically expected seasonal forcing. Keywords. Meteorology and atmospheric dynamics (Middle atmosphere dynamics; Waves and tides; Climatology)

scholarly journals On the influence of neutral turbulence on ambipolar diffusivities deduced from meteor trail expansion

2002 ◽  
Vol 20 (11) ◽  
pp. 1857-1862 ◽  
Author(s):  
C. M. Hall
Keyword(s):  
Middle Atmosphere ◽  
Atmospheric Dynamics ◽  
Meteorology And Atmospheric Dynamics ◽  
Middle Atmosphere Dynamics ◽  
Radar Echoes ◽  
Meteor Trail ◽  
Meteor Trails

Abstract. By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect the meteor trail diffusion rate.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence)

scholarly journals An explanation for some fallstreak clouds

2002 ◽  
Vol 20 (5) ◽  
pp. 711-715 ◽  
Author(s):  
R. M. Worthington
Keyword(s):  
Radar Data ◽  
Atmospheric Dynamics ◽  
Atmospheric Composition ◽  
Cloud Physics ◽  
Mountain Wave ◽  
Mountain Waves ◽  
Meteorology And Atmospheric Dynamics ◽  
Composition And Structure ◽  
Waves And Tides ◽  
Stratospheric Clouds

Abstract. Fallstreak cirrus clouds are associated with super-saturated air, together with waves, instabilities and/or turbulence; however, their precise cause is usually uncertain. This paper uses already-published satellite, radiosonde and radar data, reanalysed to study some large fallstreaks which had been previously overlooked. The fallstreaks – up to 60 km long with a parent cloud 20 km wide – are caused by lifting and/or turbulence from a mountain wave, rather than, for example, Kelvin-Helmholtz instabilities. If turbulent breaking of mountain waves affects ice particle formation, this may be relevant for the seeder-feeder effect on orographic rain, and the efficiency of mountain-wave polar stratospheric clouds for ozone depletion.Key words. Meteorology and atmospheric dynamics (turbulence; waves and tides) – Atmospheric composition and structure (cloud physics and chemistry)

scholarly journals The Antarctic Oscillation Structure in an AOGCM with Interactive Stratospheric Ozone

2012 ◽  
Vol 2012 ◽  
pp. 1-12
Author(s):  
S. Brand ◽  
K. Dethloff ◽  
D. Handorf
Keyword(s):  
General Circulation ◽  
Planetary Wave ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Circulation Model ◽  
Wave Activity ◽  
Antarctic Oscillation ◽  
Wave Dynamics ◽  
Hemisphere Winter ◽  
The Antarctic

Based on 150-year equilibrium simulations using the atmosphere-ocean-sea ice general circulation model (AOGCM) ECHO-GiSP, the southern hemisphere winter circulation is examined focusing on tropo-stratosphere coupling and wave dynamics. The model covers the troposphere and strato-mesosphere up to 80 km height and includes an interactive stratospheric chemistry. Compared to the reference simulation without interactive chemistry, the interactive simulation shows a weaker polar vortex in the middle atmosphere and is shifted towards the negative phase of the Antarctic Oscillation (AAO) in the troposphere. Differing from the northern hemisphere winter situation, the tropospheric planetary wave activity is weakened. A detailed analysis shows, that the modelled AAO zonal mean signal behaves antisymmetrically between troposphere and strato-mesosphere. This conclusion is supported by reanalysis data and a discussion of planetary wave dynamics in terms of Eliassen-Palm fluxes. Thereby, the tropospheric planetary wave activity appears to be controlled from the middle atmosphere.

scholarly journals Stratosphere-troposphere exchange in an extratropical cyclone, calculated with a Lagrangian method

2000 ◽  
Vol 18 (5) ◽  
pp. 573-582 ◽  
Author(s):  
M. Sigmond ◽  
J. Meloen ◽  
P. C. Siegmund
Keyword(s):  
Wind Shear ◽  
Total Ozone ◽  
General Circulation ◽  
Middle Atmosphere ◽  
Statistical Significance ◽  
Atmospheric Dynamics ◽  
Extratropical Cyclone ◽  
Northwest Coast ◽  
Mesoscale Meteorology ◽  
Meteorology And Atmospheric Dynamics

Abstract. A Lagrangian technique is developed and applied to calculate stratosphere-troposphere exchange in an extratropical cyclone. This exchange is computed from the potential vorticity or PV along trajectories, calculated from ECMWF circulation data. Special emphasis is put on the statistical significance of the results. The computed field of the cross-tropopause flux is dominated by elongated patterns of statistically significant large downward and small upward fluxes. The downward fluxes mainly occur in the lower part of the considered tropopause folds. The upward fluxes are found near the entrance of the folds, in the tropopause ridges. The ratio between the area averaged downward and upward cross-tropopause fluxes increases with increasing strength of the cyclone. Since the largest fluxes are shown to occur in the regions with the largest wind shear, where PV-mixing is thought to cause large cross-tropopause fluxes, the results are expected to be reliable, at least in a qualitative sense. The position of a tropopause fold along the northwest coast of Africa is confirmed by total ozone observations. The results indicate that the applied Lagrangian technique is an appropriate tool for diagnosing stratosphere-troposphere exchange.Key words: Meteorology and atmospheric dynamics (general circulation; mesoscale meteorology; middle atmosphere dynamics)

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