Equatorial sporadic E and cross-field instability

The occurrence of sporadic E at an equatorial station during magnetically quiet daytime conditions corresponds almost exactly to the time during which the horizontal component of the earth’s magnetic field is above the mean night time level. Any large decrease of H below the night time level is accompanied by the disappearance of equatorial E_s?q reflections precisely for the period when the value of H remains below its night time level. Such disappearance of E_s?q can be attributed to the reversal of the current equal to, or greater than, the normal eastward equatorial electrojet current. During magnetically disturbed conditions, however, the depressions in H are not always accompanied by the disappearance of E_s?q. Whenever the normal E and sporadic E reflections can be resolved on the equatorial ionograms, the minimum virtual height of the normal E is seen to be clearly greater than that of the sporadic E layer. The creation of E region irregularities at equatorial latitudes giving the appearance of an E_s?q layer in daytime ionograms is suggested to be due to cross-field (plasma gradient) instability. The horizontal magnetic field and the upward Hall polarisation (electric) field produce irregularities in the lower E-region where the rate of increase of ambient electron density is large and directed upward. A temporary reversal of the electrojet current indicated by a decrease in H below the night time level and the disappearance of E_s?q are due to the temporary reversal of the vertical Hall polarisation field making it downward instead of upward which being opposite to the direction of the gradient of plasma density inhibits the cross-field instabilities.     

The effect of polar magnetic sub-storms on the equatorial sporadic E

It is known that equatorial sporadic E disappears at night when dynamo field is east to west. During some DP₂ type magnetic sub-storms, which cause a depression of the geomagnetic horizontal field at the equator, theq type of sporadic E is found to disappear at the equatorial stations Huancayo and Kodaikanal. This suggests that one of the mechanisms causing the temporary disappearance of E _s —q during daytime in equatorial ionograms is the replacement of the east to west dynamo electric field by a west to east electric field due to the imposition of an electric field opposing the normal daytime S _q field.     

The disappearance of equatorial E s and the reversal of electrojet current

Based on simultaneous observations of the horizontal geomagnetic field component H, sporadic E (E _s ) and E-W electron drifts at stations close to the dip equator within the equatorial electrojet region, it has been found that on quiet days and sometimes on disturbed days, when there is an abnormal large decrease in H during daytime, there is a simultaneous disappearance of E _s and a reversal of the direction of drift of electrons from westward to eastward. This suggests that the disappearance of equatorial E _s during day-time is due to a temporary reversal of the electrojet current, which is caused by the imposition of an additional electrostatic field opposite in direction to that of normal S _a field.     

A study of blanketing sporadic E in the Indian equatorial region

The paper describes the nature of the sporadic E layer of blanketing type observed at Kodaikanal (Lat. 10°·2 N; Long. 77°·5 E; dip: 3°·5 N). It is shown that in the Indian equatorial region, the frequency of occurrence of this type of E _s is abnormally large when compared to similar latitudes in the west and that changes of large magnitudes occur in the F2 layer of the ionosphere as well as in the horizontal force of the earth’s magnetic field simultaneously with the appearance of the blanketing E _s . Lunar effects have also been shown to exist both in the time of appearance of blanketing E _s and in its strength. Some evidence exists to show that blanketing E _s as well as the blanketing frequency,f _b E _s , have a biennial maximum. These characteristics are discussed as part of the Far East Anomaly.     

On the simultaneous existence of eastward and westward flowing equatorial electrojet currents

The counter-electrojet currents are evidenced by the disappearance of theq type ofEs layer (Es-q) or the appearance of the blanketing type ofEs (Es-b) at Kodaikanal, associated with the depression of the geomagneticH field and the reveisal of ionospheric drift at Thumba. The necessary condition for such an event is not the decrease of theH field below the night level but that the difference of theH field between an equatorial and a non-equatorial station should decrease below its night level. The different kinds of association between the disappearance ofEs-q and the depression in theH field are suggested due to superimposition over theSq current system (at about 107 km) of a separate westward current system at a lower level (about 100 km). The source of the reversed current over the dip equator during the daytime hours is sought in the current system generated by the lunar tides or in various magnetospheric processes generating the polar substorms. Large day-to-day variations of the solar daily range ofH at the equator independent ofSq variation at tropical latitudes are suggested to be due to superimposition at the equator of the two rather independent current systems.     

Low latitude ionospheric effects near longitude 120°E during the great geomagnetic storm of July 2000

A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about -300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120(E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O2 or N2 to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in foF2 during these days, and the diurnal variation of foF2 was less clear than before.     

