Showing papers on "Space weather published in 2006"

Differences between CME‐driven storms and CIR‐driven storms

Abstract: Twenty one differences between CME-driven geomagnetic storms and CIR-driven geomagnetic storms are tabulated. (CME-driven includes driving by CME sheaths, by magnetic clouds, and by ejecta; CIR-driven includes driving by the associated recurring high-speed streams.) These differences involve the bow shock, the magnetosheath, the radiation belts, the ring current, the aurora, the Earth's plasma sheet, magnetospheric convection, ULF pulsations, spacecraft charging in the magnetosphere, and the saturation of the polar cap potential. CME-driven storms are brief, have denser plasma sheets, have strong ring currents and Dst, have solar energetic particle events, and can produce great auroras and dangerous geomagnetically induced currents; CIR-driven storms are of longer duration, have hotter plasmas and stronger spacecraft charging, and produce high fluxes of relativistic electrons. Further, the magnetosphere is more likely to be preconditioned with dense plasmas prior to CIR-driven storms than it is prior to CME-driven storms. CME-driven storms pose more of a problem for Earth-based electrical systems; CIR-driven storms pose more of a problem for space-based assets.

Swarm: A constellation to study the Earth’s magnetic field

Abstract: The Swarm mission was selected as the 5th mission in ESA’s Earth Explorer Programme in 2004. The mission will provide the best ever survey of the geomagnetic field and its temporal evolution that will lead to new insights into the Earth system by improving our understanding of the Earth’s interior and its effect on Geospace, the vast region around the Earth where electrodynamic processes are influenced by the Earth’s magnetic field. Scheduled for launch in 2010, the mission will comprise a constellation of three satellites, with two spacecraft flying sideby- side at lower altitude (450 km initial altitude), thereby measuring the East-West gradient of the magnetic field, and the third one flying at higher altitude (530 km). High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the necessary observations that are required to separate and model the various sources of the geomagnetic field. This results in a unique “view” inside the Earth from space to study the composition and processes of its interior. It also allows analysing the Sun’s influence within the Earth system. In addition practical applications in many different areas, such as space weather, radiation hazards, navigation and resource management, will benefit from the Swarm concept.

Space Weather: The Solar Perspective

Abstract: The term space weather refers to conditions on the Sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and that can affect human life and health. Our modern hi-tech society has become increasingly vulnerable to disturbances from outside the Earth system, in particular to those initiated by explosive events on the Sun: Flares release flashes of radiation that can heat up the terrestrial atmosphere such that satellites are slowed down and drop into lower orbits, solar energetic particles accelerated to near-relativistic energies may endanger astronauts traveling through interplanetary space, and coronal mass ejections are gigantic clouds of ionized gas ejected into interplanetary space that after a few hours or days may hit the Earth and cause geomagnetic storms. In this review, I describe the several chains of actions originating in our parent star, the Sun, that affect Earth, with particular attention to the solar phenomena and the subsequent effects in interplanetary space.

Evolution of Coronal Mass Ejections in the Inner Heliosphere: A Study using White-light and Scintillation Images

Abstract: Knowledge of the radial evolution of the coronal mass ejection (CME) is important for the understanding of its arrival at the near-Earth space and of its interaction with the disturbed/ambient solar wind in the course of its travel to 1 AU and further. In this paper, the radial evolution of 30 large CMEs (angular width > 150∘, i.e., halo and partial halo CMEs) has been investigated between the Sun and the Earth using (i) the white-light images of the near-Sun region from the Large Angle Spectroscopic Coronagraph (LASCO) onboard SOHO mission and (ii) the interplanetary scintillation (IPS) images of the inner heliosphere obtained from the Ooty Radio Telescope (ORT). In the LASCO field of view at heliocentric distances R≤30 solar radii (R ⊙), these CMEs cover an order of magnitude range of initial speeds, V CME≈260–2600 km s−1. Following results have been obtained from the speed evolution of these CMEs in the Sun–Earth distance range: (1) the speed profile of the CME shows dependence on its initial speed; (2) the propagation of the CME goes through continuous changes, which depend on the interaction of the CME with the surrounding solar wind encountered on the way; (3) the radial-speed profiles obtained by combining the LASCO and IPS images yield the factual view of the propagation of CMEs in the inner heliosphere and transit times and speeds at 1 AU computed from these profiles are in good agreement with the actual measurements; (4) the mean travel time curve for different initial speeds and the shape of the radial-speed profiles suggest that up to a distance of ∼80 R ⊙, the internal energy of the CME (or the expansion of the CME) dominates and however, at larger distances, the CME's interaction with the solar wind controls the propagation; (5) most of the CMEs tend to attain the speed of the ambient flow at 1 AU or further out of the Earth's orbit. The results of this study are useful to quantify the drag force imposed on a CME by the interaction with the ambient solar wind and it is essential in modeling the CME propagation. This study also has a great importance in understanding the prediction of CME-associated space weather at the near-Earth environment.

