Advanced Composition Explorer Data Research Articles

Probabilistic Forecasting of Ground Magnetic Perturbation Spikes at Mid‐Latitude Stations

AbstractThe prediction of large fluctuations in the ground magnetic field (dB/dt) is essential for preventing damage from Geomagnetically Induced Currents. Directly forecasting these fluctuations has proven difficult, but accurately determining the risk of extreme events can allow for the worst of the damage to be prevented. Here we trained Convolutional Neural Network models for eight mid‐latitude magnetometers to predict the probability that dB/dt will exceed the 99th percentile threshold 30–60 min in the future. Two model frameworks were compared, a model trained using solar wind data from the Advanced Composition Explorer (ACE) satellite, and another model trained on both ACE and SuperMAG ground magnetometer data. The models were compared to examine if the addition of current ground magnetometer data significantly improved the forecasts of dB/dt in the future prediction window. A bootstrapping method was employed using a random split of the training and validation data to provide a measure of uncertainty in model predictions. The models were evaluated on the ground truth data during eight geomagnetic storms and a suite of evaluation metrics are presented. The models were also compared to a persistence model to ensure that the model using both datasets did not over‐rely on dB/dt values in making its predictions. Overall, we find that the models using both the solar wind and ground magnetometer data had better metric scores than the solar wind only and persistence models, and was able to capture more spatially localized variations in the dB/dt threshold crossings.

Von Karman correlation similarity in solar wind magnetohydrodynamic turbulence.

A major development underlying hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth, here extended empirically to plasma turbulence in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here, we analyze an ensemble of Elsässer autocorrelation functions computed from Advanced Composition Explorer data at 1 astronomical unit (AU), and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman's hypothesis applied to weakly compressive magnetohydrodynamic turbulence. This provides a firm empirical basis for employing the similarity decay hypothesis to the Elsässer correlations that represent the incompressive turbulence cascade. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.

Von Karman Correlation Similarity of the Turbulent Interplanetary Magnetic Field

Abstract A major development underlying much of hydrodynamic turbulence theory is the similarity decay hypothesis due to von Karman and Howarth here extended empirically to magnetic field fluctuations in the solar wind. In similarity decay the second-order correlation experiences a continuous transformation based on a universal functional form and a rescaling of energy and characteristic length. Solar wind turbulence follows many principles adapted from classical fluid turbulence, but previously this similarity property has not been examined explicitly. Here we analyze an ensemble of magnetic correlation functions computed from Advanced Composition Explorer data at 1 au, and demonstrate explicitly that the two-point correlation functions undergo a collapse to a similarity form of the type anticipated from von Karman’s hypothesis. This provides for the first time a firm empirical basis for employing the similarity decay hypothesis to the magnetic field, one of the primitive variables of magnetohydrodynamics, and one frequently more accessible from spacecraft instruments. This approach is of substantial utility in space turbulence data analysis, and for adopting von Karman-type heating rates in global and subgrid-scale dynamical modeling.

Solar Wind Turbulence from 1 to 45 au. I. Evidence for Dissipation of Magnetic Fluctuations Using Voyager and ACE Observations

Abstract As part of a published effort to study low-frequency magnetic waves excited by newborn interstellar pickup ions seen by the Voyager spacecraft, we developed a set of control intervals that represent the background turbulence when the observations are not dominated by wave excitation. This paper begins an effort to better understand solar wind turbulence from 1 to 45 au while spanning greater than one solar cycle. We first focus on the diagnostics marking the onset of dissipation. This includes an expected break in the power spectrum at frequencies greater than the proton cyclotron frequency and a resultant steepening of the spectrum at higher frequencies. Contrary to what is established at 1 au, we only see the spectral break in rare instances. The expected scaling of the spectral index with the turbulence rate is seen, but it is not as clearly established as it was at 1 au. We also find that both Voyager data from 1 to 45 au and Advanced Composition Explorer data from 1 au show significant bias of the magnetic helicity at dissipation scales when the dissipation-range power-law spectral index steepens. We conclude that dissipation dynamics are similar throughout the heliosphere in so far as we have examined to date.