Low latitude ionospheric effects near longitude 120°E during the great geomagnetic storm of july 2000

A great geomagnetic storm occurred on July 15/16, 2000 with a minimum value of about ?300 nT in Dst index. Collecting digisonde data from ionospheric stations at Chungli, Wuhan, Kokubunji and Anyang, the ionospheric responses at the low latitudes near longitude 120°E during this storm are analyzed in this paper. There was a strong negative phase storm at low latitudes on July 16. The G-condition in the ionograms was clearly seen on the early first day after the commencement of geomagnetic storm. Those were considered to be caused by the storm-induced increase in the concentration ratios of neutral molecular O₂ or N₂ to atom O. On July 17 and some days thereafter, a positive phase storm appeared. In addition, anomalous equatorial ionization anomaly (EIA) inhibitions and developments were observed on July 16 and 17. There were also prominent nighttime enhancements in f₀F₂ during these days, and the diurnal variation of f₀F₂ was less clear than before.     

Spectra and ionization potential of cyanoacetylene

The spectrum of cyanoacetylene has been photographed in the vacuum ultraviolet region and its analysis made. The ionization potential has been calculated from an observed Rydberg series to be 11.6 eV. The first Rydberg band has been compared with the photoelectron spectrum of the molecule and conclusions about the initial orbital have been drawn.     

Nonlinearly Coupled KdV Equations Describing the Interaction of Equatorial and Midlatitude Rossby Waves

Amplitude equations governing the nonlinear resonant interaction of equatorial baroclinic and barotropic Rossby waves were derived by Majda and Biello and used as a model for long range interactions （teleconnections） between the tropical and midlatitude troposphere. An overview of that derivation is nonlinear wave theory, but not in atmospheric presented and geared to readers versed in sciences. In the course of the derivation, two other sets of asymptotic equations are presented： the long equatorial wave equations and the weakly nonlinear, long equatorial wave equations. A linear transformation recasts the amplitude equations as nonlinear and linearly coupled KdV equations governing the amplitude of two types of modes, each of which consists of a coupled tropical/midlatitude flow. In the limit of Rossby waves with equal dispersion, the transformed amplitude equations become two KdV equations coupled only through nonlinear fluxes. Four numerical integrations are presented which show （i） the interaction of two solitons, one from either mode, （ii） and （iii） the interaction of a soliton in the presence of different mean wind shears, and （iv） the interaction of two solitons mediated by the presence of a mean wind shear.     

Blow-up and propagation of disturbances for fast diffusion equations

This paper is concerned with the Cauchy problem for the fast diffusion equation _ut−Δu^m=αu^_p1$u_t-\Delta u^m=\alpha u^{p_1}$ in R^N${\mathbb{R}}^N$ (N≥1$N\ge 1$), where m∈(0,1)$m\in (0,1)$, _p1>1$p_1>1$ and α>0$\alpha >0$. The initial condition _u0$u_0$ is assumed to be continuous, nonnegative and bounded. Using a technique of subsolutions, we set up sufficient conditions on the initial value _u0$u_0$ so that u(t,x)$u(t,x)$ blows up in finite time, and we show how to get estimates on the profile of u(t,x)$u(t,x)$ for small enough values of t>0$t>0$.     

6300 Å night airglow and the geomagnetic control of the equatorial anomaly

The intertropical red arc in the night airglow studied from a low latitude station (Mt. Abu, India) shows that in the years of high solar activity and on the magnetically quiet nights the arc is well developed and can be detected up to midnight or even in the early morning hours. In the beginning of the night and on many nights the arc appears overhead at 12° to 15° geomagnetic latitude. As the night progresses the movement of the arc towards the magnetic equator can be traced by azimuthal 6300 Å scanning. The intensity of the arc and its equatorward velocity vary from night to night. On the magnetically disturbed nights the arc is poorly developed, fades before midnight and its southward velocity is less. In the years of low sunspot activity also the arc is weak. These observations are consistent with those of the F-region Appelton equatorial anomaly at night time which presumably shows that the bulk of 6300 Å is due to the dissociative recombination of electrons with oxygen (and nitrogen) ions.     

The Effect of Meridional and Vertical Shear on the Interaction of Equatorial Baroclinic and Barotropic Rossby Waves

Simplified asymptotic equations describing the resonant nonlinear interaction of equatorial Rossby waves with barotropic Rossby waves with significant midlatitude projection in the presence of arbitrary vertically and meridionally sheared zonal mean winds are developed. The three mode equations presented here are an extension of the two mode equations derived by Majda and Biello [ 1 ] and arise in the physically relevant regime produced by seasonal heating when the vertical (baroclinic) mean shear has both symmetric and antisymmetric components; the dynamics of the equatorial baroclinic and both symmetric and antisymmetric barotropic waves is developed. The equations described here are novel in several respects and involve a linear dispersive wave system coupled through quadratic nonlinearities. Numerical simulations are used to explore the effect of antisymmetric baroclinic shear on the exchange of energy between equatorial baroclinic and barotropic waves; the main effect of moderate antisymmetric winds is to shift the barotropic waves meridionally. A purely meridionally antisymmetric mean shear yields highly asymmetric waves which often propagate across the equator. The two mode equations appropriate to Ref. [ 1 ] are shown to have analytic solitary wave solutions and some representative examples with their velocity fields are presented.     

