Apr. 25
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Class Presentations:
- Yao Tang, Estimation of global CO2 flux
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A novel non-gradient model was proposed for estimating CO2 fluxes from
single-level time-series record of near-surface CO2 concentration. The model
formulation is based on a diffusion equation describing the one-dimensional
turbulent transport of CO2 in the atmospheric boundary layer. A new
parameterization of eddy-diffusivity is used to reduce the sensitivity
of the modeled CO2 fluxes to the uncertainties of the model inputs and parameters.
The newly formulated non-gradient model facilitates remote sensing applications as the new
model does not use bulk gradient of CO2 concentration, wind speed, surface roughness, and
vegetation specific data. Tests of the new model using remote sensing data demonstrate
its usefulness and potential.
- George McDonald, Examining atmospheric water vapor content over sites of seasonal flows on Mars
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The recent spectral evidence supporting the hypothesis that Recurring Slope Lineae
(RSL) on Mars are modern-day active flows of liquid water (Ojha et al., 2015), has called
into question both the formation mechanism for the flows and the factors that affect their
activity. We utilize nadir observations from the Thermal Emission Spectrometer (TES) aboard
Mars Global Surveyor to test our hypothesis that the RSL serve as a sink or source for atmospheric
water vapor. This involves a retrieval of the column atmospheric water vapor abundance from TES
observations of RSL sites---through use of a radiative transfer model. The presented retrievals
use an emission and absorption only model. We will also discuss the development of a radiative
transfer model including the effects of multiple scattering. We present retrievals of the column
water vapor abundance over RSL sites in the southern and northern midlatitudes as well as the
equatorial region. Specifically, we look for enhancements in the column water vapor abundance over
RSL sites relative to the surrounding regions. This also involves dividing out the dominant
seasonal trends in the water vapor abundance (enhancement in northern summer) to look for these
small-scale enhancements. Our study provides constraints on the extent of interaction between the
RSL and atmospheric water vapor through evaporation.
- Longlei Li, Incorporation of multi-components into a fully coupled WRF-Chem-DuMo model for Central Asia
Show/Hide Abstract
An important factor that determines the optical property of mineral dust is its
components because of varied reflective indexes for different chemical species
and different ways these components aggregated. In addition, the component is
important to dust transport and interaction of dust with microphysical processes.
However, currently mineral particles are uniformly assigned in a regional model
and only in a few articles they were treated as multi-component ones but limited
in global model which typically has a low spatial resolution. Here we
incorporated several size-resolved mineral components (clay-sized and
silt-sized) based on situ observations from literatures into a fully coupled
WRF-Chem-DuMo (3.7.1) for Central Asia. The mineralogy fraction differs among
varied sub-regions in Central Asia through being linked directly with the parent
soil. However, Iron oxides were added uniformly as impurities at the expense of
other components. Using this model, we consider an internally mixed mineralogy
to simulate the daily mean net radiative forcing (short and long wavelength)
by dust at both top of the atmosphere (TOA) and surface in Central Asia. In
the simulation, we also employed a series set of different surface albedo and
regional land cover and land use (LCLU) states to reflect effects of both
regional climate change and/or human activity under various meteorology
conditions. The modeled aerosol optical depth (AOD) was compared with available
satellite retrievals and AERONET measurement in this region.
- Mohammad Salut, Remote Sensing of the Lower Ionosphere Using Very Low Frequency Radio Atmospherics Associated with Lightning
Show/Hide Abstract
Tweek atmospherics generated by lightning discharges can be utilized to monitor the
night-time upper atmosphere. This paper aims to estimate the night-time upper atmospheric
very low frequency reflection heights (h), equivalent electron densities (ne) at the tweek
atmospherics reflection heights and the tweek propagation distance (d). The D?region reflection
height estimated 74.8 km before sunset, and rose to 94.8 km at night. The tweek reflection
dropped significantly to 78.1 km during sunrise. The equivalent electron density varies
from 21.6 to 27.4 cm-3. Analysis revealed that the propagation distance varies from 500 to 8700 km.
