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Seminars (for Scientists) Fall 2010

Below is the schedule of LASP Science Seminars for the Fall 2011 semester. Most dates and speakers will be finalized within one week of the seminar, so check this site often for the most current information. All LASP seminars are open to the public EXCEPT those labeled “internal”.

LASP science seminars are generally on Thursdays from 4:00-5:00 p.m., with refreshments served at 3:45 p.m. Seminars at LSTB (in the East Campus Research Park) are in the main auditorium, room 299, while the seminars at the on-campus Duane building are in room D-142 unless otherwise noted.

Seminars with an asterisk (*) next to its date are not on Thursdays.

For more information or if you have questions contact:

  • Sebastian Schmid
    • Phone: 303-492-6401
    • email: firstname.lastname@lasp.colorado.edu

Fall Semester 2010 Schedule:

DATE Speaker/comment Title/abstract Location
*Dec 10 Oleg Dubovik
(Laboratoire d’Optique Atmosphérique, Université de Lille 1, France)
The retrievals of detailed aerosol from AERONET sun/sky-radiometers: Overview of inversion principles, products and advances. 

The AERONET operational retrievals rely on the algorithm by Dubovik and King [2000]. This algorithm is based on the principles of optimized statistical estimations and derives detailed size distribution and spectral complex refractive index by fitting measurements of both direct and diffuse radiation. It also provides such radiative characteristics as aerosol spectral single scattering albedo and phase functions. At the same time, the utilization of this retrieval over the years resulted in a number of the algorithm modifications. The modifications were driven by the desires to improve the retrieval accuracy and to provide user requested additional retrieval products. For example, forward modeling was updated by refining the assumptions on aerosol particle shape, modeling of surface reflectance, accounting for polarization effects. Such new products were developed as: fraction of non-spherical particles, estimates of broad band-radiative fluxes and aerosol forcing, extinction-to-backscatter and depolarization lidar ratios, error bars for each retrieved parameter, etc. Unfortunately, some of the newest inversion developments are not yet fully explained in the publications and may remain unclear for the users. The purpose of this presentation is to provide a synopsis of the retrieval algorithm principles, outline the important modifications in the AERONET retrieval and their rational, as well as, to overview all available and incoming retrieval products and their value.

Duane D-142
Dec 9 Oleg Dubovik
(Laboratoire d’Optique Atmosphérique, Université de Lille 1, France)
Development of the approach for comprehensive retrieval of aerosol properties from enhanced satellite observations 

We propose to enhance aerosol retrievals by emphasizing statistical optimization in inversion of advanced satellite observations. The concept improves retrieval accuracy relying on pronounced data redundancy (excess of the measurements number over number of unknowns). The concept has been successfully adopted and refined in the operational AERONET algorithm retrieving the detailed aerosol properties from ground-based sun-photometer observations, however the required redundancy of observations is not common in satellites observations. Nonetheless, the observations by POLDER imager on board of the PARASOL micro-satellite registering spectral polarized reflected atmospheric radiation in up to 16 viewing directions over each observed pixel provide sufficient basis for applying the proposed methodology. Moreover, the observations by POLDER can be further enhanced by the synchronized observations of other satellite sensors of A-Train constellation, such as MODIS and CALIPSO. 

The retrieval scheme is designed as statistically optimized multi-variable fitting of complete observation set including both measurements of total radiances and polarized at all available spectral channels. Based on this strategy, the algorithm is driven by large number of unknowns and aimed on retrieval of an extended set of parameters affecting measured radiation. This approach is expected to allow robust retrieval of both the optical properties of aerosol and underlying surface from satellite observations over ocean and land. Even over land, the algorithm provides more detailed (compare to current operational PARASOL algorithm) information about aerosol properties including some information about aerosol sizes, shape, absorption and composition (refractive index).

In addition, the algorithm is developed as simultaneous inversion of a large group of pixels within one or several images. Such, multi-pixel retrieval regime takes advantage from known limitations on spatial and temporal variability in both aerosol and surfaces properties. Specifically the pixel-to-pixel or day-to-day variations of the retrieved parameters are enforced to be smooth by additional appropriately set a priori constraints. This concept is expected to provide retrieval of higher consistency for aerosol retrievals from satellites, because the retrieval over each single pixel will be benefiting from co-incident aerosol information from neighboring pixels, as well, from the information about surface reflectance (over land) obtained in preceding and consequent observation over the same pixels. It should be noted that the approach considerably relies on the accumulated experience and many aspect of the retrieval. Also, actual computer tools were inherited from precedent efforts on developing the AERONET operational retrieval and the currently operating PARASOL algorithm.

