Numerical modeling of inhomogeneous orographic wave influence on planetary waves in the middle atmosphere

Parameterization of dynamical and thermal effects of stationary orographic gravity waves (OGWs) generated by the Earth’s surface topography is incorporated into a numerical model of general circulation of the middle and upper atmosphere. Responses of atmospheric general circulation and characteristics of planetary waves at altitudes from the troposphere up to the thermosphere to the effects of OGWs propagating from the earth surface are studied. Changes in atmospheric circulation and amplitudes of planetary waves due to variations of OGW generation and propagation in different seasons are considered. It is shown that during solstices the main OGW dynamical and heat effects occur in the middle atmosphere of winter hemispheres, where changes in planetary wave amplitudes due to OGWs may reach up to 50%. During equinoxes OGW effects are distributed more homogeneously between northern and southern hemispheres.     

Aura/MLS与TIMED/SABER观测全球重力波特性

大气重力波是临近空间环境主要大气波动之一,对全球环流具有重要影响。卫星上搭载的临边探测器能够探测临近空间大气温度,可用于临近空间大气重力波研究。利用2012－2014年Aura的微波临边探测器（MLS）和TIMED的红外临边探测器（SABER）的探测数据,对20~50 km高度的大气重力波扰动分布特征开展了分析研究,两种观测重力波活动基本一致,重力波随季节、纬度及高度的变化显著。冬季半球高纬度重力波扰动较强,赤道和夏季半球近赤道地区上空也存在明显重力波活动区域,夏季半球高纬度重力波扰动最弱。重力波扰动强度随高度增加。TIMED/SABER重力波扰动强度数值比 Aura/MLS略强。      

Remote sounding of atmospheric gravity waves with satellite limb and nadir techniques

Recent advances in satellite techniques hold great potential for mapping global gravity wave (GW) processes at various altitudes. Poor understanding of small-scale GWs has been a major limitation to numerical climate and weather models for making reliable forecasts. Observations of short-scale features have important implication for validating and improving future high-resolution numerical models. This paper summarizes recent GW observations and sensitivities from several satellite instruments, including MLS, AMSU-A, AIRS, GPS, and CLAES. It is shown in an example that mountain waves with horizontal wavelengths as short as 30 km now can be observed by AIRS, reflecting the superior horizontal resolution in these modern satellite instruments. Our studies show that MLS, AMSU-A and AIRS observations reveal similar GW characteristics, with the observed variances correlated well with background winds. As a complementary technique, limb sounding instruments like CRISTA, CLAES, and GPS can detect GWs with better vertical but poorer horizontal resolutions. To resolve different parts of the broad GW spectrum, both satellite limb and nadir observing techniques are needed, and a better understanding of GW complexities requires joint analyses of these data and dedicated high-resolution model simulations.     

一种全天空气辉成像仪数据预处理方法和初步结果

大气重力波是大气中的基本波动形式之一,在中高层大气动力和热力学过程中起着十分重要的作用.全天空气辉成像仪是一种以大气气辉辐射为示踪物,能够有效对大气重力波成像的仪器.本文针对中国科学院国家空间科学中心空间天气学国家重点实验室中高层大气组自主研制的全天空气辉成像仪所观测的数据,提出了一种气辉图像预处理方法,进行平场校正、方位校正、星光去除和坐标映射等数据订正.利用该方法处理2015年5月17日21:00BLT至次日05:00BLT西宁台站（36.6°N,101.7°E）的OH气辉数据,发现一次重力波事件,分析并获得了该重力波的水平波长、观测水平相速度和传播方向（分别为17.72km,47m·s-1,339°）.研究结果表明该方法是可行的.      

Estimated errors in a global gravity wave climatology from GPS radio occultation temperature profiles

In a previous paper by Schmidt et al. (2008), from CHAllenging Minisatellite Payload (CHAMP) Global Positioning System (GPS) radio occultation data, a comparison was made between a Gaussian filter applied to the “complete” temperature profile and to its “separate” tropospheric and stratospheric height intervals, for gravity wave analyses. It was found that the separate filtering method considerably reduces a wave activity artificial enhancement near the tropopause, presumably due to the isolation process of the wave component. We now propose a simple approach to estimate the uncertainty in the calculation of the mean specific wave potential energy content, due exclusively to the filtering process of vertical temperature profiles, independently of the experimental origin of the data. The approach is developed through a statistical simulation, built up from the superposition of synthetic wave perturbations. These are adjusted by a recent gravity wave (GW) climatology and temperature profiles from reanalyses. A systematic overestimation of the mean specific wave potential energy content is detected and its variability with latitude, altitude, season and averaging height interval is highlighted.     

