**3. Equatorial plasma bubble by GPS**

The study of the spatial and temporal progress of EPBs formed in the ionosphere has been carried out using two different techniques radio waves as well as optical imaging over the globe. The optical imaging techniques have a limited coverage area, but have high resolution, while the radio wave techniques have a wide coverage area but can have low resolution for the ionospheric studies. The all sky imager is widely used instrument for the optical imaging of plasma bubble while GPS receivers used to study the ionospheric irregularities using radio waves. The **Figure 2** illustrates the occurrence of EPBs as D1 and D2 in the TEC measurements. The nocturnal variation in TEC with respect to local time (Indian Standard Time) observed on April 1, 2011 and April 2, 2011. The EPBs in TEC is indicated by D1 and D2. The occurrence period of EPBs is indicated by rectangular in the **Figure 2**.

Nishioka et al. [38] did a comprehensive study of the occurrence of plasma bubbles using ground-based GPS receiver from dip equator stations. They have considered Data from 2000 to 2006 from a network of 23 GPS receivers such as network of International GNSS Service (IGS), a GPS network by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and Scripps Orbit Permanent Array Center (SOPAC), etc. They found a different characteristic rate of EPB occurrence in different regions also the dependency of the occurrence on the solar activity was different among the regions. They concluded that the sunset time lag effect plays an important role for the monthly variation and two asymmetries which could not be explained with the sunset time lag scenario (1) asymmetry between two solstices and (2) asymmetry between two equinoxes. They also found that the plasma bubble occurrence was high and constant for a stations having height on the dip equator (HODE) was <700 km and it is began to decrease for stations having HODE was higher than 700 km and was almost zero for the stations having HODE

**61**

the bubbles.

magnetic cycle is also studied.

*Study of Equatorial Plasma Bubbles Using ASI and GPS Systems*

higher than 900 km.. They defined HODE as shown in figure as an altitude of the geomagnetic field line on the magnetic dip equator which passes 400 km altitude

*The nocturnal variation in TEC with respect to local time (Indian Standard Time) observed on 01-02 April 2011. The EPBs in TEC is indicated by D1 and D2. The occurrence period of EPBs is indicated by rectangular.*

Haase et al. [39] have studied the Propagation of plasma bubbles over Brazil from GPS and airglow data. They have mapped the airglow data to the GPS lineof-sight geometry for the direct comparison and revealing of resolvable westward tilt of the plasma depletion that may be due to vertical shear. They found the direct correspondence between integrated electron content (IEC) depletions and characteristics of depletions seen in horizontal airglow images, with very consistent

The EPB is monitored by using data provided by ground-based GNSS receiver Network over the South American continent by Takahashi et al. [40]. They have mapped the total electron content which could cover almost all of the continent within 4000 km distance in longitude and latitude. The TEC variability is monitored continuously with a time resolution of 10 min. The bubble structures are compared with simultaneous observations of OI630 nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W). The formation and development of the bubble and eastward drifting features were successfully monitored and analyzed in this study. They found that the plasma bubbles observed during the December solstice has a periodic spacing, which is a periodic seeding mechanism of

The occurrence and characteristics of EPBs have been analyzed using the TEC data from GPS receivers over Hong Kong during 2001–2012 by Kumar et al. [41]. They found that the maximum occurrences of EPBs during the equinoctial months while minimum during the December solstice throughout 2001–2012. They also used the TEC data from different GNSS receivers over the Hong Kong. They concluded that the asymmetry in the EPB occurrences could be caused by the suppression of the growth rate of the instability by inter hemispheric neutral winds, which is known to be a primary cause for triggering EPB or ESF. The influence of solar and

observations of scale, amplitude, drift velocity and timing.

*DOI: http://dx.doi.org/10.5772/intechopen.85604*

above a site of GPS receiver.

