Asymmetries in mesospheric tidal structure

Radar wind measurements made at Adelaide (35°S, 138°E) and Kyoto (35°N, 136°E) are used to construct climatologies of solar tidal wind motions in the 80–185 km region. The climatologies, in the form of contour plots of amplitude and phase of the diurnal (24 h) and semidiurnal (12 h) tides, show that there are significant asymmetries between Adelaide and Kyoto. The amplitude of the diurnal tide is significantly larger at Adelaide than at Kyoto. At both stations the phase changes in a systematic way with lime such that the phases of the zonal wind components tend to be in anti-phase at the solstices. At Adelaide, there is more evidence of the propagating (1,1) diurnal mode. At both stations, the semidiurnal tide is strongest and has the longest vertical wavelengths (>100 km) in late summer; short vertical wavelength (~ 50–80 km) oscillations are most in evidence in winter. In order to place the Adelaide and Kyoto observations in context they are compared with observations made at other latitudes and with recent numerical simulations. There is encouraging agreement between the observations and models, especially for the semidiurnal tide.     

The propagation of the mesospheric two-day wave in the southern hemisphere

The results of an analysis of mesospheric wind data collected simultaneously at Grahamstown (South Africa) and Adelaide (South Australia) during the summer appearances of the quasi-two-day wave over a period of eight years are presented and discussed. It is concluded that the apparent zonal wave-number k which characterises the westward travelling wave is significantly less than the value of 3 suggested by current theories. Differences in local conditions and/or observing techniques are found to be unlikely causes of the discrepancy. It is shown that these results, as well as certain global features observed by satellite, could arise as a result of the superposition of modes with different k but similar frequencies.     

Identification of mesospheric heavy ion ledge

For the first time a ground based technique, i.e. incoherent scatter observation of the mesospheric spectra has been utilized in identifying the ‘transition height’ of simple molecular ions to complex cluster ions around 80–90 km in the D-region. This transition height also matches with the electron density ledge. A substantial diurnal variation of this height is observed. The transition height varies by about 10km during the course of a day, the lowest being 80 km, near noon. There is also a strong likelihood that both the neutral temperature and effective positive ion mass vary during the course of a day.     

The EISCAT mesospheric measurements during the CAMP campaign

A brief outline is given of the experimental technique used during the Cold Arctic Mesopause Project to record the first D-region ion line spectra with the EISCAT incoherent scatter radar. The data analysis shows that echoes from mesospheric heights between about 70 km and 90 km can be detected during disturbed periods of enhanced electron density during particle precipitation events. Electron density profiles were determined which show a fairly high density, up to 5 × 10¹⁰ m⁻³ in the upper D-region. The measured meridional winds were lower than 10 m s⁻¹. A fit of the measured height profile of spectral width to temperature and neutral density models yielded a measured temperature profile in good agreement with simultaneous rocket data. The mesopause temperature was determined to be as low as 130 K. This detailed analysis of the spectral width profile indicates that below about 77–80 km the ratio of negative ions to electrons exceeded unity. Finally, some discussions are added on the limitations and significance of these first mesosphere observations.     

Lidar sounding of the mesospheric sodium layer at high latitude

Long series of laser sounding of the sodium layer have been performed at Heyss Island (80.4°N) during the polar winters of 1977–1978 and 1978–1979. The measurements show large and rapid variations of the sodium total content (a factor of 2, about 1000s). Those variations and the correlated modification of the sodium layer could be interpreted as the response of the layer to internal gravity waves.     

Solar cycle and long-period variations of mesospheric temperatures

Evidence for a temperature variation above about 55 km between years of high and low solar activity is found in rocket data of Volgograd (49°N, 44°E) 1969–1983, reaching a solar-cycle amplitude of 6K, whereas below 55 km no statistically significant solar cycle effect is detected. This mesospheric temperature variation is in qualitative agreement with a pressure variation at 80 km derived from lower ionosphere radio reflection heights near 51°N, 13°E, measured at Kühlungsborn/GDR, covering almost two solar cycles. When the solar cycle variation has been removed from these 80 km pressure data by means of a regression analysis, there remains a quasi-cycle of about 20 yr, which agrees well with observations of a general cooling of the northern mid-latitude stratosphere between 1965 and 1977, reported by other authors.     

Lidar observation of the mesospheric sodium layer over Urbana,Illinois

Atmospheric sodium has been observed over Urbana (40°10′N, 88°10′W) using a monostatic lidar tuned to 589.0 nm. The photocount data are processed using digital smoothing filters to obtain continuous estimates of the sodium density versus altitude. The filter cutoff frequency is related to the height resolution and accuracy of the estimated profile. Wavelike structures in the sodium layer have been observed with typical wavelengths of 3–15 km and phase velocities of 1–3 m s⁻¹. The layer is characterized by a sharp falloff on the bottomside and often an undulatory motion of the bottomside of the layer accompanies the wave motion. The topside gradient of the layer is frequently observed to decrease through the night.     

