LASP: Laboratory for Atmospheric and Space Physics

DATE

Speaker/comment

Title/abstract

Location

Aug 28

Professor Robert L. McPherron
Institute of Geophysics and Planetary Physics,
University of California Los Angeles

THEMIS spacecraft and ground observations of Substorms in the Earth's Magnetotail

Abstract:
Turbulence in the equatorial magnetic field 8 and 12 Re behind the Earth near midnight is known to be associated with the onset of the substorm expansion phase. It has been suggested by many researchers that this turbulence is some intrinsic instability of the inner edge of the tail current sheet. They postulate that convection and current sheet thinning during the substorm growth phase produce conditions allowing instability to develop. An alternate hypothesis is that the turbulence is created by the arrival of a fast plasma flow from the midtail region produced by magnetic reconnection. We use observations from five THEMIS spacecraft during a major conjunction on February 26, 2008 to study possible causes of this turbulence. For two events that occurred during extremely weak electrojet activity we show that the turbulence begins after the arrival of a fast flow. Furthermore, Pi 2 activity at the foot points of the spacecraft is delayed relative to the arrival of the flow and the onset of turbulence. In a separate paper by members of the THEMIS team it is demonstrated that these flows are produced by X-lines Earthward of 23 Re.

LSTB

Sep 4

4-5:00 P.M.

Stefan Eriksson, LASP

FTE Dynamics and Effects on Local and Remote Regions Near the Dayside Magnetopause Reconnection Layer

Abstract:
The Themis mission consists of five identical spacecraft (TH-A, B, C, D, E) that were launched on 17 February 2007 into a near-equatorial Earth orbit. The initial coast phase of the mission with all five probes in the same 1.07 by 15.4 RE configuration lasted until mid-September 2007. The maximum distance between the four leading probes during this string-of-pearl phase was often 1.5 RE or less and provides a unique opportunity to study spatio-temporal behavior of dayside magnetopause magnetic reconnection exhausts such as the dynamics of so-called Flux Transfer Events (FTEs) which are believed to be generated as the rate of reconnection changes.
Several near-simultaneous bipolar magnetic field signatures were observed by Themis on 8 June 2007 during an outbound postnoon magnetopause (MP) crossing in a string-of-pearl configuration. We interpret each as an FTE event. Whether observed in the magnetosheath or in the dayside magnetosphere, we show that each FTE event is unambiguously linked to the MP layer and the northward reconnection exhausts during these steady southward IMF conditions.
Unlike the other probes, TH-C observed a bifurcated MP current as it traversed the active MP layer. This MP crossing was also unique in that it lacked any clear bipolar signatures. A high-resolution BATSRUS MHD simulation (0.0626 RE) suggests that the bifurcation can be generated temporarily in the wake of a passing FTE.
The same MHD simulation suggests that all of the simultaneously observed FTE signatures can be explained in terms of a single flux rope within the active MP layer and its remote effects on the dayside magnetosphere and the magnetosheath adjacent to the MP. Cold ions in the dayside magnetosphere with characteristic time-of-flight energy dispersions are likely one such remote effect of the passing FTEs in the nearby MP layer as indicated by the generation of a standing wave train in the normal component of the simulated plasma velocity (VN) and corroborated by the observed VN.

LSTB, A200

Sep 11

Xinlin Li, LASP

THEMIS Mission, a miracle! (low cost and high science return)

Abstract:
THEMIS, an acronym for Time History of Events and Macroscale Interactions During Substorms and also represents the goddess of justice in Greek mythology, was successfully launched on 2/17/2007 the Cape Canaveral, Florida. It was the first time in NASA's history to launch five identical space probes with a single launch vehicle (Delta-II). The five space probes are placed in desired orbits to measure charged particles over a broad energy range, and electric and magnetic fields. Its primary science objective is to answer fundamental questions regarding the magnetospheric substorm instability, a dominant mechanism of transport and explosive release of solar wind energy within Geospace. It will also help to address the source populations of the radiation belt electrons and study the bow shock and magnetopause. In the presentation, I will describe some engineering challenges associated with THEMIS mission and some science high lights achieved and LASP's involvement in this great mission.

LSTB 299

Sep 18

Seminar
Cancelled

Please note:

This seminar has been rescheduled.

Simone Tilmes will now be speaking on October 23rd.

