Monthly simulations of the solar semidiurnal tide in the mesosphere and lower thermosphere

Monthly simulations of the solar semidiurnal tide in the 80–100 km height regime are presented. These calculations benefit from the recent heating rates provided by Groves G. V. (1982a,b) (J. atmos. terr. Phys. 44, 111; 44, 281), the zonally-averaged wind, temperature and pressure fields developed for the new COSPAR international reference atmosphere [Labitzke K., Barnett J. J. and Edwards B. (1985) Handbook for MAP 16, 318], and eddy diffusivities determined from gravity wave saturation climatologies and used by Garcia R. R. and Solomon S. (1985) (J. geophys. Res. 90, 3850) to simulate oxygen photochemistry and transport in the mesosphere and lower thermosphere. Some of the main characteristics of the observed semidiurnal tide at middle and high latitudes are reproduced in our simulations: larger amplitudes in winter months than in summer months, and the bi-modal behavior of the phase with summer-like and winter-like months separated by a quick transition around the two equinoxes. The phase transition is also more rapid in the spring, consistent with observations. The wavelengths are also longer in summer than in winter, at least below 95 km (whereas in July and August the simulations exhibit some discrepancies above this altitude), similar to the observational data. Semidiurnal amplitudes are generally smaller and the phases more seasonally symmetric at middle and low latitudes, as compared with the tidal structures above about 50° latitude. In addition, hemispheric differences in the mean zonal wind result in marked asymmetries in tidal behavior between the Arctic and Antarctic regions, and suggest that a comparative study of tide, gravity wave and mean flow interactions in the Arctic and Antarctic mesosphere and lower thermosphere would be fruitful.     

Infrared radiative cooling in the mesosphere and lower thermosphere

This paper discusses the current status of calculating infrared cooling by CO₂ in the mesosphere and lower thermosphere. It is desirable to have fast but accurate procedures for use in dynamic models. The most difficult region is from 70 to 90 km, where cooling rates are strongly influenced or, in the case of the summer mesopause region, dominated by the absorption of radiation emitted by underlying layers, with the hot bands and isotopic bands playing a significant role. A three-energy-level model is derived for the excited population levels of a CO₂ molecule. Vibrational-vibrational coupling between isotopes is also included as significant. Results from model calculations for cooling rates and NLTE source functions are presented. Global average infrared cooling rates appear to be in reasonable balance with solar heating rates, considering the uncertainties in calculating both these terms. Radiative cooling rates by CO₂ above 100 km are strongly dependent on atomic oxygen concentrations and on the rate of energy exchange between atomic oxygen and CO₂. Likewise, NO cooling, which is important above 120 km, is proportional to atomic oxygen concentrations. Since CO₂, NO and O concentrations can all vary with motions, these dependencies suggest interesting feedbacks to atmospheric dynamics.     

The impact of gravity waves on nitric oxide in the lower thermosphere

Observations of nitric oxide (NO) by the Solar Mesosphere Explorer (SME) during equinox indicate a lower-thermosphere equatorial minimum which is at variance with theoretical predictions. To address this discrepancy a zonally averaged model of the thermosphere and upper mesosphere is used to evaluate the influence of a latitude variation in turbulence. Five numerical simulations were performed with different latitude structures of eddy diffusion (K_T), ranging from uniform in latitude, peaks at low, mid-, or high-latitude, to a hemispherically asymmetric distribution. A local increase in eddy diffusion causes the lower thermosphere to cool and induces a latitude pressure gradient that drives horizontal and vertical winds. The circulation, turbulent transport and temperature dependent chemistry act to change the distribution of species. Comparison of the model predictions of NO with SME data, and simulated wind and temperature structure with empirical climatology, indicates a preference for a midlatitude peak in K_T.     

The semidiurnal tides at the midlatitude lower thermosphere over East Siberia

Results from the study of semidiurnal tides in the horizontal wind field at 85–95 km over East Siberia are presented. The seasonal variation of tidal amplitudes and the effects of stratospheric warmings are discussed.     