**Figure 2.**

*Study of Equatorial Plasma Bubbles Using ASI and GPS Systems DOI: http://dx.doi.org/10.5772/intechopen.85604*

#### **Figure 2.**

*Geographic Information Systems in Geospatial Intelligence*

(*tL*1) at L2. The resulting equation is (Jain et al., 2011),

<sup>∆</sup>(*t*)= 40.3 <sup>×</sup> *TEC* <sup>×</sup> ( *fL*<sup>1</sup>

60°. The STEC is measured at every 30 s by the GPS receiver.

*TEC* = \_\_\_\_ <sup>1</sup>

**3. Equatorial plasma bubble by GPS**

∆(*t*) = *tL*<sup>1</sup> − *tL*<sup>2</sup> (1)

Here, ∆(*t*) is a time delay in the pseudo-range (*tL*1) at L1 and pseudo-range

where *fL*1 and *fL*2 are the group path lengths corresponding to the high and low GPS frequencies *fL*<sup>1</sup> = 1575.42 *MHz* and *fL*<sup>2</sup> = 1227.60 *MHz*, respectively and "*c*" is speed of light in vacuum. The TEC can be obtained by rewrite above equation as,

> <sup>2</sup> × *fL*<sup>2</sup> 2 \_\_\_\_\_\_\_\_\_ ( *fL*<sup>1</sup> <sup>2</sup> − *fL*<sup>2</sup> 2 )

The signal from different GPS satellites, at random elevation angles, recorded as a TEC measurements. These different satellites are identified by a pseudo-random number (PRN). The portions of the ionosphere cross by GPS signal depend on the elevation angle of GPS satellite. Therefore, in the present work the TEC data of only those GPS satellites, having elevation angles above 30° to avoid the multipath effect of signals, are considered. The maximum elevation angle over Hyderabad station is

The study of the spatial and temporal progress of EPBs formed in the ionosphere has been carried out using two different techniques radio waves as well as optical imaging over the globe. The optical imaging techniques have a limited coverage area, but have high resolution, while the radio wave techniques have a wide coverage area but can have low resolution for the ionospheric studies. The all sky imager is widely used instrument for the optical imaging of plasma bubble while GPS receivers used to study the ionospheric irregularities using radio waves. The **Figure 2** illustrates the occurrence of EPBs as D1 and D2 in the TEC measurements. The nocturnal variation in TEC with respect to local time (Indian Standard Time) observed on April 1, 2011 and April 2, 2011. The EPBs in TEC is indicated by D1 and D2. The occurrence period of EPBs is indicated by rectangu-

Nishioka et al. [38] did a comprehensive study of the occurrence of plasma bubbles using ground-based GPS receiver from dip equator stations. They have considered Data from 2000 to 2006 from a network of 23 GPS receivers such as network of International GNSS Service (IGS), a GPS network by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and Scripps Orbit Permanent Array Center (SOPAC), etc. They found a different characteristic rate of EPB occurrence in different regions also the dependency of the occurrence on the solar activity was different among the regions. They concluded that the sunset time lag effect plays an important role for the monthly variation and two asymmetries which could not be explained with the sunset time lag scenario (1) asymmetry between two solstices and (2) asymmetry between two equinoxes. They also found that the plasma bubble occurrence was high and constant for a stations having height on the dip equator (HODE) was <700 km and it is began to decrease for stations having HODE was higher than 700 km and was almost zero for the stations having HODE

40.3 <sup>×</sup> *<sup>c</sup>* <sup>×</sup> *fL*<sup>1</sup>

<sup>2</sup> − *fL*<sup>2</sup> <sup>2</sup> ) \_\_\_\_\_\_\_\_\_ *c* × *fL*<sup>1</sup> <sup>2</sup> × *fL*<sup>2</sup>

<sup>2</sup> (2)

× ∆(*t*) (3)

**60**

lar in the **Figure 2**.

*The nocturnal variation in TEC with respect to local time (Indian Standard Time) observed on 01-02 April 2011. The EPBs in TEC is indicated by D1 and D2. The occurrence period of EPBs is indicated by rectangular.*

higher than 900 km.. They defined HODE as shown in figure as an altitude of the geomagnetic field line on the magnetic dip equator which passes 400 km altitude above a site of GPS receiver.

