INTRODUCTION:
We propose a mission to study coupling of the thermosphere and ionosphere with
emphasis on times of magnetic activity. During these periods, energy in the form of
Poynting flux enters the high-latitude ionosphere. This energy is converted and
partitioned into Joule heat (thermal energy) and neutral winds (kinetic energy). The
winds transport Joule heat to lower latitudes. The effects are manifest in the
thermosphere as an increase in neutral density at any specific altitude. This has been
demonstrated in many studies since the CHAMP and GRACE spacecraft were launched.
While the scenario described above has been indirectly verified, the physics has received
little attention due to a lack of observations in this region. In particular, neutral winds
are almost unknown in the global ionosphere-thermosphere (IT) system, the only useful
data in situ coming from DE-2, a short-lived mission launched in 1981.
The specific goal of our proposed mission is an improvement in forecasting of satellite
drag. We describe the details below. However there are multiple science questions
which are addressed, all relevant to an understanding of ion-neutral coupling in the IT
system.
Question #1: What are the primary observations necessary to understand energy
deposition, partitioning and transport in the IT system?
Question #2: How accurately can the neutral winds be measured remotely, and what
is their global distribution with respect to solar flux and geomagnetic activity?
Question #3: What is the altitude profile of neutral wind?
Question # 4: What is the thermospheric response to energy input from geomagnetic
and solar disturbances in terms of density, composition, and winds perturbations?
What are the time scales of the responses and how do they manifest themselves locally
and globally?
Question #5: What is the amount, spatial and temporal distribution of energy
deposited in the IT system during geomagnetic disturbances?
Question #6: Exactly how and where is the input energy distributed in the
thermosphere?
Question #7: Quantitatively how do variations of the satellite drag coefficient affect
the measurement of neutral density and how much error can they introduce to this
measurement?
THERMOSPHERE-IONOSPHERE COUPLING AND ORBIT PREDICTION
SYSTEM:
A schematic of the physics addressed in the mission is given below. Input to the IT
system is from the sun above and the troposphere below, and output in the form of drag
is shown at right. The boxed area at center left indicates the ion-neutral coupling which
takes place in the IT system, in particular energy input at polar and auroral latitudes,
partitioning into thermal and kinetic energy, and mass transport.
Figure 1: Schematic of the IT system
The mission, titled “Thermosphere-Ionosphere Coupling and Orbit Prediction System”
will measure all the quantities in the satellite drag equation, thus enabling improved
specification and nowcast of drag. It will measure the required observables in the IT
system –neutral density, winds and composition, ion temperature and velocity, particle
precipitation and magnetic field. These will enable the fundamental physics of coupling
to be addressed and also provide data to assimilation models of the IT system. Results
from this mission will improve forecasting of satellite drag and precise orbit
determination.
The mission leverages off a Multidisciplinary University Research Initiative awarded to
the University of Colorado to study the processes leading to improved input for physical
modeling of the thermosphere relevant to satellite drag.
Figure 2: Schematic of proposed mission
TICOPS is a constellation of satellites to measure directly ALL the quantities in the
satellite drag equation, enabling (1) immediate radical improvement in nowcasts and
forecasts of atmospheric density, winds and composition; (2) input to physics-based
data assimilative models which will form the next generation products used in drag
prediction.
The mission comprises 3 satellites, 2 I-COPS at high altitude (500km), and T-COPS at
low altitude (300km), each flying in high-inclination orbit. The two I-COPS will each
carry a remote neutral wind sensor, the Doppler Asymmetric Spatial Heterodyne
spectrometer (DASH). DASH is a remote sensing limb imager. Directed toward the
horizon, a vertical profile of neutral winds can be obtained. DASH can also be tuned to
specific frequencies. One I-COPS DASH will be tuned to the red line, the second to the
green line, enabling detailed wind measurements in both E and F layers. This captures
energy deposition and mass transport across the ionosphere. Angular spacing of the
two I-COPS by 30° allows for full remote sensing across the globe with overlap in
coverage from the two spacecraft.
In addition to DASH, I-COPS will carry instruments to measure ion drifts and densities,
magnetometers and precipitating particle detectors. These specify the energy input to
the IT system in the form of Poynting flux obtained from the magnetometers and ion
drift meters, and particle energy. Particle precipitation also allows Pedersen
conductivity below the satellite to be estimated.
T-COPS will carry instruments to measure the ion velocity, neutral density, composition
and in situ winds. Ion measurements are necessary to analyze the conversion of
electromagnetic energy into thermal and kinetic energy. Neutral density and
composition measurements specify the thermospheric response to energy deposition
and dissipation. In situ winds are included as a validation experiment for DASH and to
expand the database of neutral winds.
T-COPS will also carry a deployable structure which allows the coefficient of drag to be
estimated. By changing the acceleration due to drag, we obtain a direct measure of the
drag coefficient. Experiments to determine drag coefficients have not been performed
for over 40 years. Current ballistic coefficients (drag coefficient*area/mass) have error
bars comparable with the values themselves. This leads to errors in the estimates of
neutral mass density and hence, satellite drag. By measuring the coefficient of drag, the
neutral density, winds and composition we will have direct quantitative measurements
of the drag acceleration. This will be the first time these quantities have been all been
measured simultaneously and will be valuable in future research into drag prediction.
SUMMARY:
•
TICOPS is a constellation of satellites to study ion-neutral coupling in the IT
system. It will measure directly ALL the quantities in the satellite drag equation,
enabling (1) immediate radical improvement in nowcasts and forecasts of
atmospheric density, winds and composition; (2) input to physics-based data
assimilative models which will form the next generation products used in drag
prediction.
•
Mission comprises 3 polar satellites, two at 500 km altitude and one at ~300 km
altitudes. Conjunctions of the 3 satellites provides simultaneous measurements of
the full electromagnetic and kinetic energy input to the thermosphere as well as
the full thermospheric response