Man-Lian Zhang

An analysis of the scale heights in the lower topside ionosphere based on the Arecibo incoherent scatter radar measurements

[1] We statistically analyze the ionospheric scale heights in the lower topside ionosphere based on the electron density (Ne) and temperature profiles observed from the incoherent scatter radar (ISR) at Arecibo (293.2E, 18.3N), Puerto Rico. In this study, a database containing the Arecibo ISR observations from 1966 to 2002 has been used in order to investigate the diurnal and seasonal variations and solar activity dependences of the vertical scale height (VSH), which is deduced from the electron concentration profiles

Topside ionospheric scale heights retrieved from Constellation Observing System for Meteorology, Ionosphere, and Climate radio occultation measurements

[1] The vertical scale height (VSH) in the topside ionosphere can be derived from electron density profiles. In this study, the electron density profiles retrieved from the COSMIC/FORMOSAT-3 (a Constellation Observing System for Meteorology, Ionosphere, and Climate mission; C/F3 for short) ionospheric radio occultation (IRO) observations have been collected to investigate the local time, seasonal, latitudinal, and longitudinal variations of the VSH. With the postprocessed C/F3 IRO electron density profiles during the interval from day of year (DOY) 194 in 2006 to DOY 60 in 2008, we conduct an analysis on the behaviors of VSH at an altitude of 400 km. There are appreciable latitudinal variations in VSH. A new finding is a significant peak around dip equator during daytime in four seasons. Away from the equatorial peak, it is obvious that the VSH generally increases at higher latitudes. The equatorial VSH undergoes a significant diurnal variation with a local noon maximum. The peak shifts to sunrise time with increasing dip latitude, and the values of daytime VSH become comparable with those at nighttime at low latitude in both hemispheres, which is somewhat different from the feature revealed from Arecibo incoherent scatter radar observations. One of the crucial findings in our results is the most outstanding feature of VSH, that is, the presence of a substantial longitudinal structure in equatorial regions. A wave-like longitudinal feature is found in equatorial VSH during the daytime in four seasons, while it becomes weaker or absent at other local time intervals and at higher latitudes. This investigation also confirms that the behaviors of VSH are not strongly consistent with those of the neutral or plasma-scale heights.

A comparison of the lower transition height obtained with a theoretical model and with IRI

The ionospheric low transition height obtained from a theoretical mode1 is compared to the IRI model using the standard ion composition option and the Danilov and Yaichinikov mode1 option, and to Oliver’s model. It is found that 1) the three models agree rather well by day except in summer for low solar activity, while large differences exist by night; 2) the day-night difference of the transition height by the IRl standard option is much smaller in summer and in winter, but is larger in equinox seasons in low solar activity, while the Danilov and Yaichnikov mode1 always yields a rather small difference; 3) increasing solar activity leads to higher theoretical levels particularly by night, while IRl shows an opposite trend. 4) due to transport by wind the simulation gives a transition height depending on local time, while both IRl options take the solar zenith angle for variable. As for the ion composition above 150 km, the distributions of the relative percentage of Of as well as NO+ at noon in summer and winter under low solar activity predicted by the theoretical model are approximately consistent with those of the Danilov and Yaichnikov model.

Results of the modeling of the topside electron density profile using the Chapman and Epstein functions

An attempt has been made to model the topside electron density profile by using the data obtained by the incoherent scatter radar in Malvern (-2.34degreesE, 52.1degreesN), UK and the topside sounder data over the European PRIME region (0-35degreesE, 30-70degreesN). Both the Chapman distribution function and the Epstein function are used to do the modeling. It is found that both functions cannot fit well the topside profiles if the thickness parameters are assumed to be constant along all the heights above the F2-peak. Our study showed that by assuming the thickness parameter changes linearly with height (H-S = H-0+a (h-h(max)) for Chapman function and B-2 = B-0+k (h-h(max)) for Epstein function), the result of the fitting could be improved very much. We found that with the two-parameter fitting, the topside profiles can be fitted to a height of about 400km above the F2-peak quite satisfactorily, while with the one-parameter fitting by fixing the slope parameter in the linear relationship, the results obtained are still good enough when the fitting is made to a height of about 300km above the 172-peak. The results showed that the thickness parameter near F2-peak varies very complicatedly. The correlation relationships of B-0 with hmF2, NmF2, Ap and F107 are also studied

