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Metal Species and Meteor Activity 5 Discussion J Atmos. Chem. Phys. Discuss., 9, 18705–18726, 2009 Atmospheric www.atmos-chem-phys-discuss.net/9/18705/2009/ Chemistry ACPD © Author(s) 2009. This work is distributed under and Physics 9, 18705–18726, 2009 the Creative Commons Attribution 3.0 License. Discussions This discussion paper is/has been under review for the journal Atmospheric Chemistry Metal species and and Physics (ACP). Please refer to the corresponding final paper in ACP if available. meteor activity J. Correira et al. Title Page Metal concentrations in the upper Abstract Introduction atmosphere during meteor showers Conclusions References J. Correira1,*, A. C. Aikin1, J. M. Grebowsky2, and J. P. Burrows3 Tables Figures 1 The Catholic University of America, Institute for Astrophysics and Computational Sciences J I Department of Physics, Washington, DC 20064, USA 2 NASA Goddard Space Flight Center, Code 695, Greenbelt, MD 20771, USA J I 3Institute of Environmental Physics (IUP), University of Bremen, Bremen, Germany Back Close *now at: Computational Physics, Inc., Springfield, Virginia, USA Full Screen / Esc Received: 30 June 2009 – Accepted: 10 August 2009 – Published: 10 September 2009 Correspondence to: J. Correira ([email protected]) Printer-friendly Version Published by Copernicus Publications on behalf of the European Geosciences Union. Interactive Discussion 18705 Abstract ACPD Using the nadir-viewing Global Ozone Measuring Experiment (GOME) UV/VIS spec- trometer on the ERS-2 satellite, we investigate short term variations in the vertical mag- 9, 18705–18726, 2009 nesium column densities in the atmosphere and any connection to possible enhanced 5 mass deposition during a meteor shower. Time-dependent mass influx rates are de- Metal species and rived for all the major meteor showers using published estimates of mass density and meteor activity temporal profiles of meteor showers. An average daily sporadic background mass flux rate is also calculated and used as a baseline against which calculated shower mass J. Correira et al. flux rates are compared. These theoretical mass flux rates are then compared with + 10 GOME derived metal vertical column densities of Mg and Mg from the years 1996– 2001. There is no correlation between theoretical mass flux rates and changes in the Title Page + Mg and Mg metal column densities. A possible explanation for the lack of a shower Abstract Introduction related increase in metal concentrations may be differences in the mass regimes dom- inating the average background mass flux and shower mass flux. Conclusions References Tables Figures 15 1 Introduction J I Meteor showers are the most obvious manifestation of the interaction between meteors and the Earth’s atmosphere. Written records going back thousands of years describe J I in vivid terms what we today call colloquially “shooting stars” raining down from the Back Close heavens. Apart from the impressive visual display, the impact of meteor showers on 20 the Earth’s atmosphere has been a matter of debate. Various sources assert that Full Screen / Esc meteor showers are a small fraction of the total mass input to Earth (Williams, 2001), while other authors state that there could be observable effects of meteor showers in Printer-friendly Version the total abundance of meteoric atoms in the atmosphere (e.g. McNeil et al., 2001). Studies have investigated the E-region of the ionosphere during meteor showers and Interactive Discussion 25 found enhancements during showers (e.g. Zhou et al., 1999), but these seem to be of a transient nature. 18706 In addition to being an awe inspiring sight, meteors are also of interest because they allow the general public to make a significant contribution to scientific research, much ACPD as amateur astronomers do with the magnitudes of variable stars. This paper and sim- 9, 18705–18726, 2009 ilar analysis would be impossible without the contribution of these observers. The work 5 of Jenniskens (1994), used extensively in this work, relies on the data collected by 16 observers, totaling 4482 h of observations over the span of several years. The detec- Metal species and tion of visual meteors can also be accomplished by way of video observation (Hawkes meteor activity and Jones, 1986; Hawkes, 1993), with several sophisticated software packages avail- able for post-detection analysis (Molau and Gural, 2005). The availibility of CCD’s and J. Correira et al. 10 their relatively inexpensive cost has encouraged the continue growth of this method of observation. Title Page Here we will utilize GOME (Global Ozone Monitoring Experiment) data, from the ERS-2 satellite, to probe short term variations in the magnesium atoms (neutrals and Abstract Introduction ions) vertical column densities and explore the connection