Duane

Sep 25

Melissa Trainer, Research Associate, LASP, University of Colorado

A Closer Look at the Chemistry of Organic Hazes on Titan and the Early Earth

Abstract:
Recent exploration by the Cassini/Huygens mission has stimulated a great deal of interest in Saturn’s moon, Titan. One of Titan’s most captivating features is the thick organic haze layer surrounding the moon, formed in the CH₄/N₂ atmosphere. It has been suggested that a similar haze layer may have formed on the early Earth. However, due to differences in atmospheric chemistry, the aerosols formed on the early Earth may have had distinct chemical and optical properties from those suspected to make up the hazes on Titan. We have conducted laboratory experiments to demonstrate the properties of haze likely to form via photochemistry on Titan and early Earth. Our past studies of the chemical composition of these aerosols used a quadrupole (unit resolution) Aerosol Mass Spectrometer (AMS) to determine that a large variety of organic molecules is produced from the photolysis of these simple gas mixtures. New work on the hazes utilizing a high resolution Time-of-Flight AMS has provided exact mass identification of molecular fragments, and thus enriching new detail regarding the chemical make-up of the haze particles. This seminar will discuss why the chemistry of the organic hazes is interesting, and why the chemistry may be even more interesting than previously thought.

Duane
D-142

Oct 2

Dr. Hanspeter Schaub,
Department of Aerospace Engineering Sciences, U. of Colorado

Title: Electrostatic Spacecraft Relative Control Applications

Abstract:
Recently the concept of controlling the relative motion of spacecraft using electrostatic charging (Coulomb forces) has been proposed. For tight spacecraft formations with separation distances ranging from 10--100 meters, the Coulomb forces between the spacecraft can be exploited to provide an extremely fuel and power efficient means of propulsion with a fast response time and large control bandwidth. This relative motion control methods enables interesting new close proximity flying operators to yield distributed or inter-connected structures with variable size and shapes. Applications range from docking maneuvers, circumnavigation of probes about a mother craft, virtual Coulomb tethers, virtual Coulomb structures to spinning interferometric systems. The presentation will discuss the Coulomb thrusting concept and present 2 recent research projects. First novel closed- and open-loop close-proximity collision avoidance control strategies are discussed. Here the spacecraft charge is servoed to produce a combination of repulsive and attractive forces to enforce a desired minimum separation distance while avoiding drastic changes to the initial relative velocity vectors. Second, a new light weight space structure concept called the Tethered Coulomb Structure (TCS) is discussed. Here the structure is composed of a distributed set of nodes which are interconnected through thin tethers. To enable three dimensional shapes which in Earth's orbit, the nodes are charged to produce repulsive forces which ensure tether tension at all times. This system creates a deployable structure dozens of meters in size which can change its shape and size by varying the tether lengths. The initial studies show that the required repulsive forces are similar to those that occur due to natural charging at GEO.

Speaker-Bio:
Dr. Schaub is an associate professor and an H. Joseph Smead Fellow of the Aerospace Engineering Sciences department at the University of Colorado at Boudler. He is an associate fellow of AIAA and member of AAS. His 13 years of professional interests are in nonlinear dynamics and control applications, with a special emphasis on astrodynamics. He has performed research in spacecraft attitude and control, exploiting nonlinear dynamics of control moment gyros to avoid classical CMG singularities, as well as extensive research in spacecraft formation flying dynamics and control problems. His current interests include charged relative motion dynamics and control, as well as visual servoing of autonomous vehicles. Dr. Schaub's prior work experience includes 4 years at the Sandia National Labs Intelligent Systems and Robotics Center (ISRC), and 4 years at the Virginia Tech aerospace and ocean engineering department as an assistant professor. He has authored about 40+ peer reviewed papers, presented 60+ conference papers, published a text book on analytical mechanics of space systems, and holds a patent on a noncontact position and orientation measurement system.

LSTB

Oct 9

Lars Hoffmann,

Forschungszentrum Juelich, ICG-1, Juelich, Germany

New Satellite Measurements of Stratospheric Gravity Waves

LSTB

Oct 16

Scott Palo/The DANDE Team

The Drag and Atmospheric Neutral Density Explorer (DANDE) An Innovative Student Built Satellite for Upper Atmospheric Research

DANDE Team: S. Palo, M. Pilinski, B. Davis, B. Gilles, M. Grusin, A. Tomchek

Abstract:
Neutral density, composition, and wind measurements are increasingly needed to further scientific understanding of the upper atmosphere. To address this need, the Drag and Atmospheric Neutral Density Explorer (DANDE), a low-cost system which makes in-situ measurements of the neutral atmosphere at altitudes of 200 - 350 km is being developed at CU as a part of the Air Force sponsored University Nanosat Program. This is the first spacecraft to be specifically designed to measure winds, drag, and number densities simultaneously. These measurements will reduce the uncertainty in drag-deduced density values especially during storms when in-track winds can contribute significantly to spacecraft drag. To accomplish this, DANDE will carry a novel drag measuring system as well as a Wind and Temperature Spectrometer which will characterize the horizontal wind vector. The project is a joint venture between Colorado Space Grant Consortium and the Aerospace Engineering Sciences department wherein students design and build the hardware under the mentorship of faculty, government and industry advisors. As such, DANDE has a positive educational impact while providing an improved method for in-situ thermospheric research with applications to precise orbit prediction, re-entry analysis, and rendezvous operations.