LSTB-A200
*Dec 8 Alexander Kokhanovsky Seminar Cancelled 

Abstract pending

Location: TBD
Dec 3 Brian Toon (ATOC/LASP) Towards an improved understanding of the Tropical Tropopause Transition Layer, TC4, ATTREX and SEAC4RS 

The talk will describe some of the scientific issues that are driving research in this area, results from recent studies, and plans for future field missions.

Duane, Gamow tower
Nov 18 Miodrag Sremcevic Saturn’s rings under a microscope: Cassini UVIS results 

After 6 years of Cassini mission the Ultraviolet Imaging Spectrograph (UVIS) instrument recorded more than hundred stellar occultations by Saturn’s rings. Most of the observed occultations have excellent resolution on the order of ten meters or even better. In this talk we give overview of UVIS results on the rings small scale structure. The high resolution and multitude of observations allows us to infer the orientation and two-dimensional picture of the underlying ring structure. Saturnian main rings are anything but bland and homogeneous at meters scale. Most of the A ring and outer B ring show 10-50m structures pitched by about 20 degrees from the orbital motion. These observations are consistent with Toomre type self-gravity wakes, and allow us to directly infer their spatial scalings. The inner A ring and lower optical depth regions in the B ring show 100-200m scale regular waves. These waves have no pitch angle and are consistent with a viscous oscillatory instability, better known as overstability. The most surprising aspect of these waves is their patchy appearance throughout the rings. In higher optical depth regions of the B ring the most dominant structure is irregular with spatial scales of about 100m. The B ring results are the most puzzling, as one explanation hints at surprisingly low total mass of the B ring.

Duane D-142
*Nov 12 Karen Rosenlof (ATOC/LASP) Stratospheric circulation changes and their relation to species distributions 

Results from two recent papers discussing changes in stratospheric constituents driven by changes in the circulation and some associated impacts on climate will be presented. In the first paper (Solomon et al., 2010), we show that a significant decrease in stratospheric water vapor a consequence of an increase in the mass flux into the tropical stratosphere. This change is water vapor is also shown to be radiatively significant, slowing the increase in global surface temperature over the 2000-2009 period by about 25% compared to what would have occurred due only to carbon dioxide and other greenhouse gas increases. In the second paper (Ray et al., 2010), we show how changes in the stratospheric circulation and mixing impact tracer concentrations through use of a leaky pipe model. We conclude that observed changes in constituents that give indications with age of air in the stratosphere are not inconsistent with increases in the strength of the mean meridional circulation when one takes into account possible changes in mid latitude to tropical mixing.

Duane, Gamow tower
Nov 11 Hubert Klahr (Max-Planck Institute for Astronomy, Heidelberg) The nature of Turbulence in Circumstellar disks: Magnetorotational and Baroclinic Instability 

Turbulence in circumstellar disks diffuses small solid material, leads to collisions among larger objects, concentrates boulders promoting planetesimal formation via gravity and also has an impact on planet migration. Despite the importance of turbulence, its nature is not completely understood so far. In certain regions of the disk the gas is sufficiently ionized for magneto-hydrodynamics to lead to turbulence. Other regions being too cold or dusty could now either be dead zones without turbulence or develop a different kind of instability. Realistic radial entropy gradients and thermal diffusion times in typical accretion disks around young stars can lead to baroclinic instability and the formation of vortices and the generation of turbulent viscosity. I summarize the state of field of baroclinic instability in accretion disks and show latest results from numerical simulations.

Duane D-142
Nov 4
(postponed to March 3rd)
Richard Hodges The Lunar Atmosphere: Some Ado About Almost Nothing 

Prior to the Apollo era the lunar atmosphere was thought to be a collision-less, ballistic conduit for thermal evaporation that balances the inflow of solar wind ions with their loss as neutrals. However, the first atmospheric species to be identified on the moon was radiogenic argon-40, and its identification was the indirect result of a search for an explanation of implanted parentless argon-40 in Apollo 11 soil samples. Subsequently, a neutral mass spectrometer at the Apollo 17 site confirmed the presence of atmospheric argon-40 along with helium of both solar and radiogenic origin. These data, although meagre, have guided research into the processes that control the escape of gases from the moon and other bodies that have surface-bounded exospheres. Briefly, the dynamic characteristics of the atmosphere are dominated by ballistic transport, and perturbed by radiation pressure, charge exchange, photo-ionization, and escape to earth orbit. Other, more important, atmospheric processes are related to the surface physics of regolith grains, that is, diffusion, adsorption, desorption, and elastic scattering, which in turn are affected by the influences of orography and heat flow on regolith temperature. With the upcoming launch of the Lunar Atmosphere and Dust Environment Explorer mission, new light should be shed on these processes as well as on the much-expected existence of other constituents.