On the origin of aurorae on Mars

Abstract: ] We report observations by Mars Global Surveyor(MGS) of thousands of peaked electron energy spectrasimilar to terrestrial auroral electrons. They are observed onthe Martian nightside, near strong crustal magnetic sources.The spectra have peak energies ranging from 100 eV –2.5 keV, and fluxes near the peak are 10–10000 timeshigher than typical nightside spectra. They occur onmagnetic field lines that connect the shocked solar windto crustal magnetic fields, and on adjacent closed field lines.Their detection is directly controlled by the solar wind,suggesting that magnetic reconnection is required for theirobservation. We calculate that the most energeticdistributions could produce atmospheric emission withintensity comparable to that recently reported from theMars Express (MEX) spacecraft. Half of the most energeticexamples occur during the passage of space weather eventspast Mars, suggesting that a disturbed plasma environmentis favorable for electron acceleration along magnetic fieldlines.

Satellite constellation monitors global and space weather

Abstract: Six identical microsatellites were successfully launched into a circular low-Earth orbit from Vandenberg Air Force Base, Calif., at 0140 UTC on 15 April 2006. Termed the Formosa Satellite 3 and Constellation Observing System for Meteorology Ionosphere, and Climate (FORMOSAT-3/COSMIC) mission, the new constellation's primary science goal is to obtain vertical profiles in nearreal time of temperature, pressure, and water vapor in the neutral atmosphere and electron density in the ionosphere. The observations will be used to support operational global weather prediction, climate monitoring and research, space weather forecasting, and ionospheric research.

Tracking halo coronal mass ejections from 0-1 AU and space weather forecasting using the Solar Mass Ejection Imager (SMEI)

Abstract: [1] The Solar Mass Ejection Imager (SMEI) has been tracking coronal mass ejections (CMEs) from the Sun to the Earth and beyond since it came online in February 2003. This paper presents some results from the first 19 months of data from SMEI, when over 140 transients of many kinds were observed in SMEI's all-sky cameras. We focus specifically on 20 earthward directed transients, and compare distance-time plots obtained from the SMEI transients with those observed in halo CMEs by Large-Angle Spectrometric Coronograph (LASCO) aboard Solar and Heliospheric Observatory (SOHO), and the arrival time of the shock observed by ACE at 0.99 AU. The geometry of one particular transient is compared using both LASCO and SMEI images in a first attempt to investigate geometry evolution as the transient propagates through the interplanetary medium. For some events, the halo CME, SMEI transient, and shock at 0.99 AU do not match, suggesting that some transients may not correspond to a halo CME. Finally, an evaluation of the potential of SMEI to be used as a predictor of space weather is presented, by comparing the transients observed in SMEI with the 22 geomagnetic storms which occurred during this timeframe. A transient was observed in 14 cases, and distance-time profiles would have allowed a prediction of the arrival time at ACE within 2 hours of its actual arrival for three events, and within 10 hours for eight events. Of these eight events, seven were detected by SMEI more than 1 day before the transient's arrival at the Earth.

Forecasting total electron content maps by neural network technique

Abstract: [1] Near-Earth space processes are highly nonlinear. Since the 1990s, a small group at the Middle East Technical University in Ankara has been working on a data-driven generic model of such processes, that is, forecasting and nowcasting of a near-Earth space parameter of interest. The model developed is called the Middle East Technical University Neural Network (METU-NN) model. The METU-NN is a data-driven neural network model of one hidden layer and several neurons. In order to understand more about the complex response of the magnetosphere and ionosphere to extreme solar events, we chose this time the series of space weather events in November 2003. Total electron content (TEC) values of the ionosphere are forecast during these space weather events. In order to facilitate an easier interpretation of the forecast TEC values, maps of TEC are produced by using the Bezier surface-fitting technique.