A comparison of three methods of measuring tidal oscillations in the lower thermosphere using EISCAT common programmes

The EISCAT Common Programme can be used in three ways to monitor tidal oscillations in the lower thermosphere. In Common Programme One (CPI) tristatic observations provide measurements of the ion-velocity vector at several heights in the E-region and one height in the F-region. In Common Programme Two (CP2) monostatic measurements give profiles of ion velocity in the E-region while tristatic measurements give continuous measurements of ion velocity in the F-region. From the ion velocities and the ion-neutral collision frequency, the vector of the E-region neutral wind can be determined and both east-west and north-south components of the diurnal, semi-diurnal and ter-diurnal oscillations can be identified. CP1 and CP2 also provide profiles of the field-aligned ion velocity, and these can be used to calculate the north-south component of the neutral wind without knowing the ion-neutral collision frequency, but the result is affected by any vertical component of neutral velocity. The three methods are compared and the advantages of CP2 demonstrated.     

Intense turbulence in the polar mesosphere : rocket and radar measurements

Simultaneous observations of polar mesospheric summer echoes (PMSE) have been made with two different frequency radars during the launch of a sounding rocket designed to measure the fluctuations in the electron density in the same height range. The cross-section for radar backscatter deduced from the rocket probe data under the assumption of isotropic turbulence is in reasonable agreement with the measured signals at both 53.5 MHz with the mobile SOUSY radar and 224 MHz with the EISCAT VHF radar, which correspond to backscatter wavelengths of about 3 and 0.75 m, respectively. Some controversy exists over the relative roles of turbulent scatter vs specular reflections in PMSE. A number of characteristics of the data obtained in this experiment are consistent with nearly isotropic, intense meter-scale turbulence on this particular day. Since equally compelling arguments for the importance of an anisotropic-type mechanism have been presented by other experimenters studying PMSE, we conclude that both isotropic and anisotropic mechanisms must operate. We have found the inner scale for the electron fluctuation spectrum, which corresponds to the diffusive subrange for that fluid, and have compared it to the inner scale for the neutral gas. The latter was found from the Kolmogorov microscale, which in turn depends on the energy dissipation rate in the gas. We found the dissipation rate from the spectral width of the 53.5 MHz backscatter signal and from the rocket electron density fluctuation data. The diffusive subrange was found to occur at a wavelength a factor of about 10 times smaller than the viscous subrange. This corresponds to a Schmidt number of about 100. High Schmidt numbers have been reported in recent measurements of the diffusion coefficient of the electrons in this height range made with the EISCAT incoherent scatter radar. About 15 min after the rocket flight an extremely high radar reflectivity was found with the SOUSY system. We have been able to reproduce this high level theoretically by scaling the rocket data with an increase in the neutral turbulence energy dissipation rate by a factor of 14 as deduced from the SOUSY spectral width, an increase in the electron density which is consistent with riometer data, and a 33% decrease in the electron density gradient scale length which is hypothesized. We also estimate the radar reflectivity at 933 MHz and conclude that signals in excess of thermal scatter levels would have occurred at the peak of the event studied, provided that the electron fluctuation spectrum decreases as k⁻⁷ in the viscous subrange. If the spectrum has an exponential form, however, a turbulent source cannot explain the enhanced 933 MHz echoes reported by EISCAT.     

Vertical winds in the midlatitude thermosphere from Fabry-Perot interferometer measurements

Monostatic and bistatic measurements of thermospheric winds have been made with Fabry-Perot Interferometers at the Millstone Hill and Laurel Ridge Observatories. Synchronized observing sequences have been chosen to enable the determination of vertical winds from the measurements. The vertical winds are found to be significant on some nights with velocities of tens of m/s. For geomagnetically quiet nights, the averaged values for eight samples in the July–October 1992 period show little variation during the night, averaging ∼10 m/s downward. The average for three geomagnetically disturbed nights oscillates from a downward maximum of ∼50 m/s at ∼02 UT to an upward maximum of ∼20 m/s at ∼07 UT. Temporal variations in the vertical motions suggest oscillatory behavior with periods of ∼0.7, ∼1.8 and ∼3.4 h, respectively, on three quiet nights, possibly associated with gravity wave or tidal-harmonic effects.     