Haase et al. [39] have studied the Propagation of plasma bubbles over Brazil from GPS and airglow data. They have mapped the airglow data to the GPS lineof-sight geometry for the direct comparison and revealing of resolvable westward tilt of the plasma depletion that may be due to vertical shear. They found the direct correspondence between integrated electron content (IEC) depletions and characteristics of depletions seen in horizontal airglow images, with very consistent observations of scale, amplitude, drift velocity and timing.

The EPB is monitored by using data provided by ground-based GNSS receiver Network over the South American continent by Takahashi et al. [40]. They have mapped the total electron content which could cover almost all of the continent within 4000 km distance in longitude and latitude. The TEC variability is monitored continuously with a time resolution of 10 min. The bubble structures are compared with simultaneous observations of OI630 nm all-sky image at Cachoeira Paulista (22.7°S, 45.0°W) and Cariri (7.4°S, 36.5°W). The formation and development of the bubble and eastward drifting features were successfully monitored and analyzed in this study. They found that the plasma bubbles observed during the December solstice has a periodic spacing, which is a periodic seeding mechanism of the bubbles.

The occurrence and characteristics of EPBs have been analyzed using the TEC data from GPS receivers over Hong Kong during 2001–2012 by Kumar et al. [41]. They found that the maximum occurrences of EPBs during the equinoctial months while minimum during the December solstice throughout 2001–2012. They also used the TEC data from different GNSS receivers over the Hong Kong. They concluded that the asymmetry in the EPB occurrences could be caused by the suppression of the growth rate of the instability by inter hemispheric neutral winds, which is known to be a primary cause for triggering EPB or ESF. The influence of solar and magnetic cycle is also studied.

Magdaleno et al. [42] studied the Climatology characterization of EPB using GPS data for the period 1998–2008. They have considered the slant total electron content (sTEC) derived from global positioning system (GPS) data from 67 International GNSS Service (IGS) stations distributed worldwide around the geomagnetic equator and the region of the ionospheric equatorial anomaly (IEA). The Ionospheric Bubble Seeker method is used to detect and distinguishes TEC depletions associated with EPBs. They found the largest occurrence rate of EPBs over the South America-Africa region and shown that the occurrence rate goes on decreasing as we go from the magnetic equator to higher latitudes.

First time study of the occurrence frequency of EPB over West Africa is done by Okoh et al. [42] using an ASI and GNSS Receivers from June 9, 2015 to January 31, 2017. This ASI is installed at Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S) which covers almost the entire airspace of Nigeria. They found most occurrences of EPB during equinoxes and least occurrences during solstices also the occurrence rate of EPBs were highest around local midnight and lower for hours farther away. They also observed that the on/off status of EPB in airglow and GNSS observations are in 70% agreement.

Kumar [43] has studied the morphology of the EPB with respect of the solar activity over the Indian region from 2007 to 2012. The sTEC data are also considered from ground-based GPS receiver at Hyderabad (17.41° N, 78.55° E, Mag Lat 08.81° N) and two receivers at Bangalore (13.02°/13.03° N, 77.57°/77.51° E, Mag. Lat. 04.53°/04.55° N) in Indian region. He also observes that the occurrence of EPB is maximum in equinoctial months. He concluded that the equinox maximum in EPB occurrences for high solar activity years may be caused by the vertical F-layer drift due to pre-reversal electric field (PRE). This is expected to be maximum when daynight terminator aligns with the magnetic meridian, i.e., during the equinox months, whereas maximum occurrences during the solstice months of solar minimum could be caused by the seed perturbation in plasma density induced by gravity waves from tropospheric origins. The seasonal dependence of the EPBs occurrence is also studied.

