C. S. Deehr

Improvements to the HAF solar wind model for space weather predictions

We have assembled and tested, in real time, a space weather modeling system that starts at the Sun and extends to the Earth through a set of coupled, modular components. We describe recent efforts to improve the Hakamada-Akasofu-Fry (HAF) solar wind model that is presently used in our geomagnetic storm prediction system. We also present some results of these improvement efforts. In a related paper, Akasofu [2001] discusses the results of the first 2 decades using this system as a research tool and for space weather predictions. One key goal of our efforts is to provide quantitative forecasts of geoeffective solar wind conditions at the L1 satellite point and at Earth. Notably, we are addressing a key problem for space weather research: the prediction of the north-south component (Bz) of the interplanetary magnetic field. This parameter is important for the transfer of energy from the solar wind to the terrestrial environment that results in space weather impacts upon society. We describe internal improvements, the incorporation of timely and accurate boundary conditions based upon solar observations, and the prediction of solar wind speed, density, magnetic field, and dynamic pressure. HAF model predictions of shock arrival time at the L1 satellite location are compared with the prediction skill of the two operational shock propagation models: the interplanetary shock propagation model (ISPM) and the shock-time-of-arrival (STOA) model. We also show model simulations of shock propagation compared with interplanetary scintillation observations. Our modeling results provide a new appreciation of the importance of accurately characterizing event drivers and for the influences of the background heliospheric plasma on propagating interplanetary disturbances.

SCIFER‐Dayside auroral signatures of magnetospheric energetic electrons

The SCIFER sounding rocket was launched over the dayside aurora, at 10 hr Magnetic Local Time (MLT) on January 25, 1995. Meridian-scanning photometers (MSP) and all-sky television (ASTV) systems were operated at Longyearbyen (LYR) and Ny-Alesund (NYA) on Svalbard under the flight apogee to facilitate the launch decision and identify the ionospheric signatures of the various energetic particle populations observed at the rocket. The characteristics of the 0.3 eV–15.5 KeV electron populations producing the observed aurora were identified from the time, energy and pitch angle electron spectrometer data throughout the SCIFER flight. The optical data clearly showed the location of the trapping boundary seen by the SCIFER energetic electron spectra. Equatorward of the boundary, pulsating patches of auroral luminosity corresponded in pulsation period and location to the >4 keV energy-dispersed electrons observed at SCIFER. The 10 eV electron flux rather uniformly distributed equatorward from the trapping boundary is accounted for by photoelectrons from the conjugate region, producing most of the 6300 A [OI] emission observed south of the zenith in the MSP data. Poleward of the trapping boundary, relatively bright, discrete arcs and bands typical of the dayside auroral oval were observed. These corresponded to the inverted V and field-aligned electron populations which were observed at SCIFER to be < 1 keV characteristic energy and to range from 2 to 5 ergs cm−2 sec−1. The electron populations and the resulting arcs were remarkably similar to those observed on the high latitude nightside (poleward of the trapping boundary) but with obviously different source region. There was no persistent 6300 A [OI] auroral emission observed poleward of the trapping boundary consistent with the particle observations. Hydrogen emissions were associated with the discrete aurora, indicating that the main proton energy flux was poleward of the trapping boundary.

Polar cap oh airglow rotational temperatures at the mesopause during a stratospheric warming event

Abstract OH (8-3) band rotational temperature was observed at 78.4°N during a stratospheric wanning event. A negative temperature wave of the order of 40 K observed near the mesopause seems to be associated with a corresponding stratospheric warming of the order of 20 K. A 1–2-day delay is observed between the maximum stratospheric warming and the maximum cooling near the mesopause seen in the OH rotational temperature change.

Multiple brightenings of transient dayside auroral forms during oval expansions

Poleward moving transients have been proposed to be ionospheric signatures of plasma transfer events taking place at the dayside magnetopause. They are usually observed to brighten at the equatorward edge of the dayside auroral oval and fade as they move into the polar cap. This paper reports the observation of a new type of poleward moving dayside auroral transient which has several cycles of intensity variations. Observations of these transients show a series of intensifications in brightness along the arc or rayed band during poleward motion accompanied by a brightening in the auroral oval. As they reach their extreme poleward position they brighten and then fade from view. This brightening sequence may be explained by multiple reconnection of the magnetic flux tube associated with the transient. 24 refs., 5 figs.

Effects of interplanetary magnetic field and magnetospheric substorm variations on the dayside aurora