LSTB

Oct 23

Simone Tilmes, NCAR

Impact of Geo-engineered Aerosols on the Troposphere and Stratosphere

Abstract:
Geo-engineering schemes have been proposed to alleviate the consequences of global warming by continuous injection of sulfur into the stratosphere. Volcanic eruptions in the past have shown that strongly enhanced sulfate aerosols in the stratosphere result in a higher planetary albedo, leading to surface cooling. However, the increase of sulfate aerosol surface area enhances heterogeneous reactions in the stratosphere that lead to ozone loss. The potential for exceedingly high Arctic ozone depletion in the context of geo-engineering is known. On the other hand, decreasing halogen compounds in the atmosphere result in a recovery of the ozone layer and lessen the potential impact of aerosols. In this presentation, two papers are discussed. In the first part of the seminar, the sensitivity of polar ozone depletion to proposed geo-engineering schemes is presented for future halogen conditions.

A significant increase of polar stratospheric ozone depletion in the Northern Hemisphere up to the end of this century was found as a result of geo-engineering, based on an empirical projection of past observations to future conditions. Further, the recovery of the Antarctic ozone hole was found to be delayed by several decades. In the second part of the seminar, results of the NCAR, Whole Atmosphere Community Climate Model (WACCM) are presented, studying impact of Geo-engineering on the troposphere as well as on stratospheric chemistry and dynamics. Besides the cooling of the troposphere, a decrease in the precipitation as a result of geo-engineering was found. Further, changes in stratospheric chemistry and dynamics slow down the recover of ozone for mid- and high latitudes. An increase of ozone depletion in polar regions was also simulated.

Duane

Oct 29

Katja Matthes, Institut für Meteorologie, Freie Universität Berlin, Germany,
and NCAR

Modeling Solar Cycle and QBO Effects In the Atmosphere

Abstract:
The 11-year solar cycle has an impact on the chemical, thermal, and dynamical structure of the atmosphere. Observational and modeling studies have shown that direct radiative changes in the upper stratosphere can lead to indirect dynamical changes throughout the atmosphere. However, the understanding of the interaction with the equatorial stratospheric Quasi-Biennial Oscillation is still a challenging topic. Discrepancy exists in separating the solar and QBO signals in observations partly due to the short length of existing data sets. Therefore modeling studies are useful to enhance the understanding of the underlying physical mechanism(s).

An overview of the ability of current chemistry climate models to simulate the response to the 11-year solar cycle is given with special emphasis on the role of the QBO. Among others a comprehensive set of experiments made with NCAR’s Whole Atmosphere Community Climate Model (WACCM3), in which only a realistic time varying solar cycle, only a synthetic, time varying QBO or both the solar cycle and the QBO were included, will be presented. It turns out that the QBO determines the vertical structure of the tropical solar signal in the middle to lower stratosphere. The signal is opposite for QBO east and QBO west conditions in the tropical and extratropical stratosphere. The qualitative agreement with observations and other mechanistic model studies will be discussed as well as the transfer of the solar signal from the upper to the lower atmosphere.

LSTB 299

Oct 30

Dan Marsh, NCAR

LSTB

Nov 6

Linnea Avallone, LASP

In situ measurements in rocket and Space Shuttle exhaust plumes: What we’ve learned about stratospheric chemistry and dynamics

Abstract:
The impacts of rocket exhaust on the stratosphere were first studied seriously in the 1970s with a focus on modeling the chemistry of nitrogen oxides and chlorine compounds in the exhaust plumes. It was concluded that the effects could be significant, but were likely to be important only on local scales. A resurgence of interest in rocket effects on the stratosphere came in the late 1980s following the discovery of the Antarctic “ozone hole” and a renewed recognition of the importance of anthropogenic chlorine chemistry. However, researchers once again found no quantifiable global impact of rocket exhaust, even with projections of extensive growth in launches over the coming decade. My research group has been involved with a decade-long series of airborne observations of exhaust plumes from various rockets and the Space Shuttle. These measurements have been motivated not by global impact, but by recognition that exhaust plumes can serve as unique laboratories from which to learn about chemical, microphysical and dynamical properties of the lower stratosphere. In this talk, I will describe the projects in which we have been involved and will highlight several results that have implications for our understanding issues such as the dispersion of pollutants in the stratosphere, the accuracy of water vapor measurements, and the potential consequences of using rockets to carry out geo-engineering projects.

