http://hdl.handle.net/2122/97 2013-05-20T16:55:57Z http://hdl.handle.net/2122/8133 Title: Retrieval of thermospheric parameters from routine ionospheric observations: assessment of method’s performance at mid-latitudes daytime hours Authors: Mikhailov, A. V.; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow Region 142190, Russia; Belehaki, A.; Institute for Space Applications and Remote Sensing, National Observatory of Athens, Metaxa and Vas. Pavlou, Palaia Penteli, 15236 Greece; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Tsagouri, I.; Institute for Space Applications and Remote Sensing, National Observatory of Athens, Metaxa and Vas. Pavlou, Palaia Penteli, 15236 Greece Abstract: A new method has been developed to retrieve neutral temperature Tn and composition [O], [N2], [O2] from electron density profiles in the daytime mid-latitude F2-region under both quiet and disturbed conditions. A comparison with CHAMP neutral gas density observations in the vicinity of Millstone Hill Incoherent Scatter Radar (ISR) has shown that the retrieved neutral gas densities coincide with the observed ones within the announced accuracy of CHAMP observations, provided that accurate Ne(h) ISR profiles are used for the retrieval. The performance of the method has also been tested ingesting Digisonde Ne(h) profiles. In this case the agreement with CHAMP neutral gas density observations is less successful. Possible factors that can influence the performance accuracy are investigated. These are mostly related to limitations due to the ionogram scaling and inversion methods, including performance limitations of the sounding technique itself, like for instance during G-conditions. Several tests presented here demonstrate that discrepancies in the hmF2 values provided by the Digisondes could have an important impact on the performance of the method. It should be noted that in all tests performed here using Digisonde Ne(h) profiles, the topside part is approximated with the NeQuick model and any assessment concerning the impact of the topside profiler on the accuracy of the method is beyond the scope of this investigation. Despite the limitations related to the use of Digisonde profiles, the proposed method has the potential to monitor the thermosphere at least with ISR Ne(h) profiles. Digisonde electron density profiles can also be used if quality improvements are made concerning the ionogram inversion methods. 2012-05-31T22:00:00Z http://hdl.handle.net/2122/8131 Title: Two types of positive disturbances in the daytime mid-latitude F2-layer: Morphology and formation mechanisms Authors: Mikhailov, A. V.; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), Troitsk, Moscow Region 142190, Russia; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Smirnova, N. V.; Institute of Geosphere Dynamics (IDG RAS), Lenin Avenue 38, Moscow 117334, Russia Abstract: Morphological analysis of foF2 variations for the periods of daytime positive disturbances over three ionospheric stations St. Petersburg (sub-auroral zone), Slough (middle latitudes), and Alma-Ata (middle-low latitudes) has confirmed the existence of two types of positive F2-layer disturbances with different morphology. Type I is referred to those followed by quiet or positively disturbed ionospheric conditions. They occur under low or moderate level of geomagnetic activity. Positive disturbances of type II are related to strong geomagnetic storms and they are followed by negative ionospheric disturbances. The two types manifest different occurrence frequency distribution and its dependence on latitude and level of geomagnetic activity. They also exhibit different duration and magnitude. This tells that two types of disturbances belong to different classes of events and may have different formation mechanisms. Millstone Hill ISR and digisonde hmF2 and foF2 observations for some selected periods of F2-layer positive disturbances of both types were analyzed. The original earlier developed self-consistent method to extract thermospheric parameters from ISR observations was used to estimate the contribution of various aeronomic parameters to the observed storm time F2-layer variations. Our analysis of a well-pronounced positive disturbances of type II on December 14, 2006 has confirmed the well-known concept by Pr ¨olss (1993a,b, 1995)—daytime midlatitude positive disturbances of type II are mainly produced by TADs and following them disturbed equatorward winds. However our calculations have shown that about half of the observed positive storm effect may be attributed to thermospheric parameter (neutral composition and temperature) variations. The type II of positive disturbances presents the first phase of a two-phase (positive/negative) ionospheric storm. For this reason their occurrence frequency distribution is similar to that for negative disturbances. The driving force for both disturbances is the same—the thermosphere heating in the auroral zone. Situation with positive disturbances of type I is more complicated. Electric fields on April 03, 2004, and neutral composition (mainly atomic oxygen) variations on April 11, 2000 were shown to be responsible for the observed positive storm effect. The difference in the two cases is presumably related with the localization (longitudinal sector) of the auroral heating. 2012-05-31T22:00:00Z http://hdl.handle.net/2122/7964 Title: Variability of foF2 over Rome and Gibilmanna during three solar cycles (1976-2000) Authors: Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Hourly validated values of the F2-layer critical frequency (foF2) recorded at Rome, Italy (geographic coordinates 41.8ºN, 12.5ºE; geomagnetic coordinates 42.0ºN, 93.8ºE), and Gibilmanna, Italy (geographic coordinates 37.6ºN, 14.0ºE; geomagnetic coordinates 38.1ºN, 93.6ºE), along with the hourly quiet time reference values of foF2 (foF2QTRV) were considered around periods of minimum and maximum solar activity over the years 1976–2000. The foF2 data set was specifically organized in order to obtain an overall trend both for low and high solar activity, and different dispersion indices were used. The results obtained show that (1) at Rome, the foF2 variability is always greater during periods of high solar activity (HSA) in the hourly ranges 00:00–02:00 UT and 20:00–23:00 UT during winter months, and in the hourly ranges 00:00–10:00 UT and 04:00–16:00 UT during equinoctial and summer months respectively; (2) on the whole, around midday, for low solar activity (LSA), the foF2 variability is smaller at the equinoxes than at the solstices; for HSA, it is greater at equinoxes than at solstices; (3) for LSA, at Gibilmanna the foF2 variability is in general larger than at Rome, especially in summer, and it is characterized by a number of relative minimums and maximums greater than those observed at Rome; (4) at Rome, for both LSA and HSA, the passage of solar terminator at sunset significantly affects ionospheric variability in January, April, August, and November, at Gibilmanna in August, September, and November; (5) several variability peaks before sunrise and after sunset are observed in both stations; (6) on a monthly basis, for both LSA and HSA, a semiannual variation of foF2 variability is observed at both Rome and Gibilmanna; and (7) evidence of ionospheric variability at the typical heights of the F region, connected to upward propagating gravity waves triggered by solar terminator, is observed at Rome during some days characterized by HSA in the equinoctial months. 2012-05-15T22:00:00Z http://hdl.handle.net/2122/7933 Title: Atypical nighttime spread-F structure observed near the southern crest of the ionospheric equatorial ionization anomaly Authors: Fagundes, P. R.; Bittencourt, J. A.; Abreu, A. J.; Moor, L. P.; Muella, M. T. A. H.; Sahai, Y.; Abalde, J. R.; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Sobral, J. H. A.; Abdu, M. A.; Pimenta, A. A.; Amorim, D. C. M. Abstract: An atypical nighttime spread-F structure is observed on ionograms at or above the F2 trace, near the crest of the ionospheric equatorial ionization anomaly (EIA) region. This ionospheric atypical spread-F phenomenon was observed using two closed spaced( 115 km) ionospheric soundings stations located in Sao Jose dos Campos (23.21 S, 45.97 W) and Cachoeira Paulista (22.70 S, 45.01 W), Brazil, in a low-latitude station (near the southern crest of the EIA region), during nighttime, low solar activity, and quiet geomagnetic conditions. This structure, in the initial phase, appears in the ionogram as a faint spread-F trace above or at the F2-layer peak height. After a few minutes, it develops into a strong spread-F trace, and afterwards, it moves to altitudes below the F2-layer peak heights. Finally, the atypical nighttime F-layer trace structure may remain for a while between the F-layer bottom side and peak height or can move to an altitude above the F-layer peak height, and then it disappears. In order to have a comprehensive view of the ionospheric environment characterizing the phenomenon under study, complementary data from six GPS station were used to investigate the ionosphere environment conditions, during both events. The six GPS stations used in this study are distributed from near the equatorial region to low latitudes and provide evidence that the atypical nighttime spread-F structures are not related with large scale equatorial irregularities (plasma bubbles). 