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Solar and Space Physics: A Science for a Technological Society
62
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
The storm response of the ionosphere and thermosphere produces structures over a wide range of
time and spatial scales. To understand the storm-time behavior of this system, researchers must address
the following science challenge: AIMI-1. Understand how the ionosphere-thermosphere system responds
to, and regulates, magnetospheric forcing over global, regional, and local scales.
An important element of the dynamics of the IT system is the transfer of energy and momentum between
the plasma and neutral components of the system and the role that electric and magnetic fields serve in
accentuating and sometimes moderating this interchange. The pathways through which ions and neutrals
interact are of course fundamental to space physics, given that they occur at all planets with atmospheres,
at comets, and within the magnetospheres of Jupiter and Saturn. For example, in Earth’s ionosphere at an
altitude from 100 to 130 km the collisions between ions and electrons and neutrals enable current to flow
across the local magnetic field, which facilitates closure of currents flowing along magnetic fields from
the magnetosphere. The proper description of these cross-field currents requires the development of an
accurate model of the plasma “conductivity,” yet the dynamics of ionospheric conductivity are among the
most poorly quantified parameters of the IT system. Earth’s equatorial region is a rich laboratory for the
investigation of plasma-neutral coupling in the presence of a magnetic field. The behavior can be extraordinarily complex: plasma-neutral collisions and associated neutral winds drive turbulence that cascades
to very small spatial scales and regularly disrupts communications. The chemical interaction of a variety
of ion species further complicates the dynamics.
A different suite of interactions occurs at middle latitudes. Spontaneous airglow emissions at 6,300 Å
exhibit waves propagating to the south-west. They are thought to originate as neutral density waves at high
latitudes which then interact with the mid-latitude ionosphere to create the structures, but their occurrence
is curiously unrelated to levels of magnetic activity.
Thus, plasma-neutral coupling plays a critical role in ionospheric dynamics across the full range of
latitudes. Researchers must therefore address the following challenge: AIMI-2. Understand the plasmaneutral coupling processes that give rise to local, regional, and global-scale structures and dynamics in
the AIM system.
Numerous recent observations and simulations show that the IT system owes much of its longitudinal,
local-time, seasonal, and even day-to-day variability to meteorological processes in the troposphere and
stratosphere. The primary mechanism through which energy and momentum are transferred from the lower
atmosphere to the upper atmosphere and ionosphere is through the generation and propagation of waves.
The absorption of solar radiation (e.g., by tropospheric H 2 O and stratospheric O 3 ) excites a spectrum
of thermal tides. Figure 2.11 shows the spatial structure in daytime convective clouds that is believed to
introduce longitudinal structure in the ionosphere, seen in Figure 2.11 in ultraviolet emissions. Surface
topography and unstable shear flows excite planetary waves and gravity waves extending from planetary
to very small (~tens to hundreds of kilometers) spatial scales and having periods from tens of days down
to minutes. Convective tropospheric weather systems radiate additional thermal tides, gravity waves, and
other classes of waves.
Those waves that propagate vertically grow exponentially with height into the more rarified atmosphere. Some of the waves spawn additional waves and turbulence. Figure 2.12 shows sodium layer
observations revealing amazing wave structures at the base of the thermosphere, illustrating the rich spectrum of dynamics that occurs. Although the presence and the importance of waves are not in dispute, the
relevant coupling processes operating between the neutral atmosphere and ionosphere involve a host of
multiscale dynamics that are not understood at present. This leads to another major scientific challenge:
AIMI-3. Understand how forcing from the lower atmosphere via tidal, planetary, and gravity waves influences the ionosphere and thermosphere.
Solar and Space Physics: A Science for a Technological Society
62
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
The storm response of the ionosphere and thermosphere produces structures over a wide range of
time and spatial scales. To understand the storm-time behavior of this system, researchers must address
the following science challenge: AIMI-1. Understand how the ionosphere-thermosphere system responds
to, and regulates, magnetospheric forcing over global, regional, and local scales.
An important element of the dynamics of the IT system is the transfer of energy and momentum between
the plasma and neutral components of the system and the role that electric and magnetic fields serve in
accentuating and sometimes moderating this interchange. The pathways through which ions and neutrals
interact are of course fundamental to space physics, given that they occur at all planets with atmospheres,
at comets, and within the magnetospheres of Jupiter and Saturn. For example, in Earth’s ionosphere at an
altitude from 100 to 130 km the collisions between ions and electrons and neutrals enable current to flow
across the local magnetic field, which facilitates closure of currents flowing along magnetic fields from
the magnetosphere. The proper description of these cross-field currents requires the development of an
accurate model of the plasma “conductivity,” yet the dynamics of ionospheric conductivity are among the
most poorly quantified parameters of the IT system. Earth’s equatorial region is a rich laboratory for the
investigation of plasma-neutral coupling in the presence of a magnetic field. The behavior can be extraordinarily complex: plasma-neutral collisions and associated neutral winds drive turbulence that cascades
to very small spatial scales and regularly disrupts communications. The chemical interaction of a variety
of ion species further complicates the dynamics.
A different suite of interactions occurs at middle latitudes. Spontaneous airglow emissions at 6,300 Å
exhibit waves propagating to the south-west. They are thought to originate as neutral density waves at high
latitudes which then interact with the mid-latitude ionosphere to create the structures, but their occurrence
is curiously unrelated to levels of magnetic activity.
Thus, plasma-neutral coupling plays a critical role in ionospheric dynamics across the full range of
latitudes. Researchers must therefore address the following challenge: AIMI-2. Understand the plasmaneutral coupling processes that give rise to local, regional, and global-scale structures and dynamics in
the AIM system.
Numerous recent observations and simulations show that the IT system owes much of its longitudinal,
local-time, seasonal, and even day-to-day variability to meteorological processes in the troposphere and
stratosphere. The primary mechanism through which energy and momentum are transferred from the lower
atmosphere to the upper atmosphere and ionosphere is through the generation and propagation of waves.
The absorption of solar radiation (e.g., by tropospheric H 2 O and stratospheric O 3 ) excites a spectrum
of thermal tides. Figure 2.11 shows the spatial structure in daytime convective clouds that is believed to
introduce longitudinal structure in the ionosphere, seen in Figure 2.11 in ultraviolet emissions. Surface
topography and unstable shear flows excite planetary waves and gravity waves extending from planetary
to very small (~tens to hundreds of kilometers) spatial scales and having periods from tens of days down
to minutes. Convective tropospheric weather systems radiate additional thermal tides, gravity waves, and
other classes of waves.
Those waves that propagate vertically grow exponentially with height into the more rarified atmosphere. Some of the waves spawn additional waves and turbulence. Figure 2.12 shows sodium layer
observations revealing amazing wave structures at the base of the thermosphere, illustrating the rich spectrum of dynamics that occurs. Although the presence and the importance of waves are not in dispute, the
relevant coupling processes operating between the neutral atmosphere and ionosphere involve a host of
multiscale dynamics that are not understood at present. This leads to another major scientific challenge:
AIMI-3. Understand how forcing from the lower atmosphere via tidal, planetary, and gravity waves influences the ionosphere and thermosphere.