Drift Velocity Of Plasma Bubbles Research Articles

Drift Velocity Estimation of Ionospheric Bubbles Using GNSS Observations

AbstractEquatorial plasma bubble (EPB) irregularities are large‐scale plasma depleted structures that exist in the equatorial and low‐latitude ionosphere. Thus, particularly in these regions, much attention must be given to the effects of the EPBs in the life critical applications based on global navigation satellite systems (GNSS). The study on the dynamics of plasma bubbles, particularly in the determination of their drift velocities, and their impact on ground‐based augmentation system is of fundamental importance for civilian aviation. In this regard, we proposed a methodology to estimate the zonal drift velocities of the plasma bubble irregularities using slant total electron content (TEC) measurements derived from two spaced ground‐based GNSS receivers. The experiments were performed with the purpose to evaluate if the drift velocities obtained using the methodology proposed in this study agree with the velocities deduced from all‐sky imaging systems. The results revealed that the TEC‐estimated mean eastward drift velocities were comparable with the values deduced from the airglow techniques, and with the results obtained from previous studies. Therefore, the methodology proposed in this work to infer the plasma bubble drift velocities seem to have the potential in future investigations to provide a new data source in this field.

An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region

There is increasing interest to understand thermospheric neutral wind and ionized plasma coupling, especially by using empirical observations. This is the first study that reports simultaneous measurements of thermospheric neutral wind and equatorial plasma bubble (EPB) speeds over the African equatorial region. Neutral wind speeds were obtained using a Fabry-Perot interferometer (FPI), while EPB speeds were obtained using an all-sky optical imager. Both instruments are co-located in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S). Data for 11 nights of coincident neutral wind and EPB speed observations were used. The neutral wind speeds were in the range of about −30 to 300 m/s, while EPB speeds were in the range of about 15–400 m/s. The speeds of both neutral winds and EPBs were generally observed to be faster during the early night hours and to slow down towards midnight. In some instances, the neutral wind and EPB speeds were comparable, an observation that is in agreement with full development of the F region dynamo. There were also instances in which the EPBs were faster or slower than the neutral winds. In one of the nights, a southward turning of the IMF-Bz was observed to cause a sudden increase in the EPB speed. For some nights, the neutral winds were faster than the EPBs during earlier hours of the nights, and the disparity reduced during the later hours of the nights. This was attributed to the possibility that the F region dynamo was yet to be fully developed during the earlier hours.

An Experimental Investigation into the Possible Connections between the Zonal Neutral Wind Speeds and Equatorial Plasma Bubble Drift Velocities Over the African Equatorial Region

An Experimental Investigation into the Possible Connections between the Zonal Neutral Wind Speeds and Equatorial Plasma Bubble Drift Velocities Over the African Equatorial Region

A New Method for Deriving Equatorial Plasma Bubble Velocity by Tracing OI 630 nm All‐Sky Images

AbstractA new method for estimating the equatorial plasma bubbles (EPBs) motions from airglow emission all‐sky images is presented in this paper. This method, which is called cloud motion wind (CMW) and widely used in satellite observation of wind, could reasonably derive zonal and meridional velocity vectors of EPBs drift by tracking a series of successive airglow images. Airglow emission images data are available from all‐sky airglow camera in Hainan Fuke (19.5°N, 109.2°E) supported by China Meridional Project, which can receive the 630.0 nm emission from ionosphere F region at low latitudes to observe plasma bubbles. A series of pretreatment technology is utilized to preprocess the raw observation. Then the regions of plasma bubble extracted from the images are divided into several small tracing windows, and each tracing window can find a target window in the searching area in following image, which is considered as the position tracing window moved to. According to this, velocity of each tracing window was calculated by CMW. The maximum correlation coefficient is adopted to analyze the velocity of plasma bubbles due to its better performance than histogram of oriented gradient. All‐sky images from Hainan Fuke, an example on 17 September 2014, are analyzed to investigate the plasma bubble drift velocities using CMW. For comparison and validation, EPBs motions obtained from three traditional methods are also investigated. The advantages and disadvantages of using CMW are discussed. The results of CMW are compared with slant total electron contents data and show a good consistency, but some errors are also discussed.