Surveying in the Antarctic

A Naturalist in Mid‐Africa. Being an account of a Journey to the Mountains of the Moon and Tanganyika. By G. F. Scott Elliot, M.A., F.L.S., F.E.G.S. Pp. xvi + 413, 49 figs., frontispiece, and 4 maps. 8vo. London: A. D. Innes and Co., 1896. Pp. xiii + 413. Price 16s.

A Breath from the Veldt. By John Guille Millais, F.Z.S. London: Henry Sotheran and Co., 1895. Pp. 236. Price £3, 3s. net.

Peru. Von E. W. Middendorf. III. Band : Das Hochland von Peru. Berlin : Robert Oppenheim (Gustav Schimdt), 1895.

Tafilet. The Narrative of a Journey of Exploration in the Atlas Mountains and the Oases of the North‐West Sahara. By Walter B. Harris, F.E.G.S., author of “A Journey through the Yemen,” “The Land of an African Sultan,” VOL. XII. Q

“Travels in Morocco,” etc. Illustrated by Maurice Romberg from Sketches and Photographs by the Author. Edinburgh and London: William Blackwood and Sons, 1895. Pages xii + 386. Price 12s.

From Far Formosa: The Island, its People, and Missions. By G. L. Mackay, D.D. Edited by the Rev. J. A. Macdonald. Edinburgh : Oliphant, Anderson, and Ferrier, 1896. 346 pp. Price 7s. 6d.

The Geology and Scenery of Sutherland. By H. M. Cadell, B.Sc., etc. Second edition. Edinburgh : Douglas, 1896. Pp. 104. Price 4s.

The Place‐Names of Fife and Kinross. By W. J. N. Liddall, M.A., Advocate. Edinburgh : W. Green and Sons, 1896. 8vo., pp. xiv. + 58.

Die Liparischen Inseln. Fünftes Heft—Filicuri. Prag : Heinr. Mercy, 1895.

Australien und Ozeanien. Eine allgemeine Landeskunde von Professor Dr. Wilhelm Sievers. Mit 137 Abbildungen im Text, 12 Kartenbeilagen, und 20 Tafeln in Holzschnitt und Farbendruck. Leipzig und Wien. Bibliographisches Institut, 1895. Pp. 521. Price 16 M.

Ritters Geographisch‐Statistisches Lexikon. Achte Auflage: Unter der Redaktion [von Johs. Penzler. Zweiter Band, L‐Z. Leipzig, 1895. 1202 pp.

The Natural History of Plants: their Forms, Growth, Reproduction and Distribution. From the German of Anton Kerner von Marilaun, Professor of Botany in the University of Vienna. Translated and edited by F. W. Oliver, M.A., D.Sc., Quain Professor of Botany in University College, London, with the assistance of Marian Busk, B.Sc., and Mart F. Ewart, B.Sc. With about 2000 original woodcut illustrations and sixteen plates in colours. Vol. i., Biology and Configuration of Plants, pp. xiv. + 777 ; vol. ii., The History of Plants, pp. xiv.+983. London and Glasgow: Blackie and Son, Limited, 1894 and 1895.

Handbook for Travellers in Algeria and Tunis. By Sir R. Lambert Platfair, K.C.M.G. Fifth edition, thoroughly revised. London : John Murray, 1895. Pp. 363. Price 10s. 6d.

Cassell's New Geographical Readers. Fifth Book—Europe. Sixth Book—The British Colonies and Dependencies. Seventh Book—The United States. London, etc. : Cassell and Co., 1895. Prices 1s. 6d., 1s. 6d., 1s. 9d., respectively.

The Statesman's Year‐Book. Statistical and Historical Annual of the States of the World for the Year 1896. Edited by J. Scott Keltie, Assistant Secretary of the Royal Geographical Society, with the assistance of I. P. A. Renwick, M.A., LL.B. London : Macmillan and Co., 1896. Pp. xxxii+1164.

The Australian Handbook, Shippers’ and Importers’ Directory and Business Guide for 1896. London, Melbourne, etc. : Gordon and Gotch. Pp. 632.

