The photochemical time constants of minor constituents and their families in the middle atmosphere

Shimazaki, Tatsuo

doi:10.1016/0021-9169(84)90143-0

Cited by 45 publications

(23 citation statements)

References 16 publications

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“…The model includes a chemical scheme of several hundred reactions, and takes into account external forcing due to solar UV and soft X-ray radiation, electron and proton precipitation, and galactic cosmic rays. The background neutral atmosphere is generated using the MSISE-90 model (Hedin, 1991) and tables given by Shimazaki (1984). The solar flux is estimated by the SOLAR2000 model (Tobiska et al, 2000), version 2.27.…”

Section: Modelling the Spe Effects In The Magnetic Cutoff Transition mentioning

confidence: 99%

Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl

et al. 2007

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Abstract. We utilise hydroxyl observations from the MLS/Aura satellite instrument to study the latitudinal extent of particle forcing in the northern polar region during the January 2005 solar proton event. MLS is the first satellite instrument to observe HO x changes during such an event. We also predict the hydroxyl changes with respect to the magnetic latitude by the Sodankylä Ion and Neutral Chemistry model, estimating the variable magnetic cutoff energies for protons using a parameterisation based on magnetosphere modelling and the planetary magnetic index K p . In the middle and lower mesosphere, HO x species are good indicators of the changes in the atmosphere during solar proton events, because they respond rapidly to both increases and decreases in proton forcing. Also, atmospheric transport has a negligible effect on HO x because of its short chemical lifetime.The observations indicate the boundary of the proton forcing and a transition region, from none to the "full" effect, which ranges from about 57 to 64 degrees of magnetic latitude. When saturating the rigidity cutoff K p at 6 in the model, as suggested by earlier studies using observations of cosmic radio noise absorption, the equatorward boundary of the transition region is offset by ≈2 degrees polewards compared with the data, thus the latitudinal extent of the proton forcing in the atmosphere is underestimated. However, the model predictions are in reasonable agreement with the MLS measurements when the K p index is allowed to vary within its nominal range, i.e., from 1 to 9 in the cutoff calculation.

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Section: Modelling the Spe Effects In The Magnetic Cutoff Transition mentioning

confidence: 99%

Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl

et al. 2007

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“…The SIC code includes a vertical transport [Chabrillat et al, 2002] which takes into account molecular [Banks and Kockarts, 1973] and eddy diffusion with a fixed eddy diffusion coefficient profile. The background neutral atmosphere is calculated using the MSISE-90 model [Hedin, 1991] and tables given by Shimazaki [1984]. Transport and chemistry are advanced in intervals of 5 or 15 minutes.…”

Section: Nighttime Riometer Absorption Using the Sodankylä Ion And Nementioning

confidence: 99%

Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy

et al. 2007

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[1] In the polar atmosphere, significant chemical and ionization changes occur during solar proton events (SPEs). The access of solar protons to this region is limited by the dynamically changing geomagnetic field. In this study, we have used riometer absorption observations to investigate the accuracy of a model to predict K p -dependent geomagnetic rigidity cutoffs, and hence the changing proton fluxes. The imaging riometer at Halley, Antarctica is ideally situated for such a study, as the rigidity cutoff sweeps back and forth across the instrument's field of view, providing a severe test of the rigidity cutoff model. Using observations from this riometer during five solar proton events, we have confirmed the basic accuracy of this rigidity model. However, we find that the model can be improved by setting a lower K p limit (i.e., K p = 5 instead of 6) at which the rigidity modeling saturates. We also find that, for L > 4.5, the apparent L-shell of the beam moves equatorward. In addition, the Sodankylä Ion and Neutral Chemistry (SIC) model is used to determine an empirical relationship between integral proton precipitation fluxes and nighttime ionosphere riometer absorption, in order to allow consideration of wintertime SPEs. We find that during the nighttime, the proton flux energy threshold is lowered to include protons with energies of >5 MeV in comparison with >10 MeV for the daytime empirical relationships. In addition, we provide an indication of the southern and northern geographic regions inside which SPEs play a role in modifying the neutral chemistry of the stratosphere and mesosphere.Citation: Clilverd, M. A., C. J. Rodger, T. Moffat-Griffin, and P. T. Verronen (2007), Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy,

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“…The SIC code includes vertical transport (Chabrillat et al, 2002) which takes into account molecular diffusion coefficients (Banks and Kockarts, 1973). The background neutral atmosphere is calculated using the MSISE-90 model (Hedin, 1991) and tables given by Shimazaki (1984). Transport and chemistry are advanced in intervals of 5 or 15 min, while within each interval exponentially increasing time steps are used because of the wide range of chemical time constants of the modelled species.…”

Section: Sodankylä Ion Chemistry Modelmentioning

confidence: 99%

Lightning-driven inner radiation belt energy deposition into the atmosphere: implications for ionisation-levels and neutral chemistry

Rodger

Enell²,

Turunen³

et al. 2007

Ann. Geophys.

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Abstract. Lightning-generated whistlers lead to coupling between the troposphere, the Van Allen radiation belts and the lower-ionosphere through Whistler-induced electron precipitation (WEP). Lightning produced whistlers interact with cyclotron resonant radiation belt electrons, leading to pitchangle scattering into the bounce loss cone and precipitation into the atmosphere. Here we consider the relative significance of WEP to the lower ionosphere and atmosphere by contrasting WEP produced ionisation rate changes with those from Galactic Cosmic Radiation (GCR) and solar photoionisation. During the day, WEP is never a significant source of ionisation in the lower ionosphere for any location or altitude. At nighttime, GCR is more significant than WEP at altitudes <68 km for all locations, above which WEP starts to dominate in North America and Central Europe. Between 75 and 80 km altitude WEP becomes more significant than GCR for the majority of spatial locations at which WEP deposits energy. The size of the regions in which WEP is the most important nighttime ionisation source peaks at ∼80 km, depending on the relative contributions of WEP and nighttime solar Lyman-α. We also used the Sodankylä Ion Chemistry (SIC) model to consider the atmospheric consequences of WEP, focusing on a case-study period. Previous studies have also shown that energetic particle precipitation can lead to large-scale changes in the chemical makeup of the neutral atmosphere by enhancing minor chemical species that play a key role in the ozone balance of the middle atmosphere. However, SIC modelling indicates that the neutral atmospheric changes driven by WEP are insignificant due to the short timescale of the WEP bursts. Overall we find that WEP is a significant energy input into some parts of the lower ionosphere, depending on the latitude/longitude and altitude, but does not play a significant role in the neutral chemistry of the mesosphere.

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The photochemical time constants of minor constituents and their families in the middle atmosphere

Cited by 45 publications

References 16 publications

Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl

Latitudinal extent of the January 2005 solar proton event in the Northern Hemisphere from satellite observations of hydroxyl

Improved dynamic geomagnetic rigidity cutoff modeling: Testing predictive accuracy

Lightning-driven inner radiation belt energy deposition into the atmosphere: implications for ionisation-levels and neutral chemistry

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