Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 58, Number 12
Friday–Saturday, October 18–19, 2013; Denver, Colorado
Session M2: Atmospheric Physics |
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Chair: Shane Larson, Northwestern University Room: 254 |
Saturday, October 19, 2013 2:15PM - 2:39PM |
M2.00001: On the Importance of Stratospheric Chemistry to the Physics of Climate Invited Speaker: Ken Minschwaner The vast majority of climate studies have been focused on physical processes in the troposphere - the lowest 10 to 15 km of the atmosphere near the Earth's surface. It makes perfect sense to focus on tropospheric processes since they generally exert a dominant influence on climate variables of most interest, such as surface temperature, precipitation, and circulation patterns. However, there are a number of chemical and photochemical processes occurring in the stratosphere - above about 15 km altitude - that can play an important role in shaping the climate system. The most obvious case is that of stratospheric ozone, but there are other trace gases and stratospheric chemical systems that exert both direct and indirect effects on climate. This talk will include an overview of some of the more important processes and present findings from recent research, such as estimating atmospheric lifetimes for many of the important non-CO$_2$ greenhouse gases. [Preview Abstract] |
Saturday, October 19, 2013 2:39PM - 2:51PM |
M2.00002: Digital Interferometry for Studies of Leaders in Natural Lightning Richard Sonnenfeld, Jeff LaPierre, Mike Stock, Paul Krehbiel, Manabu Akita Fully digital broadband (20-80 MHz) radio interferometers (DITFs) optimized to study lightning are a new development. They overcome the ``phase-wrap'' problem of earlier narrow-band analog interferometers and can locate a source in a lightning channel as often as every 10 nanoseconds. DITFs show phenomena long suspected, but not previously visible. For example, K-changes, (millisecond steps in electric field after a cloud-to-ground discharge), are shown by the DITF to be recoil streamers along a previously formed channel. Used in concert with a lightning mapping array and slow-antenna (1-50000 Hz) electric field sensors, DITFs are also allowing discovery and understanding of new features of lightning. For example, on 8/12/2012, at 21:45:42 UT, a ``bolt-from-the-blue'' negative leader emerged from a cloud-top 30-miles Southeast of Langmuir Laboratory in New Mexico. Slow-antenna measurements showed electric field steps of 0.001 s duration looking much like K-changes, but occurring BEFORE the first return-stroke of this long leader. We speculate that these steps (which we call U-changes -- U for ``unknown'') are (like K-changes) reionization waves that feed the growing channel and keep it hot enough to proceed all the way to ground. During a U-change, the DITF shows channels reilluminated over several kilometers of altitude. [Preview Abstract] |
Saturday, October 19, 2013 2:51PM - 3:03PM |
M2.00003: A Study of Lightning Discharges over Costa Rica during a Period of Intense Electrical Activity: May and June of 2009 Jose Martinez, Walter Fernandez, Ileana Mora Intense electrical activity in storm clouds is a common characteristic of rainy seasons in Costa Rica. The most common type of electrical discharge observed in this study was cloud-ground (CG) lightning, which is generally linked to its destructive potential on property and human lives. Intra-cloud (IC) lightning events, which are known to occur much more frequently on a global scale than CG events, are also present during intense storms. Using the National Network for Detection and Analysis of Electrical Discharges, operated by the Costa Rican Institute of Electricity (ICE), more than a million stroke events were recorded by the network during months of May and June 2009. Analysis of spatial and temporal distributions of lightning events show that CG discharges occur more frequently during the day, with a maximum in the afternoon, while IC discharges occur more frequently during the night. During these months, a higher concentration of both types of discharges were observed on the Pacific side of Costa Rica, rather than in the Atlantic side. This spatial and temporal information can be related to sea breeze circulations and the diurnal cycle for convective activity in tropical regions. [Preview Abstract] |
Saturday, October 19, 2013 3:03PM - 3:15PM |
M2.00004: Utilizing Yagi antennas in Lightning Mapping Array to detect low-power VHF signals Julia Tilles, Ronald Thomas, Harald Edens, Paul Krehbiel, William Rison The New Mexico Tech VHF Lightning Mapping Array (LMA), operated by Langmuir Laboratory, is comprised of 22 stations, each utilizing a vertical half-wave dipole (azimuthally ``omni-directional'') antenna. The stations detect RF impulses from lightning---from the multiple detection sites, a 3-D map of lightning can be constructed. LMA maps greatly aid research of the initiation and structure of lightning. In 2012, four higher-gain Yagi (``directional'') antennas were installed, co-located with four LMA stations. The purpose was to test if an array of higher-gain directional antennas would improve detection of low-power sources associated with the initiation of lightning, e.g. sources resulting from positive breakdown (a weakly radiating stage of lightning initiation) or from (weakly radiating) lightning precursor events. The greater detection sensitivity of the Yagi antennas (in the on-axis direction) was demonstrated. However, preliminary results show that the use of Yagi antennas provide no new significant insight into the flash structure for either positive or negative breakdown channels. This (negative) result may provide the LMA research community with new limits to the detection of weakly-radiating discharges; alternatively, it may be due to a need for more Yagi stations. [Preview Abstract] |
Saturday, October 19, 2013 3:15PM - 3:27PM |
M2.00005: Organization of atmospheric convection in a simplified atmospheric model Stipo Sentic, Sharon Sessions Atmospheric convection can spontaneously aggregate into intensely precipitating regions surrounded by extremely dry air. This phenomena may be related to hurricane formation, and may be especially important in a warming climate. Modeling self-aggregation of deep convection is difficult because some numerical models are able to reproduce the phenomenon while others are not and it is not understood why. A recent study by Craig and Mack (2013) modeled convective self-aggregation by assuming an experimental relationship between precipitation and atmospheric moisture content. The actual relationship between moisture and precipitation is still under scientific debate, so we explore the sensitivity of self-aggregation in the Craig and Mack model do different precipitation-moisture dependencies. We find that the specific precipitation-moisture relationship strongly influences aggregation in this model. This finding may help us understand why more complex numerical models do not produce self-aggregation of convection, based on their intrinsic precipitation-moisture relationships. [Preview Abstract] |
Saturday, October 19, 2013 3:27PM - 3:39PM |
M2.00006: Modeling the propagation of spectacular Chelyabinsk meteor Alexander Panin On March 15, 2013 about 9:20 local time a small asteroid entered Earth atmosphere at shallow angle and after $\sim$ 700 km travel exploded at about 25 km altitude near Chelyabinsk, Russian Federation with the peak brightness dwarfing Sun. The generated shock wave blasted windows in thousands of buildings injuring several hundred people (mostly by flying glass and debris) and was detected all around the globe. Numerous videos of propagating bolide were recorded by dash and security cameras. Using simple collisional model we numerically simulated the propagation of such asteroid through the atmosphere and present here the results - such as asteroid trajectory, air drag, generated thermal power, shock wave intensity, damage areas, etc. Using this model we will also discuss the possible impact of various other asteroids ranging in size from a few meters to few a kilometers. [Preview Abstract] |
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