Manifestation of gravitational tides and planetary waves in long-term variations in geophysical parameters

Long-term variations in the parameters of the Earth’s upper atmosphere and geophysical activity have been studied based on the current spectra. The main sources of quasiperiodic oscillations in the atmosphere (including variations in the solar radiation, geomagnetic activity, and gravity) have been considered. It was shown that the most stable quasiharmonic variations are related to tidal gravitational oscillations and Rossby planetary waves with stable spectra. These oscillatory processes substantially contribute to the dynamics of the middle and upper atmosphere and manifest themselves in ionospheric parameters.     

Long-term variations in geomagnetic and solar activities and secular variations of the geomagnetic field components

Summary After the removal of the eleven-year periodicity, long-term patterns of the aa indices of geomagnetic activity and of Wolf's sunspot numbers are defined. The positions of maxima and minima exhibit the same regularities as the secular variations of the geomagnetic filed components. This result is associated with the motion of the Sun round the barycentre of the solar system.Presented at symposium Planet 88, Tihany, September 1988.     

Tidal components of geomagnetic variations

The natural geomagnetic field is constantly disturbed. The total registered effect of geomagnetic variations depends on both planetary and local processes. Planetary sources and sources in the Earth’s core respond to tidal effects. In the accepted model, the complex MHD processes in the Earth’s outer core are approximated by the assumed ring current in the equatorial plain of the liquid core. The geomagnetic variation originating as a result of tidal deformations of ring currents are ～10^?4 and 0.10–1 nT in the liquid core and magnetosphere, respectively. The calculated values coincide in order of magnitude with the processed geomagnetic measurements at Paratunka observatory (Kamchatka region).     

Comparison of geomagnetic planetary reference fields over Italy

Geomagnetic field measurements on a network at 106 repeat stations (1/3000 km²), and a second order network at 2550 stations (1/100 km²), were completed in 1981. Total intensity and the horizontal and vertical component of the field were measured at all stations, and in addition declination was measured at the first order stations. Normal fields for each element were computed from the first order network measurements (using a second degree polynomial in latitude and longitude), and comparisons were made for total intensity with 3 planetary reference fields. The use of the polynomial normal normal field is suggested to draw anomaly maps.     

Traveling planetary waves in the stratosphere

This paper reviews the theory and observations of some traveling planetary waves in the stratosphere. Two categories of waves which appear prominently in the literature are discussed: westward propagating waves of periods in the range 3–7 days (the 5-day wave) and in the range 10–20 days (the 16-day wave). Although the observations seem to indicate that these waves are waves of the Rossby type (planetary waves), the evidence is less clear regarding (1) the question of whether these waves are forced internal waves or free (resonant) external waves, and (2) the identification of the observed waves with specific theoretical waves of the Rossby type. When recent observations are compared with theory, the evidence seems to favor the notion that the 5-day and 16-day waves of longitudinal wave number 1 may be identified, respectively, with the gravest and next gravest symmetric free Rossby modes. However, the observational evidence seems to be less clear regarding the nature of the 16-day wave than the 5-day wave.     

Gabriel graph of geomagnetic Sq variations

This paper describes the pattern of geomagnetic solar quiet day, Sq, variations recorded at the Indian geomagnetic observatories. The extent to which the high and low latitude ionosphere is interlinked electromagnetically during periods of quiet geomagnetic conditions is a point of debate. The concept of Gabriel graph is applied to derive the boundaries for the variations of horizontal, vertical, and declination components of the earth’s magnetic field during geomagnetically quiet periods. Data of the six Indian geomagnetic observatories (Alibag, Hyderabad, Nagpur, Pondicherry, Visakapatnam, and Trivandrum) are considered for this analysis. This graph theoretical model is complementary to the classical data analysis techniques. Analytical method and the results of the analysis are presented in the paper.     

Long period divergent planetary waves

Abstract

A simple first order perturbation procedure is used to obtain an equation for divergent planetary waves when the period is much greater than the pendulum day. For unbounded regions the equation is the s2me as one derived by Longuet-Higgins (1965), but in bounded basins it is different. As an example, the eigen frequencies of a rectangular basin are calculated for a number of values of the parameters.

