Ann. Geophys., 35, 413–422, 2017 www.ann-geophys.net/35/413/2017/ doi:10.5194/angeo-35-413-2017 © Author(s) 2017. CC Attribution 3.0 License. Rocket in situ observation of equatorial plasma irregularities in the region between E and F layers over Brazil Siomel Savio Odriozola1,2, Francisco Carlos de Meneses Jr.1,3, Polinaya Muralikrishna1, Alexandre Alvares Pimenta1, and Esfhan Alam Kherani1 1National Institute for Space Research – INPE, Av. dos Astronautas, 1758, Jd. Granja-CEP: 12227-010 SJC, SP, Brazil 2Department of Space Geophysics, Institute of Geophysics and Astronomy – IGA, Calle 212, 2906, La Coronela, La Lisa, Havana, Cuba 3State Key Laboratory of Space Weather, National Space Science Center NSSC, Chinese Academy of Sciences (CAS), No. 1 Nanertiao, Zhongguancun, Haidian district, 100190, Beijing, China Correspondence to: Siomel Savio Odriozola ([email protected]) Received: 30 July 2016 – Revised: 23 February 2017 – Accepted: 23 February 2017 – Published: 16 March 2017 Abstract. A two-stage VS-30 Orion rocket was launched LaBelle, 1998; Muralikrishna et al., 2004). Studies using in from the equatorial rocket launching station in Alcântara, situ measurements of equatorial nighttime E region irregular- Brazil, on 8 December 2012 soon after sunset (19:00 LT), ities, however, are quite a few, as noted by Sinha et al.(2011). carrying a Langmuir probe operating alternately in swept and The lack of references is most noticeable when it comes to constant bias modes. At the time of launch, ground equip- the intermediate region between the E and F layers ( ∼ 130– ment operated at equatorial stations showed rapid rise in the 300 km). base of the F layer, indicating the pre-reversal enhancement Although data from other studies show irregular structures of the F region vertical drift and creating ionospheric con- in the electron concentration in the F valley region (Abdu ditions favorable for the generation of plasma bubbles. Ver- et al., 1991; Vickrey et al., 1984; Sinha et al., 1999; Raizada tical profiles of electron density estimated from Langmuir and Sinha, 2000; Hysell et al., 2005; Muralikrishna and probe data showed wave patterns and small- and medium- Abdu, 2006), up to now, only Vickrey et al.(1984) and scale plasma irregularities in the valley region (100–300 km) Raizada and Sinha(2000) have analyzed the irregularities during the rocket upleg and downleg. These irregularities re- detected in this region. Both studies used measurements ob- semble those detected by the very high frequency (VHF) tained using a Langmuir probe onboard rockets that flew in radar installed at Jicamarca and so-called equatorial quasi- low-latitude trajectories. periodic echoes. We present evidence suggesting that these Plasma irregularities located at typical E and F valley observations could be the first detection of this type of irreg- heights have been studied before using VHF radar observa- ularity made by instruments onboard a rocket. tions. Woodman and Chau(2001) were the first to character- Keywords. Ionosphere (equatorial ionosphere; plasma tem- ize irregular structures in E and lower F regions using obser- perature and density; plasma waves and instabilities) vations from the Jicamarca Radio Observatory (JRO). They used the term “Equatorial QuasiPeriodic” or EQP to label these irregular echoes. More recently, Chau and Hysell(2004) reported large- 1 Introduction scale plasma waves at high altitude in the E region over Jicamarca and around twilight. Using an aperture synthesis Many ionospheric studies using rocket-borne probes have fo- imaging technique, the authors were able to show a striking cused their attention on nighttime equatorial plasma irregu- and complex set of striations evidencing different levels of larities. A significant part of these studies has been devoted signal-to-noise ratio (SNR), representing a range of different to the analysis of irregularities located at typical F region electron density regions. heights (e.g., Rino et al., 1981; LaBelle et al., 1986; Jahn and Published by Copernicus Publications on behalf of the European Geosciences Union. 414 S. Savio Odriozola et al.: Rocket observation of equatorial plasma irregularities Figure 1. Rocket trajectory (a) and flight details (b). The blue parabola in (b) is the projection of the trajectory onto a vertical plane. In the equatorial region over Brazil, a statistical study with station in Alcântara (CLA) located at 2.4◦ S, 44.4◦ W (dip observations made during 581 nights (from 2001 to 2008) latitude 5.5◦ S), Brazil, on 8 December 2012 (LT D UT − 3). was conducted by Kherani et al.