On the nature of nighttime ionisation enhancements observed with the Athens Digisonde

International audienceTrue height electron density profiles observed with the Athens Digisonde were analyzed together with geomagnetic data indices for six magnetic storms in September and October 2000 in an effort to define the ionospheric structure during events of nighttime ionisation enhancements and to discuss the physical processes that may cause them. An upwelling of the F2-layer, limited to the dark hemisphere, was evident in all storm events as the ionospheric response to enhanced geomagnetic activity, but nighttime positive effects and nighttime height enhancements are attributed to two distinct mechanisms, according to our findings. Height enhancements are wavelike disturbances and the time delay of their occurrence at middle latitudes depends on the increase rate of the AE index, and consequently, on the rate that the solar wind input energy dissipates in the auroral ionosphere. Thus, they most probably originated in the auroral oval region and propagated toward the equator-like TID disturbances, with a periodicity that depends on the ionisation density. On the other hand, foF2 increases do not share the same wavy appearance, which could mean that they are not connected to TIDs and are not of auroral oval origin. The increased nighttime density can only be speculated to be due to increased downward fluxes from the plasmasphere

Study of the longitudinal expansion velocity of the substorm current wedge

International audienceIn this work we examine simultaneous observations from the two geosynchronous satellites GOES-5 and GOES-6 located at 282°E and 265°E respectively, and from middle and low latitude ground observatories located within 250°E and 294°E geographic longitude, during isolated substorms of moderate activity. The spatial distribution of our observation points allows us to make a detailed study of the azimuthal expansion of the substorm current wedge. The data analysis shows evidence that the substorm initiation and development mechanism include the cross-tail current diversion/ disruption, the substorm current wedge formation and the azimuthal expansion of the inner plasma sheet. The triggering mechanism is initially confined in a longitudinally narrow sector, estimated to be less than 15° and located very close to local midnight to the east or to the west. The current disruption region expands both eastward and westward in the magnetotail, so that the location of major field-aligned currents flowing into the ionosphere shifts successively eastward, and the location of the currents flowing out of the ionosphere shifts successively westward. Evidence was found that the perturbation travels toward the west with velocities greater than those expanding the wedge eastward. The drastic decrease of the velocity with the azimuthal distance from the location of the disturbance initiation, i.e., the onset sector, indicates that the energy release is a very localized phenomenon. Finally, the transient D perturbation observed by the geosynchronous satellites suggests that the field-aligned currents forming the wedge have a longitudunally limited extent

A dynamic system to forecast ionospheric storm disturbances based on solar wind conditions

For the reliable performance of technologically advanced radio communications systems under geomagnetically disturbed conditions, the forecast and modelling of the ionospheric response during storms is a high priority. The ionospheric storm forecasting models that are currently in operation have shown a high degree of reliability during quiet conditions, but they have proved inadequate during storm events. To improve their prediction accuracy, we have to take advantage of the deeper understanding in ionospheric storm dynamics that is currently available, indicating a correlation between the Interplanetary Magnetic Field (IMF) disturbances and the qualitative signature of ionospheric storm disturbances at middle latitude stations. In this paper we analyse observations of the foF2 critical frequency parameter from one mid-latitude European ionospheric station (Chilton) in conjunction with observations of IMF parameters (total magnitude, Bt and Bz-IMF component) from the ACE spacecraft mission for eight storm events. The determination of the time delay in the ionospheric response to the interplanetary medium disturbances leads to significant results concerning the forecast of the ionospheric storms onset and their development during the first 24 h. In this way the real-time ACE observations of the solar wind parameters may be used in the development of a real-time dynamic ionospheric storm model with adequate accuracy

On the possible use of radio occultation middle latitude electron density profiles to retrieve thermospheric parameters

This paper investigates possible use of middle latitude daytime COSMIC and CHAMP ionospheric radio occultation (IRO) electron density profiles (EDPs) to retrieve thermospheric parameters, based on the Mikhailov et al. (2012) method. The aim of this investigation is to assess the applicability of this type of observations for the routine implementation of the method. According to the results extracted from the analysis presented here, about half of COSMIC IRO EDP observed under solar minimum (2007–2008) conditions gave neutral gas density with an inaccuracy close to the declared absolute inaccuracy ±(10–15)% of CHAMP observations, with the results being better than the empirical models JB-2008 and MSISE-00 provide. For the other half of IRO EDP, either the solution provided by the method had to be rejected due to insufficient accuracy or no solution could be obtained. For these cases, the parameters foF2 and hmF2 extracted from the corresponding IRO profiles have been found to be inconsistent with the classic mid-latitude daytime F2-layer formalism that the method relies on, and they are incompatible with the general trend provided by the IRI model. For solar maximum conditions (2002) the method was tested with IRO EDP from CHAMP and it is indicated that its performance is quite stable in the sense that a solution could be obtained for all the cases analyzed here. However available CHAMP EDP are confined by ~ 400 km in altitude and this might be the reason for the 20% bias of the retrieved densities toward larger values in respect to the observed densities. IRO observations up to 600 km under solar maximum are required to confirm the exact performance of the method

Retrieval of thermospheric parameters from routinely observed F2-layer Ne(h) profiles at the geomagnetic equator