2012-04-06T22:00:00Z http://hdl.handle.net/2122/7239 Title: Unusual nighttime impulsive foF2 enhancement below the southern anomaly crest under geomagnetically quiet conditions Authors: Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Fagundes, P. R.; Ciraolo, L.; Correia, E.; Cabrera, M. A.; Ezquer, R. G. Abstract: An unusual nighttime impulsive electron density enhancement was observed on 6 March 2010 over a wide region of South America, below the southern crest of the equatorial anomaly, under low solar activity and quiet geomagnetic conditions. The phenomenon was observed almost simultaneously by the F2 layer critical frequency ( foF2) recorded at three ionospheric stations which are widely distributed in space, namely Cachoeira Paulista (22.4°S, 44.6°W, magnetic latitude 13.4°S), São José dos Campos (23.2°S, 45.9°W, magnetic latitude 14.1°S), Brazil, and Tucumán (26.9°S, 65.4°W, magnetic latitude 16.8°S), Argentina. Although in a more restricted region over Tucumán, the phenomenon was also observed by the total electron content (TEC) maps computed by usingmeasurements from 12 GPS receivers. The investigated phenomenon is very particular because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. This compression was clearly visible both by the virtual height of the base of the F region (h′F) recorded at the aforementioned ionospheric stations, and by both the vertical electron density profiles and the slab thickness computed over Tucumán. Consequently, neither an enhanced fountain effect nor plasma diffusion from the plasmasphere can be considered as the single cause of this unusual event. A thorough analysis of isoheight and isofrequency ionosonde plots suggest that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could have likely played a significant role in causing the phenomenon. 2011-12-08T23:00:00Z http://hdl.handle.net/2122/7073 Title: FORMOSAT-3/COSMIC E region observations and daytime foE at middle latitudes Authors: Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Mikhailov, A. V.; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Russia; Korsunova, L. P.; Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Russia Abstract: Ionosonde observations at Rome and Gibilmanna (Sicily) for some months of 2006–2007 were analyzed in the connection with recent COSMIC NmE results. Italy was completely located in the NmE enhanced zone according to COSMIC observations for the periods in question. COSMIC‐observed NmE values in the NmE enhanced zone do not coincide with NmE scaled from ionograms in accordance with the URSI Recommendations, but the IRI model correctly describes monthly median NmE contrary to the Chu et al. (2009) conclusion. Three month averaged COSMIC NmE values turn out to be close to monthly median NmE corresponding to the blanketing frequency fbEs. A conclusion is made that sporadic E practically permanently existing during daytime hours in summer strongly contributes to NmE observed by COSMIC. Possible reasons for the occurrence of the NmE enhanced zones at middle latitudes are discussed. 2011-06-07T22:00:00Z http://hdl.handle.net/2122/7072 Title: On the mechanism of seasonal and solar cycle NmF2 variations: A quantitative estimate of the main parameters contribution using incoherent scatter radar observations Authors: Mikhailov, A. V.; Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Russia; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Seasonal (winter/summer) and solar cycle NmF2 variations as well as summer saturation effect in NmF2 have been analyzed using Millstone Hill incoherent scatter radar (ISR) daytime observations. A self‐consistent approach to the Ne(h) modeling has been applied to extract from ISR observations a consistent set of main aeronomic parameters and to estimate their quantitative contribution to the observed NmF2 variations. The retrieved aeronomic parameters are independent of uncertainties in thermosphere and solar EUV empirical models, and this is a distinguishing feature of the present consideration. Different temperatures in winter and in summer in the course of solar cycle overlapped on the O++N2 reaction rate coefficient temperature dependence result in different NmF2 dependences on solar activity: a steep practically linear increase with a tendency to turn up in January (contrary to international reference ionosphere