世界航空动力技术的现状及发展动向

讲述了喷气战斗机动力的发展历程.推重比8一级发动机是目前世界各发达国家现役主战机种的动力,配装推重比10一级发动机的第4代战斗机预计在2003～2007年后陆续装备使用,成为美国、部分西方国家甚至我国部分周边国家和地区2010年后的主战机种.概括了民用涡扇发动机和直升机动力的发展及其主要关键技术.列举了21世纪航空动力主要关键技术的发展方向.     

比斯开湾上空电子总量对磁暴的响应

本文论述过去十年中,在英国Aberystwyth城观测同步卫星Intelsat IIF2和SIRIO信标时获得的大西洋比斯开湾上空电子总量对磁暴的响应。所选择的地磁-电离层暴分属前后两个太阳活动较高周期,主要集中在春秋分阶段和冬夏至阶段。文中指出,春分期间连续型磁暴使TEC在正相效应之后出现加长的凋落周期,集中型磁暴导致TEC在正相之后产生凋落周期缩短;春秋分和冬夏至时磁暴伴生的电子总量形态受制于急始时刻与次数、磁暴主相、磁暴指数(即暴时位置和暴情指数)等因素。      

A gravity wave analysis near to the Andes Range from GPS radio occultation data and mesoscale numerical simulations: Two case studies

Global maps of potential wave energy per unit mass, recently performed with the Global Positioning System (GPS) Radio Occultation (RO) technique and different satellite missions (CHAMP and SAC-C since 2001, GRACE and COSMIC since 2006) revealed in Argentina, at the eastern side of the highest Andes Mountains, a considerable wave activity (WA) in comparison with other extra-tropical regions. The main gravity wave (GW) sources in this natural laboratory are deep convection (mainly during late Spring and Summer), topographic forcing and geostrophic adjustment.     

The temporal variation of mean gravity of atmosphere

One of the precise widely used global Zenith Hydrostatic Delay (ZHD) model is based on the gravity value at the centroid of the atmospheric column at the station of observation and gravity value at the centroid is constant in this model for a specific location throughout the year. However, as the content and extent of atmosphere varies temporally, its centroid and consequently gravity value at the centroid also varies. Apart from this, the actual atmospheric condition of different region is not alike. Therefore, there is a need to develop a regional mean gravity model and development of such model has been discussed in this paper. To obtain the mean gravity model, first a regional model of centroid height of atmospheric column was developed as a function of the surface pressure and temperature. It was developed by multiple regressions between estimated centroid of the atmosphere and surface pressure, surface temperature using radiosonde data of five radiosonde stations spread over the Indian subcontinent. Three years radiosonde data from 2006 to 2008 was used for each station. The root mean square error in estimating centroid of the atmospheric column is about ±326 m, which is negligible considering the variability of the atmosphere and its content. The centroid height model has been used to formulate the mean gravity model, considering uniform lapse rate in gravity with height. It is found that proposed mean gravity model provides temporal variation of mean gravity values at the centroid and thus matches with the reality. The interesting advantage of the developed model is that the model shows diurnal variation of mean gravity. The accuracy of ZHD has shown of the order of about 0.3 mm using the developed regional mean gravity model. However, already developed ZHD model has shown a slight inferior result compared to the developed model. These models have shown accuracy of about 0.8 mm and 0.6 mm.     

Characterisation of residual ionospheric errors in bending angles using GNSS RO end-to-end simulations

Global Navigation Satellite System (GNSS) radio occultation (RO) is an innovative meteorological remote sensing technique for measuring atmospheric parameters such as refractivity, temperature, water vapour and pressure for the improvement of numerical weather prediction (NWP) and global climate monitoring (GCM). GNSS RO has many unique characteristics including global coverage, long-term stability of observations, as well as high accuracy and high vertical resolution of the derived atmospheric profiles. One of the main error sources in GNSS RO observations that significantly affect the accuracy of the derived atmospheric parameters in the stratosphere is the ionospheric error. In order to mitigate the effect of this error, the linear ionospheric correction approach for dual-frequency GNSS RO observations is commonly used. However, the residual ionospheric errors (RIEs) can be still significant, especially when large ionospheric disturbances occur and prevail such as during the periods of active space weather. In this study, the RIEs were investigated under different local time, propagation direction and solar activity conditions and their effects on RO bending angles are characterised using end-to-end simulations. A three-step simulation study was designed to investigate the characteristics of the RIEs through comparing the bending angles with and without the effects of the RIEs. This research forms an important step forward in improving the accuracy of the atmospheric profiles derived from the GNSS RO technique.     