A principal possibility to retrieve basic thermospheric parameters (neutral temperature Tex, atomic [O] and molecular [O2] oxygen as well as molecular nitrogen [N2] concentrations) from the observed daytime electron density profiles Ne(h) in the equatorial F2-region is demonstrated for the first time. The reduction of a 2D continuity equation for electron concentration in the low-latitude F2-region at the geomagnetic equator (I = 0) results in a simple 1D equation which can be efficiently solved. The method was tested using Jicamarca Incoherent Scatter Radar (ISR) and Digisonde Ne(h) profiles for the periods when CHAMP and GRACE neutral gas density observations are available in the vicinity of the Jicamarca Observatory. The retrieved from ISR Ne(h) neutral gas densities were shown to be close to the observed ones (MRD < 10%) being within the announced absolute uncertainty (10–15%) of the neutral gas density observations and more successful than the predictions of the empirical models JB-2008 (MRD = 32%) and MSISE-00 (MRD = 27%) for the analyzed cases. The implementation of the method with Jicamarca Digisonde Ne(h) profiles has also shown acceptable results especially for solar minimum conditions (MRD ~ 12%) and higher prediction accuracy than modern empirical models provide. This finding seems to open a way for the practical exploitation of the method for thermospheric monitoring purposes

Progress in space weather modeling in an operational environment

YesThis paper aims at providing an overview of latest advances in space weather modeling in an operational environment in Europe, including both the introduction of new models and improvements to existing codes and algorithms that address the broad range of space weather's prediction requirements from the Sun to the Earth. For each case, we consider the model's input data, the output parameters, products or services, its operational status, and whether it is supported by validation results, in order to build a solid basis for future developments. This work is the output of the Sub Group 1.3 "Improvement of operational models'' of the European Cooperation in Science and Technology (COST) Action ES0803 "Developing Space Weather Products and services in Europe'' and therefore this review focuses on the progress achieved by European research teams involved in the action

Evidence of gravity waves into the atmosphere during the March 2006 total solar eclipse

This study aims at providing experimental evidence, to support the hypothesis according to which the movement of the moon&apos;s shadow sweeping the ozone layer at supersonic speed, during a solar eclipse, creates gravity waves in the atmosphere. An experiment was conducted to study eclipse induced thermal fluctuations in the ozone layer (via measurements of total ozone column, ozone photolysis rates and UV irradiance), the ionosphere (Ionosonde Total Electron Content &amp;ndash; ITEC, peak electron density height &amp;ndash; hmF2), and the troposphere (temperature, relative humidity), before, during and after the total solar eclipse of 29 March 2006. We found the existence of eclipse induced dominant oscillations in the parameters related to the ozone layer and the ionosphere, with periods ranging between 30&amp;ndash;40 min. Cross-spectrum analyses resulted to statistically significant square coherences between the observed oscillations, strengthening thermal stratospheric ozone forcing as the main mechanism for GWs. Additional support for a source below the ionosphere was provided by the amplitude of the oscillations in the ionospheric electron density, which increased upwards from 160 to 220 km height. Even though similar oscillations were shown in surface temperature and relative humidity data, no clear evidence for tropospheric influence could be derived from this study, due to the modest amplitude of these waves and the manifold rationale inside the boundary layer

COST 296 scientific results designed for operational use

The main objective of the COST 296 Action «Mitigation of Ionospheric Effects on Radio Systems» is the establishment/ improvement of ionospheric services by coordinating the development of specific algorithms, models, and tools capable of operating in a near-real-time mode. Key elements of these activities are contributions related to monitoring, modelling, and imaging of customer-relevant ionospheric quantities. COST stimulates, coordinates, and supports Europe’s goals of development and global cooperation by providing high quality information and knowledge of ionospheric and plasmaspheric conditions enabling high quality and reliable operation of radio systems. It also provides a platform for sharing such tools as algorithms or models, and for the joint development of advanced technologies. It takes advantage of many national and European service initiatives, for example DIAS (http://dias.space.noa.gr), SWACI (http://w3swaci.dlr.de), ESWUA (http://www.eswua.ingv.it/ingv), RWC-Warsaw (http://www.cbk.waw.pl/rwc), the COST Prompt Ionospheric Database http://www.wdc.rl.ac.uk/cgibin/ digisondes/cost_database.pl, http://www.izmiran.ru/services, and others. Existing national capabilities are taken into account to develop synergies and avoid duplication. The enhancement of environment monitoring networks and associated instrumentation yields mutual advantages for European and regional services specialized for local user needs. It structurally increases the integration of limited-area services, and generates a platform employing the same approach to each task differing mostly in input and output data. In doing so it also provides a complementary description of the environmental state within issued information, as well as providing a platform for interaction among local end users, who define what kind of information they need, for system providers, who finalize the tools necessary to obtain required information, and for local service providers, who do the actual processing of data, tailoring it to specific users’ needs. Such an initiative creates a unique opportunity for small national services to consolidate their product design so that is no longer limited to their own activity, but can serve the wider European services. The development and improvement of techniques for mitigating ionospheric effects on radio systems by the COST 296 Action prepared those services that implemented the new design techniques for the newly announced EU and ESA policy-Space Situation Awareness (SSA). COST 296 developments applied to nowcasting and forecasting services are an essential input to the Operational SSA Ionosphere