9 research outputs found
Diagnosing the Meteorological Conditions Associated with Sprites and Lightning with Large Change Moment Charges (CMC) over Oklahoma
Sprites are a category of Transient Luminous Events (TLE's) that occur in the upper atmosphere above the tops of Mesoscale Convective Systems (MCSs). They are commonly associated with lightning strokes that produce large charge moment changes (CMCs). Synergistic use of satellite and radar-retrieved observations together with sounding data, forecasts, and lightning-detection-networks allowed the diagnosis and analysis of the meteorological conditions associated with sprites as well as large-CMC lightning over Oklahom
Diagnosing Meteorological Conditions Associated with Sprites and Lightning with Large Charge Moment Changes (CMC) over Oklahoma
Sprites are a category of Transient Luminous Events (TLEs) that occur in the upper atmosphere above the tops of Mesoscale Convective Systems (MCSs). They are commonly associated with lightning strokes that produce large charge moment changes (CMCs). Synergistic use of satellite and radar-retrieved observations together with sounding data, forecasts, and lightning-detection networks allowed the diagnosis and analysis of the meteorological conditions associated with sprites as well as large-CMC lightning over Oklahoma. One goal of the NASA-funded effort reported herein is the investigation of the potential for sprite interference with aerospace activities in the 20- 100km altitude range, including research balloons, space missions and other aviation transports
Diagnosing Meteorological Conditions Associated with Sprites and Lightning with Large Charge Moment Changes (CMC) over Oklahoma
Sprites are a category of Transient Luminous Events (TLEs) that occur in the upper atmosphere above the tops of Mesoscale Convective Systems (MCSs). They are commonly associated with lightning that produce large charge moment changes (CMCs). Synergistic use of satellite and radarretrieved observations together with sounding data, forecasts, and lightningdetection networks allowed the diagnosis and analysis of the meteorological conditions associated with sprites as well as largeCMC lightning over Oklahoma
Hydrodynamical simulations of protoplanetary disks including irradiation of stellar photons. I. Resolution study for Vertical Shear Instability (VSI)
In recent years hydrodynamical (HD) models have become important to describe
the gas kinematics in protoplanetary disks, especially in combination with
models of photoevaporation and/or magnetic-driven winds. We focus on diagnosing
the the vertical extent of the VSI at 203 cells per scale height and allude at
what resolution per scale height we obtain convergence. Finally, we determine
the regions where EUV, FUV and X-Rays are dominant in the disk. We perform
global HD simulations using the PLUTO code. We adopt a global isothermal
accretion disk setup, 2.5D (2 dimensions, 3 components) which covers a radial
domain from 0.5 to 5.0 and an approximately full meridional extension. We
determine the 50 cells per scale height to be the lower limit to resolve the
VSI. For higher resolutions, greater than 50 cells per scale height, we observe
the convergence for the saturation level of the kinetic energy. We are also
able to identify the growth of the `body' modes, with higher growth rate for
higher resolution. Full energy saturation and a turbulent steady state is
reached after 70 local orbits. We determine the location of the EUV-heated
region defined by the radial column density to be 10 cm located
at , and the FUV/X-Rays-heated boundary layer defined by
10 cm located at , making it necessary to
introduce the need of a hot atmosphere. For the first time, we report the
presence of small scale vortices in the r-Z plane, between the characteristic
layers of large scale vertical velocity motions. Such vortices could lead to
dust concentration, promoting grain growth. Our results highlight the
importance to combine photoevaporation processes in the future high-resolution
studies of the turbulence and accretion processes in disks
Large Charge Moment Change Lightning in an Oklahoma Mesoscale Convective System
On 31 May 2013, a line of severe thunderstorms developed during the local afternoon in central Oklahoma, USA. One of the supercells produced the El Reno tornado, which caused significant damage and killed several people. During the 2300 UTC hour (during the mature supercell stage and just after the tornado began), the storm produced several positive cloud-to-ground (+CG) lightning strokes that featured large (> 100 C km) impulse charge moment changes (iCMCs; charge moment during the first 2 ms after the return stroke). These discharges occurred mainly in convection, in contrast to the typical pattern of large-CMC and sprite-parent +CGs occurring mainly in stratiform precipitation regions. After this time, the line of thunderstorms evolved over several hours into a large mesoscale convective system (MCS). By the 0700 UTC hour on 1 June 2013, the large-CMC pattern had changed markedly. Large-CMC negative CGs, which were absent early in the storm's lifetime, occurred frequently within convection. Meanwhile, large-CMC +CGs had switched to occurring mainly within the broad stratiform region that had developed during the intervening period. The evolution of the large-CMC lightning in this case will be examined using a mix of national mosaics of radar reflectivity, the Oklahoma Lightning Mapping Array (OKLMA), the Charge Moment Change Network (CMCN), and the National Lightning Detection Network (NLDN). A major goal of this study is understanding how storm structure and evolution affected the production of large-CMC lightning. It is anticipated that this will lead to further insight into how and why storms produce the powerful lightning that commonly causes sprites in the upper atmosphere
Large Charge Moment Change Lightning in an Oklahoma Mesoscale Convective System
No abstract availabl
EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc
Earth-sized exoplanets that transit nearby, late spectral type red dwarfs
will be prime targets for atmospheric characterization in the coming decade.
