134 research outputs found
Long-term tendencies in the MLT prevailing winds and tides over Antarctica as observed by radars at Molodezhnaya, Mawson and Davis
No full textLong-term tendencies in horizontal neutral wind parameters in the southern polar mesosphere/lower thermosphere are presented. The wind data analyzed were obtained from meteor and MF radars situated at Molodezhnaya (45.9°E, 67.7°S), Mawson (62.9°E, 67.6°S) and Davis (78.0°E, 68.6°S). The composite dataset covers years from 1970 to 2006. A Bayesian approach in the form proposed by Wang and Zivot [2000. A Bayesian time series model of multiple structural changes in level, trend and variance. Journal of Business and Economic Statistics 8, 374-386] is used for the trend assessment. This approach allows structural breaks to be identified in the trend parameters (slope, mean or variance of residuals) or demonstrates their absence. The results of our analysis have shown persistence through such structural breaks in trends of the winter and summer prevailing winds and in meridional tidal components. It is demonstrated that the wind parameters exhibit different stable states with transitions between the states. Correlations between the southern polar MLT wind and indices of atmospheric variability (Northern annular mode, Southern annular mode, Multivariate El-Niño/Southern Oscillation Index) were then considered. The results show that statistically significant correlations exist during some periods of observations that do not exist during others. © 2008 Elsevier Ltd. All rights reserved.E.G. Merzlyakov, D.J. Murphy, R.A. Vincent and Yu.I. Portnyagi
PEER REVIEW IN TEACHING FOREIGN LANGUAGE WRITING
No full textPeer review is one of the methods of problem-based learning, aimed at students conducting mutual assessment of written work in terms of their compliance with the structure of the study, as well as in content, style, punctuation, lexical and grammatical aspects, with a view to their further improvement taking into account the recommendations made. This method involves students to exchange brief informal comments as well as more detailed comments that contribute to improving the quality of their papers. In this paper, the author gives an analysis of the academic literature on the use of peer review in teaching foreign language writing. The analysis is presented on aspects to testify the didactic potential of the method. Every aspect is formulated as didactic function of peer review, under which the author understands the internal organization and regulation of the process of learning a foreign language on the basis of this method. As a result, the author proposes to include the following language didactic functions of peer review: a) the transfer of the share of responsibility for the result of mastering the educational material from the teacher to the students themselves; b) the role of the teacher / instructor is to monitor teaching and learning activities of pupils and students; c) the organization of students’ interaction in the course of performance of educational tasks; d) the creation of didactic conditions for increasing the amount of out of class work and its combination with the classroom activities; e) the creation of conditions for teaching students to recognize their own strengths and weaknesses; f) reduction of time for evaluation of students’ works. The article describes in detail each of their functions
Understanding Creolized Text in the System “Author-Reader” on the Example of Texts with Graphic and Realistic Images
No full textLong-period meteor radar temperature variations over Collm (51°N, 13°E) and Kazan (56°N, 49°E)
No full textWe have estimated temperatures from meteor radar measurements using the gradient method and the full width at half maximum method over Kazan (56°N 49°E) and Collm (51°N, 13°E). The time series cover the period 2016–2019. The temperature gradient model is constructed from SABER temperature observations. We demonstrate that annual mean, amplitudes and phases of the annual and semiannual oscillations of the radar temperatures are close to those of the MLS and SABER temperatures. The annual mean temperatures over Kazan and Collm differ non-significantly. The seasonal variability of the radar temperature is mostly due to the annual cycle which tends to grow with latitude. The gradient method produces temperatures which agree with the SABER temperatures better than with the MLS ones. The harmonics of the annual oscillations from periods of 73 days up to periods of about 40 days are the most significant day-to-day temperature oscillations and have zonal wavenumber zero. Their periods and phases are in good correspondence with those of the MLS and SABER ones. We also show some results which demonstrate that at 56°N the FWHM method is not as robust as the gradient method
Longitudinal MLT wind structure at higher mid-latitudes as seen by meteor radars at central and Eastern Europe (13°E/49°E)