Visibility-Graph Analysis of the Solar Wind Velocity

We analyze in situ measurements of solar wind velocity obtained by Advanced Composition Explorer (ACE) spacecraft and Helios spacecraft during the years 1998-2012 and 1975-1983 respectively. The data belong to mainly solar cycle 23 (1996-2008) and solar cycle 21 (1976-1986) respectively. We use Directed Horizontal Visibility graph (DHVg) algorithm and estimate a graph functional, namely, the degree distance (D) as the Kullback-Leibler divergence (KLD) argument to understand time irreversibility of solar wind time series. We estimate this degree distance irreversibility parameter for these time series at different phases of solar activity cycle. Irreversibility parameter is first established for known dynamical data and then applied for solar wind velocity time series. It is observed that irreversibility in solar wind velocity fluctuations show similar behaviour at 0.3 AU (Helios data) and 1 AU (ACE data). Moreover it changes over the different phases of solar activity cycle.

Space Weather Monitoring and Forecasting Activity in NICT

Disturbances of Space environment around the Earth (geospace) is controlled by the activity of the Sun and the solar wind. Disturbances in geospace sometimes cause serious problems to satellites, astronauts, and telecommunications. To minimize the effect of the problems, space weather forecasting is necessary. In Japan, NICT (National Institute of Information and Communications Technology) is in charge of space weather forecasting services as a regional warning center of International Space Environment Service. With help of geospace environment data exchanging among the international cooperation, NICT operates daily space weather forecast service every day to provide information on nowcasts and forecasts of solar flare, geomagnetic disturbances, solar proton event, and radio-wave propagation conditions in the ionosphere. For prompt reporting of space weather information, we also conduct our original observation networks from the Sun to the upper atmosphere: Hiraiso solar observatory, domestic ionosonde networks, magnetometer & HF radar observations in far-east Siberia and Alaska, and south-east Asia low-latitude ionospheric network (SEALION). ACE (Advanced Composition Explorer) and STEREO (Solar TErrestrial RElations Observatory) real-time beacon data are received using our antenna facilities to monitor the solar and solar wind conditions in near real-time. Our current activities and future perspective of space weather monitoring and forecasting will be introduced in this report.

Third Space Weather Summit Held for Industry and Government Agencies

The potential for space weather effects has been increasing significantly in recent years. For instance, in 2008 airlines flew about 8000 transpolar flights, which experience greater exposure to space weather than nontranspolar flights. This is up from 368 transpolar flights in 2000, and the number of such flights is expected to continue to grow. Transpolar flights are just one example of the diverse technologies susceptible to space weather effects identified by the National Research Council’s Severe Space Weather Events—Understanding Societal and Economic Impacts: A Workshop Report (2008). To discuss issues related to the increasing need for reliable space weather information, experts from industry and government agencies met at the third summit of the Commercial Space Weather Interest Group (CSWIG) and the National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center (SWPC), held 30 April 2009 during Space Weather Week (SWW), in Boulder, Colo. Devrie Intriligator (Carmel Research Center, Inc.) and W. Kent Tobiska (Space Environment Technologies (SET)) cochaired the summit. In opening the session, Intriligator praised SWPC and Thomas Bogdan, its director, for implementing CSWIG’s request for External Space Weather Data Store (E-SWDS), a near–real time operational database electronic communication method between SWPC and external core partner users. Bogdan discussed SWPC priorities, goals, and plans. Bogdan said he anticipates that more stable budgets will enable SWPC to continue hardware modernization, hire and train forecasters, and put the ENLIL model into operation. He noted that SWPC is working with NOAA aviation and other core entities on overlapping concerns involving space weather. David Bouwer (SET), who represented CSWIG during the E-SWDS implementation, praised the SWPC staff, summarized E-SWDS’s advantages, and answered questions about E-SWDS. Intriligator raised CSWIG’s concerns about the quality and availability of data, including data from a possible replacement for the Advanced Composition Explorer (ACE) satellite at Lagrange point L1 and from satellites such as National Polar-orbiting Operational Environmental Satellite System (NPOESS), Geostationary Operational Environmental Satellites (GOES), and Defense Meteorological Satellites Program (DMSP). Intriligator stressed that a rapid launch of an L1 replacement is urgently needed because ACE is unable to return reliable real-time solar wind data during space weather events such as the 2003 Halloween storm (NOAA Technical Memorandum OAR SEC-88, “Halloween space weather storms of 2003”). In addition, other ACE instruments, such as its low-energy particle detectors, have suffered degradation. Many space weather forecasts need ACE and other data as inputs. If the crucial real-time input data are not available, the space weather community may not be able to test and validate forecasting models during the upcoming solar maximum. To address this situation, Bogdan discussed two possible options: buying data from a commercial satellite at L1, and an interagency cooperative launch of Deep Space Climate Observatory (DSCOVR), a satellite that NASA has built but not launched due to funding issues. Bogdan also summarized the National Space Weather Program (NSWP) participation in the Committee for Space Environmental Sensor Mitigation Options (CSESMO) with Office of Science and Technology Policy and Office of Management and Budget staff. Michael Bonadonna (Office of the Federal Coordinator for Meteorology) summarized recent NSWP activities, including updating NSWP, determining the scope of CSESMO activities, and organizing the 2009 Space Weather Enterprise Forum. In addition, Bonadonna discussed the 2006 “Report of the Assessment Committee for the National Space Weather Program”