The energy density of planetary waves is also considered with results which correct those of Buchwald (1972) in the case of bounded basins.     

Solitary and cnoidal planetary waves

Abstract

A class of long planetary waves in a zonal channel analogous to the solitary and cnoidal waves of surface and internal gravity wave theory is discussed. On a mid-latitude β-plane, such waves exist as the result of divergence, non-uniform zonal velocity fields or bottom topography. In all cases studied the wave profile along the channel was found to satisfy the Korteweg-de Vries equation.     

Seasonal variations in the occurrence of geomagnetic storms

Seasonal variations in the onset of magnetic storms are investigated. For the purposes of this study storms have been defined as events in which Dst falls below -50 nT for at least four consecutive hours. The storms have been classified as either storm sudden commencements (SSCs; storms initiated by a sudden commencement) or as storm gradual commencements (SGCs; all other storms). It is found that the semi-annual variation of magnetic activity is reflected in the occurrence statistics of SGC events only, indicative that the solar wind origin is different for SSCs and SGCs. It is suggested that the heliospheric latitude model of seasonal magnetic activity is relatively ineffective in modulating the previously observed seasonal variations in the occurrence of magnetic storms.     

Types of variations in the geomagnetic field spectrum

The purpose of archaeomagnetic research is to investigate the structure of the geomagnetic field and its evolution. This paper is a study of this type. In our preceding studies, we divided the geomagnetic field into dipole and nondipole components. It was then shown that the dipole component consists of the predominant 1200-yr variation and the remainder δ. The δ variation is the subject of this paper. Detailed study and comparison of the characteristic features of two 1200-yr variations (the dipole and δ variations) in both the declination and inclination indicates that, according to most of their features, they can be assigned to different types of waves, namely, traveling waves (the dipole variation) and standing waves (the δ variation). Successive averaging in time and space yielded averaged data on δI and δD not only for various parts of the world (Europe, Asia, and America) but also for the western and eastern hemispheres.     

Magnetospheric contributions to geomagnetic daily variations

The contribution of magnetospheric current systems to geomagnetic daily variations is analyzed by means of a spherical harmonic analysis (SHA) using elementary models as well as the Tsyganenko model of the magnetosphere. It is discovered that the magnetospheric contribution to some SHA coefficients is much higher than the known average value of about 20%, especially when considering non-local time terms and solstitial conditions.     

关于地磁场超低频脉动(ULF)的研究

本文是关于地磁场超低频脉动研究的综述,内容包括：（1）历史和内容提要;（2）脉动分类的探究;（3）关于“四多”（多观测仪器、多卫星和飞船、多地面和网络、多分析方法）;（4）其它行星ULF波的探求.     

On regularities in long-term solar quiet geomagnetic variations

We propose a simple model to describe the behaviour of solar quiet geomagnetic variations Sq over a long time. We assume that Sq variations can be expressed through 24-h components and their harmonics subject to three modulations: 1 year, 11 years and several tens years. We started from the observation that the spectral lines of 30-year geomagnetic data series are split in accordance with yearly modulation. Our model gives good approximation of Sq variations and discloses a striking correlation of amplitudes and phases of modulating functions with the sunspot number and 2.8 GHz solar radio emission. It is also a tool for monitoring the Sq variations.     

Short-period planetary waves in the Antarctic middle atmosphere

Planetary waves with periods between two and four days in the middle atmosphere over Antarctica are characterized using one year of data from the medium-frequency spaced antenna (MFSA) radars at Scott Base, Rothera, and Davis. In order to investigate the origin of the observed waves, the ground-based data are complemented by temperature measurements from the Earth Observing System Microwave Limb Sounder (EOS MLS) instrument on the Aura satellite as well as wind velocity data from the United Kingdom Met. Office (UKMO) stratospheric assimilation. Observed characteristics of waves with a period of approximately two days in summer are consistent with the quasi-two-day wave (QTDW) generally found after the summer solstice at low- and mid-latitudes. The Scott Base observations of the QTDW presented here are the highest-latitude ground-based observations of this wave to date. Waves with preferred periods of two and four days occur in bursts throughout the winter with maximum activity in June, July, and August. The mean of the two- and four-day wave amplitudes is relatively constant, suggesting constant wave forcing. When several waves with different periods occur at the same time, they often have similar phase velocities, supporting suggestions that they are quasi-non-dispersive. In 2005, a “warmpool” lasts from late July to late August. An alternative interpretation of this phenomenon is the presence of a structure propagating with the background wind. Consideration of the role of vertical shear (baroclinic instabilities) and horizontal shear (barotropic instabilities) of the zonal wind suggests that instabilities are likely to play a role in the forcing of the two- and four-day waves, which are near-resonant modes and thus supported by the atmosphere.     