A total electron content space weather study of the nighttime weddell sea Anomaly of 1996/1997 southern summer with TOPEX/Poseidon radar altimetry

Abstract: This paper reports on a total electron content space weather study of the nighttime Weddell Sea Anomaly, overlooked by previously published TOPEX/Poseidon climate studies, and of the nighttime ionosphere during the 1996/1997 southern summer. To ascertain the morphology of spatial TEC distribution over the oceans in terms of hourly, geomagnetic, longitudinal and summer-winter variations, the TOPEX TEC, magnetic, and published neutral wind velocity data are utilized. To understand the underlying physical processes, the TEC results are combined with inclination and declination data plus global magnetic field-line maps. To investigate spatial and temporal TEC variations, geographic/magnetic latitudes and local times are computed. As results show, the nighttime Weddell Sea Anomaly is a large (∼1,600(°)2; ∼22 million km2 estimated for a steady ionosphere) space weather feature. Extending between 200°E and 300°E (geographic), it is an ionization enhancement peaking at 50°S–60°S/250°E–270°E and continuing beyond 66°S. It develops where the spacing between the magnetic field lines is wide/medium, easterly declination is large-medium (20°–50°), and inclination is optimum (∼55°S). Its development and hourly variations are closely correlated with wind speed variations. There is a noticeable (∼43%) reduction in its average area during the high magnetic activity period investigated. Southern summer nighttime TECs follow closely the variations of declination and field-line configuration and therefore introduce a longitudinal division of four (Indian, western/eastern Pacific, Atlantic). Northern winter nighttime TECs measured over a limited area are rather uniform longitudinally because of the small declination variation. TOPEX maps depict the expected strong asymmetry in TEC distribution about the magnetic dip equator.

A statistical comparison of solar wind sources of moderate and intense geomagnetic storms at solar minimum and maximum

Abstract: [1] Superposed epoch analyses of 549 storms are performed to make a comparison of solar wind features of geomagnetic storm events at solar minimum (July 1974 to June 1977; July 1984 to June 1987; July 1994 to June 1997) and solar maximum (January 1979 to December 1981; January 1989 to December 1991; July 1999 to June 2002). In this study, geomagnetic storms are defined by the pressure-corrected Dst (Dst*) and classified into moderate storms (−100 nT < Dst* ≤ −50 nT) and intense storms (Dst* ≤ −100 nT). The average values of interplanetary magnetic field (IMF), solar wind plasma, NOAA/POES hemispheric power, Kp, and Dst* are analyzed and compared among the different storm categories. During the main phase of storms in each category, the average solar wind plasma parameters and IMF components are disturbed and compressed by a relative high-speed plasma stream. It is shown that the peak of the average solar wind density leads the minimum Dst* (the zero epoch time) by 4.3–7.0 hours, which is longer than the peak time difference (0.3–1.0 hour) between the average IMF Bs and Dst*min. For intense storms at solar minimum, the average IMF By is greatly disturbed during both the main phase and the recovery phase. In addition, the average solar wind density is enhanced up to 28 cm−3, but the average solar wind bulk flow in this storm category is lower than those in all other categories. A significant finding is that the average interplanetary causes of intense storms at solar minimum are found to be against the well-known empirical criteria (Bs ≥ 10 nT or VBs ≥ 5.0 mV/m for ≥3 hours), having a long interval of average Bs = ∼10 nT with dual peaks separated by ∼4.0 hours. The interplanetary and solar origins of storms in the different storm categories are also discussed.

US-TEC: A new data assimilation product from the Space Environment Center characterizing the ionospheric total electron content using real-time GPS data

Abstract: [1] The potential of data assimilation for operational numerical weather forecasting has been appreciated for many years. For space weather it is a new path that we are just beginning to explore. With the emergence of satellite constellations and the networks of ground-based observations, sufficient data sources are now available to make the application of data assimilation techniques a viable option. The first space weather product at Space Environment Center (SEC) utilizing data assimilation techniques, US-TEC, was launched as a test operational product in November 2004. US-TEC characterizes the ionospheric total electron content (TEC) over the continental United States (CONUS) every 15 min with about a 15-min latency. US-TEC is based on a Kalman filter data assimilation scheme driven by a ground-based network of real-time GPS stations. The product includes a map of the vertical TEC, an estimate of the uncertainty in the map, and the departure of the TEC from a 10-day average at that particular universal time. In addition, data files are provided for vertical TEC and the line-of-sight electron content to all GPS satellites in view over the CONUS at that time. The information can be used to improve single-frequency GPS positioning by providing more accurate corrections for the ionospheric signal delay, or it can be used to initialize rapid integer ambiguity resolution schemes for dual-frequency GPS systems. Validation of US-TEC indicates an accuracy of the line-of-sight electron content of between 2 and 3 TEC units (1 TECU = 1016 el m−2), equivalent to less than 50 cm signal delay at L1 frequencies, which promises value for GPS users. This is the first step along a path that will likely lead to major improvement in space weather forecasting, paralleling the advances achieved in meteorological weather forecasting.

