scholarly journals More evidence for a planetary wave link with midlatitude <i>E</i> region coherent backscatter and sporadic <i>E</i> layers

2000 ◽  
Vol 18 (9) ◽  
pp. 1182-1196 ◽  
Author(s):  
M. Voiculescu ◽  
C. Haldoupis ◽  
D. Pancheva ◽  
M. Ignat ◽  
K. Schlegel ◽  
...  
Keyword(s):  
Planetary Wave ◽  
Close Relation ◽  
Planetary Waves ◽  
Neutral Wind ◽  
Spectral Peaks ◽  
Direct Indication ◽  
E Region ◽  
Waves And Tides ◽  
Coherent Backscatter

Abstract. Measurements of midlatitude E region coherent backscatter obtained during four summers with SESCAT, a 50 MHz Doppler system operating in Crete, Greece, and concurrent ionosonde recordings from the same ionospheric volume obtained with a CADI for one of these summers, are used to analyse the long-term variability in echo and Es occurrence. Echo and Es layer occurrences, computed in percent of time over a 12-h nighttime interval, take the form of time sequences. Linear power spectrum analysis shows that there are dominant spectral peaks in the range of 2–9 days, the most commonly observed periods appearing in two preferential bands, of 2–3 days and 4–7 days. No connection with geomagnetic activity was found. The characteristics of these periodicities compare well with similar properties of planetary waves, which suggests the possibility that planetary waves are responsible for the observed long-term periodicities. These findings indicate also a likely close relation between planetary wave (PW) activity and the well known but not well understood seasonal Es dependence. To test the PW postulation, we used simultaneous neutral wind data from the mesopause region around 95 km, measured from Collm, Germany. Direct comparison of the long-term periodicities in echo and Es layer occurrence with those in the neutral wind show some reasonable agreement. This new evidence, although not fully conclusive, is the first direct indication in favour of a planetary wave role on the unstable midlatitude E region ionosphere. Our results suggest that planetary waves observation is a viable option and a new element into the physics of midlatitude Es layers that needs to be considered and investigated.Key words: Ionosphere (ionosphere irregularities; mid-latitude ionosphere) – Meteorology and atmospheric dynamics (waves and tides)

scholarly journals A Short-Term Negative Eddy Feedback on Midlatitude Jet Variability due to Planetary Wave Reflection

2016 ◽  
Vol 73 (11) ◽  
pp. 4311-4328 ◽  
Author(s):  
Gwendal Rivière ◽  
Loïc Robert ◽  
Francis Codron
Keyword(s):  
Planetary Wave ◽  
Physical Nature ◽  
Planetary Waves ◽  
Critical Layer ◽  
Zonal Wavenumber ◽  
Acceleration And Deceleration ◽  
Poleward Shift ◽  
Jet Variability ◽  
Quasigeostrophic Model

Abstract A three-level quasigeostrophic model on the sphere is used to identify the physical nature of the negative planetary wave feedback on midlatitude jet variability. A first approach consists of studying the nonlinear evolution of normal-mode disturbances in a baroclinic westerly zonal jet. For a low-zonal-wavenumber disturbance, successive acceleration and deceleration of the jet occur as a result of reflection of the wave on either side of the jet. The planetary wave deposits momentum in opposite ways during its poleward or equatorward propagation. In contrast, a high-zonal-wavenumber disturbance is not reflected but absorbed within the subtropical critical layer. It thus only induces poleward momentum fluxes, which accelerate the jet and shift it slightly poleward. A long-term simulation forced by a relaxation toward a zonally symmetric temperature profile is then analyzed. Planetary waves are shown to be baroclinically excited. When they propagate equatorward, they induce an acceleration of the jet together with a slight poleward shift. About two-thirds of the planetary waves are absorbed by the subtropical critical layer, which allows the accelerated poleward-shifted jet to persist for a while. For the remaining third, the potential vorticity equatorward of the jet is so well homogenized that a reflection occurs. It is followed by an abrupt jet deceleration during the subsequent poleward propagation. The reflection of planetary waves on the poleward side of the jet is more systematic because of the quasi-permanent presence of a turning latitude there. This negative planetary wave feedback is shown to act more on pulses of the jet than on its latitudinal shifts.

The upper atmospheric responses to tidal and planetary waves

2020 ◽  
Author(s):  
Sheng-Yang Gu
Keyword(s):  
Planetary Wave ◽  
Lower Thermosphere ◽  
Satellite System ◽  
Planetary Waves ◽  
Spatial Structures ◽  
Ionospheric Effect ◽  
Ion Drift ◽  
E Region ◽  
Mesosphere And Lower Thermosphere ◽  
Tide Interaction