Quasi-stationary planetary waves in the middle atmosphere of Mars

Using the temperature profiles retrieved from the Mars Climate Sounder(MCS) instrument onboard Mars Reconnaissance Orbiter(MRO) satellite between November 2006 and April 2013, we studied the seasonal and interannual variability of QuasiStationary Planetary Waves(QSPWs) in the Martian middle atmosphere. The QSPW amplitudes in the Southern Hemisphere(SH) high latitudes are significantly stronger than those in the Northern Hemisphere(NH). Seasonal variation with maximum amplitude near winter solstice of each hemisphere is clearly seen. The vertical structure of the QSPW in temperature shows double-layer feature with one peak near 50 Pa and the other peak near 1 Pa. The QSPW in geopotential height is clearly maximized in the region between two temperature peaks. The maximum amplitude of QSPW for s=1 is ~8–10 K in temperature and ~1 km in geopotential height in the SH high latitudes. The maximum amplitude at the SH high latitudes in Mars Year(MY) 31 is ~2 K stronger than those in other MYs, suggesting the clear interannual variability. We compared the satellite results with those obtained from the Mars Climate Database(MCD) simulation version 5.0; a reasonable agreement was found. The MCD simulation further suggested that the variability of dust might partially contribute to the interannual variability of QSPW amplitude.     

Do geomagnetic variations affect plant function?

Relatively little is known about the effects of geomagnetism on plants. Such fundamental questions as (1) whether or not plants perceive the Earth's magnetic field, (2) the physical nature of the magnetic receptor(s) and (3) whether or not the geomagnetic field has any bearing on the physiology and survival of plants remain largely unanswered. The present review examines the possibility that three classes of unexplained biological rhythms in plants may relate to the sensitivity of plants to variations in the geomagnetic field. The first section examines the possibility that a class of plant rhythms, here termed 0.2–5 Hz rhythms, may be reflections of the sensitivity of plants to Pc1 geomagnetic pulsations. The second section reviews recent evidence that plants are affected by geomagnetic storms. The third section examines the possibility that circa-weekly, circa-fortnightly and circa-monthly rhythms in plants may be reflections of the solar rotation cycle and its sub-harmonics.     

Components of geomagnetic variations with tidal wave frequencies

This work studies regular variations caused by the effect of O ₁ and M ₂ tidal waves on magnetospheric current systems. The response to the tidal effect has been calculated using the magnetic field paraboloid model. A model of origination of the geomagnetic variations with O ₁ and M ₂ tidal wave periods has been developed. The values of such variations, which originate as a result of tidal deformations of the current system in the magnetosphere, are 0.2÷0.9 nT. The calculated values coincide in magnitude with the processed geomagnetic data obtained at the Paratunka geophysical observatory.     

Regional features of the geomagnetic field secular variations

The secular variations in the geomagnetic field have been studied based on the satellite vector magnetic survey. A high data accuracy made it possible to estimate the spatial and temporal characteristics of different variation types on the interval 1980–2007. The growth and decomposition of midlatitude foci have been qualitatively estimated, and the structure and velocity of a drifting equatorial anomaly have been determined.     

滇西北地区地磁短周期变化特征研究

利用滇西北地磁台阵8个测点的秒采样观测数据,对短周期事件的地磁三分量变化幅度进行统计,得到不同周期的垂直分量和水平分量变化幅度比值ΔZ/ΔH在观测区的空间分布,由此推测地下存在一条NNW走向的高导带,从地壳延伸至上地幔,且位置随深度不断变化。