No full text© 2019 COSPAR The mid-latitude mesosphere and lower thermosphere (MLT) wind speeds measured by two SKiYMET meteor radars (MRs) at Collm (51°N, 13°E) and Kazan (56°N, 49°E) during 2016–2017 were analyzed to study longitudinal wind structures. The differences between monthly mean prevailing wind speeds and tidal amplitudes were compared with the corresponding differences obtained from TIMED/TIDI satellite winds and gradient wind speeds from the AURA/MLS instrument. It is shown that the MR wind difference between the two sites is statistically significant. The difference of the horizontal prevailing winds can be explained by a superposition of the background zonal flow, which is different at the two latitudes, with stationary planetary waves of different origin. Non-migrating tides contribute significantly to the difference of the semidiurnal tidal winds between the two sites
Quasi-two-day wave in an unstable summer atmosphere - some numerical results on excitation and propagation
No full textInternational audienceBased on numerical calculations we demonstrate that small changes in the smooth climatological background atmosphere may lead to an unstable mean zonal wind distribution in the summer middle atmosphere. We relate these changes to small ones because locations and power of the main circulation structures are conserved, except for the acceleration of the easterly jet in the stratosphere/mesosphere. The instability forces oscillations propagating westward with a period of about 2 days and zonal wave numbers s=3 and/or 4. There are variations in the mean zonal wind distribution due to the excitation and transient propagation of these waves, and the numerical results correspond to features of these variations observed in experimental studies. The growing waves tend to remove the source of excitation. This process is effective enough to reduce the strong easterly jet and to remove the strong negative gradient of the zonal mean potential vorticity in the region of the instability. Therefore, when these parameters are calculated as mean values over a long time interval, the obtained values are too small to provide the instability. Strong 2-day waves, in turn, are unstable and can generate secondary waves with longer periods and lower zonal wave numbers. This effect is only significant for extremely strong 2-day waves. Another process is found to be more effective to produce secondary waves. We demonstrated that the 2-day wave with s=3 forced by nonlinear interaction between the 10-14 day planetary waves and the 2-day wave of zonal wave number 4 is unstable. This wave instability generates secondary waves with amplitudes that are large enough to be observed by ground-based radars, for example
Climatological lower thermosphere winds as seen by ground-based and space-based instruments
No full textComparisons are made between climatological dynamic fields obtained from ground-based (GB) and space-based (SB) instruments with a view towards identifying SB/GB intercalibration issues for TIMED and other future aeronomy satellite missions. SB measurements are made from the High Resolution Doppler Imager (HRDI) instrument on the Upper Atmosphere Research Satellite (UARS). The GB data originate from meteor radars at Obninsk, (55° N, 37° E), Shigaraki (35° N, 136° E) and Jakarta (6° S, 107° E) and MF spaced-antenna radars at Hawaii (22° N, 160° W), Christmas I. (2° N, 158° W) and Adelaide (35° S, 138° E). We focus on monthly-mean prevailing, diurnal and semidiurnal wind components at 96km, averaged over the 1991-1999 period. We perform space-based (SB) analyses for 90° longitude sectors including the GB sites, as well as for the zonal mean. Taking the monthly prevailing zonal winds from these stations as a whole, on average, SB zonal winds exceed GB determinations by ~63%, whereas meridional winds are in much better agreement. The origin of this discrepancy remains unknown, and should receive high priority in initial GB/SB comparisons during the TIMED mission. We perform detailed comparisons between monthly climatologies from Jakarta and the geographically conjugate sites of Shigaraki and Adelaide, including some analyses of interannual variations. SB prevailing, diurnal and semidiurnal tides exceed those measured over Jakarta by factors, on the average, of the order of 2.0, 1.6, 1.3, respectively, for the eastward wind, although much variability exists. For the meridional component, SB/GB ratios for the diurnal and semidiurnal tide are about 1.6 and 1.7. Prevailing and tidal amplitudes at Adelaide are significantly lower than SB values, whereas similar net differences do not occur at the conjugate Northern Hemisphere location of Shigaraki. Adelaide diurnal phases lag SB phases by several hours, but excellent agreement between the two data sources exists for semidiurnal tidal phases throughout the year. These results are consistent with phase retardation effects in the MF radar technique that are thought to exist above about 90km. Prevailing and tidal amplitudes from Shigaraki track year-to-year variations in SB fields, whereas in the Southern Hemisphere poorer agreement exists. The above hemispheric differences are due in part to MF vs. meteor radar techniques, but zonal asymmetries and day-to-day variability, combined with inadequate sampling, may also be playing a role. Based on these results, some obvious recommendations emerge that are relevant to combined GB/SB studies as part of TIMED and other future aeronomy missions.J. M. Forbes, Yu. I. Portnyagin, W. Skinner, R. A. Vincent, T. Solovjova, E. Merzlyakov, T. Nakamura, and S. Pal