MAGDAS project and its application for space weather

Abstract: We introduce a real-time MAGnetic Data Acquisition System of Circum-pan Pacific Magnetometer Network, i.e. MAGDAS/CPMN for space weather study and application, and its preliminary results. By using this system, we will conduct real-time monitoring and modeling of (1) global 3-dimensional current system, (2) plasma mass density, and (3) penetrating process of polar electric fields into the equatorial ionosphere, in order to understand electromagnetic and plasma environment changes in the geospace during the period of ILWS/CAWSES/IHY.

Preparing for COSMIC: Inversion and Analysis of Ionospheric Data Products

Abstract: The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is scheduled for launch in 2006. COSMIC will consist of six low earth orbiting satellites in planes separated by 24° to provide global atmospheric and ionospheric observations. One of the goals is to demonstrate near real-time processing of data products for numerical weather prediction and space weather applications. Each COSMIC satellite will carry three payloads: (1) a Global Positioning System (GPS) occultation receiver with two high-gain limb viewing antennas and two antennas for precision orbit determination, (2) a Tiny Ionospheric Photometer (TIP) for monitoring the electron density via nadir radiance measurements along the sub-satellite track, and (3) a Tri-Band Beacon (TBB) transmitter for ionospheric tomography and scintillation studies. The data from all these payloads will be processed at the COSMIC Data Analysis and Archival Center (CDAAC). Here we give an overview of the ionospheric data products from COSMIC and focus on the plans and preliminary simulation studies for analyzing the ionospheric occultation data and combining them with ground-based GPS, TIP, and TBB observations.

Real-time cosmic ray monitoring system for space weather

Abstract: [1] We have developed a real-time system to monitor high-energy cosmic rays for use in space weather forecasting and specification. Neutron monitors and muon detectors are used for our system, making it possible to observe cosmic rays with dual energy range observations. In large solar energetic particle (SEP) events, the ground level enhancement (GLE) can provide the earliest alert for the onset of the SEP event. The loss cone precursor anisotropy predicts the arrival of interplanetary shocks and the associated interplanetary coronal mass ejections (ICMEs), while the occurrence of bidirectional cosmic ray streaming indicates that Earth is within a large ICME. This article describes a set of real-time Web displays that clearly show the appearance of the GLE, loss cone precursor, and other space weather phenomena related to cosmic rays.

Dynamic geomagnetic rigidity cutoff variations during a solar proton event

Abstract: [1] Solar proton events (SPE) are major, though infrequent, space weather phenomena that can produce hazardous effects in the near-Earth space environment. A detailed understanding of their effects depends upon knowledge of the dynamic rigidity cutoffs imposed by the changing total magnetic field. For the first time we investigate detailed comparisons between theoretical cutoff rigidities and ground-based measurements during the large geomagnetic disturbance of 4–10 November 2001. We make use of the imaging riometer (IRIS) at Halley, Antarctica, fortunately situated such that the rigidity cutoff sweeps back and forth across the instrument's field of view during the SPE period. The Kp-dependent geomagnetic rigidity cutoff energies are determined from satellite observations combined with previously reported particle-tracing results. We find that the predicted absorption levels show good agreement with those experimentally observed for low and middle levels of geomagnetic disturbance (Kp < 5). However, during more disturbed geomagnetic conditions the cutoff modeling overestimates the stretching of the geomagnetic field, underestimating the rigidity cutoff energies, and hence leading to riometer absorption predictions that are too high. In very disturbed conditions (Kp ≈ 7–9) the rigidity energy cutoffs indicated by the IRIS observations appear to be equivalent to those predicted for Kp ≈ 6 by the particle-tracing approach. Examples of changing rigidity cutoff contours for increasing levels of geomagnetic disturbance are presented.