LSTB-299
*Oct 29 Linnea Avallone (LASP/ATOC) Exploring the Antarctic Ozone Hole using Long-Duration Balloons 

The Antarctic “Ozone Hole” was first reported in the literature 25 years ago by Farman et al. [1985]. Despite intense research in the ensuing years into the chemical, microphysical and dynamical processes that create this phenomenon, there remain sufficient gaps in our knowledge that we cannot say with certainty when in the future the “ozone hole” will disappear. In this talk, I will discuss the recent (August-October 2010) Concordiasi campaign – a series of balloon-borne payloads designed to address some of the outstanding issues related to polar stratospheric ozone loss. I will describe the experiment design, including the unique super-pressure balloon platform and scientific instruments, and will present some preliminary data from ozone sensors still circumnavigating the Antarctic stratosphere.

Duane, Gamow tower
Oct 21 Hal Levison (SwRI) Oort Cloud Formation – The Role of the Sun’s Birth Cluster 

Oort cloud comets are currently believed to have formed in the Sun’s proto-planetary disk, and to have been ejected to large heliocentric orbits by the giant planets. I will review the evolution of our understanding of Oort cloud formation. I will present the currently best models and show that they fail to reproduce all of the available observational constraints. In particular, the Oort cloud appears to be significantly more populous than the models predict. I will present new models of an alternative scenario which appear to solve this problem. If this new scenario is correct, we have been misinterpreting what comets have been telling us about the origin of
the Solar System.

Duane D-142
*Oct 15 Thomas Ryerson/Joost de Gouw (ATOC/LASP) Seminar Cancelled 

Abstract pending

Duane, Gamow tower
*Oct 8 Martin Tingley (ATOC/LASP) Reconstructing Pre-Historic Temperatures from Natural Proxies: Statistical Methods in Paleoclimate Research 

The instrumental temperature record covers at most 150 years. Because a longer record is needed to characterize the natural variability of the climate system, it is necessary to call upon climate proxy data, which are noisy and sparsely distributed in space. Information about pre-historic temperatures can be derived from elements of the natural world sensitive to local temperature variations, such as tree rings, ice cores, and lake-floor sediment cores. 

Reconstructing the spatial pattern of a climate field through time from incomplete instrumental and climate proxy time series poses both scientific and statistical challenges. Over the last two decades, the statistics community has made major advances in the modeling and analysis of space-time processes. Many of these advances have not yet been applied to the paleoclimate reconstruction problem, and doing so has the potential to improve understanding of the climate of the past.

I begin by outlining both the scientific and statistical challenges involved in reconstructing past climate, and then discuss popular approaches that have been used to overcome them. I then outline a unifying, hierarchical space–time modeling framework for the paleoclimate reconstruction problem, and indicate how modern statistical expertise can be brought to bear upon the problem. Within this framework, the modeling assumptions made by a number of published methods can be understood as special cases, and the distinction between modeling assumptions and analysis or inference choices becomes more transparent.

As a demonstration of the power of hierarchical space-time models in this context, I present an analysis of a 600-year high-northern-latitude temperature proxy data set based on simple data-level and process-level assumptions.

Duane, Gamow tower
Sep 30 Tom Woods, Rachel Hock, Frank Eparvier, and Andrew Jones First Results from SDO Extreme Ultraviolet Variability Experiment (EVE) 

The Extreme ultraviolet Variability Experiment (EVE) aboard the NASA Solar Dynamics Observatory (SDO) was launched on 11 February 2010. The EVE instruments measure the solar extreme ultraviolet (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy (20% or better). This seminar will discuss some of the first results from the SDO observations.

The Flood (Woods): The data rate from EVE observations is a mere 7 Mbps (as compared to the 140 Mbps from the SDO imagers), and yet three months of EVE observations are more data than LASP has obtained from all previous satellite observations over the 60 year history of LASP. Introduction to the SDO mission and EVE observations will be given.