A ONE-SIDED ASPECT OF ALFVENIC FLUCTUATIONS IN THE SOLAR WIND

Using Advanced Composition Explorer (ACE) 64 s data at 1 AU we find that Alfvenic fluctuations propagating outward from the Sun along the magnetic field, B , in the solar wind often produce one-sided variations in one of the equatorial components of B and velocity, V . This is a natural consequence of the fact that the Alfvenic fluctuations are transverse fluctuations in which |B| remains nearly constant. Thus, fluctuations in the field component that defines the underlying background field direction are always relative to a base value rather than to an average value. This suggests that conclusions derived from statistical analyses of fluctuations in the solar wind that assume the fluctuations in all field components are relative to average values need to be re-examined. We also find that discrete, sunward-propagating Alfvenic fluctuations or rotational discontinuities are extremely rare in the pristine solar wind; thus far we have identified such discrete events in ACE data only in association with events identified as magnetic reconnection exhausts and/or in association with backstreaming ions from reverse shocks, including Earth's bow shock.

STATISTICAL ANALYSIS OF DISCONTINUITIES IN SOLAR WIND ACE DATA AND COMPARISON WITH INTERMITTENT MHD TURBULENCE

The comparison between Advanced Composition Explorer (ACE) solar wind data and simulations of magnetohydrodynamic (MHD) turbulence shows a good agreement in the waiting-time analysis of magnetic field increments. Similarity between classical discontinuity identification and intermittency analysis suggests a dynamical connection between solar wind discontinuities and intermittent MHD turbulence. Probability distribution functions of increments in ACE data and in simulations reveal a robust structure consisting of small random currents, current cores, and intermittent current sheets. This adds to evidence that solar wind magnetic structures may emerge fast and locally from MHD turbulence.

On the combination of ACE data with numerical simulations to determine the initial characteristics of a CME

Aims. Our goal is to combine the Advanced Composition Explorer (ACE) data with numerical simulations to determine the initial characteristics of the halo coronal mass ejection (CME), which was observed on April 4, 2000. Methods. The evolution of a CME from the Sun to 1 AU is simulated in the framework of 2.5 D (axi-symmetric) ideal Magnetohydrodynamics (MHD). The initial parameters of the CME model are adjusted to reproduce the ACE data as accurately as possible. The initial parameters leading to the best fit are then assumed to be the most plausible initial parameters of the CME event. Results. Once the ACE data and the transit time were successfully reproduced, we concluded that, at 1.5 R ⊙ , the CME had a maximal magnetic field strength of 2.5 × 10 -4 T and a total mass of 6.7 x 10 12 kg, and the CME linear speed up to 30 R ⊙ was 1524 km s -1 .

Ion Charge States in Halo Coronal Mass Ejections: What Can We Learn about the Explosion?