A study on the evolution of plasma bubbles using the single station‐multisatellite and multistation‐single satellite techniques

AbstractThe characteristics of plasma bubble‐induced ionospheric irregularities were analyzed by estimating the drift velocity of plasma bubbles, their percentage of occurrence, seasonal/LT distributions, and east‐west spatial width using multifrequency Global Navigation Satellite Systems (GNSS) receiver systems at Trivandrum, Bangalore, Hyderabad, Delhi, and Hanle. Two techniques, namely, single station‐multisatellite and multistation‐single satellite observations, were used in the analysis by tracking two geostationary Indian satellites GSAT‐8 (PRN 127) and GSAT‐10 (PRN 128) for the year 2014. In addition, GNSS receiver data from a recently commissioned near‐equatorial station at Changanacherry, Kerala, were used to evaluate 15 plasma bubble events during the period of 29 October 2015 to 31 October 2016. Using, single station‐multisatellite technique, the distribution of drift velocity measurements from plasma bubble scintillations lies in the range of 120–140 m/s for Trivandrum, Changanacherry, and Hyderabad. For Bangalore, and Delhi, the most probable ranges of drift velocity were 120–160 m/s and 80–100 m/s, respectively. The highest probable value of east‐west width of plasma bubble evolution for Trivandrum and Changanacherry was within the range of 100–150 km. However, the same at Bangalore and Hyderabad was in the range of 150–200 km and 100–200 km for Delhi. The maximum probable LT of occurrence of plasma bubble is premidnight sector over the equator. The comparison of the characteristics of plasma bubble evolution over equatorial/low‐latitude Indian sector considering six stations by employing two unique techniques and an objective correlation method is the first time attempt.

Effects of solar and geomagnetic activities on the zonal drift of equatorial plasma bubbles

AbstractEquatorial plasma bubbles are mostly generated in the postsunset sector and then move in the zonal direction. Plasma bubbles can last for several hours and move over hundreds of kilometers (even more than 1000 km). In this study, we use measurements of ion density by the Communication/Navigation Outage Forecasting System satellite to determine the orbit‐averaged drift velocity of plasma bubbles. The objective of the study is to identify the dependence of the bubble drift on the solar radio flux and geomagnetic activities. In total, 5463 drift velocities are derived over May 2008 to April 2014, and a statistical analysis is performed. The average pattern of the bubble drift is in good agreement with the zonal drift of the equatorial F region plasma. The zonal drift velocity of plasma bubbles increases with the solar radio flux. However, the increase shows different features at different local times. Geomagnetic activities cause a decrease of the eastward drift velocity of plasma bubbles, equivalent to the occurrence of a westward drift, through disturbance dynamo process. In particular, the decrease of the eastward drift velocity appears to become accelerated when the Dst index is smaller than −60 nT or Kp is larger than 4.

Simultaneous optical measurements of equatorial plasma bubble (EPB) from Kolhapur (16.8°N, 74.2°E) and Gadanki (13.5°N, 79.2°E)

In this paper, we study the Equatorial Plasma Bubble (EPB) features using All sky imager (ASI) observations of O(1D) 630.0nm night airglow emission from Kolhapur (16.8°N, 74.2°E, 10.6°N dip lat.) and Gadanki (13.5°N, 79.2°E, 6.5°N dip lat.) during March 2012. The optical data was supported by the ionosonde measurements from Tirunelveli (8.7°N, 77.8°E, 0.5°N dip lat.) which revealed the occurrence of equatorial spread-F. The EPBs were monitored at both locations as nearly north–south aligned intensity depleted regions. We computed east–west plasma drift velocity over Kolhapur and Gadanki for the nights having coordinated measurements. Also, the observed plasma bubble drift velocities are compared with the zonal neutral wind velocities obtained from the HWM-07 model and the empirical drift model of England and Immel (2012). We observed that, generally, the mean zonal drift velocities of the plasma bubbles tend to decrease with local time (after midnight). Our results reveal the drift velocity noted in Kolhapur data varies from 124m/s to 181.8m/s, while from the Gadanki data show the drift velocity to range from 116.3m/s to 160.3m/s.

Comparison of nighttime zonal neutral winds and equatorial plasma bubble drift velocities over Brazil

We present results from the first extended period of coincident observations of thermospheric zonal neutral winds and equatorial plasma bubble (EPB) zonal drift velocities over northeastern Brazil during the October to December months of 2009 and 2010. The EPB zonal drift velocities are estimated utilizing images of the O I 630.0 nm emissions recorded by a wide‐angle imaging system at Cajazeiras. Thermospheric neutral wind estimates are based upon common volume observations made by a bistatic Fabry‐Perot interferometer (FPI) experiment using FPIs located at Cajazeiras and Cariri in Brazil observing the Doppler shift of the O I 630.0 nm emission. The results illustrate a similar pattern of nighttime and night‐to‐night variations in the zonal neutral winds and EPB zonal drift velocities. In general, the geomagnetic zonal neutral winds and the EPB velocities show an excellent agreement illustrating that the F region dynamo is fully developed. However, in the early evening hours the EPB zonal speed is slower than that of the background winds on several occasions. We conclude that this indicates that during the bubble evolution period in the early evening the F region dynamo is not fully activated.