Chaos game representation of the Dst index and prediction of geomagnetic storm events

This paper proposes a two-dimensional chaos game representation (CGR) for the D_st index. The CGR provides an effective method to characterize the multifractality of the D_st time series. The probability measure of this representation is then modeled as a recurrent iterated function system in fractal theory, which leads to an algorithm for prediction of a storm event. We present an analysis and modeling of the D_st time series over the period 1963–2003. The numerical results obtained indicate that the method is useful in predicting storm events one day ahead.     

Variations of intensity and anisotropy of cosmic rays measured at the geomagnetic equator

A study of cosmic ray intensity variations has been conducted during 1956–57 at the equatorial mountain station of Kodaikanal, using a standard neutron monitor. The data have been examined to look for the relationship between the day-to-day changes of intensity, the variance of bi-hourly deviations, the occurrence of large bi-hourly deviations at different hours of the day and the associated parameters of the daily variation. The results are related to the electromagnetic state of interplanetary space as determined by streams of solar matter in the neighbourhood of the earth, carrying with them frozen magnetic fields. Comparison is made with the model elaborated by Dorman. The principal conclusions are as follows:

1. (1)
   Day-to-day changes of intensity involve increases as well as decreases with respect to a base intensity for the period in question.     
   
   

赤道东太平洋海气耦合振荡的非线性分析及ENSO循环的极限环理论

把赤道东太平洋地区大气对流层,海洋混合层看作是在定常热源（太阳辐射）驱动下的动力系统,利用一个局域平均的热力学气候模式,建立了海气耦合自激振荡模型,得到了一个封闭的自治的二次系统,对系统进行了线性和非线性分析．结合系统稳定的极限环解,对海气耦合的物理机制进行了探讨．和观测事实的比较表明,在赤道东太平洋区域平均的以500 hPa为代表的大气对流层的温度距平和海表温度距平,在相平面上和极限环解定性上很一致．这为研究热带海气相互作用的年际变化提供了一个理论模型．     

前列腺素E1对肝切除术后肝功能的保护作用

目的探讨前列腺素E1（PGE1）对肝切除术后肝功能的保护作用及机制。方法选取118例接受肝大部切除术患者,其中A组36例（术后常规治疗）,B组40例（术后常规治疗＋PGE,20μg／d,静脉注射,连续14d）。C组42例（术中门静脉阻断再开放时行Lipo—PGE,20ug门静脉灌注＋B组方案）。分别检测3组患者术前与术后1、3、5、9、14、28d外周血ALT及TNF-α、IL-6、IL-10、IFN-γ水平,以及术前与术后1、7、28d门静脉血流量的变化。结果3组患者术前各指标差异均无统计学意义（均P〉005）。术后各组患者ALT、TNF—α、IL-6、IL-10水平均明显升高,然后逐渐恢复,但B、C组升高幅度明显低于A组（均P〈0．01）,且恢复时间快于A组;A组IFN-γ水平在手术前后无明显改变,但B、C组在术后28d,IFN-γ水平明显持续升高（均P〈0．01）。A组门静脉血流量手术前后无明显改变,而B、C组术后门静脉血流量在观察时段内明显且逐渐增高（均P〈0．05）。以上所有PGE,干预引起的变化,C组均较B组明显。结论PGE,有利于肝切除术后早期功能的恢复,其作用机制可能与调节细胞因子水平及增加门静脉血流有关。     

Asymptotic distributions of regression and autoregression coefficients with martingale difference disturbances

In this paper a form of the Lindeberg condition appropriate for martingale differences is used to obtain asymptotic normality of statistics for regression and autoregression. The regression model is y_t = Bz_t + v_t. The unobserved error sequence {v_t} is a sequence of martingale differences with conditional covariance matrices {Σ_t} and satisfying sup_{t=1,…, n} {v′_tv_tI(v′_tv_t>a) |z_t, v_t−1, z_t−1, …} 0 as a → ∞. The sample covariance of the independent variables z₁, …, z_n, is assumed to have a probability limit M, constant and nonsingular; max_t=1,…,nz′_tz_t/n 0. If (1/n)Σ_t=1ⁿΣ_t Σ, constant, then √nvec( _n−B) N(0,M⁻¹Σ) and _n Σ. The autoregression model is x_t = Bx_{t − 1} + v_t with the maximum absolute value of the characteristic roots of B less than one, the above conditions on {v_t}, and (1/n)Σ_t=max(r,s)+1(Σ_tv_t−1−rv′_t−1−s) δ_rs(ΣΣ), where δ_rs is the Kronecker delta. Then √nvec( _n−B) N(0,Γ⁻¹Σ), where Γ = Σ_{s = 0}^∞B^sΣ(B′)^s.