We study the occurrence of relativistic microbursts observed by the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX) satellite. An algorithm is used to identify 193,694 relativistic microbursts in the > 1.05 MeV electron fluxes occurring across the time period 23 August 1996 to 11 August 2007, nearly a full solar cycle. Our observations are normalized to provide the change in absolute occurrence rates with various parameters. We find that relativistic microbursts are mostly confined to the outer radiation belt, from L = 3–8, occurring primarily on the morningside, between 0 and 13 magnetic local time (MLT). This L and MLT distribution is consistent with the L and MLT distribution of whistler mode chorus amplitude. Thus, our observations favor whistler mode chorus wave activity as a driver of relativistic microbursts. Relativistic microbursts become more frequent as the geomagnetic activity level increases and are more frequent during equinoxes than during the solstices. The peak occurrence frequency of the relativistic microbursts moves to lower L as the geomagnetic activity increases, reaching a peak occurrence rate of one microburst every 10.4 s (on average) at L = 4 for 6.6 ≤ Kp ≤ 8.7. Microbursts primarily occur outside of the plasmapause and track the inward movement of the plasmapause with increasing geomagnetic activity. The L and MLT distribution of the relativistic microbursts exhibits a peak occurrence of one microburst every 8.6 (98.0) s during active (disturbed) conditions, with the peak located at L = 5 (L = 5.5) and 08 (08) MLT.

Relativistic electron microbursts are short‐duration, high‐energy precipitation events that are an important loss mechanism for radiation belt particles. Previous work to estimate their atmospheric impacts found no significant changes in atmospheric chemistry. Recent research on microbursts revealed that both the fluxes and frequency of microbursts are much higher than previously thought. We test the seasonal range of atmospheric impacts using this latest microburst information as input forcing to the Sodankylä Ion and Neutral Chemistry model. A modeled 6 h microburst storm increased mesospheric HOx by 15–25%/800–1,200% (summer/winter) and NOx by 1,500–2,250%/80–120%. Together, these drive 7–12%/12–20% upper mesospheric ozone losses, with a further 10–12% longer‐term middle mesospheric loss during winter. Our results suggest that existing electron precipitation proxies, which do not yet take relativistic microburst energies into account, are likely missing a significant source of precipitation that contributes to atmospheric ozone balance.

Relativistic electron microbursts are an important electron loss process from the radiation belts into the atmosphere. These precipitation events have been shown to significantly impact the radiation belt fluxes and atmospheric chemistry. In this study we address a lack of knowledge about the relativistic microburst intensity using measurements of 21,746 microbursts from the Solar Anomalous Magnetospheric Particle Explorer (SAMPEX). We find that the relativistic microburst intensity increases as we move inward in L, with a higher proportion of low‐intensity microbursts (<2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region. The mean microburst intensity increases by a factor of 1.7 as the geomagnetic activity level increases and the proportion of high‐intensity relativistic microbursts (>2,250 [MeV cm2 sr s]−1) in the 03–11 magnetic local time region increases as geomagnetic activity increases, consistent with changes in the whistler mode chorus wave activity. Comparisons between relativistic microburst properties and trapped fluxes suggest that the microburst intensities are not limited by the trapped flux present alongside the scattering processes. However, microburst activity appears to correspond to the changing trapped flux; more microbursts occur when the trapped fluxes are enhancing, suggesting that microbursts are linked to processes causing the increased trapped fluxes. Finally, modeling of the impact of a published microburst spectra on a flux tube shows that microbursts are capable of depleting <500‐keV electrons within 1 hr and depleting higher‐energy electrons in 1–23 hr.

Relativistic electron microbursts are a known radiation belt particle precipitation phenomenon; however, experimental evidence of their drivers in space have just begun to be observed. Recent modeling efforts have shown that two different wave modes (whistler mode chorus waves and electromagnetic ion cyclotron (EMIC) waves) are capable of causing relativistic microbursts. We use the very low frequency/extremely low frequency Logger Experiment and search coil magnetometer at Halley, Antarctica, to investigate the ground‐based wave activity at the time of the relativistic microbursts observed by the Solar Anomalous Magnetospheric Particle Explorer. We present three case studies of relativistic microburst events, which have one or both of the wave modes present in ground‐based observations at Halley. To extend and solidify our case study results, we conduct superposed epoch analyses of the wave activity present at the time of the relativistic microburst events. Increased very low frequency wave amplitude is present at the time of the relativistic microburst events, identified as whistler mode chorus wave activity. However, there is also an increase in Pc1–Pc2 wave power at the time of the relativistic microburst events, but it is identified as broadband noise and not structured EMIC emissions. We conclude that whistler mode chorus waves are, most likely, the primary drivers of relativistic microbursts. However, case studies confirm the potential of EMIC waves as an occasional driver of relativistic microbursts.

We use the World Wide Lightning Location Network to investigate lightning strike variations in 8 years of categories 4 and 5 tropical cyclones. A cross‐correlation analysis is performed between the lightning and maximum sustained wind variations, giving lag and lead times related to the peak linear correlation for each tropical cyclone. A previous study of 58 cyclones by Price et al. (2009) is reexamined using the International Best Track Archive for Climate Stewardship database for the maximum sustained wind speeds of each tropical cyclone showing a moderate to strong correlation between lightning and wind variations. An 8 year data set of 144 tropical cyclones are analyzed in the same way, with a 10° square window, giving similar results to the smaller data set. Using a radial lightning collection window of < 500 km, we confirm the general results of previous studies that lightning can be used on a ∼1 day timescale to predict the evolution of the winds in tropical cyclones. Investigation of different lightning collection window sizes indicates that the lightning lead times are highly dependent upon the window size. Smaller collection windows have modal lightning lead times of ∼2.75 and 0 days, indicating that the lightning location inside the cyclone is as important as the total lightning variation. We have also performed a fixed time lag correlation which shows that preexisting knowledge of what time lag to use is needed in order to use this approach as a predictive tool.