LSTB

Nov 13

Bodil Karlsson, LASP

Duane

Nov 20

Charles Bardeen, LASP

Microphysics of Polar Mesospheric Clouds: Lessons from WACCM/CARMA simulations and comparisons with AIM

Abstract:
Polar mesospheric clouds (PMC) routinely form at high latitude in the cold summer mesopause region when water vapor condenses to form ice. Recent simulations of the distribution of meteoric dust indicate that because of the meridional circulation, there are fewer large particles than have traditionally been assumed to be necessary for the heterogeneous nucleation of PMCs. Simulations of meteoric dust and PMCs have been performed using WACCM/CARMA, a new three-dimensional chemistry-climate model based upon the Whole-Atmosphere Community Climate Model (WACCM) with sectional microphysics from the Community Aerosol and Radiation Model for Atmospheres (CARMA). Cloud properties from these simulations are presented and are shown to compare well to observations from the Solar Occultation for Ice Experiment (SOFIE) and the Cloud Imaging and Particle Size Experiment (CIPS) from the Aeronomy of Ice in the Mesosphere (AIM) mission. Sensitivity tests show that these PMC simulations are very sensitive to the temperature structure of the summer mesopause, which in the model is largely dependent upon vertically propagating gravity waves. Surprisingly, these simulations are not very sensitive to large changes in the nucleation rate created by changing the contact angle; although, a recent laboratory study of ice nucleation on silicates suggests even higher barriers to nucleation may be possible. The relative lack of sensitivity to nucleation rate indicates that large supersaturations created within the model overcome the relatively low numbers of larger meteoric dust particles and the high barriers to new particle formation. These simulations are also sensitive to cloud radiative heating, with heating rates of up to 8 K/day.

Duane

Nov 27

No Seminar - Thanksgiving

Dec 4

Lori Bruhwiler, NOAA

Title: The Evolution of the Recent Atmospheric Methane Budget

Abstract:
After a decade of near-zero growth, atmospheric methane increased globally by almost 8 ppb in 2007. The increase appears to have been caused by increases in Arctic and tropical emissions, and it is noteworthy that, although previous methane growth rate anomalies have been associated with the El Nino phase of the ENSO, 2007 was not an El Nino year. Drivers for increased emissions include anomalously high temperatures and precipitation in wetland regions as well as biomass burning. Due to anomalously high Arctic temperatures during 2007 there may have been a further contribution from destabilizing permafrost in the Arctic, which can enhance wetland area and make labile carbon available for methanogenesis. While the unusual meteorological conditions in the Arctic during 2007 have so far been rare, the occurrence of such conditions could become more frequent in the future, with a potentially large positive feedback on climate from the resulting carbon emissions. In addition to the anomalous growth in methane during 2007, the current understanding of the atmospheric methane budget, and tools for monitoring changes in emissions will be discussed.

Duane 142

Dec 11

Markus Rapp

Leibniz-Institute of Atmospheric Physics at the University of
Rostock, Kuehlungsborn, Germany

Abstract:
The mesosphere is host to a number of different aerosol species like meteor smoke particles and ice particles, where the latter may form under the extreme conditions of the polar summer mesopause region. Properties of these aerosols have been subject to intense research in recent years, in part because they are thought to be potential indicators of climate change. Besides their potential climate relevance, however, it is mostly the exciting and complex physics of these particles and their environment which pose a real challenge to our understanding and make them a fascinating field of research. Just to mention one challenging issue, it is now appreciated that the nucleation process of mesospheric ice clouds is poorly understood and commonly made assumptions are probably flawed. In the current presentation, an overview of new measurements with radars, lidars and sounding rockets of mesospheric ice clouds and meteoric smoke particles is given which shed light on microphysical properties of these mesospheric aerosol species. These observational results are discussed in the light of currently available models which treat microphysical processes and global transport in a self-consistent manner. Particular findings to be emphasized are the very pronounced variability in meteoric smoke particles as observed during several recent sounding rocket flights and an unexpectedly large temperature variability leading to immense supersaturation in the very high latitude mesopause region over Svalbard (78°N). Finally, plans for future experiments and model investigations will be described with which we hope to quantify the overall importance of dynamically induced changes in the mesospheric temperature field on the microphysics of mesospheric ice clouds.

Dec 18

AGU – NO Seminar