prediction) and a slow increase with a tendency to saturate at high solar activity in July despite increasing solar EUV irradiation. In winter the EUV flux and thermospheric parameters provide approximately equal contributions to the NmF2 increase, while in summer the contribution of thermospheric parameters is small. Both in winter and in summer the variations of atomic oxygen [O] are small at the F2 layer peak, and its contribution is small compared to linear loss coefficient, b. It is shown that the summer saturation effect in NmF2 under high solar activity is not just reduced to O/N2 or EUV flux solar cycle variations but is determined by b via the g1 temperature dependence. A new mechanism (qualitative) to explain the December anomaly in NmF2 is proposed. It is based on the idea that the areas of atomic oxygen production and its loss are spatially separated and that time is required to transfer [O] from one area to the other where [O] associates in a three‐body collision. Therefore, under a 7% increase in the O2 dissociation rate due to the Sun‐Earth distance decrease in December–January compared to June–July, an accumulation of atomic oxygen should take place in the thermosphere in the vicinity of the December solstice resulting in a 21% NmF2 increase, which is close to the observed global December effect. 2011-03-17T23:00:00Z http://hdl.handle.net/2122/7069 Title: L'osservatorio ionosferico in Artide e Antartide: osservazioni sperimentali e risultati scientifici Authors: De Franceschi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Alfonsi, Lu.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Romano, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Spogli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Italian Upper Atmosphere Observatory at polar latitude was firstly established during the Antarctic campaign 1990-1991 to support the telecommunication logistic activity of the National Program for Antarctic Research (PNRA). The Istituto Nazionale di Geofisica e Vulcanologia (INGV), formerly Istituto Nazionale di Geofisica (ING), was involved in this action as the long time experience in HF radar, ionospheric sounding and ionospheric prediction services for radio communication purposes, managing two of the most important and historical ionospheric observatories all over the world: Rome (41.8N, 12.5E) and Gibilmanna (37.9 N, 14.0 E). Since that time, starting from 1993 up to now, several research projects have been carried on focusing on the multi instruments upper atmosphere observations in Arctic and Antarctica with the aim to study the polar ionosphere in different time and space domains, contributing both to the Global Change and to the emerging Space Weather needs. Here we briefly report on the experimental activities as well on the main scientific results obtained highlighting the latest findings in the field of bipolar GNSS (Global Navigation Satellite Systems) ionospheric scintillation measurements and investigation. 2009-12-31T23:00:00Z http://hdl.handle.net/2122/6404 Title: Coerenza: A software tool for computing the maximum coherence times of the ionosphere Authors: Pietrella, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Power–height (PH) observations of the radio echo reflected from the ionosphere were performed every 15 min at a frequency of 3 MHz at the Rome ionospheric observatory, during the period 3–22 January 2008. This work describes software that can calculate the maximum coherence times of the ionosphere from PH data. The applications for this software are also discussed. 2010-11-30T23:00:00Z http://hdl.handle.net/2122/6012 Title: Satellite traces, range spread-F occurrence, and gravity wave propagation at the southern anomaly crest Authors: Cabrera, M. A.; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Zuccheretti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Ezquer, R. G. Abstract: Range spread-F (RSF) and occurrence of “satellite” traces prior to RSF onset were studied at the southern peak of the ionospheric equatorial anomaly (EA). Ionograms recorded in September 2007 at the new ionospheric station of Tucumán, Argentina (26.9° S, 294.6° E, dip latitude 15.5° S), by the Advanced Ionospheric Sounder (AIS) developed at the Istituto Nazionale di Geofisica e Vulcanologia INGV), were considered. Satellite traces (STs) are confirmed to be a necessary precursor to the appearance of an RSF trace on the ionograms. Moreover, an analysis of isoheight contours of electron density seems to suggest a relationship between RSF occurrence and gravity wave (GW) propagation. 2010-05-17T22:00:00Z