Rocket observations of the interaction of auroral electrons with the atmosphere

Electron spectra obtained during the flight of Black Brant VB-31 on August 17, 1970 through a stable aurora to a height of 268 km have been analyzed in detail to obtain the pitch angle distributions from 25 to 155° and the electron energy distributions over an energy range of 18 keV to 20 eV through the region of atmospheric interaction down to 97 km. Backscatter ratios for 140° pitch angle range from 0.065 for 18 keV electrons to 0.22 for 1 keV electrons. Backscatter of lower energy electrons decreases with atmospheric depth below 200 km. The effect of the interactions between auroral electrons and the atmosphere is such as to give a peak in electron flux which moves progressively to higher energies with penetration depth. The secondary electron flux increases monotonically with height up to 200 km. The secondary electron spectrum can be approximated by an energy power over small energy ranges but its form is somewhat dependent on height and on the primary electron spectrum.     

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

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 (B_z). 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 ΔH = 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.     

Landslide Research at the British Geological Survey:Capture,Storage and Interpretation on a National and Site-Specific Scale

Abstract: Landslide research at the British Geological Survey (BGS) is carried out through a number of activities, including surveying, database development and real-time monitoring of landslides. Landslide mapping across the UK has been carried out since BGS started geological mapping in 1835. Today, BGS geologists use a combination of remote sensing and ground-based investigations to survey landslides. The development of waterproof tablet computers (BGS·SIGMAmobile), with inbuilt GPS and GIS for field data capture provides an accurate and rapid mapping methodology for field surveys. Regional and national mapping of landslides is carried out in conjunction with site-specific monitoring, using terrestrial LiDAR and differential GPS technologies, which BGS has successfully developed for this application. In addition to surface monitoring, BGS is currently developing geophysical ground-imaging systems for landslide monitoring, which provide real-time information on subsurface changes prior to failure events. BGS’s mapping and monitoring activities directly feed into the BGS National Landslide Database, the most extensive source of information on landslides in Great Britain. It currently holds over 14?000 records of landslide events. By combining BGS’s corporate datasets with expert knowledge, BGS has developed a landslide hazard assessment tool, GeoSure, which provides information on the relative landslide hazard susceptibility at national scale.     

Variability in the determination of total atmospheric ozone using remote sensing spectroscopic techniques

A spectroscopic method for optical remote sensing of total ozone (O₃) is described. It involves detailed spectral matching of near ultraviolet solar observations with synthetic profiles containing various amounts of ozone absorption. Application of this technique is made to airborne solar measurements in the 3100 to 3600 Å wavelength region. In the 3100 to 3200 Å region, measurements made above the tropopause (around geographic latitude 36.7°N, longitude 121.7°W at 0045 UT on 1/23/74) generally fit synthetic profiles constructed with 0.3 atm cm of O₃ absorption andBroadfoot's (1972) extra-terrestrial solar irradiance values. However, there are several sections of the solar spectra where the observed intensity is either significantly higher or lower than the calculated value. In addition, several maxima and minima in the observed spectra do not coincide in wavelength with corresponding features in the synthetic profile. Such problems also appear when comparison is made with synthetic profiles based onArvesen et al.'s (1969) extra-terrestrial solar irradiance measurements. These discrepancies may arise from a combination of sources, including errors in laboratory measured O₃ absorption coefficients, the extra-terrestrial solar irradiance values and the presence of other UV absorbing species in the stratosphere.     

Ground-based observations of O2 (b1Σ+g−X3Σ−g) atmospheric bands in high latitude auroras

Analysis of observed spectrograms is based on comparison with synthetic spectra. The O₂(b¹Σ⁺_g?X³Σ^?_g Atm. (1,1) band in high latitude auroras observed from the ground is found to be the strongest in the Δv = 0 sequence. It is enhanced with altitude relative to the N₂ 1P(2, 0)and N⁺₂ M(2,0) bands, but the O₂ Atm. (2, 2) band has an unexpected low intensity. The range of rotational temperatures of the O₂ Atm. bands varies from approx. 200 to above 500 K which indicates that the altitude of the centroid of the emission region varies from about 100 km to the F-region. The highest temperature is found in the midday aurora associated with the magnetospheric cusp. Conspicuous relative variations between the intensities of N₂ and O₂ spectra are documented, but a satisfactory explanation of the variety is not given. Deviations of the observed O₂ Atm. band intensities from the vibrational intensity distribution predicted by Franck-Condor factors indicate that the excitation of the O₂ Atm. bands in aurora is not mainly due to particle impact on O₂, and the contribution due to energy transfer from hot O(¹D) atoms has to be found in future research.     

Temporal variations in night-time hydroxyl rotational temperature

Airborne and groundbased OH measurements showing short-term temporal variations in OH rotational temperature are presented. The variations are interpreted on the basis of a dynamic model of the OH emitting region; they are also employed to clarify the apparent contradiction in latitude dependence of OH intensity reported in the literature.     

Thermospheric winds in the cusp: Dependence of the latitude of the cusp

The dayside thermospheric wind pattern as observed from Spitsbergen generally shows moderately strong westward winds with a small poleward component. The flow is almost zonal, frequently with sufficient westward velocity that parcels of air cross the noon meridian travelling towards the morning before turning antisunward towards the nightside across the polar cap. There have been some exceptions which are characterized by much weaker winds having been increased in the poleward direction but with a very much reduced westward component. Making use of the meridian scanning photometer data obtained simultaneously on the same site, it is clearly shown that the normal behaviour occurs when the cusp, as indicated by the region of high $\text{630}\text{428}\text{nm}$ and $\text{630}\text{558}\text{nm}$ photometric intensity ratios, is to the North of the station. Just below the latitude of the cusp, the strong thermospheric flow generated by neutral coupling to the strong westward convection in the dusk sector continues across the dayside. It is maintained in the zonal direction because of the balance between the poleward Coriolis force and the equatorward pressure force caused by cusp heating. Poleward of the high pressure region at the cusp the flow is diverted northward and initially makes much slower progress across the Polar Cap. When the auroral oval has expanded such that the cusp is well to the South of our Spitsbergen station, the thermosphere in the sampled region has been found to be within this slow flow zone. On such occasions, the nightside speeds are well in excess of those on the dayside, in contrast to the normal behavior of comparable dayside and nightside wind speeds.     

Particle and optical measurements in the magnetic noon sector of the auroral oval

Simultaneous airborne photometric and satellite particle measurements in the mid-day sector of the auroral oval, around magnetic local noon, are presented. The two sets of measurements are employed independently to delineate various magnetospheric boundaries. The results derived from the particle measurements are compared with those from the photometric observations to assess the reliability of the photometric technique in identifying various magnetospheric regions.