&lt;p&gt;Tidal and planetary waves (PWs) in the mesosphere and lower thermosphere region could have significant impact on the upper thermosphere/ionosphere system through direct propagations, E region wind dynamo, and the change of residual circulations. We would like to show some results from BeiDou and COSMIC observations, as well as TIME-GCM simulations, to illustrate the lower/upper atmospheric couplings through different mechanisms. Generally, the spatial structures of the ionospheric responses to planetary waves agree with the ionospheric fountain effect, which indicates the important roles of equatorial wind dynamos in transmitting planetary wave signals to the ionosphere. The TIME-GCM simulations show that the zonal and meridional components of the planetary waves could result in evident vertical ion drift perturbations, while the net ionospheric effect is related to both their latitudinal structures and phases. The simulations also show that the change of tidal amplitudes and secondary PWs generated by PW-tide interaction are also important to the ionospheric variabilities. Besides, the couplings through PW-induced residual circulations are exhibited by both model simulations and TEC observations from BeiDou satellite system.&lt;/p&gt;

scholarly journals A model of mid-latitude E-region plasma convergence inside a planetary wave cyclonic vortex

2002 ◽  
Vol 20 (8) ◽  
pp. 1193-1201 ◽  
Author(s):  
S. Shalimov ◽  
C. Haldoupis
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Planetary Wave ◽  
Numerical Solutions ◽  
Lower Thermosphere ◽  
Plasma Transport ◽  
Neutral Wind ◽  
Prevailing Wind Direction ◽  
E Region ◽  
Region Plasma

Abstract. Recently, Shalimov et al. (1999) proposed a new mechanism for large-scale accumulation of long-lived metallic ions in the mid-latitude ionosphere driven by planetary waves in the lower thermosphere. In this mechanism, the combined action of frictional and horizontal magnetic field forces at E-region altitudes causes the plasma to converge and accumulate in large areas of positive neutral wind vorticity within a propagating planetary wave. The present paper provides a theoretical formulation for this mechanism by modelling both horizontal and vertical plasma transport effects within a planetary wave vortex, of cyclonic neutral wind. Non-steady-state numerical solutions of the ion continuity equation show that the proposed accumulation process can enhance the ionization significantly inside the planetary wave vortex but its efficiency depends strongly on altitude, whereas on the other hand, it can be complicated by vertical plasma motions. The latter, which are driven by the same planetary wave wind field under the action of the vertical Lorentz force and meridional wind forcing along the magnetic field lines, can lead to either plasma compressions or depletions, depending on the prevailing wind direction. We conclude that, for shorter times, vertical plasma transport may act constructively to the horizontal gathering process to produce considerable E-region plasma accumulation over large sectors of a planetary wave vortex of cyclonic winds.Key words. Ionosphere (ionosphere-atmosphere interactions; mid-latitude ionosphere; sporadic E-layers) – Meteorology and atmospheric dynamics (waves and tides)

scholarly journals Mid-latitude <i>E</i>-region bulk motions inferred from digital ionosonde and HF radar measurements

2004 ◽  
Vol 22 (11) ◽  
pp. 3789-3798 ◽  
Author(s):  
G. C. Hussey ◽  
C. Haldoupis ◽  
A. Bourdillon ◽  
J. Delloue ◽  
J. T. Wiensz
Keyword(s):  
Hf Radar ◽  
Neutral Wind ◽  
Angle Of Arrival ◽  
Neutral Winds ◽  
Sporadic E Layers ◽  
E Region ◽  
Radar Measurements ◽  
Sporadic E ◽  
Coherent Radar ◽  
Coherent Backscatter

Abstract. In the mid-latitude E-region there is now evidence suggesting that neutral winds play a significant role in driving the local plasma instabilities and electrodynamics inside sporadicE layers. Neutral winds can be inferred from coherent radar backscatter measurements of the range-/azimuth-time-intensity (RTI/ATI) striations of quasi-periodic (QP) echoes, or from radar interferometer/imaging observations. In addition, neutral winds in the E-region can be estimated from angle-of-arrival ionosonde measurements of sporadic-E layers. In the present paper we analyse concurrent ionosonde and HF coherent backscatter observations obtained when a Canadian Advanced Digital Ionosonde (CADI) was operated under a portion of the field-of-view of the Valensole high frequency (HF) radar. The Valensole radar, a mid-latitude radar located in the south of France with a large azimuthal scanning capability of 82° (24° E to 58° W), was used to deduce zonal bulk motions of QP echoing regions using ATI analysis. The CADI was used to measure angle-of-arrival information in two orthogonal horizontal directions and thus derive the motion of sporadic-E patches drifting with the neutral wind. This paper compares the neutral wind drifts of the unstable sporadic-E patches as determined by the two instruments. The CADI measurements show a predominantly westward aligned motion, but the measured zonal drifts are underestimated relative to those observed with the Valensole radar.

scholarly journals Vertical motion of ionization induced by the linear interaction of tides with planetary waves

2003 ◽  
Vol 21 (7) ◽  
pp. 1521-1529 ◽  
Author(s):  
M. Voiculescu ◽  
M. Ignat
Keyword(s):  
Planetary Wave ◽  
Vertical Motion ◽  
Quantitative Model ◽  
Planetary Waves ◽  
Ion Content ◽  
Linear Interaction ◽  
Sporadic E Layers ◽  
Sporadic E ◽  
Experimental Findings

