MF radar observations of mean winds over Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E)

Continuous MF radar measurements of mesospheric mean winds are in progress at the observatories in Yamagawa (31.2°N, 130.6°E) and Wakkanai (45.4°N, 141.7°E). The observations at Yamagawa and Wakkanai were started in August 1994 and September 1996, respectively. The real-time wind data are used for the study of major large scale dynamic features of the middle atmosphere such as mean winds, tides, planetary waves, and gravity waves, etc. In the present study of mean winds, we have utilized the data collected until June 1999, which include the simultaneous observation period of little more than two and a half years, for the two sites. The database permits us to draw conclusions on the characteristics of mean winds and to compare the mean wind structure over these sites. The mean prevailing zonal winds at both sites are dominated by westward/eastward motions in summer/winter seasons below 90 km. Meridional circulation at meteor heights is generally southward during most times of the year and it extends to lower mesospheric heights during summer also. The summer westward jet at Wakkanai is consistently stronger than those at Yamagawa. However, the winter eastward winds have identical strength at both locations. Meridional winds also show larger values at Wakkanai. The mean wind climatology has been examined and compared with the MU radar observations over Shigaraki (34.9°N, 136.1°E). The paper also presents the results of the comparison between the MF radar winds and the latest empirical model values (HWM93 model) proposed by Hedin et al. (1996. Journal of Atmospheric and Terrestrial Physics 58, 1421–1447). Hodograph analyses of mean winds conducted for the summer and winter seasons show interesting similarities and discrepancies.     

Analysis of gravity waves in the tropical middle atmosphere over La Reunion Island (21°S, 55°E) with lidar using wavelet techniques

The capabilities of the continuous wavelet transform (CWT) and the multiresolution analysis (MRA) are presented in this work to measure vertical gravity wave characteristics. Wave properties are extracted from the first data set of Rayleigh lidar obtained between heights of 30 km and 60 km over La Reunion Island (21°S, 55°E) during the Austral winter in 1994 under subtropical conditions. The altitude-wavelength representations deduced from these methods provide information on the time and spatial evolution of the wave parameters of the observed dominant modes in vertical profiles such as the vertical wavelengths, the vertical phase speeds, the amplitudes of temperature perturbations and the distribution of wave energy. The spectra derived from measurements show the presence of localized quasi-monochromatic structures with vertical wavelengths <10 km. Three methods based on the wavelet techniques show evidence of a downward phase progression. A first climatology of the dominant modes observed during the Austral winter period reveals a dominant night activity of 2 or 3 quasi-monochromatic structures with vertical wavelengths between 1/2 km from the stratopause, 3/4 km and 6/10 km observed between heights of 30 km and 60 km. In addition, it reveals a dominant activity of modes with a vertical phase speed of –0.3 m/s and observed periods peaking at 3/4 h and 9 h. The characteristics of averaged vertical wavelengths appear to be similar to those observed during winter in the southern equatorial region and in the Northern Hemisphere at mid-latitudes.     

Comparison of ground-based OH temperature data measured at Irkutsk (52°N, 103°E) and Zvenigorod (56°N, 37°E) stations with Aura MLS v3.3

Data about the variations of mesopause temperature (～87 km) obtained from ground-based spectrographic measurements of the OH emission (834.0 nm, band (6-2)) at Irkutsk and Zvenigorod observatories were compared with satellite data on vertical temperature distribution in the atmosphere from Aura MLS v3.3. We analyzed MLS data for two geopotential height levels: 0.005 hPa (～84 km) and 0.002 hPa (～88 km) as the closest to OH height (～87 km). We revealed that Aura MLS temperature data have lower values than ground-based (cold bias). In summer periods, that difference increases. Aura cold biases compared with OH(6-2) at Irkutsk and Zvenigorod were calculated. For the 0.002 hPa height level, the biases are 10.1 and 9.4 K, and for 0.005 hPa they are 10.5 and 10.2 K at Irkutsk and Zvenigorod, respectively. When the bias is accounted for, an agreement between Aura MLS and OH(6-2) data obtained at both Irkutsk and Zvenigorod is remarkable.     

Climatology of short-period mesospheric gravity waves over Halley,Antarctica (76°S, 27°W)

We present a first detailed climatological study of individual quasi-monochromatic mesospheric, short-period gravity-wave events observed over Antarctica. The measurements were made using an all-sky airglow imager located at Halley Station (76°S, 27°W) and encompass the 2000 and 2001 austral winter seasons. Distributions of wave parameters were found to be similar to findings at other latitudes. The wave headings exhibited unusually strong anisotropy with a dominant preference for motion towards the Antarctic continent and a rotation from westward during fall, to poleward in mid-winter, to eastward in spring. This rotation was accompanied by a systematic increase of ～50% in the magnitudes of the horizontal wavelengths and observed phase speeds. It is postulated that the observed wave anisotropy was due to a succession of wave sources of different characteristics lying equatorward of Halley, or a dominant source mechanism evolving with time during the winter months.     