Recently, Takahashi et al. [44] in detail studied the Occurrences of EPB (EPBs) and medium-scale traveling ionospheric disturbances (MSTIDs). They have used the GPS satellite data-based total electron content mapping, ionograms, and 630 nm all-sky airglow images observed over the South American continent during the period of 2014–2015. They observed a close relationship between the interbubble distance and the horizontal wavelength of the MSTIDs. They concluded that the MSTIDs are followed by EPBs primarily in the afternoon to the evening period due to the strong tropospheric convective activities (cold fronts and/or intertropical convergence zones) and the MSTIDs could be one of the seeding sources of EPBs.

Barros et al. [45] used ground-based network of GNSS receivers used to monitor EPB (EPBs) by mapping the total electron content (TEC map). They considered TEC data from GNSS receivers over South America for the period between November 2012 and January 2016. They found the latitudinal gradient varying from 123 ms<sup>−</sup><sup>1</sup> at the Equator to 65 ms<sup>−</sup><sup>1</sup> for 35° S latitude in the zonal drift velocities of the EPBs. They concluded that the latitudinal gradient in the inter-bubble distances seems to be related to the difference in the zonal drift velocity of the EPB from the Equator to middle latitudes and to the difference in the westward movement of the terminator.

Over the Thailand region, the statistical analysis of the separation distance between EPB is carried by Bumrungkit et al. [46]. The separation distance between EPBs is calculated using the Haversine formula technique in which the dual frequency GPS signal used. Their results show that the separation distances between EPBs on disturbed days in 2015 are in the range of 100–1200 km.

**63**

*Study of Equatorial Plasma Bubbles Using ASI and GPS Systems*

The effects of the R-T instability and EPB on the GPS signal are also studied by Panda et al. [47]. They have considered various instances of ionospheric disturbances triggered by natural processes such as earthquakes and volcanic eruption in the recent decade to investigate the spatiotemporal and seasonal effects of ionospheric irregularities on the GNSS signals. They found that the co-seismic ionospheric disturbances are difficult to study at the equatorial region due to mask of the EPBs but over the high latitude region these co-seismic ionospheric anomaly

The effects of plasma bubbles on the GPS signal path and the positioning issue is studied by Moraes et al. [48]. The analysis focused on data from November 15, 2014 to November 30, 2014 and from February 4, 2015 to February 18, 2015, at São José DOS Campos, Brazil. They found that passing through the EPB, the radio signal may take a longer propagation path and have more losses of signal lock. The posi-

Rajesh et al. [49] demonstrate that the EPBs appear to extend toward equator or pole as a result of the descending F layer and the recombination between free electrons of F layer and ions of the E layer at different latitudes. The apparent extension would vary from night to night depending on the post sunset vertical velocity of the F layer. Over equatorial region background electron density may be playing a vital role in providing the equinoctial asymmetry in the occurrence of ESF irregularities [16]. The effect of equatorial height variation of F region on ionospheric irregularities in the low latitude F region is also an important aspect. The apex height is also contributing in the occurrence of EPBs. Haaser et al. [50] suggested that EPBs occurred near the geomagnetic dip equator (<20° dip), typically within the nighttime ionospheric anomaly, while plasma blobs occurred mainly away from the geomagnetic dip equator, outside the anomaly regions (>15° dip). Yokoyama et al. [51] reported that the zonal structure of the plasma blobs in the northern hemisphere corresponded to that of the topside EPB in the southern hemisphere on a common magnetic flux tube, although the plasma blobs and the EPBs are separated

Based on satellite data, Le et al. [52] reported that the localized eastward polarized electric field plays an important role in the creation of EPBs and plasma blobs. The strength of localized eastward polarized electric field is may depend on the virtual height of the F region at dip equator. They are directly proportional to each other. The fluctuations in the virtual height of the equatorial F region creates oscillations of F region in wave nature along the latitudes which is started from the magnetic equator to low latitude (±20°) crest of a wave. The background plasma density and fluctuations in plasma density are important factors for characterizing