Beobachtungen der Russischen Polarstation an der Lenamündung. 1. Theil. Astronomische und Magnetische Beobachtungen. 1882–4. Bearbeitet von V. Fuss, F. Müller, and K. Jürgens. St. Petersburg : 1895.     

Planetary waves in the strato- and mesosphere during the Western European Winter Anomaly Campaign 1975/76 and their relation to ionospheric absorption

The planetary-scale circulation features have been analysed for the period 28 December 1975 to 11 February 1976 by means of radiosonde, rocketsonde, and satellite data (infrared radiances). Geostrophic horizontal winds, vertical motions, and amplitudes and phases of the planetary waves are provided from the stratosphere to the mesosphere (from 20 to 80 km). The development in time and space of the planetary-scale waves is discussed and it is shown how the ionospheric absorption over Spain and Germany during the Winter Anomaly Campaign is connected with these waves which can be traced from the stratosphere through the whole mesosphere.     

Britain and the British Antarctic Territory in the wider geopolitics of the Antarctic and the Southern Ocean

Britain's contemporary and future relationship with the British Antarctic Territory and the wider region is the subject matter of this article. In the aftermath of the ill‐fated plans for a merger of British Antarctic Survey (BAS) and the National Oceanography Centre, it is timely to ask how the UK projects influence and secures its scientific, resource and strategic interests. The contemporary Antarctic is increasingly characterized by tension over resource management and conservation politics as Antarctic Treaty parties disagree, both in private and public, over the purpose of legal instruments and the regulation of activities such as fishing and marine conservation. While we do not predict the collapse of the Antarctic Treaty System (ATS), our analysis suggests that the effectiveness and legitimacy of the ATS is increasingly under challenge. The United Kingdom's position as a claimant state and original signatory to the Antarctic Treaty is complicated by the presence of counter‐claimants (Argentina and Chile) and a wider preoccupation with other overseas territories, such as South Georgia and South Sandwich Islands and the Falkland Islands. Polar science, carried out by BAS and other British agents, remains critical not only for maintaining the UK's ‘soft power’ but also increasingly for cementing a ‘strategic presence’ in the Antarctic. The article ends with a cautionary note: scientific excellence is no longer sufficient to guarantee geopolitical/strategic interests and there is growing evidence that claimant and non‐claimant states alike are no longer regarding Antarctica as an area that will remain free of intensifying and diversifying resource exploitation.     

On the structure and circulation of the polar thermosphere under magnetically quiet conditions

A theoretical study is presented bearing on the thermospheric circulation and composition at polar latitudes. The observed motions and density perturbations in N₂, O and He have signatures which may be understood in terms of two different source mechanisms. We consider electric field momentum coupling and Joule heating as well as interactions between both processes. A spectral model in terms of vector spherical harmonics (with magnetic coordinates) is used, delineating the diurnal and mean (time independent) components. The important non-linearities are evaluated in configuration space. The electric field model of Volland and the global average density and temperature variations of Hedin (MSIS) are adopted as input. Our analysis leads to the following conclusions. (1) The vortex type double cell polar circulation (zonal wave number m = 1) is primarily driven by collisional momentum transfer from electric field induced ion convection. (2) Because of the thermospheric low pass filter, a large time independent component (zonal wave number m = 0) is produced by Joule heating; the heavier species (N₂) being concentrated where the lighter ones (O, He) are depleted, and vice versa due to wind induced diffusion (3) The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations (from Joule heating), producing primarily diurnal variations (m = 1) in the temperature and composition near the pole and at auroral latitudes, again the heavier and lighter species varying out of phase. The above results are in substantial agreement with observations. It is worth noting that momentum rectification associated with the diurnally varying electric field and conductivity induces a weak zonally symmetric (single cell) prograde polar vortex. However, this motion is partially compensated by a retrograde vortex from geostrophic balance due to Joule heating, which dominates near the pole. These motions are small compared with the diurnally varying component in the polar circulation.     