Monitoring and Forecasting the Ionosphere Over Europe: The DIAS Project

Abstract: Knowledge of the state of the upper atmosphere, and in particular its ionospheric part, is very important in several applications affected by space weather, especially the communications and navigation systems that rely on radio transmission. To better classify the ionosphere and forecast its disturbances over Europe, a data collection endeavour called the European Digital Upper Atmosphere Server (DIAS) was initiated in 2004 by a consortium formed around several European ionospheric stations that transmit in real-time ionospheric parameters automatically scaled. The DIAS project is a collaborative venture of eight institutions funded by the European Commission eContent Programme. The project seeks to improve access to digital information collected by public European institutes and to expand its use. The main objective of the DIAS project is to develop a pan-European digital data collection describing the state of the upper atmosphere, based on real-time information and historical data collections provided by most of the operating ionospheric stations in Europe. Various groups of users require data specifying upper atmospheric conditions over Europe for nowcasting and forecasting purposes. The DIAS system is designed to distribute such information. The successful operation of DIAS is based on the effective use of observational data in operational applications through the development of new added-value ionospheric products and services that best fit the needs of the market. DIAS is a unique European system, and its continuous operation will efficiently support radio propagation services with the most reliable information. DIAS began providing services to users in August 2006. The Need for Accurate Ionospheric Products Radio frequency communications and satellite positioning and navigation systems are applications most affected by ionospheric disturbances. Such disturbances can cause drastic and large-scale changes in the usable ranges of high frequency (HF) or below HF bands affecting standard ground-to-ground and submarine communication systems. The characteristics of an ionospheric propagation channel, whether it is HF or transionospheric frequencies, are highly variable on timescales ranging from a few seconds to the 11-year solar cycle. Even during its quietest periods, the Sun produces electromagnetic radiation and solar wind, both of which can affect a variety of geomagnetic and ionospheric phenomena, which in turn affect radio waves propagating through the ionosphere. Hence day-to-day and hour-to-hour changes in propagation channel characteristics can occur.

CME Disturbance Forecasting

Abstract: CME disturbances at Earth arise from the sheath that arrives in front of the ICME and from the ICME itself. The geoeffective environment is qualitatively different in the sheath than within the ICME. Consequently two types of forecast procedures using solar observations of phenomena associated with the release of the CME as input parameters have been developed to treat the two types of environment. This chapter surveys efforts that have resulted in implementable (at least in principle) forecast algorithms for sheath and ICME disturbances and discusses uncertainties associated with both.

ISACCO: an Italian project to monitor the high latitudes ionosphere by means of GPS receivers

Abstract: As the high latitude ionosphere is directly connected with outer space by means of the field line reconnection of the geomagnetic field through the magnetopause, it is highly sensitive to the enhancement of the electromagnetic radiation and energetic particles coming from the Sun. Under such conditions the ionosphere may become highly turbulent showing the presence of small-scale (from centimetres to meters) structures or irregularities imbedded in the large-scale (tens of kilometres) ambient ionosphere. These irregularities can produce short-term phase and amplitude fluctuations in the carrier frequency of the radio waves which pass through them, commonly called ionospheric amplitude and phase scintillations (see, e.g., Morrissey et al. 2004, and references therein). The high latitude ionosphere encounters significant fading, with the most intense fading depths in the polar cap regions and less intense fading in the auroral regions. Severe amplitude fading and strong phase scintillation affect the reliability of GPS navigational systems and satellite communications. As the scarceness of a continuous and systematic monitoring of ionospheric scintillations over polar and auroral regions, the deployment of network(s) of GPS receivers, opportunely configured to observe the ionosphere under quiet and stormy conditions, could represent an important achievement for both space weather purposes and scientific aims. In this paper, a general overview on ISACCO (Ionospheric Scintillations Arctic Campaign Coordinated Observation) is given. ISACCO is an Italian project to monitor ionospheric scintillations at polar regions by means of modified GPS receivers. After some historical and technical notes on the project, the paper presents examples of some of our current investigations based on the data acquired during the almost 3 years of the ISACCO project.

On the geomagnetic effects of solar wind interplanetary magnetic structures

Abstract: [1] We present in this work a statistical study of the geoeffectiveness of the solar wind magnetic interplanetary structures over the entire observational period (1964--2003). The structures studied were magnetic clouds (MCs, 170 events), corotating interaction regions (CIRs, 727 events) and interplanetary shocks (830 events). The geoeffectiveness was assessed in terms of the geomagnetic index Kp, AE, and Dst peak values within 2 days after the interplanetary structure had passed near Earth’s orbit. Frequency distributions were obtained that give the probability of every interplanetary structure being followed by intense, moderate, weak, or quiet (none) magnetic activity levels. The knowledge of probability distribution is important in schemes to forecast space weather conditions after the detection, by in situ solar wind observations, of an interplanetary structure approaching Earth. We observed that magnetic clouds are more efficient than shocks or CIRs in producing all the geomagnetic activity disturbances; CIRs are themselves more geoeffective as measured by the AE activity. We have confirmed that compound structures (shocks plus MCs) are more geoeffective in every type of magnetospheric activity than isolated structures.