Abstract Photometric observations of dayside auroras are compared with simultaneous measurements of geomagnetic disturbances from meridian chains of stations on the dayside and on the nightside to document the dynamics of dayside auroras in relation to local and global disturbances. These observations are related to measurements of the interplanetary magnetic field (IMF) from the satellites ISEE-1 and 3. It is shown that the dayside auroral zone shifts equatorward and poleward with the growth and decay of the circum-oval/polar cap geomagnetic disturbance and with negative and positive changes in the north-south component of the interplanetary magnetic field (Bz). The geomagnetic disturbance associated with the auroral shift is identified as the DP2 mode. In the post-noon sector the horizontal disturbance vector of the geomagnetic field changes from southward to northward with decreasing latitude, thereby changing sign near the center of the oval precipitation region. Discrete auroral forms are observed close to or equatorward of the Δ H = 0 line which separates positive and negative H-component deflections. This reversal moves in latitude with the aurora and it probably reflects a transition of the electric field direction at the polar cap boundary. Thus, the discrete auroral forms observed on the dayside are in the region of sunward-convecting field lines. A model is proposed to explain the equatorward and poleward movement of the dayside oval in terms of a dayside current system which is intensified by a southward movement of the IMF vector. According to this model, the Pedersen component of the ionospheric current is connected with the magnetopause boundary layer via field-aligned current (FAC) sheets. Enhanced current intensity, corresponding to southward auroral shift, is consistent with increased energy extraction from the solar wind. In this way the observed association of DP2 current system variations and auroral oval expansion/contraction is explained as an effect of a global, ‘direct’ response of the electromagnetic state of the magnetosphere due to the influence of the solar wind magnetic field. Estimates of electric field, current, and the rate of Joule heat dissipation in the polar cap ionosphere are obtained from the model.

A verification method for space weather forecasting models using solar data to predict arrivals of interplanetary shocks at Earth

The ability to predict the arrival of interplanetary shocks near earth is of great interest in space weather because of their relationship to sudden impulses and geomagnetic storms. A number of models have been developed for this purpose. For models to be used in forecasting, it is important to provide verification in the operational environment using standard statistical techniques because this enables the intercomparison of different models. A verification method is described here, comparing the prediction capabilities of four models that use solar observations for input. Three of the models are based on metric Type II radio burst observations, and one uses halo/partial-halo coronal mass ejections. A method of associating solar events with interplanetary shocks is described. The predictions are compared to associated shocks observed at L1 by the Advanced Composition Explorer (ACE) spacecraft. The time period of this study is January 2002-May 2002. Although the data sample is small, the statistical intercomparison of the results of these models is presented as a demonstration of the verification method.

The SCIFER Experiment

The Sounding of the Cleft Ion Fountain Energization Region (SCIFER) experiment was conducted to investigate the ionospheric origin of the Cleft Ion Fountain (CIF). In the previous decade several high altitude spacecraft studies concluded that the CIF is the principal source of mass for the magnetosphere, especially O+. Yet the ionospheric cleft in the altitude range between 1000 km and 2000 km had not been explored since the ISIS spacecraft experiments in the 1970s. SCIFER was designed to fill that gap with instrumentation that provided continuous spatial/temporal resolution two orders of magnitude better than that achieved by previous orbiting spacecraft.

Modeling and observations of dayside auroral hydrogen emission Doppler profiles

We present a three-dimensional, collision by collision model of the transport and energy degradation of energetic protons incident on the atmosphere. A test of the model was carried out using NOAA 12 satellite measurements of incoming energetic protons as input and simultaneous spectrometric measurements of the resulting dayside auroral hydrogen emission. There is a good match between the calculated and the observed emission profiles. The emission peak of the narrow and symmetric emission profile is positioned 4 A to the blue of the unshifted line center, which is characteristic of the monoenergetic proton precipitation associated with the magnetospheric cusp/cleft, and the “velocity filter” resulting from dayside magnetic field line merging and convection. The intensities of the emission was reproduced using a proton number flux of approximately one-half of that which was obtained by NOAA. The portion of the emission profile to the red of the unshifted line was well within the instrumental broadening. From this we conclude that the contribution of upward moving hydrogen atoms to the observed dayside H emission must be of the order of 10 percent.

Mid-winter hydroxyl night airglow emission intensities in the northern polar region

Abstract Ground-based spectrophotometric measurements of night airglow OH (8-3) band absolute intensities in the polar cap region (78.4°N) during winter solstice are reported. A mean value of 425 ± 40 R is found for the absolute intensity of the OH (8-3) band. Maximum and minimum daily mean values were 770 and 320 R respectively with hourly mean values ranging from 180 to 1020 R. Neither a winter solstice minimum or maximum in the intensity is obvious from the data. No consistent correlation was found between the absolute intensity and geomagnetic and solar activity. A mean transport of O and O 3 into the polar cap region corresponding to a meridional wind speed of at least 20 m s −1 at 90 km height seems necessary to maintain the observed intensity. A dominant semidiurnal tide component is found in the intensity data, both on a 20-day and a 3-day time scale.

The 20-year change of the Svalbard OH-temperatures

Abstract The Meinel bands of OH in the night airglow have been monitored from the Northern Lights Station near Longyearbyen, Svalbard (15°E, 78°N) for the past 20 years. The rotational lines of the (6–2) and (8–3) bands yield a trustworthy measure of the neutral temperature in the upper mesosphere. There is a seasonal winter maximum, but wide variations predominate throughout the winter months. The variations of less than one day have been shown to be due to direct gravity wave forcing and those greater than one day are correlated with warmings in the polar stratosphere. Our analysis shows that the polar upper mesospheric temperature variations correlate best overall with the zonal stratospheric wind at 45°N and 30 hPa, indicating gravity wave filtering at that height and gravity wave forcing from that latitude region. The trend of the timeseries calculated from weekly averages of the rotational temperatures is −0.6 K/year. If the stratospheric wind at 45°N is included in a multiple regression the trend becomes −0.3 K/year.