Copyright © National Academy of Sciences. All rights reserved.
Solar and Space Physics: A Science for a Technological Society
168
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
currents within the ionosphere, leading to Joule heating that depends on the spatial and temporal variability
of the E fields as well as their absolute magnitudes. The peak altitude of Joule heating in turn determines
the response time of the global thermosphere to this energy input. Energetic particles also initiate a chemical pathway to create nitric oxide, which regulates the response and recovery of the neutral atmosphere
through radiative cooling. Local heating of the IT system and ionospheric flows from lower latitudes (see
Figure 8.9) serve as sources of O + to the magnetosphere, which then regulates how the magnetosphere
transfers solar wind energy to the IT system (see further details on magnetosphere-IT interactions under
“AIMI Science Goal 3”).
The interactions and feedbacks that occur between energy deposition, dynamics, radiative cooling,
energetic particles, electric fields, and plasma and neutral constituents and temperatures are how the global
IT system regulates its response to magnetospheric forcing, and how it also regulates the response of the
magnetosphere to solar wind forcing. The complexity of the AIM system is such that emergent behaviors
occur, sometimes involving coupling across spatial and temporal scales (see further details under “AIMI
Science Goal 4”).
The AIMI panel concluded that a major goal of the coming decade, therefore, is to understand how
regulation of the IT system occurs, and how connectivity between multiple scales arises within this regulation process.
Making the required coincident multi-parameter measurements of the system over local, regional,
and global scales poses major challenges in terms of observational strategies. Strategies that employ an
optimal combination of ground-based, suborbital and space-based platforms involving innovative in situ
and remote-sensing instrumentation will be required. The panel’s implementation strategies are presented
in the section “Implementation Strategies and Enabling Capabilities” below.
8.4.2 AIMI Science Goal 2. Meteorological Driving of the IT System
How does lower-atmosphere variability affect geospace?
Numerous observational and modeling studies conducted since the 2003 decadal survey have unequivocally revealed that the IT system owes much of its longitudinal, local-time, seasonal-latitudinal, and dayto-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 (Figure 8.10).
Owing to rotation of the planet, periodic absorption of solar radiation in local time (LT) and longitude
(e.g., by troposphere H 2 O and stratosphere O 3 ) excites a spectrum of thermal tides having periods and
zonal (east-west) wavenumbers (or harmonics) defined by the planetary rotation period and longitudinal
variability, respectively. Surface topography and unstable shear flows arising due to solar forcing excite
planetary waves (PWs) and gravity waves (GWs) extending from planetary to very small (approximately
tens to hundreds of kilometers) spatial scales and periods ranging from 2 to 20 days down to minutes.
The absorption of solar radiation at the surface and the subsequent release of latent heat of evaporation
in convective clouds radiate additional thermal tides, GWs, and other classes of waves. Those waves that
propagate vertically grow exponentially with height into the more rarified atmosphere, ultimately achieving large amplitudes. Some parts of the wave spectrum achieve convective instability, spawning additional
waves or turbulence. Other parts of the wave spectrum are ultimately dissipated by molecular diffusion in
the 100- to 150-km-height region, and some fraction of those waves penetrate all the way to the base of the
exosphere (ca. 500-600 km). Along the way, nonlinear interactions between different wave types occur,
modifying the interacting waves and giving rise to secondary waves. Finally, the IT wind perturbations
Solar and Space Physics: A Science for a Technological Society
168
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
currents within the ionosphere, leading to Joule heating that depends on the spatial and temporal variability
of the E fields as well as their absolute magnitudes. The peak altitude of Joule heating in turn determines
the response time of the global thermosphere to this energy input. Energetic particles also initiate a chemical pathway to create nitric oxide, which regulates the response and recovery of the neutral atmosphere
through radiative cooling. Local heating of the IT system and ionospheric flows from lower latitudes (see
Figure 8.9) serve as sources of O + to the magnetosphere, which then regulates how the magnetosphere
transfers solar wind energy to the IT system (see further details on magnetosphere-IT interactions under
“AIMI Science Goal 3”).
The interactions and feedbacks that occur between energy deposition, dynamics, radiative cooling,
energetic particles, electric fields, and plasma and neutral constituents and temperatures are how the global
IT system regulates its response to magnetospheric forcing, and how it also regulates the response of the
magnetosphere to solar wind forcing. The complexity of the AIM system is such that emergent behaviors
occur, sometimes involving coupling across spatial and temporal scales (see further details under “AIMI
Science Goal 4”).
The AIMI panel concluded that a major goal of the coming decade, therefore, is to understand how
regulation of the IT system occurs, and how connectivity between multiple scales arises within this regulation process.
Making the required coincident multi-parameter measurements of the system over local, regional,
and global scales poses major challenges in terms of observational strategies. Strategies that employ an
optimal combination of ground-based, suborbital and space-based platforms involving innovative in situ
and remote-sensing instrumentation will be required. The panel’s implementation strategies are presented
in the section “Implementation Strategies and Enabling Capabilities” below.
8.4.2 AIMI Science Goal 2. Meteorological Driving of the IT System
How does lower-atmosphere variability affect geospace?
Numerous observational and modeling studies conducted since the 2003 decadal survey have unequivocally revealed that the IT system owes much of its longitudinal, local-time, seasonal-latitudinal, and dayto-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 (Figure 8.10).
Owing to rotation of the planet, periodic absorption of solar radiation in local time (LT) and longitude
(e.g., by troposphere H 2 O and stratosphere O 3 ) excites a spectrum of thermal tides having periods and
zonal (east-west) wavenumbers (or harmonics) defined by the planetary rotation period and longitudinal
variability, respectively. Surface topography and unstable shear flows arising due to solar forcing excite
planetary waves (PWs) and gravity waves (GWs) extending from planetary to very small (approximately
tens to hundreds of kilometers) spatial scales and periods ranging from 2 to 20 days down to minutes.
The absorption of solar radiation at the surface and the subsequent release of latent heat of evaporation
in convective clouds radiate additional thermal tides, GWs, and other classes of waves. Those waves that
propagate vertically grow exponentially with height into the more rarified atmosphere, ultimately achieving large amplitudes. Some parts of the wave spectrum achieve convective instability, spawning additional
waves or turbulence. Other parts of the wave spectrum are ultimately dissipated by molecular diffusion in
the 100- to 150-km-height region, and some fraction of those waves penetrate all the way to the base of the
exosphere (ca. 500-600 km). Along the way, nonlinear interactions between different wave types occur,
modifying the interacting waves and giving rise to secondary waves. Finally, the IT wind perturbations