The ionospheric effect of atmospheric gravity waves excited prior to strong earthquake

We have computed perturbations in the nighttime mid-latitude F2 region ionosphere that could be produced by internal atmospheric gravity waves generated before strong earthquakes through ionospheric Joule heating due to the seismogenic electric field of short duration. There is a strong anisotropy of the atmospheric gravity wave effect with respect to the imminent earthquake epicentre, the electron density changes being maximum poleward and equatorward of the epicentre and being minimum eastward and westward of it. It should be noted that the duration of the electron density perturbation in the F2 region ionosphere is much longer than the duration of the primary precursor of an earthquake – the enhancement of the vertical electric field at the Earth’s surface, which initiates the atmospheric gravity wave generation. This fact is important from the practical point of view of predicting catastrophic earthquakes.     

重力波非线性传播过程中的饱和与破碎

采用水平方向的显式算法与垂直方向的隐式算法相结合的时间分裂法,建立了二维可压缩大气中重力波非线性传播的数值模式.用本模式对小振幅重力波传播过程的模拟结果与线性重力波理论预测的结果吻合很好,从而验证了本模式的正确性.我们用此模式模拟了有限振幅重力波在非线性传播过程中的饱和与破碎,结果表明,(1)翻转出现在饱和之前,但向破碎演化仍需要一段时间,由于非线性波-波和波-流相互作用使得非线性数值模拟的饱和高度(出现时间)高(早)于线性饱和理论预测的结果;(2)重力波在不稳定之前已经有能量向背景场中转移,破碎直接导致非线性波-波相互作用,造成能量向小尺度短波上转移;(3)背景风场的加速方向,形成射流的方向与重力波的水平传播方向一致,表明重力波与背景流的非线性相互作用加剧了背景风剪切和不稳定性的发展.      

Gravity waves generated by thunderstorms: South-East Asia tropical region study

Gravity waves are recognized as an integral part of earth’s atmosphere which are mainly responsible for energy and momentum distribution among different layers and regions in the atmosphere. Various sources present in land, ocean, and atmosphere such as mountains, convection, jets and fronts etc. are responsible for gravity waves generation. Thunderstorms (deep convection) are one of the major sources of gravity waves in the tropical region, capable of generating waves with a wide range of frequencies and scales and significantly affecting the existing waves. Previous numerical studies have characterised the wave properties that are generated from thunderstorms, but there are no statistically quantified studies. In this paper, we have modelled the relationship between the latent heat generated inside a thunderstorm and the gravity wave properties at the geo-collocated points. Gravity waves are identified over Singapore radiosonde station (with data available until 30?km altitude with 12?h temporal resolution) in the stratosphere using wavelet studies. Based on the GROGRAT ray tracing methods to identify the thunderstorm locations, and RAMS cloud-resolving models simulations to obtain the latent heating of the thunderstorm, a regression analysis is performed using 200 cases of gravity waves. Furthermore, cloud-top momentum flux analysis is performed for various cases latent heat. This study is expected to provide more quantified and concrete information on the coupling between the thunderstorm and gravity wave which includes the variance in these relationships due to wave frequency spectrum and generation mechanisms.     

Indication of convectively generated gravity waves observed by CLAES

Cryogenic Limb Array Etalon Spectrometer temperature data are analyzed for gravity waves (GWs) using the same methods previously employed for CRISTA data. We obtain nearly 1.5 years of continuous GW data between 34°S and 34°N and good coverage at higher latitudes depending on UARS yaw maneuvers. Correlations of GW variances with sea surface temperature indicate strong convective forcing above the Gulf of Mexico and the Kuro-Shio stream as well as above source regions in the southern subtropics during the summer months of the respective hemisphere. However, it appears difficult to clearly separate between convective forcing and the effects of the background winds, for which similar correlations are found. Further progress in accessing GW sources therefore can be expected mainly from improved measurements, which could provide also information about the GW horizontal wavelength as well as from quantitative comparisons to model predictions.     

Post-midnight equatorial irregularity distributions and vertical drift velocity variations during solstices

Longitudinal distributions of post-midnight equatorial ionospheric irregularity occurrences observed by ROCSAT-1 (1st satellite of the Republic of China) during moderate to high solar activity years in two solstices are studied with respect to the vertical drift velocity and density variations. The post-midnight irregularity distributions are found to be similar to the well-documented pre-midnight ones, but are different from some published distributions taken during solar minimum years. Even though the post-midnight ionosphere is sinking in general, longitudes of frequent positive vertical drift and high density seems to coincide with the longitudes of high irregularity occurrences. Large scatters found in the vertical drift velocity and density around the dip equator in different ROCSAT-1 orbits indicate the existence of large and frequent variations in the vertical drift velocity and density that seem to be able to provide sufficient perturbations for the Rayleigh-Taylor (RT) instability to cause the irregularity occurrences. The need of seeding agents such as gravity waves from atmospheric convective clouds to initiate the Rayleigh-Taylor instability may not be necessary.     