Some numerical results on the quasi-two-day wave excitation andpropagation in the unstable summer middle atmosphere
No full textMit Hilfe numerischer Simulationen wird gezeigt, dass manche Änderungen des klimatologischen Hintergrundwindfeldes zu instabilem mittleren Zonalwind in der mittleren Atmosphäre Sommerhemisphäre führen. Diese Instabilität treibt Oszillationen mit einer Periode um 2 Tage an, welche eine zonale Wellenzahl von s = 3 oder 4 aufweisen. Beobachtete Variationen des mittleren Windes stehen in Verbindung mit diesen numerisch gefundenen Schwingungen. Starke 2-Tage-Wellen wiederum sind instabil und können daher Wellen längerer Periodendauer und kleinerer Wellanzahl anregen. Dieser Effekt ist jedoch nur für sehr starke 2-Tage-Wellen signifikant. Effektiver ist ein Prozess, bei dem nichtlineare Wechselwirkung zwischen einer 10-14-Tage-Welle und der 2-Tage-Welle der zonalen Wellenzahl 4 eine neue quasi-2-Tage-Welle mit einer Periodendauer von 55-60 Stunden anregt. Diese Welle generiert sekundäre Wellen effektiver als die ursprüngliche 2-Tage-Wellen; die sekundären Wellen können beobachtet werden.Basing on numerical calculations we have demonstrated that some changing of the climatological background atmosphere could lead to an unstable mean zonal wind distribution in the summer middle atmosphere. This instability forces oscillations propagating westward with a period of about 2 days and zonal wavenumbers s = 3 and/or 4. There are variations in the mean zonal wind distribution due to the excitation and transient propagation of these waves and numerical results correspond to features of these changes obtained in experimental studies. Strong 2-day waves in turn are unstable and can generate secondary waves with longer periods and lower zonal wavenumbers. This effect is significant only for very strong 2-day waves. It is shown that the 2-day wave with s=3 forced by non-linear interaction between 10-14 day planetary waves and the 2-day wave of zonal wave number 4 is unstable. This wave generates secondary waves of lower zonal wavenumbers more easily than the primary 2-day waves and these secondary waves may be observed
A comparison of optical and radar measurements of mesospheric winds and tides
No full textOptical measurements of mesospheric winds by Fabry‐Perot spectrometers, FPSs, at Mawson, 67.6°S 62.9°E, and Davis, 68.6°S 78.0°E, Antarctica are compared with similar measurements obtained using a spaced‐antenna MF radar at Davis. The FPSs observed the OH emission. Different analysis procedures, used to determine the mean wind, and amplitude and phase of the semidiurnal tide, have been compared. At these latitudes the diurnal tide is weak and the semi‐diurnal tide, although highly variable in amplitude, is usually the dominant periodicity. When comparing the amplitude and phase of the semidiurnal tide good agreement is obtained between measurements by the two instruments
Mesosphere/lower thermosphere prevailing wind model
No full textCopyright © 2004 COSPAR. Published by Elsevier Ltd.The mesosphere/lower thermosphere (MLT) wind data from the 46 ground-based (GB) MF and meteor radar (MR) stations, located at the different latitudes over the globe, and the space-based (SB) HRDI data were used for constructing of the empirical global climatic 2-D prevailing wind model at 80–100 km heights for all months of the year. The main data set is obtained during 1990–2001 period. It is shown that the three datasets (MF, MR, HRDI) are mainly well correlated. However, a certain systematic bias between the GB and SB data at 96 km exists, as well as that between the MF and MR data higher 88 km. Simple correction factors are proposed to minimize these biases. The 2-D distant-weighted least-square interpolation procedure for some arbitrary collection of points was used for drawing model contour plots. The model is available in the computer readable form and may be used for construction of the new CIRA model.Yu. Portnyagin, T. Solovjova, E. Merzlyakov, J. Forbes, S. Palo, D. Ortland, W. Hocking, J. MacDougall, T. Thayaparan, A. Manson, C. Meek, P. Hoffmann, W. Singer, N. Mitchell, D. Pancheva, K. Igarashi, Y. Murayama, Ch. Jacobi, D. Kuerschner, A. Fahrutdinova, D. Korotyshkin, R. Clark, M. Taylor, S. Franke, D. Fritts, T. Tsuda, T. Nakamura, S. Gurubaran, R. Rajaram, R. Vincent, S. Kovalam, P. Batista, G. Poole, S. Malinga, G. Fraser, D. Murphy, D. Riggin, T. Aso and M. Tsutsumihttp://www.elsevier.com/wps/find/journaldescription.cws_home/644/description#descriptio
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