Tidal associated temperature disturbances observed at the middle atmosphere (30–65 km) by a Rayleigh lidar at 23°S

A lidar has been operated in São José dos Campos, Brazil (23.2°S, 45.8°W) since 1972, mainly dedicated to the study of mesospheric sodium at the 589 nm resonant line. The molecular Rayleigh scattering can also be used provided we limit the height to ∼75 km where the sodium scattering begins. Nevertheless, the weak signal obtained only permits the determination of density and temperature profiles by accumulating a large number of shots giving only nocturnal average profiles. Temporal variations in density and temperature on the scale of hours can however, be obtained by performing a superposed epoch analysis for a given time interval and covering a period of several days. In this way we obtained hourly mean profiles grouped by months, seasons and overall, with data acquired from 1993 to 2004. The difference between the hourly temperatures and the nocturnal means shows for some months, with enough data coverage, downward propagating structures that apparently have tidal origin. The seasonal averages show a recurrent feature with high temperatures before and low temperatures after midnight above 50 km. Some similarity is found with the GSWM model, but the observed temperature amplitudes are twice of that for the model.     

Observations of non-migrating tides and ionospheric perturbations of O(D) airglow by ISUAL instrument

In this paper, we present the spatial variations of O(¹D) airglow observed by the ISUAL (Imager of Sprites and Upper Atmospheric Lightning) instrument on board the FORMOSAT-2 satellite. With a CCD camera and a 630 nm filter, ISUAL can measure global atmospheric emissions lying between the heights of 80 and 300 km. In days of 3–6 September 2008 and 25–27 February 2009, ISUAL has measured the emissions of O(¹D) airglow with results showing strong longitudinal peak-3 and peak-4 structures. The Lomb-Scargle analyses for these two cases show periods of longitudes of 120° and 90° supporting the DE2 and DE3 non-migrating tides. The 630 nm emissions are enhanced in equatorial regions and are lying along the equator. Over Africa its intensity can sometimes increase up to 80% relative to other longitudes. The perturbation is so strong that non-migrating tides are erased. A case of bimodal distribution with strong emissions at latitudes in equator and mid-latitude in geographic coordinates was observed.     

Ocean Tides in GRACE Monthly Averaged Gravity Fields

The GRACE mission will map the Earth's gravity fields and its variations with unprecedented accuracy during its 5-year lifetime. Unless ocean tide signals and their load upon the solid earth are removed from the GRACE data, their long period aliases obscure more subtle climate signals which GRACE aims at. In this analysis the results of Knudsen and Andersen (2002) have been verified using actual post-launch orbit parameter of the GRACE mission. The current ocean tide models are not accurate enough to correct GRACE data at harmonic degrees lower than 47. The accumulated tidal errors may affect the GRACE data up to harmonic degree 60. A study of the revised alias frequencies confirm that the ocean tide errors will not cancel in the GRACE monthly averaged temporal gravity fields. The S₂ and the K₂ terms have alias frequencies much longer than 30 days, so they remain almost unreduced in the monthly averages. Those results have been verified using a simulated 30 days GRACE orbit. The results show that the magnitudes of the monthly averaged values are slightly higher than the previous values. This may be caused by insufficient sampling to fully resolve and reduce the tidal signals at short wavelengths and close to the poles. This revised version was published online in August 2006 with corrections to the Cover Date.     

Global structure,seasonal and interannual variability of the eastward propagating tides seen in the SABER/TIMED temperatures (2002–2007)

The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the most stable in amplitude and phase eastward propagating diurnal and semidiurnal tides with zonal wavenumbers 2 and 3 derived from the SABER/TIMED temperatures for full 6 years (January 2002–December 2007). The tidal results are obtained by an analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally travelling, zonally symmetric and stationary) are simultaneously extracted from the satellite data. It has been found that the structures of the eastward propagating diurnal tides with zonal wavenumbers 3 and 2 change from antisymmetric with respect to the equator below ∼85 km height, to more symmetric above ∼95 km. The seasonal behavior of the DE3 is dominated by annual variation with maximum in August–September reaching average (2002–2007) amplitude of ∼15 K, while that of the DE2 by semiannual variation with solstice maxima and with average amplitude of ∼8 K. These tides revealed some interannual variability with a period of quasi-2 years. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 2 in the southern hemisphere (SH) is dominated by annual variation with maximum in the austral summer (November–January) while that in the northern hemisphere (NH) by semiannual variation with equinoctial maxima. The SE2 maximizes near 115 km height and at latitude of ∼30° reaching an average amplitude of ∼6 K. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 3 in both hemispheres indicates a main maximum during June solstice and a secondary one during December solstice. The tide maximizes near 110–115 km height and at a latitude of ∼30° reaching an average amplitude of ∼4.8 K in the SH and ∼4 K in the NH. The tidal structures of the two eastward propagating semidiurnal tides are predominantly antisymmetric about the equator.     