Simulating planetary wave propagation to the upper atmosphere during stratospheric warming events at different mountain wave scenarios

Parameterization schemes of atmospheric normal modes (NMs) and orographic gravity waves (OGWs) have been implemented into the mechanistic Middle and Upper Atmosphere Model (MUAM) simulating atmospheric general circulation. Based on the 12-members ensemble of runs with the MUAM, a composite of the stratospheric warming (SW) has been constructed using the UK Met Office data as the lower boundary conditions. The simulation results show that OGW amplitudes increase at altitudes above 30 km in the Northern Hemisphere after the SW event. At altitudes of about 50 km, OGWs have largest amplitudes over North American and European mountain systems before and during the composite SW, and over Himalayas after the SW. Simulations demonstrate substantial (up to 50–70%) variations of amplitudes of stationary planetary waves (PWs) during and after the SW in the mesosphere-lower thermosphere of the Northern Hemisphere. Westward travelling NMs have amplitude maxima not only in the Northern, but also in the Southern Hemisphere, where these modes have waveguides in the middle and upper atmosphere. Simulated variations of PW and NM amplitudes correspond to changes in the mean zonal wind, EP-fluxes and wave refractive index at different phases of the composite SW events. Inclusion of the parameterization of OGW effects leads to decreases in amplitudes (up to 15%) of almost all SPWs before and after the SW event and their increase (up to 40–60%) after the SW in the stratosphere and mesosphere at middle and high northern latitudes. It is suggested that observed changes in NM amplitudes in the Southern Hemisphere during SW could be caused by divergence of increased southward EP-flux. This EP-flux increases due to OGW drag before SW and extends into the Southern Hemisphere.     

地形产生的山地波及其传播过程模拟研究

气流经过地形产生的山地波是大气重力波研究的重要类别之一.从大气运动的控制方程组出发,建立模拟地形产生的山地波及其传播过程的二维数值模式.利用水平背景风场、地形和垂直速度之间的关系,在模式中引入垂直速度扰动作为地形产生山地波的激发源.通过模拟该激发源引起的扰动即山地波在大气中的传播过程,再现了山地波的产生、传播及充分发展过程.通过分析水平波长、垂直波长、位温扰动、流线,在空间尺度上描述了山地波的产生、传播及充分发展的过程.在气流经过地形产生的山地波的传播过程中,其水平波长λ_x的范围为2.5~5km,垂直波长λ_z约为2.5km.这些结果与利用山地波线性理论计算的垂直波长一致,从而验证了本模式能够模拟地形产生的山地波及其传播过程,为深入了解山地波的产生过程及其在中高层大气中的传播机制和效应奠定了基础.      

Effect of the seed perturbation amplitude on the equatorial spread F initiation during solar minimum

The contribution of gravity wave (GW) to the initiation/development of spread F during a solar minimum year was investigated through the comparison of the observed precursory parameters and characteristics of the corresponding equatorial spread F (ESF) events. The ionospheric parameters were recorded at the magnetic equatorial station Sao Luis (2.3°S, 44°W, dip latitude 2°S) during March and October 2010. These data were used to estimate the influence of the relative gravity wave amplitude and the ambient ionospheric condition on the diurnal variation of the spread F initiation. The vertical velocity drift indicated a clear control and defines the threshold for the seasonal variability of the ESF occurrence. However, it was insufficient to solely determine or predict the day to day variation of ESF occurrence. Thus, few days with contrasting ambient ionospheric condition and magnitude of GW amplitude were analysed in order to investigate the role of the different precursory factors in the observed diurnal variation of the plasma irregularity development. The density scale length and gravity wave amplitude were shown to immensely contribute to the linear instability growth rate, especially during the days with a low post-sunset rise. Thus, the experimental observations have demonstrated the strong inter-dependence between the precursory factors and they have also highlighted the probable control of the ESF morphology.     

A simulation study for anticipated accuracy of lunar gravity field model by SELENE tracking data

Results of numerical simulations are presented to examine the global gravity field recovery capability of the Japanese lunar exploration project SELENE (SELenological and ENgineering Explorer) which will be launched in 2007. New characteristics of the SELENE lunar gravimetry include 4-way satellite-to-satellite Doppler tracking of main orbiter and differential VLBI tracking of two small free-flier satellites. It is shown that the proposed satellite constellation will provide the first truly global satellite tracking data coverage. The expected results from these data are; (1) drastic reduction in far-side gravity error, (2) estimation of many gravity coefficients by the observation, not by a priori information, and (3) one order of magnitude improvement over existing gravity models for low-degree field.