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<p>The effect of the full solar eclipse of 8 April 2024 on the urban boundary layer over downtown Montreal is investigated. Doppler Lidar operating in velocity azimuth scanning mode was used to measure various velocity moments and backscattered signal coefficients within the atmospheric boundary layer. It is observed that the urban boundary layer height of order of approximately 1&#xa0;km during the eclipse increases from solar noon until the onset of the eclipse and then stabilizes over a 20-min timescale, which is consistent with the timescale of subsidence aloft until the eclipse concludes. The mean horizontal wind speed increases from about 4 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathrm {m~s}}^{-1}\)</EquationSource> </InlineEquation> before totality to over 6 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\mathrm {m~s}}^{-1}\)</EquationSource> </InlineEquation> after totality, while relatively intense downdrafts are observed near the beginning of the eclipse with descending velocities increasing with height. A nocturnal jet forms prior to the end of the eclipse due to truncated night conditions, with local parcels of large integral time scales appearing at low heights shortly after totality and ascending as the eclipse progresses. A localized convergence zone is measured before totality at a height of 150&#xa0;m, coinciding with an area of upward vertical velocity. It is argued that the surface layer is more unstable at solar noon compared to totality, which resembles early sunset conditions that enhance atmospheric stability. Finally, all components of the Reynolds stress tensor decrease near the totality. The results offer an opportunity to study the effect of sudden changes in solar radiation on the dynamics of the urban boundary layer.</p>

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Doppler Lidar Observations of Urban Boundary Layer Response to the 8 April 2024 Total Solar Eclipse in Montreal

  • 期刊论文

  • 发表日期：

    2025年12月1日

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  • Ruiqi Chen,
  • Masoud Moeini,
  • Djordje Romanic

摘要

The effect of the full solar eclipse of 8 April 2024 on the urban boundary layer over downtown Montreal is investigated. Doppler Lidar operating in velocity azimuth scanning mode was used to measure various velocity moments and backscattered signal coefficients within the atmospheric boundary layer. It is observed that the urban boundary layer height of order of approximately 1 km during the eclipse increases from solar noon until the onset of the eclipse and then stabilizes over a 20-min timescale, which is consistent with the timescale of subsidence aloft until the eclipse concludes. The mean horizontal wind speed increases from about 4 \({\mathrm {m~s}}^{-1}\) before totality to over 6 \({\mathrm {m~s}}^{-1}\) after totality, while relatively intense downdrafts are observed near the beginning of the eclipse with descending velocities increasing with height. A nocturnal jet forms prior to the end of the eclipse due to truncated night conditions, with local parcels of large integral time scales appearing at low heights shortly after totality and ascending as the eclipse progresses. A localized convergence zone is measured before totality at a height of 150 m, coinciding with an area of upward vertical velocity. It is argued that the surface layer is more unstable at solar noon compared to totality, which resembles early sunset conditions that enhance atmospheric stability. Finally, all components of the Reynolds stress tensor decrease near the totality. The results offer an opportunity to study the effect of sudden changes in solar radiation on the dynamics of the urban boundary layer.