大气潮汐的经典理论及有关现代模式的发展

按照历史发展, 回顾了从无耗无风背景下线性化的大气潮汐方程组出发得到一个二维定态变量可分离的基本偏微分方程及其全球Hough函数波模解的经典理论; 介绍了主要由Forbes和Hagan发展起来的在真实有耗有风背景下线性化的本质上仍是二维定态, 但纬度和高度变量不可分离的现代数值模式GSWM; 概述了近年来针对中高层大气的GCM (例如TIME-GCM, MUAM, CMAM和WACCM) 来研究潮汐非线性及非迁移潮汐等的发展趋势. 在融合理解的基础上对各模式的特点和模式间的差异进行了适当分析, 从中可以看出,半个世纪以来人们在从第一原理出发试图揭示全球大气潮汐的真实结构特征和长短期变化机制等方面进行了持续的努力, 这种努力又是与从利用地基雷达到卫星搭载仪器观测大气(特别是MLT区域的风场和温度场)的发展密不可分的.      

Structure of the migrating diurnal tide in the Whole Atmosphere Community Climate Model (WACCM)

As part of an ongoing effort to understand the migrating diurnal tide generated by the NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), we compare the WACCM3 migrating diurnal tide in the horizontal wind and temperature fields to similar results from the Global Scale Wave Model (GSWM). The WACCM3 diurnal tidal wind fields are also compared to tropical radar measurements at Kauai (22°N, 200.2°E) and Rarotonga (21.3°S, 199.7°E). The large-scale features of the WACCM3 results, such as the global spatial structure and the semiannual amplitude variation are in general agreement with past tidal studies; however, several differences do exist. WACCM3 exhibits a much higher degree of hemispheric asymmetry, lower overall amplitudes around the equinoxes, and peaks which are more confined in latitude when compared with the GSWM. Factors which may contribute to such differences between WACCM3 and GSWM are the solar heating profiles from ozone and water vapor, dissipation, and the zonal mean zonal winds. We find that the internally generated heating in WACCM3 and eddy dissipation values are both smaller than the values specified in the GSWM; the eddy dissipation fields and zonal mean zonal winds of the two models also display measurable differences in spatial structure. Comparisons with radar data show several differences in spatial and seasonal structure. In particular, the diurnal tide zonal winds in WACCM3 above Kauai are considerably larger in amplitude than those observed in the radar data, due to contributions from nonmigrating tidal components including wave numbers eastward 1 through 3, westward 2, and stationary components, which interfere constructively with the migrating component around equinox in WACCM3.     

Advances in Researches on the Middle and Upper Atmosphere in 2008-2010

This paper summarizes the results of the researches on the middle and upper atmosphere obtained by Chinese scientists in 2008-2010. The focuses are specifically placed on the researches being associated with ground-based observation capability development, dynamical processes, the property of atmospheric circulation and the chemistry-climate coupling of the middle atmospheric layers.     

Longitudinal MLT wind structure at higher mid-latitudes as seen by meteor radars at central and Eastern Europe (13°E/49°E)

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.     

Meteor radar temperatures over Collm (51.3°N, 13°E)

The method of obtaining absolute temperature estimates by measuring the ambipolar diffusion coefficient with meteor radars in the mesopause region is basically well known. However, there is still a need to refine and adjust the background temperature gradient model which is necessary to calculate the temperature values. Therefore, a detailed comparison with independent temperature measurements is necessary to evaluate the performance of the method and to obtain more information about the temperature gradient. Recent studies provide some evidence that the impact of the gradient model on temperature estimates affects the absolute temperatures, but that it is of minor importance for wave analysis. This paper focuses on a detailed evaluation of the meteor radar temperatures by comparing them with SABER satellite and OH-emission mesopause region temperatures. The seasonal variation of the observed temperatures is well reproduced by the COMMA general circulation model.     

The characteristics of the semi-diurnal tides in mesosphere/low-thermosphere (MLT) during 2002 at Wuhan (30.6°N, 114.4°E) – using canonical correlation analysis technique

In this paper, we use canonical correlation analysis (CCA) method to investigate the semi-diurnal tidal winds in mesosphere and low thermosphere (MLT) region, observed by a newly installed meteor radar at Wuhan (30.6°N, 114.4°E), during the year 2002. In general, 4(3) effective semi-diurnal tidal pairs of patterns are obtained, which represent ∼2/3 total variances of the origin data set. These patterns are expected to be corresponding to the atmospheric oscillations within the semi-diurnal frequency band excited or modulated by different sources, i.e., the seasonal variations, the modulations by the planetary wave oscillations or the solar 27-day activity. Among all the patterns, the 1st pattern, which represents ∼1/3 of total variances, is the most notable. Its amplitudes show maximum values in spring and autumn, and the vertical wavelengths are longer in summer and shorter in winter, which is in line with the results obtained from traditional harmonic analysis. The vertical wavelengths of the higher order patterns (∼50 km) suggest the classic semi-tidal mode S(2, 4)/S(2, 5) is dominant.