The eastward polarized electric field helps to combine flowing plasma with the background plasma over low latitude. Due to this combination, EPBs are generated over low latitude regions. According to literature serve, it is clear that ionospheric irregularities like EPBs or plasma blobs are not observed regularly. This may happen because of low combination or no combination of the plasma. Thus, this combination depends on the strength of eastward polarized electric field. If the strength of eastward polarized electric field is very low, then combinations will not possible while, for its particular value, low energy regions created which are captured in optical data as dark regions. These dark regions are also called as EPBs. If the strength of eastward polarized electric field is very high then, the rate of recombination will increase and high energy regions may create over low latitude regions. These high energy regions cause the enhancement in intensity of OI 630.0 nm emission, called as plasma blobs. The strength of eastward polarized electric field is also depends on the virtual height of F region at dip equator. Our results and analysis

*DOI: http://dx.doi.org/10.5772/intechopen.85604*

tioning errors may result in these cases.

by more than 20° in latitude.

plasma blobs [53].

van be studied.

*Geographic Information Systems in Geospatial Intelligence*

magnetic equator to higher latitudes.

observations are in 70% agreement.

Magdaleno et al. [42] studied the Climatology characterization of EPB using GPS data for the period 1998–2008. They have considered the slant total electron content (sTEC) derived from global positioning system (GPS) data from 67 International GNSS Service (IGS) stations distributed worldwide around the geomagnetic equator and the region of the ionospheric equatorial anomaly (IEA). The Ionospheric Bubble Seeker method is used to detect and distinguishes TEC depletions associated with EPBs. They found the largest occurrence rate of EPBs over the South America-Africa region and shown that the occurrence rate goes on decreasing as we go from the

First time study of the occurrence frequency of EPB over West Africa is done by Okoh et al. [42] using an ASI and GNSS Receivers from June 9, 2015 to January 31, 2017. This ASI is installed at Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S) which covers almost the entire airspace of Nigeria. They found most occurrences of EPB during equinoxes and least occurrences during solstices also the occurrence rate of EPBs were highest around local midnight and lower for hours farther away. They also observed that the on/off status of EPB in airglow and GNSS

Kumar [43] has studied the morphology of the EPB with respect of the solar activity over the Indian region from 2007 to 2012. The sTEC data are also considered from ground-based GPS receiver at Hyderabad (17.41° N, 78.55° E, Mag Lat 08.81° N) and two receivers at Bangalore (13.02°/13.03° N, 77.57°/77.51° E, Mag. Lat. 04.53°/04.55° N) in Indian region. He also observes that the occurrence of EPB is maximum in equinoctial months. He concluded that the equinox maximum in EPB occurrences for high solar activity years may be caused by the vertical F-layer drift due to pre-reversal electric field (PRE). This is expected to be maximum when daynight terminator aligns with the magnetic meridian, i.e., during the equinox months, whereas maximum occurrences during the solstice months of solar minimum could be caused by the seed perturbation in plasma density induced by gravity waves from tropospheric

Recently, Takahashi et al. [44] in detail studied the Occurrences of EPB (EPBs) and medium-scale traveling ionospheric disturbances (MSTIDs). They have used the GPS satellite data-based total electron content mapping, ionograms, and 630 nm all-sky airglow images observed over the South American continent during the period of 2014–2015. They observed a close relationship between the interbubble distance and the horizontal wavelength of the MSTIDs. They concluded that the MSTIDs are followed by EPBs primarily in the afternoon to the evening period due to the strong tropospheric convective activities (cold fronts and/or intertropical convergence zones) and the MSTIDs could be one of the seeding

Barros et al. [45] used ground-based network of GNSS receivers used to monitor EPB (EPBs) by mapping the total electron content (TEC map). They considered TEC data from GNSS receivers over South America for the period between November 2012 and January 2016. They found the latitudinal gradient varying from

the EPBs. They concluded that the latitudinal gradient in the inter-bubble distances seems to be related to the difference in the zonal drift velocity of the EPB from the Equator to middle latitudes and to the difference in the westward movement of the

Over the Thailand region, the statistical analysis of the separation distance between EPB is carried by Bumrungkit et al. [46]. The separation distance between EPBs is calculated using the Haversine formula technique in which the dual frequency GPS signal used. Their results show that the separation distances between

EPBs on disturbed days in 2015 are in the range of 100–1200 km.

for 35° S latitude in the zonal drift velocities of

origins. The seasonal dependence of the EPBs occurrence is also studied.