(2012) using a low-power The launch time (19:00 LT) was carefully selected in order to coherent scatter radar located at the São Luís equatorial sta- intercept irregular structures that might arise soon after sun- tion. Similar to the results of Woodman and Chau(2001), the set. Flight parameters and the rocket trajectory are shown in structures were observed during occurrences of an ascending Fig.1. irregular bottom-type or bottom-side F layer and at the same As can be seen, the trajectory was toward the magnetic time or prior to an ascending and well-developed plume. Fur- equator in the northeast. The horizontal range was ∼ 384 km, thermore, and unlike Jicamarca, the research showed that the and the apogee of the rocket reached typical F region alti- frequency of occurrence of this type of irregularity was ex- tudes (∼ 428 km). The flight was tracked by three radars over tremely low and the few observations of such events were 647 s. The rocket carried three instruments: a two-axis mag- concentrated in summer months (Southern Hemisphere) and netometer, a GPS receiver prototype and a conical Langmuir years of high solar activity. probe (CLP). Data from a GPS receiver confirm the vehicle’s In this work, the vertical distribution of electron density trajectory provided by the radars. From magnetometer data, was obtained using a Langmuir probe as a payload of a two- it was possible to estimate the rotation (∼ 5 rps) and preces- stage rocket, which flew toward the magnetic equator from sion (∼ 0:09 rps) of the rocket along the flight. the rocket launching station in Alcântara, Brazil. Both the up- leg and downleg profiles, showed small- and medium-scale 2.2 Digisonde observations plasma irregularities in the intermediate region between the E and F layers. Given the characteristics of these profiles, in ◦ ◦ our results we propose that these irregularities are the EQP Ground stations located at São Luís (2.6 S, 44.2 W, dip lat- ◦ ◦ ◦ ◦ irregularities only detected, so far, by VHF coherent scatter itude 6 S) and Fortaleza (3.9 S, 38.4 W, dip latitude 15 S) radars. In the next section, the rocket flight and payload de- regularly probe the ionosphere using digisondes at the same tails, ionosonde observations and Langmuir probe data will time of rocket launch. São Luís station is located only 35 km be presented. Later, our observations will be compared with south of CLA; therefore, it was used to monitor the ideal con- a range time intensity (RTI) map previously obtained at Jica- ditions (pre-launch rocket) that precede the bubble’s onset, marca Radio Observatory. We will conclude by summing up while Fortaleza station is positioned ∼ 684 km southeast of our results and considerations. the launch center. Evidence of the presence of plasma irreg- ularities was observed in the ionograms of both stations. A sequence of eight ionograms taken at São Luís around 2 Observations the time of launching are shown in Fig.2. Until 19:00 LT, ionograms over this station do not exhibit any spread echoes. 0 2.1 Rocket flight Minimum virtual height of the F layer (hminF), however, in- creases suddenly until a first manifestation of spreading in As part of the Iguaiba operation, a two-stage VS-30 Orion the echo received by the digisondes becomes visible around rocket was launched from the equatorial rocket launching 19:00 LT, indicating a fast upward movement of the F layer Ann. Geophys., 35, 413–422, 2017 www.ann-geophys.net/35/413/2017/ S. Savio Odriozola et al.: Rocket observation of equatorial plasma irregularities 415 Figure 2. Sequence of ionograms taken on 8 December 2012 (18:20–19:30 LT) at São Luís. Spread F begins around 19:00 LT. Figure 3. Sequence of ionograms taken on 8 December 2012 (18:20–19:30 LT) at Fortaleza. Spread F begins around 19:30 LT. prior to the sunset. The spread F condition is evident in the over Fortaleza is not as pronounced as that observed in São ionograms for the rest of the night. Luís. Figure3 shows the ionograms obtained at Fortaleza simul- From ionograms of both stations, it can be said that equa- taneously with those appearing in Fig.2. In this case the man- torial and low-latitude irregularities developed at the time of ifestation of a spread echo first appeared in a signal coming launch and after the rocket’s flight. from the north-northeast (echoes in light blue color). Sig- nals vertical above Fortaleza station show a range spread F at 19:30 LT or 30 min after the appearance of the same con- 0 dition at São Luís and the rocket’s launch. The rise of hminF www.ann-geophys.net/35/413/2017/ Ann. Geophys., 35, 413–422, 2017 416 S. Savio Odriozola et al.: Rocket observation of equatorial plasma irregularities Figure 4. Electron density profiles obtained with a Langmuir probe data onboard a VS-30 Orion rocket on 8 December 2012, 19:00 LT. 2.3 Langmuir probe measurements The Langmuir probe used in this experiment was mounted on the nose tip of the rocket and was able to operate alternately in swept and constant bias modes.