Abstract. Experimental findings have shown that travelling planetary waves modulate the occurrence of mid-latitude sporadic-E-layers. Using a simple quantitative model, we analyse the effects of the linear interaction between tides and planetary waves on ion motion. Besides an expected variation of the dumping height, it is found that the boundaries of the oscillations induced by the descending semidiurnal tide are significantly modified by the presence of the planetary wave. The height variations of the ionisation cause planetary wave modulations of the metallic ion content in the background plasma density. This could explain the long-term variation found in the occurrence of strong Es layers. The fact that the dumping height variations are strongly influenced by the tidal phase velocity and amplitude, together with the variability of the metallic ion content, could contribute to the understanding of the sporadic nature of the E-layers.Key words. Ionosphere (Ionosphere-atmosphere interactions; Mid-latitude ionosphere)

Planetary wave-tide nonlinear interactions increase the variety of MLT waves in summer 2019

2021 ◽  
Author(s):  
Maosheng He ◽  
Jorge L. Chau ◽  
Jeffrey M. Forbes ◽  
Denise Thorsen ◽  
Guozhu Li ◽  
...  
Keyword(s):  
Planetary Wave ◽  
Lower Thermosphere ◽  
Planetary Waves ◽  
Diurnal Tide ◽  
Nonlinear Interactions ◽  
Zonal Wavenumber ◽  
Spectral Peaks ◽  
Northern Hemispheric ◽  
Mesosphere And Lower Thermosphere ◽  
Diurnal Tides

&lt;p&gt;Mesospheric winds collected by multiple meteor radars at mid-latitudes in the northern hemispheric are combined to investigate wave activities in June&amp;#8212;October 2019. Dual-station approaches are developed and implemented to diagnose zonal wavenumber $m$ of spectral peaks.&amp;#160; In&amp;#160; September&amp;#8212;October, diagnosed are quasi&amp;#8208;10&amp;#8208; and 6&amp;#8208;day planetary waves (Q10DW and Q6DW,&amp;#160;$m=$1), solar semi-diurnal tides with&amp;#160;$m=$1, 2, 3 (SW1, SW2, and SW3), lunar semi-diurnal tide, and the upper and lower sidebands (USB and LSB,&amp;#160;$m=$ 1 and 3) of Q10DW&amp;#8208;SW2 nonlinear interactions.&amp;#160; During June&amp;#8212; September, diagnosed are Rossby-gravity modes ($m=$3 and 4 at periods $T=$ 2.1d and 1.7d), and their USBs and LSBs generated from interactions with diurnal, semi-diurnal, ter-diurnal, and quatra-diurnal migrating tides. These results demonstrate that the planetary wave-tide nonlinear interactions significantly increase the variety of waves in the mesosphere and lower thermosphere region (MLT).&lt;/p&gt;

Evidence for nonlinear coupling of planetary waves and tides in the Antarctic mesopause

1997 ◽  
Vol 102 (D4) ◽  
pp. 4437-4446 ◽  
Author(s):  
F. Kamalabadi ◽  
J. M. Forbes ◽  
N. M. Makarov ◽  
Yu. I. Portnyagin
Keyword(s):  
Planetary Waves ◽  
Nonlinear Coupling ◽  
Waves And Tides ◽  
The Antarctic

scholarly journals Some Problems of Perspective Planning in Pakistan

1964 ◽  
Vol 4 (2) ◽  
pp. 193-202
Author(s):  
Said Hasan
Keyword(s):  
Policy Making ◽  
Time Horizon ◽  
Close Relation ◽  
The Third ◽  
Preceding Period ◽  
The Subject ◽  
Perspective Planning ◽  
Economic Future ◽  
Work Done

The growing confidence of Pakistan's planners in the nation's economic future is indicated by the boldness of their successive plans and by the lengthening of their time horizon. As far as the latter is concerned, the First Five-Year Plan did not reflect any thinking on economic and social development beyond a specific five-year period; the Second Plan, however, contained some remarks on long-term growth; the Third Plan is being prepared in close relation to the work being done on the Perspective Plan. What fifteen years ago would have been regarded as a waste of time is now considered to be of basic import¬ance for sound planning. What nobody dared think about in the earlier days is now the subject of serious analysis and policy-making. The need for a Perspective Plan is there not only from an economic angle but there are also sound political reasons for it. From the economic angle, we realized that the five-year periods chosen for our plans are only arbitrary periods in a process stretching over a much longer time. Our decisions and policies during one plan influence the pattern of growth in the next one, and influence also the effectiveness of established policies. Therefore, any particular five-year plan has to be part of a whole chain of plans, all fitting together and building further on the work done in the preceding period.

scholarly journals Studies of the E-Region Neutral Wind in the Auroral Ionosphere Using Two Long-Run Data.

1997 ◽  
Vol 49 (5) ◽  
pp. 641-673 ◽  
Author(s):  
S. Nozawa ◽  
A. Brekke ◽  
R. Fujii
Keyword(s):  
Neutral Wind ◽  
Auroral Ionosphere ◽  
Long Run ◽  
E Region
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