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)

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 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 Freak waves - more frequent than rare!

2004 ◽  
Vol 22 (5) ◽  
pp. 1839-1842 ◽  
Author(s):  
P. C. Liu ◽  
U. F. Pinho
Keyword(s):  
Atlantic Ocean ◽  
Surface Waves ◽  
Key Words ◽  
Atmospheric Dynamics ◽  
South Atlantic Ocean ◽  
Freak Waves ◽  
Meteorology And Atmospheric Dynamics ◽  
Wave Measurements ◽  
Waves And Tides ◽  
Made In

Abstract. Contrary to the widely held notion that considers the occurrence of freak waves in the ocean as being rare, from an examination of five years of wave measurements made in the South Atlantic Ocean, we found the occurrence of freak waves is actually more frequent than rare. Key words. Meteorology and atmospheric dynamics (waves and tides) – Oceanography: physical (surface waves and tides; air-sea interaction)

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 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 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)

scholarly journals The 16-day planetary wave in the mesosphere and lower thermosphere

1999 ◽  
Vol 17 (11) ◽  
pp. 1447-1456 ◽  
Author(s):  
N. J. Mitchell ◽  
H. R. Middleton ◽  
A. G. Beard ◽  
P. J. S. Williams ◽  
H. G. Muller
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Late Summer ◽  
Wave Activity ◽  
Motion Field ◽  
Mesopause Region ◽  
Waves And Tides ◽  
Mesosphere And Lower Thermosphere ◽  
Thermospheric Dynamics ◽  
The Uk

Abstract. A meteor radar located at Sheffield in the UK has been used to measure wind oscillations with periods in the range 10–28 days in the mesosphere/lower-thermosphere region at 53.5°N, 3.9°W from January 1990 to August 1994. The data reveal a motion field in which wave activity occurs over a range of frequencies and in episodes generally lasting for less than two months. A seasonal cycle is apparent in which the largest observed amplitudes are as high as 14 ms–1 and are observed from January to mid-April. A minimum in activity occurs in late June to early July. A second, smaller, maximum follows in late summer/autumn where amplitudes reach up to 7–10 ms–1. Considerable interannual variability is apparent but wave activity is observed in the summers of all the years examined, albeit at very small amplitudes near mid summer. This behaviour suggests that the equatorial winds in the mesopause region do not completely prevent inter-hemispheric ducting of the wave from the winter hemisphere, or that it is generated in situ.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides)

scholarly journals About the direction of motion, polarity and multiplicity of lightning flashes hitting towers: a comparative analysis of data gathered in Brazil and Switzerland

2003 ◽  
Vol 21 (5) ◽  
pp. 1209-1213 ◽  
Author(s):  
O. Pinto ◽  
D. G. Guedes ◽  
M. M. F. Saba ◽  
I. R. C. A. Pinto ◽  
M. Lacerda
Keyword(s):  
Comparative Analysis ◽  
Key Words ◽  
Atmospheric Electricity ◽  
Atmospheric Dynamics ◽  
Similar Data ◽  
Meteorology And Atmospheric Dynamics ◽  
Instruments And Techniques

Abstract. After 17 years of research at Morro do Cachimbo station (MC) in Brazil, 51 flashes with strokes higher than 2 kA were registered. The data are compared with similar data obtained from the Mount San Salvatore station (SS), Switzerland, in terms of the incidence of downward or upward flashes, polarity, and flash multiplicity. The comparison indicates that at MC the percentage of upward flashes and the multiplicity of negative downward flashes are higher than at SS, while the percentage of downward positive flashes is lower. Key words. Meteorology and atmospheric dynamics (atmospheric electricity; lightning; instruments and techniques)

scholarly journals On the longitudinal structure of the transient day-to-day variation of the semidiurnal tide in the mid-latitude lower thermosphere − I. Winter season

2001 ◽  
Vol 19 (5) ◽  
pp. 545-562 ◽  
Author(s):  
E. G. Merzlyakov ◽  
Yu. I. Portnyagin ◽  
C. Jacobi ◽  
N. J. Mitchell ◽  
H. G. Muller ◽  
...  
Keyword(s):  
Middle Atmosphere ◽  
Lower Thermosphere ◽  
Winter Season ◽  
Semidiurnal Tide ◽  
Longitudinal Structure ◽  
Transient Behaviour ◽  
Meteorology And Atmospheric Dynamics ◽  
S Transform ◽  
Wind Measurements ◽  
Waves And Tides

Abstract. The longitudinal structure of the day-to-day variations of semidiurnal tide amplitudes is analysed based on coordinated mesosphere/lower thermosphere wind measurements at several stations during three winter campaigns. Possible excitation sources of these variations are discussed. Special attention is given to a nonlinear interaction between the semidiurnal tide and the day-to-day mean wind variations. Data processing includes the S-transform analysis which takes into account transient behaviour of secondary waves. It is shown that strong tidal modulations appear during a stratospheric warming and may be caused by aperiodic mean wind variations during this event.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Long-term trends in the middle atmosphere dynamics at northern middle latitudes – one regime or two different regimes?

2010 ◽  
Vol 10 (2) ◽  
pp. 2633-2668 ◽  
Author(s):  
J. Lastovicka ◽  
P. Krizan ◽  
M. Kozubek
Keyword(s):  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Atmospheric Concentration ◽  
Mesopause Region ◽  
Middle Latitudes ◽  
Middle Atmosphere Dynamics ◽  
E Region ◽  
Long Term Trends ◽  
Middle Atmospheric Dynamics

Abstract. Due to increasing atmospheric concentration of greenhouse gases and changing stratospheric ozone concentration, both of anthropogenic origin, various quantities in the middle atmosphere reveal long-term changes and trends. Lastovicka and Krizan (2006) indicated possibility of change of trends in the dynamics in the northern midlatitude middle atmosphere as a whole in the 1990s. To search for such change of trends we use data on winds in the mesopause region, on total columnar ozone, on ozone laminae, on winds in the middle and lower stratosphere, and on peak electron density in the E region of the ionosphere. One group of quantities, the mesopause region wind-like trends, changes their trends around 1990, the other one, the total ozone-like trends, in the mid-1990s. Altogether they create a skeleton of scenario of the change of the middle atmosphere dynamics trends in the 1990s. Drivers of these changes appear to be different for the first group and for the second group. Tropospheric processes seem to play a role in the changes of trends in middle atmospheric dynamics.

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