Characterizing the Global Impacts of
Solar Variability from the Ground to
the Thermosphere Using Data
Assimilation
John McCormack, Fabrizio Sassi
Space Science Division
Naval Research Laboratory
Washington, DC
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Atmospheric Structure
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Middle atmosphere (10-100
km) winds and temperatures
result from balance between
radiative heating/cooling and
effects of breaking planetary
waves and gravity waves
Changes in solar spectral
irradiance affect different parts
of the atmosphere, depending
on wavelength
Both “top-down” and bottomup effects are believed to be
important in determining
atmospheric response See e.g.,
Gray et al. (Rev. Geophys. 2010)
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Record-Low Thermospheric Density in 2008
Density (400 km altitude)
Solar Activity
Density Anomalies
Strong solar cycle variations in
extreme UV irradiance causes the
thermosphere to expand and
contract.
Recent densities were 30% lower
than the previous solar minimum,
and the lowest on record.
CO2 is the primary cooling agent of
the thermosphere; CO2 increases
have caused a gradual decrease in
density.
Recent densities are lower than
expected from solar or CO2 forcing.
Other changes in the underlying
neutral atmosphere are implicated.
See Emmert et al., GRL (2010)
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Motivation
• Understanding the atmospheric response to decadal changes in
solar irradiance is crucial for projections of future climate
• As last solar minimum demonstrates, no two solar cycles are
alike
• Our understanding of the atmospheric response to solar
variability is based on
- satellite and ground-based measurements whose spatial
and temporal coverage vary widely
- modeling studies of varying complexity
• Data assimilation approach combines both sources to best
characterize impact of solar variability on atmosphere
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NOGAPS:
Navy Operational Global Atmospheric Prediction System
- global spectral forecast model with data assimilation for NWP and research
NOGAPS-ALPHA:
From Hoppel et al., ACP, 2008.
Advanced Level Physics-High
Altitude
- Global spectral forecast model (T79),
68 hybrid s-p vertical levels (L68) from
surface to 5x10-4 hPa (see Eckermann
et al., JASTP, 2009)
- 3DVAR assimilation of standard
meteorological observations plus Aura
MLS profiles of O3, T & H2O and
SABER T profiles
- Provides global synoptic fields (e.g.,
u, v, T, H2O) every 6 hours on pressure
levels up to ~90 km
Current operational
- Analysis period: Dec. 2004 – Mar.
2010*.
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Future operational
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Research
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Extended Vertical Domain of NOGAPS-ALPHA
NOGAPS-ALPHA L74
NOGAPS-ALPHA L68
ERA-40 L91 & MERRA
ERA-40 L60
NCEP/NCAR
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NOGAPS-ALPHA Analyzed Winds
NOGAPS-ALPHA does not directly
assimilate horizontal winds. Instead, wind
increments are computed based on
assimilation of middle atmospheric
temperatures, subject to physical
constraints from the forecast model
MF radar v
Comparison of NOGAPS-ALPHA
meridional winds with MF radar winds at
88 km over Adelaide (35oS, 138oE) show
very good agreement.
NOGAPS-ALPHA v
McCormack et al., GRL, 2010
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Wind, temperature, and constituent
analyses from NOGAPS-ALPHA can
provide important diagnostics of middle
atmospheric circulation.
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T Jan 2006
H2O Jan 2006
V Jan 2006
U Jan 2006
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NOGAPS-ALPHA and WACCM
• The NCAR Whole Atmosphere Community Climate Model
(WACCM) can be configured in “specified dynamics” mode
where model circulation is specified using meteorological
fields from data assimilation
• One advantage of using NOGAPS-ALPHA meteorological
fields is the ability to specify the dynamics over a very
deep atmospheric layer.
• Combining high-altitude data assimilation with a state-ofthe-art coupled-chemistry climate model should greatly
improve our understanding of how lower atmospheric
response to solar variability affects the thermosphere
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Summary
• We are currently analyzing existing NOGAPS-ALPHA
meteorological fields to investigate whether changes
in neutral atmosphere below 90 km contrinbuted to
recent record low thermospheric densities
• This question can also be studied by using NOGAPSALPHA meteorological fields in high top GCM’s
(WACCM, WACCM-X, TIE-GCM)
• A NOGAPS-ALPHA “re-analysis” is planned…
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Future Plans
• Conduct “re-analysis” using L74 NOGAPS-ALPHA with:
– Improved treatment of ozone photochemistry in mesosphere
(diurnal cycle)
– Non-LTE CO2 cooling
– Additional MLT thermal diffusion and chemical heating terms
– Varying solar spectral irradiance
– Continuous coverage from Dec. 2004  solar cycle 23
– Transition to 4DVAR assimilation with semi-Langrangian
dynamical core
– Assimilation of additional data sets (e.g., SABER O3, TIDI
winds)
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Backup Slides
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Data Assimilation with NOGAPS-ALPHA
• NOGAPS-ALPHA is the high-altitude version of the Navy
Operational Global Atmospheric Prediction System (NOGAPS)
• NOGAPS-ALPHA combines ground-based and satellite-based
observations with a numerical weather prediction model that
includes middle atmospheric photochemistry, gravity wave
drag, and radiative heating/cooling extending from the surface
to ~90 km.
• NOGAPS-ALPHA generates global synoptic meteorological
analyses (e.g., u, v, T, O3, H2O) every 6 hours. Analyses begin in
December 2004 and currently extend up to mid-2010.
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Background
• Our understanding of the atmospheric
response to solar variability is based on
- satellite and ground-based measurements whose
spatial and temporal coverage vary widely
- modeling studies of varying complexity
• The atmospheric response extends from high
altitudes (thermosphere/ionosphere) down to
surface
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