The Flares (Hock): Despite this solar cycle 24 being a slow start, EVE has observed more than 30 flares, albeit small C-class and a few moderate M-class flares. An overview of the flare observations will be given.

The Fluctuations (Eparvier): One of our surprises in the flare observations is that EVE observes a second peak many minutes, even hours, after the main flare peak in some coronal emission lines. In addition, some of the lines decrease after a flare, and some show similar fluctuations when no earlier flare is apparent. These interesting observations and possible explanation will be presented.

The Forecast (Jones): Forecasting flares is one of the goals for the EVE program. The progress in making accurate forecast of the flare magnitude using EVE data will be presented.

LSTB-299
Sep 23 Amy Barr Formation of the Ganymede/Callisto Dichotomy and Titan’s Interior State from Impacts During the Late Heavy Bombardment 

Despite their similar sizes and compositions, Ganymede and Callisto have followed different evolutionary pathways. Ganymede has experienced extensive geological activity and has a large rock core. Callisto’s surface is ancient. Core formation in Callisto has apparently been incomplete; its interior has layers of mixed ice and rock. The Ganymede/Callisto dichotomy could have arisen during an outer solar system late heavy bombardment (LHB) triggered by dynamical events in the outer solar system. Resulting cometary LHB impacts onto Ganymede and Callisto melt their ice/rock surfaces, allowing denser rock to sink to the satellites’ centers. Once core formation in Ganymede or Callisto is 50% complete, it becomes an energetically self-sustaining process (“runaway differentiation”). A 3 dimensional model of impact-induced core formation is used to show that during an outer solar system LHB, Ganymede undergoes runaway differentiation, but Callisto does not, consistent with their present interior states. The interior state of Titan post-LHB and its similarity to estimates of its interior state based on recent Cassini data will also be discussed.

Duane D-142
Sep 16 Kalevi Mursula Title: TBD 

The heliospheric magnetic field (HMF) is hemispherically asymmetric so that the field dominant in the northern hemisphere is weaker but has a larger area than in the south. As a consequence, the heliospheric current sheet (HCS) is shifted southwards. This asymmetry, also called the bashful ballerina, typically persists during three-year intervals in the late declining to minimum phase of the solar cycle. This pattern has been verified by ecliptic satellites to occur during solar cycles 20-22, and by geomagnetic observations during SC 16-22, so during all the time when relevant measurements exist. However, using the same low-latitude observations, we find that the HCS is considerably less asymmetric during the exceptional SC 23 than in earlier cycles. In order to further study whether the bashful ballerina occurred also during SC 23, we examine the observations by the Ulysses probe around its perihelion pass in 2007. They show that the HMF at high northern latitudes was indeed weaker than in the south, and that the HCS was shifted by the same amount, roughly two degrees southwards, as during the first perihelion pass in 1994 for SC 22. Ulysses also shows that the HCS region was considerably wider during SC 23 than during SC 22, which is likely due to the large tilt angles and weak polar fields in SC 23. Thus, the HCS is indeed southward shifted even during SC 23 but the exceptionally thick HCS hides the asymmetry from low-latitude observations. (“Bashful ballerina is dancing behind a thick HCS screen”). We also note that the exceptional properties of SC 23 agree with historical evidence that the active Sun leads to a greater asymmetry in low-latitude observations, and make a prediction on the future dancing of the ballerina.

LSTB-299
Sep 9 Peter Delamere Solar Wind Interaction With the Giant Magnetospheres 

Jupiter’s and Saturn’s immense magnetospheres differ considerably from Earth’s. These magnetospheres are generated in part by a strong planetary dynamo and by rapid rotation (~10 hour period). However, key differences lie in the internal sources of plasma (100s kg/s) provided by Io and Enceladus. Centrifugal stresses acting on the corotating, low-beta plasma in the inner magnetosphere leads to radial transport of plasma via a centrifugally-driven flux tube interchange instability. Instead of cooling on adiabatic expansion, the plasma is observed to be hotter at larger radial distances. In the outer magnetosphere the systems are governed by high-beta, centrifugally-confined plasma sheets. 

Observations and theories of the dynamics of Jupiter’s and Saturn’s magnetosphere will be discussed. In particular, we will focus on studies involving “viscous” processes (e.g. Kelvin-Helmholtz instability) at the magnetopause boundary that facilitate the transport of mass, momentum, and energy from the solar wind to the magnetosphere.

LSTB-299
Sep 2 Christiane Voigt (ATOC/LASP) Title: TBD 

Abstract pending

Duane D-142