**62**

sources of EPBs.

at the Equator to 65 ms<sup>−</sup><sup>1</sup>

123 ms<sup>−</sup><sup>1</sup>

terminator.

The effects of the R-T instability and EPB on the GPS signal are also studied by Panda et al. [47]. They have considered various instances of ionospheric disturbances triggered by natural processes such as earthquakes and volcanic eruption in the recent decade to investigate the spatiotemporal and seasonal effects of ionospheric irregularities on the GNSS signals. They found that the co-seismic ionospheric disturbances are difficult to study at the equatorial region due to mask of the EPBs but over the high latitude region these co-seismic ionospheric anomaly van be studied.

The effects of plasma bubbles on the GPS signal path and the positioning issue is studied by Moraes et al. [48]. The analysis focused on data from November 15, 2014 to November 30, 2014 and from February 4, 2015 to February 18, 2015, at São José DOS Campos, Brazil. They found that passing through the EPB, the radio signal may take a longer propagation path and have more losses of signal lock. The positioning errors may result in these cases.

Rajesh et al. [49] demonstrate that the EPBs appear to extend toward equator or pole as a result of the descending F layer and the recombination between free electrons of F layer and ions of the E layer at different latitudes. The apparent extension would vary from night to night depending on the post sunset vertical velocity of the F layer. Over equatorial region background electron density may be playing a vital role in providing the equinoctial asymmetry in the occurrence of ESF irregularities [16].

The effect of equatorial height variation of F region on ionospheric irregularities in the low latitude F region is also an important aspect. The apex height is also contributing in the occurrence of EPBs. Haaser et al. [50] suggested that EPBs occurred near the geomagnetic dip equator (<20° dip), typically within the nighttime ionospheric anomaly, while plasma blobs occurred mainly away from the geomagnetic dip equator, outside the anomaly regions (>15° dip). Yokoyama et al. [51] reported that the zonal structure of the plasma blobs in the northern hemisphere corresponded to that of the topside EPB in the southern hemisphere on a common magnetic flux tube, although the plasma blobs and the EPBs are separated by more than 20° in latitude.

Based on satellite data, Le et al. [52] reported that the localized eastward polarized electric field plays an important role in the creation of EPBs and plasma blobs. The strength of localized eastward polarized electric field is may depend on the virtual height of the F region at dip equator. They are directly proportional to each other. The fluctuations in the virtual height of the equatorial F region creates oscillations of F region in wave nature along the latitudes which is started from the magnetic equator to low latitude (±20°) crest of a wave. The background plasma density and fluctuations in plasma density are important factors for characterizing plasma blobs [53].

The eastward polarized electric field helps to combine flowing plasma with the background plasma over low latitude. Due to this combination, EPBs are generated over low latitude regions. According to literature serve, it is clear that ionospheric irregularities like EPBs or plasma blobs are not observed regularly. This may happen because of low combination or no combination of the plasma. Thus, this combination depends on the strength of eastward polarized electric field. If the strength of eastward polarized electric field is very low, then combinations will not possible while, for its particular value, low energy regions created which are captured in optical data as dark regions. These dark regions are also called as EPBs. If the strength of eastward polarized electric field is very high then, the rate of recombination will increase and high energy regions may create over low latitude regions. These high energy regions cause the enhancement in intensity of OI 630.0 nm emission, called as plasma blobs. The strength of eastward polarized electric field is also depends on the virtual height of F region at dip equator. Our results and analysis

gives strong support for this statement. Herein, one more thing is that the flowing of plasma is in wavy nature, travel from the dip equator to low latitude. This nature of the flowing of plasma also makes an effect on the combination or recombination of plasma over low latitude regions. Thus to explain this nonlinear problem we need of more theoretical models.