Simultaneous observations of equatorial plasma depletion by IMAGE and ROCSAT‐1 satellites

Simultaneous observations of the equatorial ionosphere by the ROCSAT‐1 and IMAGE satellites were used to study zonal propagation characteristics of equatorial plasma bubbles. IMAGE far ultraviolet (FUV) nighttime images have indicated signatures of depression in the brightness of equatorial airglow arcs. Using the list of airglow brightness depression events observed by IMAGE, we surveyed ROCSAT‐1 Ionospheric Plasma and Electrodynamics Instrument data and found three ROCSAT‐1 passes with simultaneous plasma observations in the same local time sector. Brightness depressions seen in FUV images are found to correlate with equatorial plasma bubbles detected by ROCSAT‐1 at 600 km altitude with a separation distance between bubbles varying from 300 to 1000 km. Successive FUV images are averaged to produce a keogram with UT versus longitude, which is then used to deduce zonal drift velocity for plasma density depletions. The drift speed determined from FUV images is compared with ion drift velocities measured by ROCSAT‐1. The analysis indicates that the bubbles drift faster than the ambient plasma. The relative zonal velocity of plasma bubbles with respect to the ambient plasma is large, over 200 m/s when plasma bubbles are first created in the early evening hours. The relative zonal velocity decreases rapidly with magnetic local time (MLT) from over 200 m/s at 20 MLT to ∼30 m/s at 22 MLT. ROCSAT‐1 has detected quasiperiodic structures for equatorial plasma bubbles, corresponding to the quasiperiodic appearance of FUV brightness depression. The quasiperiodic structure of plasma bubbles has been interpreted as evidence of zonal propagation of atmospheric gravity waves with a wavelength in the range of about 300–1000 km. The observed zonal drift velocity of plasma bubbles is shown to be consistent with the horizontal propagation velocity of acoustic gravity waves. The dependence of the horizontal group velocity of acoustic gravity waves on various parameters is further investigated. The vertical wavelength of acoustic gravity waves is found to be the most sensitive parameter for determining the horizontal group velocity of acoustic gravity waves and thus presumably the zonal propagation of equatorial plasma bubbles. The relative zonal propagation of equatorial plasma bubbles might imply strong coupling between atmospheric gravity waves and the Rayleigh‐Taylor instability. The obtained results suggest that atmospheric gravity waves play an important role not only for initiating plasma bubbles but also for maintaining the horizontal motion of equatorial plasma bubbles.

Equatorial F-region plasma depletion drifts: latitudinal and seasonal variations

Abstract. The equatorial ionospheric irregularities have been observed in the past few years by different techniques (e.g. ground-based radar, digisonde, GPS, optical instruments, in situ satellite and rocket instrumentation), and its time evolution and propagation characteristics can be used to study important aspects of ionospheric dynamics and thermosphere-ionosphere coupling. At present, one of the most powerful optical techniques to study the large-scale ionospheric irregularities is the all-sky imaging photometer system, which normally measures the strong F-region nightglow 630 nm emission from atomic oxygen. The monochromatic OI 630 nm emission images usually show quasi-north-south magnetic field-aligned intensity depletion bands, which are the bottomside optical signatures of large-scale F-region plasma irregularities (also called plasma bubbles). The zonal drift velocities of the plasma bubbles can be inferred from the space-time displacement of the dark structures (low intensity regions) seen on the images. In this study, images obtained with an all-sky imaging photometer, using the OI 630 nm nightglow emission, from Cachoeira Paulista (22.7° S, 45° W, 15.8° S dip latitude), Brazil, have been used to determine the nocturnal monthly and latitudinal variation characteristics of the zonal plasma bubble drift velocities in the low latitude (16.7° S to 28.7° S) region. The east and west walls of the plasma bubble show a different evolution with time. The method used here is based on the western wall of the bubble, which presents a more stable behavior. Also, the observed zonal plasma bubble drift velocities are compared with the thermospheric zonal neutral wind velocities obtained from the HWM-90 model (Hedin et al., 1991) to investigate the thermosphere-ionosphere coupling. Salient features from this study are presented and discussed.Key words. Ionosphere (ionosphere-atmosphere interactions; ionospheric irregularities; instruments and techniques)