to the increased deposi- Conclusions References 15 tion of mass during a meteor shower. The ERS-2 satellite was launched on 21 April 1995. The spacecraft is in a retrograde, sun-synchronous, 795 km high near-polar or- Tables Figures bit with an equatorial crossing time of 10:30 AM local time and an orbital period of about 100 min. GOME data is available from 1996 until June 2003, when an on-board J I tape recorder failed. It measured earthshine spectra for wavelengths from 237 to 793 20 nm. The GOME instrument was designed to focus on the distributions of atmospheric J I constituents such as ozone, nitrogen dioxide, formaldehyde, bromine oxide, and water Back Close vapor but its spectral range includes lines of several metal atom species and their ions. Full Screen / Esc 2 Satellite Data Analysis Printer-friendly Version The determination of metal column densities using the GOME instrument was first Interactive Discussion 25 described in Aikin et al. (2005). The vertical column densities of metal atoms are 18707 derived from GOME photon counts using the airglow equation Z ACPD 4πJm = g n(z)dz (1) 9, 18705–18726, 2009 R where Jm is the radiance integrated over a metal spectral line, ndz is the sought after vertical column density, and g is the column photon emission rate, the “g-factor”, which Metal species and 5 is given by (Paxton and Anderson, 1992) meteor activity πe2 g = λ2 f πF (λ )P (θ) (2) J. Correira et al. mc2 0 2 with πF (λ0) the solar irradiance at the transition wavelength in units of photons per cm per second per nanometer and f is the transition oscillator strength. We have included Title Page P θ the anisotropic scattering phase function ( ) (see Chandrasekhar, 1960, p.50), where Abstract Introduction 10 θ is the angle between the incident solar photon and the scattered photon. The sym- bols λ, e, m, and c represent wavelength, electron charge, electron mass and the Conclusions References speed of light, respectively. Rotational Raman Scattering (RRS), also known as the Tables Figures Ring Effect, is the inelastic scatter of solar photons and fills in the metal emission lines. We fully corrected the derived metal column densities for RRS for by using the SCIA- J I 15 TRAN radiative transfer model (Rozanov et al., 2005) to estimate the magnitude of the filling-in as a function of solar zenith angle. Using this analysis Correira et al. (2008) J I studied the seasonal variations of the metal column densities. In the present paper the effects of the fleeting deposition of meteor showers will be explored. Back Close Full Screen / Esc 3 Mass Input from Meteor Showers Printer-friendly Version 20 Jenniskens (1994) found that the temporal variation of the Zenithal Hourly Rates (ZHR), the number of visible meteors an observer could see under ideal conditions, of most Interactive Discussion meteor showers could be described by max −B|λ −λ | ZHR(λ ) = ZHRmax10 (3) 18708 max where λ is the solar (or ecliptic) longitude, λ and ZHRmax are the solar longitude and ZHR at the peak of the shower, respectively, and B is the slope of a line fitted to ACPD the ZHR activity profiles when plotted on a logarithmic scale. If it is assumed that the 9, 18705–18726, 2009 mass density of the stream is proportional to the ZHR, then from Equation 3 we can 5 write in a similar way max Metal species and −B|λ −λ | ρ(λ ) = ρmax10 (4) meteor activity with ρ(λ ) the mass density of a stream at solar longitude λ and ρ is the peak max J. Correira et al. mass density of the stream. The mass accumulation rate onto the Earth, Φ, can be estimated by 2 Title Page 10 Φ = ρVG(πR⊕) (5) where VG is the geocentric velocity of the meteor stream and R⊕ is the Earth’s radius. Abstract Introduction Inserting Equation 4 into Eq. (5) yields a time-dependent expression for the incident mass flux into the Earth’s atmosphere Conclusions References max 2 −B|λ −λ | Tables Figures Φ = ρmaxVG(πR⊕)10 . (6) 15 The total mass accumulated by Earth due to a meteor stream, M can then be found T J I by integrating over the duration of the shower: end J I Z λ MT = Φ dλ . (7) Back Close start λ Another method to calculate the total mass accumulated by the Earth is to use the Full Screen / Esc “equivalent duration” (Hughes and McBride, 1989) or “equivalent cross-section” (Jen- Printer-friendly Version 20 niskens, 1994), ∆t, of the meteor shower. Multiplying the equivalent cross-section by the peak mass flux gives the total mass swept up by the Earth during its passage Interactive Discussion through the stream. The equivalent cross-section can be calculated from Z max −B|λ −λ | ∆t = 10 dλ . (8) 18709 If the slope of the ZHR activity is given by ACPD max B+ if λ < λ B = max 9, 18705–18726, 2009 B− if λ > λ then the equivalent cross-section is Metal species and 1 1 1 meteor activity 5 ∆t = + .
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