扎营苔原

正格陵兰航空的飞机清一色地浑身涂成醒目的猩红色。后来我们发现,在这一片银白色世界里,这样做实在是很聪明。高空之中,能见度很低。直到飞机下降到550米时,透过舷窗,白底黑痕的冰原和山丘方才依稀可辨。康克鲁斯瓦格是格陵兰岛唯一可起降大型飞机的入口,机场和跑道原是美军建立,后来以一个美元的对价归还了当地政府。步下舷梯,迎接我们的是幽幽飘落的大片雪花和降至冰点的气温。     

探索北极世界中的生命 13天北极游随行笔记摘选

<正>飞行在几千米高的北极上空,透过机舱舷窗俯瞰,看着厚厚白雪覆盖下连绵的黑色山脊上,这才真正感受到地球最北之地的瑰丽。一眼望去,只有蓝得让人窒息的天空和纯洁的白雪,一切如此安静。下了飞机,踏上位于北极圈内的斯瓦尔巴群岛首府朗伊尔城,终于,我来到了北极。     

探索北极世界中的生命

作为摄影顾问,我参加了天霞客组织的北极包船游,从朗伊尔城乘坐海洋精灵号SeaSpirit号开始为期13天12晚的精彩北极邮轮之旅.虽然看上去是北极邮轮之旅,但和大家常规意义上所了解的邮轮之旅完全不同,因为在北极地带,每天最精华最刺激的活动安排就是全副武装乘坐登陆艇来到斯瓦尔巴群岛或者格陵兰岛的陆地上,在专业自然向导团队的带领下开始徒步探索北极世界,每一次行程可长可短,根据体力以及天气等情况而定.因此,北极邮轮之旅真正享受的不是硬件的豪华,而是北极的壮观美景以及精彩的动物世界.     

扎营苔原

<正>格陵兰航空的飞机清一色地浑身涂成醒目的猩红色。后来我们发现,在这一片银白色世界里,这样做实在是很聪明。高空之中,能见度很低。直到飞机下降到550米时,透过舷窗,白底黑痕的冰原和山丘方才依稀可辨。康克鲁斯瓦格是格陵兰岛唯一可起降大型飞机的入口,机场和跑道原是美军建立,后来以一个美元的对价归还了当地政府。步下舷梯,迎接我们的是幽幽飘落的大片雪花和降至冰点的气温。     

探索北极世界中的生命 13天北极游随行笔记摘选

<正>飞行在几千米高的北极上空,透过机舱舷窗俯瞰,看着厚厚白雪覆盖下连绵的黑色山脊上,这才真正感受到地球最北之地的瑰丽。一眼望去,只有蓝得让人窒息的天空和纯洁的白雪,一切如此安静。下了飞机,踏上位于北极圈内的斯瓦尔巴群岛首府朗伊尔城,终于,我来到了北极。     

On the estimation of eddy diffusion coefficient in the mesosphere from partial reflection technique

Estimations of the eddy diffusion coefficient in the mesosphere are reported using observations from the Partial Reflection Technique at Buckland Park, South Australia (35°S, 139°E). The method of estimation is approximately the same as reported by Schlegel et al. (1977) with one difference i.e. in the present work the medium is considered to be moving and the effect due to horizontal winds have been incorporated. It is found that the inclusion of horizontal winds decreases the value of the eddy diffusion coefficient and the decrease is more marked as the horizontal velocity increases.     

The Arctic in the middle ages

The rather sparse and dubious data about Arctic regions known to Antiquity were taken over, mostly via Pliny, by the middle ages and reinforced and expanded in significant ways. This paper, which was delivered as an Inaugural Lecture at the University of Groningen in November 1982, reviews the activities and reports of medieval explorers, colonists and traders in or about the Arctic and considers the handful of medieval writers who display some real knowledge about Arctic regions. The generality of medieval writers on history and geography knew little or nothing. Even so, it is shown that here and there references are made to many of the features which are thought of as typically Arctic in the modern popular consciousness, with the exception of igloos and muskoxen. Commercial connections with the Arctic through Novgorod and Bergen are examined, and some account given of contacts with Iceland and the disappearance of the Norse settlement in Greenland. Polar bears and white falcons in western Europe, both of nearly indisputable Arctic origin, are discussed, attention is drawn to the very inadequate portrayal of the Arctic on medieval maps, and the paper closes with a glance at Olaus Magnus's account of northern peoples published in 1555.