Ionospheric plasma bubble zonal drift: a methodology using OI 630 nm all-sky imaging systems

With the recent advances in all-sky imaging technology for nightglow emission studies, the F-region OI 630 nm emission has become an important tool for ionospheric/thermospheric coupling studies. At equatorial and low latitude regions, the all-sky imaging observations of the OI 630 nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale F-region plasma irregularities. By observing the motion of the intensity depleted bands it is possible to infer the ionospheric plasma zonal velocity of the depletion. The north-south aligned structures seen in the field of view of the all-sky imaging system corotate with the ionospheric plasma, so that by calculating the spatial displacements occurring during successive OI 630 nm emission images we can infer the ionospheric plasma drift velocity. However, the plasma bubbles have their own internal space-time dynamics leading to changes in their shape and dimensions and this may induce some errors in the calculated drift velocities. In this paper we take into account the space-time changes in the plasma bubbles in order to calculate the ionospheric plasma zonal drift velocities using the OI 630 nm nightglow emission.     

Practical method for routine analysis of the valley parameters between E- and F-region of the ionosphere

Measurement of the virtual height and the frequency of the minimum of the F-region extraordinary trace in digital and analog ionograms can provide a world-wide survey of the main parameters for the valley between E- and F-region ionization. The two added quantities establish also the starting point for the true height analysis of the F-region ionization.     

Dependence of the F-region peak electron density (foF2) on solar activity observed in the equatorial ionospheric anomaly region in the Brazilian sector

The long-term (solar cycle) changes in the Sun and how it affects the ionospheric F-region observed at São José dos Campos (23.2° S, 45.9° W), Brazil, a location under the southern crest of the equatorial ionospheric anomaly, have been investigated in this paper. The dependence of the F-region peak electron density (foF2) on solar activity during the descending phase of the 23rd solar cycle for the periods of high, medium, and low solar activity has been studied. The ionospheric F-region peak electron densities observed during high and medium solar activity show seasonal variations with maxima close to the equinox periods, whereas during the low solar activity the maxima during the equinox periods is absent. However, during the low solar activity only change observed is a large decrease from summer to winter months. We have further investigated changes in the different ionospheric F-region parameters (minimum virtual height of the F-region (h′F), virtual height at 0.834foF2 (hpF2), and foF2) during summer to winter months in low solar activity periods, 2006–2007 and 2007–2008. Large changes in the two ionospheric parameters (hpF2 and foF2) are observed during summer to winter months in the two low solar activity periods investigated.     

Relationship between electron density and electron temperature as a function of solar activity

This paper attempts to examine the control of electron density and solar activity on the F-region electron temperature. This is achieved by obtaining coefficients relating electron temperature with electron density and solar activity by using incoherent scatter radar measurements at Arecibo for the period August 1966 to May 1977. These coefficients are then used to construct an empirical model of F-region electron temperature. The model values are compared with measurements at other locations and show reasonable agreement.     

暴时极光区热层大气焦耳加热与F区电离耗空的EISCAT雷达观测

利用ＥＩＳＣＡＴ雷达探测数据，分析计算了太阳活动高年夏季发生的一次强磁暴期间，极光区电离层对流电场、电导率以及焦耳加热速率等着重考察了Ｅ区热怪大气焦耳加热和Ｆ区离子摩擦增温与Ｆ区电子密度耗空的关系发现在下午东向极光电集流期间，电子密度最大耗空出现在Ｆ区３００－３２５ｋｍ高度，时间恰在积分的Ｅ区大气焦耳加热量大值和Ｆ区最大离子增温之后５－１０ｍｉｎ，耗空率达７０％。     

IMF polarity effects on the equatorial ionospheric F-region

An exploratory study is made of the influence, during the equinoxes, of the interplanetary magnetic field (IMF) sector structure on the ionospheric F-region using ionosonde data from several equatorial stations for a 3-yr period around the 19th sunspot cycle maximum. It is found that, compared with days having positive IMF polarity, the post-sunset increase of h'F near the dip equator and the depth of the equatorial ionization anomaly (EIA) are reduced during the vernal equinox and enhanced during the antumnal equinox on days with negative IMF polarity. Similar trends are also noted in the data for the 20th sunspot cycle maximum, but with reduced amplitude. The systematic changes in the F-region characteristics suggest a modification of the equatorial zonal electric fields in association with the IMF polarity-related changes in the semi-annual variation of geomagnetic activity.     

