June 21, 2013, 12:00 pm - 1:00 pm
June 21, 2013, 12:00 pm - 1:00 pm, Heliophysics Director's Seminar
Estimating the interplanetary dust mass input into terrestrial atmospheres
Diego Janches(674)
Layers of neutral metal atoms, such as Fe, Mg, Ca, K and Na, which peak between 85 and 95 km and are ~20 km in width, are produced by the daily ablation of billions of Interplanetary Dust Particles (IDPs). Once the meteoric metals are injected into the Earth's upper atmosphere they are responsible for a diverse range of phenomena, including the formation of layers of metal atoms and ions; nucleation of noctilucent clouds; impacts on stratospheric aerosols and O3 chemistry; and fertilization of the ocean with bio-available Fe, which has potential climate feedbacks. These phenomena extend to other planetary atmospheres in the Solar System: low-lying sporadic ion layers have also been observed recently on Mars (~90 km), Venus (~120 km) and Titan (~550 km), using radio occultation measurements from spacecraft, and noctilucent clouds have been observed in the Martian mesosphere. The total mass of the micrometeoroid input that is ablated in the upper atmosphere, which gives rise to these terrestrial phenomena, is a widely debated quantity, and estimates vary by 2 orders of magnitude. The accurate determination of the total incoming mass is a compelling question for geospace sciences and is fundamental for the understanding of all layered phenomena in the mesopause region. If the upper range of estimates is correct, then vertical transport in the middle atmosphere must be considerably faster than generally believed; whereas if the lower range is correct, then our understanding of dust evolution in the solar system, and transport from the middle atmosphere to the surface, will need substantial revision. I will summarize efforts to determine a consistent value for the IDP input, carried out by an international and interdisciplinary scientific team in order to gain a much improved understanding of the impacts of meteoric ablation throughout the atmosphere.
Fireflies in the Sun’s garden!
S. E. Guidoni (674)
High cadence observations of energy released by solar flares show discrete pulsations over a vast energy spectrum, from radio to hard x-rays. This suggests that the mechanism behind the onset of flares, magnetic reconnection, is patchy and intermittent, like fireflies blinking on and off in a garden on a summer night. In some cases, the sources of these pulsations are situated near the apex of flare loop arcades. Although it is unclear whether all the observed varieties of pulsations can be explained via a single, unified process, our recent high-resolution simulations of an eruptive flare (Karpen et al. 2012) indicate that spatially and temporally localized reconnection is a plausible candidate for these coronal bursts of radiation. I will present the motivating observations and discuss the evidence from our simulations for this explanation.
COMPTEL/CGRO Data as an Untapped Source for Gamma-ray Line Solar Flares
C. Alex Young (670)
Despite the prodigious observations of solar flares by both spacecraft and ground-based instruments, the underlying physics that drives particle acceleration is still not well understood. The best indicator of what is taking place in high-energy flares is the secondary neutral radiation that the accelerated particles produce, i.e., γ rays and neutrons. Only they have an untarnished heritage, an origin in the low corona or chromosphere and are free of transport effects between the Sun and Earth. The most sensitive instrument pointed at the Sun to measure and detect γ rays was the COMPton TELescope (COMPTEL) instrument on the Compton Observatory. Yet, the well of COMPTEL data was only superficially plumbed. This was because of the complex nature of the data processing, instrument response and significant livetime effects that it suffered during intense flares. We present a look at COMPTEL’s observations of gamma-ray solar flares and discuss an initial look at its potential for further studies.