We describe a new modeling approach to develop a more quantitative understanding of the charge state distributions of the ions of various elements detected in situ during halo Coronal Mass Ejection (CME) events by the Advanced Composition Explorer (ACE) satellite. Using a model CME hydrodynamic evolution based on observations of CMEs propagating in the plane of the sky and on theoretical models, we integrate time dependent equations for the ionization balance of various elements to compare with ACE data. We find that plasma in the CME ``core'' typically requires further heating following filament eruption, with thermal energy input similar to the kinetic energy input. This extra heating is presumably the result of post eruptive reconnection. Plasma corresponding to the CME ``cavity'' is usually not further ionized, since whether heated or not, the low density gives freeze-in close the the Sun. The current analysis is limited by ambiguities in the underlying model CME evolution. Such methods are likely to reach their full potential when applied to data to be acquired by STEREO when at optimum separation. CME evolution observed with one spacecraft may be used to interpret CME charge states detected by the other.

Badhwar–O’Neill galactic cosmic ray model update based on advanced composition explorer (ACE) energy spectra from 1997 to present

Accurate knowledge of the interplanetary Galactic Cosmic Ray (GCR) environment is critical to planning and operating manned space flight to the moon and beyond. In the early 1990s, Badhwar and O’Neill developed a GCR model based on balloon and satellite data from 1954 to 1992. Since August 1997 the Advanced Composition Explorer (ACE) has provided significantly more accurate GCR energy spectra due to its much larger collection power.The original Badhwar–O’Neill Model, updated with the new ACE data, should provide interplanetary mission planners with highly accurate GCR environment data for radiation protection for astronauts and radiation hardness assurance for electronic equipment.

Direct evidence for magnetic reconnection in the solar wind near 1 AU

We have obtained direct evidence for local magnetic reconnection in the solar wind using solar wind plasma and magnetic field data obtained by the Advanced Composition Explorer (ACE). The prime evidence consists of accelerated ion flow observed within magnetic field reversal regions in the solar wind. Here we report such observations obtained in the interior of an interplanetary coronal mass ejection (ICME) or at the interface between two ICMEs on 23 November 1997 at a time when the magnetic field was stronger than usual. The observed plasma acceleration was consistent with the Walen relationship, which relates changes in flow velocity to density‐weighted changes in the magnetic field vector. Pairs of proton beams having comparable densities and counterstreaming relative to one another along the magnetic field at a speed of ∼1.4VA, where VA was the local Alfven speed, were observed near the center of the accelerated flow event. We infer from the observations that quasi‐stationary reconnection occurred sunward of the spacecraft and that the accelerated flow occurred within a Petschek‐type reconnection exhaust region bounded by Alfven waves and having a cross section width of ∼4 × 105 km as it swept over ACE. The counterstreaming ion beams resulted from solar wind plasma entering the exhaust region from opposite directions along the reconnected magnetic field lines. We have identified a limited number (five) of other accelerated flow events in the ACE data that are remarkably similar to the 23 November 1997 event. All such events identified occurred at thin current sheets associated with moderate to large changes in magnetic field orientation (98°–162°) in plasmas characterized by low proton beta (0.01–0.15) and high Alfven speed (51–204 km/s). They also were all associated with ICMEs.

On the correlation of the solar wind observed at the L5 point and at the Earth

The L5 point is a promising location for forecasting co-rotating high-speed streams in the solar wind arriving at the Earth. We correlated the solar wind data obtained by the Nozomi spacecraft in interplanetary space and by the Advanced Composition Explorer (ACE) at the L1 point, and found that the correlation is significantly improved from that of the 27-day recurrence of ACE data. Based on the correlation between the two spacecraft observations, we estimated the correlation of the solar wind velocity between the L5 point and at the Earth, and found that the correlation coefficient was about 0.78 in late 1999, while that of the 27-day recurrence was 0.51. Eighty-eight percent of the velocity difference falls within 100 km/s between the L5 point and the Earth. This demonstrates the potential capability of solar wind monitoring at the L5 point to forecast the geomagnetic disturbances 4.5 days in advance.

In brief

Satellite improves space weather forecasts Real‐time data from NASA's Advanced Composition Explorer (ACE) satellite became part of the daily U.S space weather forecast operations in late January, providing forecasters at the National Oceanic and Atmospheric Administration's (NOAA) Space Environment Center with an important tool for improving forecasts and warnings of solar storms.Forecasters with NOAA and the U.S. Air Force—the agencies that, along with NASA, are coordinating the project—are incorp orating the ACE data into operations, allowing the agencies to predict and issue 1‐hour geomagnetic storm alerts with almost 100% accuracy, they say.