Rocket observations of propagating waves in the night time equatorial F-region over Brazil

A Brazilian SONDA III rocket carrying plasma diagnostic experiments was launched from the Brazilian rocket launching stations in Alcântara (2.31°S, 44.4°W Geog. Lat.) to measure the height profiles of electron density, electron temperature and the ambient electric field. High frequency capacitance probe was used to measure the height profile of the electron density and the Langmuir probe was used to measure the electron density and the spatial structures of plasma irregularities. An electric field double probe was used to measure the electric field fluctuations associated with the F-region plasma irregularities. Spectral analysis of the fluctuations in electron density and electric field indicated the presence of propagating waves in the night time F-region over a large height range. The electron temperatures estimated from the LP data showed abnormally high values in the base of the F-region during the upleg of the rocket and practically normal values in the same height region during the downleg. A brief study of the characteristic features of the spectra of electron density and electric field fluctuations and the associated electron temperature variations are presented and discussed here.     

Effects observed in the ionospheric F-region in the South American sector during the intense geomagnetic storm of 14 December 2006

This investigation presents observations related to the generation of equatorial ionospheric irregularities (also known as equatorial spread F (ESF)) including ionospheric plasma bubbles and dynamic behavior of the ionospheric F-region in the South American sector during an intense geomagnetic storm in December 2006 (a period of low solar activity). In this work, ionospheric sounding observations and GPS data obtained between 13 and 16 December 2006 at several stations in the South American sector are presented. On the geomagnetically disturbed night of 14 and 15 December, ionospheric plasma bubbles were observed after an unusual uplifting of the F-region during pre-reversal enhancement (PRE) period. The unusual uplifting of the F-region during PRE was possibly associated with prompt penetration of electric field of magnetospheric origin. During the geomagnetic disturbance night of 14 and 15 December, strong oscillations due to the propagation of traveling ionospheric disturbances (TIDs) by the Joule heating in the auroral region were observed in the F-region at São José dos Campos (SJC, 23.2°S, 45.9°W; dip latitude 17.6°S), Brazil, and Port Stanley (PST, 51.6°S, 57.9°W; geom. latitude 41.6°S). The VTEC-GPS observations presented on the night of 14 and 15 December 2006 show both positive and negative storm phases in the South American sector, possibly due to changes in the large-scale wind circulation and changes in the O/N₂ ratio in the southern hemisphere, respectively.     

Theoretical model of electron temperature and electron density: Comparisons with IRI and MSIS

An earlier theoretical model (UW-87) accurately predicted the electron temperature in the daytime F-region but suggested N₂ concentrations significantly greater than the predictions of MSIS-86. This discrepancy is resolved when the model is developed to include the effects of vibrationally excited nitrogen molecules and electronically excited oxygen ions on the F-region recombination rate. The revised model (UW-92) continues to predict electron temperatures close to the layer peak with great accuracy but it is now more closely consistent with MSIS. However, the electron temperatures predicted by this model, which are in close agreement with EISCAT observations, are significantly higher than the values predicted by the international Reference Ionosphere.     

冬夏典型地磁-电离层暴期间太平洋区域F层行为

本文在前人已公布的暴时电离层动态资料的基础上, 进行了太平洋地区冬至与夏至期间电子总量和F层特征的分析研究, 取得了新的结果.认为在磁暴主相出现之时, 以电子总量为表征的电离层暴达到最明显的程度.以F层为代表的电离层的行为强烈地受控于经度(暴时)、纬度、地磁格局和季节(南北半球)的缔合关系;并且电子总浓度的消长关系需从电离增长率(磁壳层收缩)-电离消矢率(损失系数加大)-电离迁移率(磁共轭迁移和电离峰谷异动)作统一考虑.文中提出了较合理的电离层暴区划意见并讨论了暴情倒相问题.      