Such systems, however, are difficult to find via wide-field transit surveys
like Kepler or TESS. Consequently, the presence of such transiting planets is
unexplored and the occurrence rates of short-period Earth-sized planets around
late M dwarfs remain poorly constrained. Here, we present the deepest
photometric monitoring campaign of 22 nearby late M dwarf stars, using data
from over 500 nights on seven 1-2 meter class telescopes. Our survey includes
all known single quiescent northern late M dwarfs within 15 pc. We use
transit-injection-and-recovery tests to quantify the completeness of our
survey, successfully identify most () transiting short-period (0.5-1 d)
super-Earths (), and are sensitive () to transiting
Earth-sized planets (). Our high sensitivity to transits with
a near-zero false positive rate demonstrates an efficient survey strategy. Our
survey does not yield a transiting planet detection, yet it provides the most
sensitive upper limits on transiting planets orbiting our target stars.
Finally, we explore multiple hypotheses about the occurrence rates of
short-period planets (from Earth-sized planets to giant planets) around late M
dwarfs. We show, for example, that giant planets at short periods ( day)
are uncommon around our target stars. Our dataset provides some insight into
occurrence rates of short-period planets around TRAPPIST-1-like stars, and our
results can help test planetary formation and system evolution models, as well
as guide future observations of nearby late M dwarfs.Comment: 27 pages, 11 figure
Connecting simulations of protoplanetary disks with forbidden emission lines observations
The big picture of the planet formation scenario is sought by understanding the interplay between the gas and dust dynamics in protoplanetary disks. In particular, the gas dynamics in accretion disks have been carefully studied in a purely hydrodynamical set up where the vertical shear instability (VSI) play a major role in the transport of the angular momentum and turbulence throughout the disk. Though, it is very difficult to directly measure the angular
momentum transport, mechanisms that affect it are the launch of magneto centrifugal winds (MHD winds), outflows, and the launch of thermal photoevaporative winds. One way to pin point these processes is by identifying forbidden emissions lines in the disk spectrum and analyze their velocity components that are originating in highly ionized gas. The exact
thermochemical conditions in active accreting disks that cause the emission of different forbidden emission lines is very challenging to determine. To understand such outflows, the wind launching mechanisms and their effects to the angular momentum transport require the knowledge of a full global picture of hydro- and thermal- dynamical configurations.
The work presented here covers a broad range of scenarios that are important for the evolution and dispersal of the protoplanetary disk. Our focus relies more on the dynamics and the thermo-chemistry conditions at the surface of the disk. We found that the VSI is active until the location of the wind base. The characteristic vertical velocity in this region is about a fraction of the sound speed. For the first time, we report small scale vortices appearing in VSI active disks which influence especially the dust evolution. From spectral and imaging observations obtained from the Multi-unit Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT), high velocity components (HVCs; 100 km~s) are detected at the inner parts of the disks as outflows/jets that are aligned within 1 degree with respect to the outer disk. With our current and upcoming global hydrodynamical models including thermochemistry and observations, we will reveal the detailed chemical and physical conditions of protoplanetary disks with active winds at the surface
Forbidden emission lines in protostellar outflows and jets with MUSE
Context. Forbidden emission lines in protoplanetary disks are a key diagnostic in studies of the evolution of the disk and the host star. They signal potential disk accretion or wind, outflow, or jet ejection processes of the material that affects the angular momentum transport of the disk as a result.
Aims. We report spatially resolved emission lines, namely, [O