M. M. Lam

Modeling the effects of radial diffusion and plasmaspheric hiss on outer radiation belt electrons

We simulate the behaviour of relativistic (976 keV) electrons in the outer radiation belt (3 ≤ L ≤ 7) during the first half of the CRRES mission. We use a 1d radial diffusion model with losses due to pitch-angle scattering by plasmaspheric hiss expressed through the electron lifetime calculated using the PADIE code driven by a global K p -dependent model of plasmaspheric hiss intensity and f pe /f ce . We use a time and energy-dependent outer boundary derived from observations. The model reproduces flux variations to within an order of magnitude for L ≤ 4 suggesting hiss is the dominant cause of electron losses in the plasmasphere near the equator. At L = 5 the model reproduces significant variations but underestimates the size of the variability. We find that during magnetic storms hiss can cause significant losses for L ≤ 6 due to its presence in plumes. Wave acceleration is partially represented by the boundary conditions.

The interplanetary magnetic field influences mid-latitude surface atmospheric pressure

The existence of a meteorological response in the polar regions to fluctuations in the interplanetary magnetic field (IMF) component By is well established. More controversially, there is evidence to suggest that this Sun–weather coupling occurs via the global atmospheric electric circuit. Consequently, it has been assumed that the effect is maximized at high latitudes and is negligible at low and mid-latitudes, because the perturbation by the IMF is concentrated in the polar regions. We demonstrate a previously unrecognized influence of the IMF By on mid-latitude surface pressure. The difference between the mean surface pressures during times of high positive and high negative IMF By possesses a statistically significant mid-latitude wave structure similar to atmospheric Rossby waves. Our results show that a mechanism that is known to produce atmospheric responses to the IMF in the polar regions is also able to modulate pre-existing weather patterns at mid-latitudes. We suggest the mechanism for this from conventional meteorology. The amplitude of the effect is comparable to typical initial analysis uncertainties in ensemble numerical weather prediction. Thus, a relatively localized small-amplitude solar influence on the upper atmosphere could have an important effect, via the nonlinear evolution of atmospheric dynamics, on critical atmospheric processes.

Solar wind‐driven geopotential height anomalies originate in the Antarctic lower troposphere

We use National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis data to estimate the altitude and time lag dependence of the correlation between the interplanetary magnetic field component, By, and the geopotential height anomaly above Antarctica. The correlation is most statistically significant within the troposphere. The peak in the correlation occurs at greater time lags at the tropopause (∼6–8 days) and in the midtroposphere (∼4 days) than in the lower troposphere (∼1 day). This supports a mechanism involving the action of the global atmospheric electric circuit, modified by variations in the solar wind, on lower tropospheric clouds. The increase in time lag with increasing altitude is consistent with the upward propagation by conventional atmospheric processes of the solar wind-induced variability in the lower troposphere. This is in contrast to the downward propagation of atmospheric effects to the lower troposphere from the stratosphere due to solar variability-driven mechanisms involving ultraviolet radiation or energetic particle precipitation.

Lightning as a space-weather hazard:UK thunderstorm activity modulated by the passage of the heliospheric current sheet

Lightning flash rates, RL, are modulated by corotating interaction regions (CIRs) and the polarity of the heliospheric magnetic field (HMF) in near-Earth space. As the HMF polarity reverses at the heliospheric current sheet (HCS), typically within a CIR, these phenomena are likely related. In this study, RL is found to be significantly enhanced at the HCS and at 27 days prior/after. The strength of the enhancement depends on the polarity of the HMF reversal at the HCS. Near-Earth solar and galactic energetic particle fluxes are also ordered by HMF polarity, though the variations qualitatively differ from RL, with the main increase occurring prior to the HCS crossing. Thus, the CIR effect on lightning is either the result of compression/amplification of the HMF (and its subsequent interaction with the terrestrial system) or that energetic particle preconditioning of the Earth system prior to the HMF polarity change is central to solar wind lightning coupling mechanism.

The effect of Forbush decreases on tropospheric parameters over South Pole

Abstract Egorova et al. (2000) conclude that Forbush decreases (FDs) in galactic cosmic rays have a significant effect on the atmosphere at Antarctic station Vostok (78.5°S, 106.9°E) via the mechanism of electrofreezing. We present the results of a similar study at South Pole (90.0°S), located ∼1000 km from Vostok, which has been conducted in order to examine the spatial extent of this phenomenon. Both Vostok and South Pole are ideal locations at which to search for such an effect since they are subject to relatively stable weather regimes. We find no observable effect of FDs on the atmosphere above South Pole. We discuss possible reasons for the disagreement between the results of the two studies and conclude that it is due to differences in methodology.