Vertical shear at the equatorial F-region ionosphere during post-sunset hours

The characteristics of the equatorial F-region zonal plasma drift during post-sunset period have been investigated using the multi-frequency HF Doppler radar. The pattern of the zonal plasma drift is such that it starts with a westward drift during the pre-sunset hours, followed by an eastward drift shortly after the E-region sunset. The zonal plasma drift is characterized by the presence of a positive vertical shear around the post-sunset period and maximum shear is observed at the time of the peak of the pre-reversal enhancement in the vertical drift. The presence of vertical shear in the zonal drift is associated with the post-sunset velocity vortex existing at the equatorial F-region.     

氮氧化物羽烟在电离层局部的光热效应

在航天器羽烟一次性抛出和呈球状近似情况下,模拟了电离层E层NO羽烟与周围大气压力平衡时的最大亮度及其随时间的变化．在110km抛出的5molNO羽烟可使它获得瞬时夜间中等偏强极光那样的亮度,在140km抛出的同样数量的NO羽烟亮度却急剧地减弱．还模拟了白天夜间温度为1000K的NO2羽烟在190km和250km两个高度、50mol和500mol两种抛出总量所造成的局部大气温度短时间内的下降．在F层下部,夜间较大抛出量所造成的冷却效应是显著的．     

On the behavior of thermospheric O1D 630.0 nm dayglow emission during counter electrojet events

This study presents the response of thermospheric O¹D 630.0 nm dayglow emission to the variability associated with equatorial Counter Electrojet (CEJ) events. The analysis based on the data from a meridian scanning Dayglow Photometer, Digital Ionosonde and Proton Precession Magnetometer over Trivandrum (8.5°N, 77°E, 0.5°dip lat.), indicates that the O¹D 630.0 nm emission behave distinctly different during the CEJ events compared to that on normal days. It has been observed that O¹D 630.0 nm emission shows enhancement during the negative excursion of the ΔH, followed by an unusual depletion during the peak CEJ time. The observed variability was found to be more pronounced in a latitudinal region of ±3° centered at around the dip equator. In addition, the emission intensities also exhibit the presence of enhanced short period oscillations of periodicity 20–30 min during the CEJ events. Analysis of the data from the collocated ionosonde revealed that the F-region electron density showed enhancement during the early phase of the CEJ and a decrease during the peak CEJ. Further, the simulation studies using a Quasi 2 dimensional ionospheric model showed that the modified plasma fountain during the CEJ can alter the plasma density at the emission centroid. The study reveals a strong dynamical coupling between the E and F-region of the dip equatorial ionosphere.     

Equatorial F-region ionization differences between March and September, 1979

Ionospheric total electron content and the F-region maximum electron density at a number of stations in the equatorial region, during the recent solar activity maximum period 1979 to 1980, show significant differences between the two equinoctial periods. Ionization during the month of March is higher than in September, irrespective of the station location both in northern and southern hemispheres, and in different longitude sectors. The observed pattern is compared with those predicted by different models, in particular with one of the authors which includes processes such as ionization production, loss, electrodynamic drifts, winds and global composition changes involved in the equatorial ionosphere. It is found that a change in the neutral composition is primarily responsible for the observed F-region density differences between March and September.     

Models for horizontal E- and F-region drifts

Plasma transport is very important for understanding the space-time variations of the ionosphere. Therefore, following a resolution of URSI Subcommission G4, an effort is made to create a computer code describing the main results of investigations the ionospheric drift which were not considered in IRI-1979.

The experimental data from 23 stations in the Northern Hemisphere were obtained between 1957 and 1970. The worldwide coverage in geographic latitude is 7°N to 71°N (7.5° to 64.1° geomagnetic) and O° to 131°E geographic longitude.