Optimal assimilation for ionospheric weather – Theoretical aspect

Observation, specification and prediction of ionospheric weather are the key scientific pursuits of space physicists, which largely based on an optimal assimilation system. The optimal assimilation system, or commonly called data assimilation system, consists of dynamic process, observation system and optimal estimation procedure. We attempt to give a complete framework in this paper under which the data assimilation procedure carries through. We discuss some crucial issues of data assimilation as follows: modeling a dynamic system for ionospheric weather; state estimation for static or steady system in sense of optimization and likelihood; state and its uncertainty estimation for dynamic process. Meanwhile we also discuss briefly the observability of an observation system; system parameter identification. Some data assimilation procedures existed at present are reviewed in the framework of this paper. As an example, a second order dynamic system is discussed in more detail to illustrate the specific optimal assimilation procedure, ranging from modeling the system, state and its uncertainty calculation, to the quantitatively integration of dynamic law, measurement to significantly reduce the estimation error. The analysis shows that the optimal assimilation model, with mathematical core of optimal estimation, differs from the theoretical, empirical and semi-empirical models in assimilating measured data, being constrained by physical law and being optimized respectively. The data assimilation technique, due to its optimization and integration feature, could obtain better accurate results than those obtained by dynamic process, measurement or their statistical analysis alone. The model based on optimal assimilation meets well with the criterion of the model or algorithm assessment by ‘space weather metrics’. More attention for optimal assimilation procedure creation should be paid to transition matrix finding, which is usually not easy for practical space weather system. High performance computing hardware and software studies should be promoted further so as to meet the requirement of large storage and extensive computation in the optimal estimation. The discussion in this paper is appropriate for the static or steady state or transition process of dynamic system. Many phenomena in space environment are unstable and chaos. So space environment study should include and integrate these two branches of learning.

Distribution of ionospheric O + ion in synchronous altitude region

Based on satellite observation data, using dynamics equation, the ionospheric O+ ion’s distribution in the synchronous altitude region for different geomagnetic activity indexKp is studied by theoretical modeling and numerical analyzing, and semi-empirical models for the O+ ion’s density and flux versus longitude in the synchronous altitude region for differentKp are given. The main results show that in the synchronous altitude region: (i) The O+ ion’s density and flux in day-side are larger than those in nightside. (ii) With longitude changing, the higher the geomagnetic activity indexKpis, the higher the O+ ion’s density and flux, and their variation amplitude will be. The O+ ion’s density and flux whenKp ≥ 6 will be about ten times as great as that whenKp= 0. (iii) WhenKp = 0 orKp ≥ 6, the O+ ion’s density reaches maximum at longitudes 120° and 240° respectively, and minimum in the magnetotail. WhenKp = 3−5, the O+ ion’s density gets to maximum at longitude 0°, and minimum in the magnetotail. However, the O+ ion’s flux reaches maximum at longitude 120° and 240° respectively, and minimum in the magnetotail for anyKp value.

On Property of Scattering Structure in Random Continua

This paper attempt to study scattering property of turbulently advected medium. A new concept, scattering structure, is defined. A cross section is given and discussed. The results revealed that the scattering structure results from Bragg and time sampling actions. Properties of the scattering structure, e.g. scattering efficiency, aspect sensitivity, frequency dependence and discreteness, are analyzed. Some of them are demonstrated by Digital ionosonde measurement. The particle‐behaved scattering structures within resolution volume are the scattering sources of pixels of the radar interferometry image.

Optimal Assimilation for Ionospheric Weather

Observation, specification and prediction of ionospheric weather are the key scientific pursuits of space physicists, which largely based on an optimal assimilation system. The optimal assimilation system, or commonly called data assimilation system, consists of dynamic process, observation system and optimal estimation procedure. We attempt to give a complete framework in this paper under which the data assimilation procedure carries through. We discuss some crucial issues of data assimilation as follows: modeling a dynamic system for ionospheric weather; state estimation for static or steady system in sense of optimization and likelihood; state and its uncertainty estimation for dynamic process. Meanwhile we also discuss briefly the observability of an observation system; system parameter identification. Some data assimilation procedures existed at present are reviewed in the framework of this paper. As an example, a second order dynamic system is discussed in more detail to illustrate the specific optimal assimilation procedure, ranging from modeling the system, state and its uncertainty calculation, to the quantitatively integration of dynamic law, measurement to significantly reduce the estimation error. The analysis shows that the optimal assimilation model, with mathematical core of optimal estimation, differs from the theoretical, empirical and semi-empirical models in assimilating measured data, being constrained by physical law and being optimized respectively. The data assimilation technique, due to its optimization and integration feature, could obtain better accurate results than those obtained by dynamic process, measurement or their statistical analysis alone. The model based on optimal assimilation meets well with the criterion of the model or algorithm assessment by ‘space weather metrics’. More attention for optimal assimilation procedure creation should be paid to transition matrix finding, which is usually not easy for practical space weather system. High performance computing hardware and software studies should be promoted further so as to meet the requirement of large storage and extensive computation in the optimal estimation. The discussion in this paper is appropriate for the static or steady state or transition process of dynamic system. Many phenomena in space environment are unstable and chaos. So space environment study should include and integrate these two branches of learning.