Simulation results of attenuation of tweeks propagating in the Earth-ionosphere waveguide
for modes m=1-3 are also presented. Moreover, observations of early VLF perturbations on the
NWC (19.8 kHz) signal received at Malaysia are presented. We examine the characteristics of both
amplitude and phase signatures of early VLF perturbations on a great circle path (GCP) near
equatorial regions. The average recovery time for the observed early VLF perturbations is ~160 s,
with just a few cases possessing the longer decay time (~20 minutes) associated with large scale gas
discharges referred to as gigantic blue jet observation. Unlike previous studies of early VLF events,
an equal distribution of positive and negative amplitude changes are observed.
- Yun Hee Park, The impact of smoke on the radiative forcing in Central Asia
Show/Hide Abstract
Smoke emitted from wildfires in Central Asia have traditionally impact on the change of
land use/land cover, air quality, and climate. Smoke is also important on Earth radiation
balance. Direct radiative forcing due to smoke can be large and might indirectly affect global
climate. Smoke particles consists of several inorganic and carbonaceous species, including black
carbon clusters, fly ash, and mineral dust. Each smoke particle have different role on the
radiative forcing, which has positive (heating) forcing and negative (cooling) forcing. Thus,
we are interested in the impact of smoke on radiative energy balance by the change of radiative
forcing of major smoke components in Central Asia. MODIS fire product (MCD14) and CERES data are
used to evaluate net radiative forcing due to smoke. During fire events, negative radiative forcing
is dominant, which implies smoke causes cooling the radiative balance. However, each component
consisting smoke plays a different role in radiative forcing. In this study, we demonstrate a
couple of samples for smoke-laden conditions to estimate radiative forcing.
- Stoyan Ivanov, Solar Plasma Effects on the Mercurian Exosphere during Nominal and CME Conditions
Show/Hide Abstract
While Mercury does not possess an atmosphere, it does possess a tenuous exosphere.
This exosphere is composed ions which include H+ liberated from the surface of Mercury by
physical collisions of micrometeorites or high-energy ion precipitation from the solar wind
(sputtering), and also, but to a much smaller degree, through the photonic excitation of surface atoms
[3,4]. In addition to this exosphere, Mercury also possesses a magnetic field which shields a
portion of its surface, particularly its equatorial region, from direct interference from the
solar wind. The distribution of these constituent ions in the exosphere is not homogenous. Indeed,
there is a noted asymmetry in the presence of Na+ planet, and even then there exists a North/South
asymmetry among the densities as well [2]. Leblanc and Johnson, 2009, show in a model that over the
course of a Mercurian year, the exospheric concentrations and distributions of Na+ in the exosphere
change as Mercury’s highly elliptical orbit alternatively moves towards or away from the sun.
Building off of that, the author proposes to compare the effects of solar conditions of the
exosphere between regular exposure to solar radiation and ions and exposure to a Coronal Mass
Ejection (CME). A CME is the sudden release of material from the corona of the sun. The density and
energy of the material released is higher than regular solar wind, sometimes by as much as an order
of magnitude. The proximity of Mercury to the sun means that it experiences CMEs more often than
most planets, and those that it does experience are less attenuated, by density, because of
Mercury’s proximity. Using a Multifluid Magnetohydrodynamic model, it would be possible to
simulate the interaction of the Mercurian exosphere to regular solar radiation and a CME event.
This simulation would be conducted using the main constituents of the Mercurian exosphere, H+ Na+
as well as Mg+ contract or expand as a result of more ion sputtering from the surface? Does this
altered exosphere show any significant changes in its optical depth and diffusivity, with respect to
the wavelengths usually absorbed and scattered by H+, as well as much heavier ions of Na+. The intent
is to discern how the exosphere reacts under CME conditions. Does it, Na++ and Mg+?
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