We have developed appropriate procedure which allow us to infer from these data the main parameters of the global ionospheric motions at E- and F-region levels.

An algorithm for computing the zonal and meridional drift components VX, VY can be found in IRI-1990.

The last version of the computer programm called DRIFT which does the test calculation of Ionospheric Drifts Global Model whith printing the tables at the Epson printer is written in Turbo ascal for the IBM PC AT 286/287 compatible computers. Program code (execute module) is about 25 Kbyte. Data files are about 10 Kbyte.

E- and F-region horizontal ionospheric irregularities drift data, worldwide obtained from 1957 to 1970 by D1 and D3 methods, are statistically analysed and a computer code for the average velocity variations in latitude and local time for some solar activity levels is constructed. The PC program DRIFT allows to determine zonal and meridional drift velocities of ionospheric irregularities at the lower (90 < h < = 140 km) and upper (h > 140 km) ionosphere.

The main block of the program DRIFT is the procedure DRIRR for calculating VX and VY for a period (P), geomagnetic (geographic) latitude (FI) and local time (LT) to be specified.

The example of the program DRIFT calculation for F-region (REG=2) and for the whole period of observations (P=1) is in Table. VX > 0 to east, VY > 0 to north. FI is geomagnetic latitude.     

Analysis of post-sunset F-region vertical plasma drifts during Counter Electrojet days using multi frequency HF Doppler Radar

In this paper, through a case study, an attempt has been made to bring out the relationship between post noon E-region electric field and post sunset F-region vertical plasma drift on quiet time Counter Electrojet (CEJ) days. Study carried out using the data from a multi frequency HF Doppler Radar and Digital Ionosonde located over Trivandrum (8.5° N; 77° E; 0.5° N dip lat.) a geomagnetic dip equatorial station in India during quite time CEJ days of the years 2004 and 2006, revealed some interesting aspects of the E region electrodynamics and post sunset F region electrodynamics. It has been observed that, in contrast to the normal electrojet (EEJ) days, the Pre-Reversal Enhancement (PRE) is either weakened or inhibited on CEJ days and the field reversal takes place much earlier than that on a normal day. It is suggested that even after the effects of the field reversal ceases to show up in the ground magnetic data, the reversed field may persist and shows up as a decrease in the PRE experienced by the F-region. In other words, the study indicates that the EEJ associated electrodynamics have a significant role in controlling the PRE.     

The nighttime mid-latitude foF2 and geomagnetic indices

The correlation between AE, Ap and Dst indices, on the one hand, and nighttime critical frequencies, on the other, in northern midlatitudes in investigated. The correlation is closest for the Dst-index. A possible mechanism involving the effect of ring currents on the electron density in the mid-latitude F-region is mentioned.     

Disturbances in the ionospheric F-region peak heights in the American longitudinal sector during geomagnetic storms of September 2005

In this paper, we use the modified GSM TIP model to explore how the thermosphere–ionosphere system in the American longitudinal sector responded to the series of geomagnetic storms on September 9–14, 2005. Comparison of modeling results with experimental data at Millstone Hill, USA (42.6°N, 71.5°W), Ramey, Puerto Rico (18.3°N, 66.8°W) and Jicamarca, Peru (11.9°S, 76.9°W) has shown a good agreement of ionospheric disturbances in the F-region maximum height. We examine in detail the formation mechanisms of these disturbances at different latitudes and describe some of the important physical processes affecting the behavior of the F-region. In addition, we consider the propagation of thermospheric wind surge and the formation of additional layers in the low-latitude ionosphere during geomagnetic storms.     

Generation of artificial ionospheric plasma density irregularities with prescribed spectra

The creation of artificial plasma density irregularities (AI) with prescribed spectra in the ionospheric heating experiments is discussed. We show that periodic successions of powerful pulses, pumped into the F-region of the ionosphere lead to obtaining AI with the controlled stationary spatial spectrum and allow us to change power low spectral index 2β at least from 2β = 2.2 to 2β = 3.4 by changing of the powerful pulse time schedule.