Large scale coherence of the mesospheric and upper stratospheric temperature fluctuations

A large set of temperature profiles has been obtained in the upper stratosphere and the mesosphere over Europe during the MAP/WINE compaign by the use of different techniques: datasondes and falling spheres launched by metrockets, ground-based OH spectrometers and a Rayleigh lidar. These data have been used to study the large scale variability of the middle atmosphere during the winter 1983–1984. The temperature variations with periods longer than 25 days are clearly related to the succession of minor upper stratospheric warmings observed during this winter. The variations in the period range 10–20 days are at least partially due to westward propagating Rossby waves, of which one mode, with a 12.5 days period, is tentatively identified as the second symmetric mode of the wave number 2.     

Predominant semi-annual oscillation of the upper mesospheric airglow intensities and temperatures in the equatorial region

The upper mesospheric and lower thermospheric airglow emissions, OI 557.7 nm, NaD 589.3 mn and the OH (9,4) band and its rotational temperature have been measured using a ground-based multichannel airglow photometer located at Fortaleza (3.9°S, 38.4°W) since 1986. The observed emission intensities show predominantly semi-annual oscillations with maxima at the equinoxes and minima during the solstices. The amplitudes of the oscillations are larger than those observed from the low latitude station, Cachoeira Paulista (22.7°S, 45.0°W). The OH rotational temperature, which represents a gas kinetic atmospheric temperature at around 85–95 km, also shows a strong semi-annual oscillation, 18 K peak to peak, with an. average value around 10 K higher than that observed from Cachoeira Paulista. These results do not agree with model atmospheres presently available. It is suggested that the differences result from the effects of seasonal variations in vertical eddy transport and/or meridional circulation.     

Tropical behavior of mesospheric ozone as observed by SMM

The seasonal behavior of low latitude mesospheric ozone, as observed by the SMM satellite solar occultation experiment, is detailed for the 1985–1989 period. Annual as well as semi-annual waves are observed in the 50–70 km altitude region. In the latitude range of ±30 the ozone phase and amplitude are functions of temperature and seasonal changes in solar flux. Temperature is the controlling factor for the equatorial region and seasonal changes in solar flux become more dominant at latitudes outside the equatorial zone (greater than ±15). There is a hemispheric asymmetry in the ozone annual wave in the 20 30 region, with northern hemispheric ozone having a larger amplitude than southern hemispheric ozone. In this region temperature is nearly in phase with ozone in both hemispheres and is reduced in amplitude in the northern hemisphere. The equatorial region is characterized by a strong semi-annual wave in addition to the annual variation, and temperature is nearly out of phase with ozone. At all latitudes there is a larger ozone concentration at sunrise than at sunset. The sunrise sunset difference increases with increasing altitude     

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 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。     

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

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.     

Further effects of charged aerosols on summer mesospheric radar scatter

In an earlier paper, we showed that charged aerosols play a crucial role in enhancing radar echoes from the summer polar mesosphere through reduced diffusion turbulent scatter and dressed aerosol scatter (Cho et al., 1992a). Here, we explore the effects of charged aerosols on radar scatter through ‘fossil’ turbulence and electron density depletion layers. We find that the former can produce radar scatter even after the decay of neutral gas turbulence, while the latter, which are probably produced by the scavenging of free electrons by ice particles, are a candidate for causing partial reflection or Fresnel scatter. Furthermore, we examine the mutual aerosol interaction restriction on dressed aerosol scatter more closely. We find that a high ambient electron density and low aerosol number density are needed for effective dressed aerosol scatter to occur. We then show that very small (less than 1 nm radii), negatively charged aerosols enhance electron diffusivity, and thus inhibit radar scatter. Also, ice aerosol sedimentation, in the light of the reduced diffusion theory, leads us to conclude that the statistical peak in Polar Mesospheric Summer Echoes (PMSE) power should be located between the mean mesopause and the average noctilucent cloud (NLC) height, which agrees with observations. Finally, we invoke time lags in the ice particle formation cycle to account for the observed non-correlation between PMSE and NLC occurrence.     

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.     

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.     

Some direct comparisons of mesospheric winds observed at Kyoto and Adelaide

Direct comparisons have been made of the prevailing and tidal wind fields observed in the 80–100 km height region using data obtained with a meteor radar at Kyoto (35°N, 136°E) and a partial reflection spaced antenna system at Adelaide (35°S, 138°E). Data taken with a partial reflection system at Townsville (19°S, 147°E) has also been included so that the latitudinal variations of the tidal structures could be taken into account. The comparisons extend over periods of up to one month duration centered on the equinoxes of 1979 and the January solstice of 1980. They show that there are often significant differences in the tidal amplitudes and phases observed at Kyoto and Adelaide, despite their near geographic conjugacy, probably indicating the presence of antisymmetrical tidal modes. The diurnal tide is appreciably stronger at Adelaide on the average, than at Kyoto, whereas the semi-diurnal amplitudes are on the average greater at Kyoto.