中国廊坊(39.4°N,116.7°E)中间层和低热层潮汐的季节变化

本文利用中国廊坊站(39.4°N,116.7°E)流星雷达在2012年4月1日至2013年3月31日期间的水平风场观测数据,分析了廊坊上空中间层和低热层(MLT,80~100 km)大气纬向风、经向风潮汐的季节变化特征.研究表明:廊坊MLT区域周日潮汐和半日潮汐波动比较显著,有明显的季节变化特征.周日潮汐振幅在88 km以下为半年变化,极大值位于2-3月和10月,极小值位于冬、夏季;在88 km以上为周年变化,振幅冬末春初最强,夏季最弱.周日潮汐相位在秋、冬季比春、夏季提前.半日潮汐主要呈现半年变化,在5月和9月最强,冬、夏季最弱.半日潮汐相位在春、夏季比秋、冬季提前.此外,廊坊风场潮汐的观测结果与WACCM4模式模拟结果进行比较,结果表明两者的主要特征相似,在细节上有显著区别.与40°N附近其他站点风场潮汐观测结果的比较结果表明中纬度MLT风场潮汐有显著的随经度变化特性.     

A comparison between mesospheric wind measurements made near Christchurch (44°S, 173°E) using the high resolution doppler imager (HRDI) and a medium frequency (MF) radar

We report on the comparison of winds measured by a medium frequency (MF) radar near Christchurch, New Zealand, and by the high resolution doppler imager (HRDI). Previous comparisons have demonstrated that there can be significant differences in the winds obtained by the two techniques, and our results are no different. However, these data show relatively good agreement in the meridional direction, but large differences in the zonal direction, where the radar is regularly measuring the zonal wind as too easterly. To do the comparison, overpasses from the satellite must be obtained when it is close to the radar site. The radar data are averaged in time around the overpass because we know the radars sample phenomena which have spatial and temporal scales which make them invisible to HRDI. There are a limited number of overpass comparisons which limit our confidence in these results, but a detailed analysis of these data show that the proximity of the overpass is often an important factor in the differences obtained. Other factors examined include the influence of the local time of the overpass, and the amount of radar data averaged around the overpass time.     

Eduard Leont’evich Afraimovich (March 12, 1940–November 8, 2009)

Obituary

Eduard Leont’evich Afraimovich (March 12, 1940–November 8, 2009)     

关于Δ≥140°的地震衍射波Pdif(P'''')

本文讨论了△≥140°的地震衍射波Pdif的走时及振幅、周期。并讨论了识别这一震相的方法,还肯定了763长周期地震仪记录衍射波Pdif的优越性。     

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Atmospheric tides and mean winds in the meteor region over Santa Maria (29.7°S; 53.8°W)

We compare meteor radar measurements of the MLT region winds at Santa Maria, Brazil (29.7°S, 53.8°W) with the Horizontal Neutral Wind Model (HWM-93) and the Global Scale Wave Model (GSWM-00). The observed annual variation of the prevailing zonal wind disagrees in some respects with the HWM-93 model. Also, the zonal diurnal tide amplitude shows an annual variation, whereas that of the GSWM-00 is semiannual, and its vertical wavelength is smaller than that suggested by the model. The observed semidiurnal tide shows seasonal and inter-annual variations and the phase is evanescent during almost the whole year.     

Estimation of equatorial wave momentum fluxes using MST radar winds observed at Gadanki (13.5°N, 79.2°E)

A method of computing the vertical flux of zonal momentum (associated with equatorial waves) from the zonal and vertical components of the winds measured by the Indian MST radar at Gadanki (13.5°N, 79.2°E) is presented. The application of the method to the radar data gives flux values of 16×10⁻³, 8.0×10⁻³ and 5.5×10⁻³ m² s⁻² for slow Kelvin (12-day period), fast Kelvin (5.33-day period) and Rossby-gravity (RG) (3.43-day period) waves, respectively, in the upper troposphere. These flux values compare quite well with the values 4×10⁻³ m² s⁻² and 1×10⁻³ m² s⁻² obtained from radiosonde zonal wind and temperature data by Wallace and Kousky, 1968for slow Kelvin and RG waves, respectively. An estimate of the error in the fluxes gives a value of ∼ 1.2×10⁻³ m² s⁻².     

Wind and wave height climate from two decades of altimeter records on the Chilean Coast (15°–56.5° S)

Ocean Dynamics - In order to look for climatological changes on significant wave height and wind magnitude distributions, two decades of altimeter data were analyzed in a monthly 1° ×...     

Short-term changes in the aerosol characteristics at Kharagpur (22°19′N, 87°19′E) during winter

In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 10⁹ m^?3 and mass loading is ~265±70 μg m^?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence.     

First results of warm mesospheric temperature over Gadanki (13.5°N, 79.2°E) during the sudden stratospheric warming of 2009

Rayleigh lidar observations at Gadanki (13.5°N, 79.2°E) show an enhancement of the nightly mean temperature by 10–15 K at altitudes 70–80 km and of gravity wave potential energy at 60–70 km during the 2009 major stratospheric warming event. An enhanced quasi-16-day wave activity is observed at 50–70 km in the wavelet spectrum of TIMED–SABER temperatures, possibly due to the absence of a critical level in the low-latitude stratosphere because of less westward winds caused by this warming event. The observed low-latitude mesospheric warming could be due to wave breaking, as waves are damped at 80 km.