<p>Accurate measurement of vertical air motion is essential for improving weather forecasts and climate models. VHF stratosphere–troposphere radars, like the 46.5 MHz Middle and Upper atmosphere (MU) radar at the Shigaraki MU Observatory in Japan, are possible tools for quantifying vertical air velocities in the tropo-stratosphere. This study examines vertical air velocity measurements taken over 38 years (1987–2024) using the MU radar at altitudes ranging from ~ 2 to ~ 20 km. The analysis uses three methods: direct vertical measurements (<InlineEquation ID="IEq189"> <EquationSource Format="TEX">${\mathit{W}}$</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="italic">W</mi> </math></EquationSource> </InlineEquation>), and calculations derived from two pairs of oblique beams (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${W}_{NS}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>W</mi> <mrow> <mi mathvariant="italic">NS</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">${W}_{EW}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>W</mi> <mrow> <mi mathvariant="italic">EW</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>), each oriented 10 degrees off zenith in the North–South and East–West directions. Statistical parameters, such as mean, standard deviation, skewness, kurtosis, percentiles, and Gini coefficient, were computed. Except for the average vertical velocity, the higher-order moments show consistent patterns across all three estimates and altitudes. Below 10 km, the profiles of <InlineEquation ID="IEq3"> <EquationSource Format="TEX">${W, W}_{NS}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>W</mi> <mo>,</mo> <mi>W</mi> </mrow> <mrow> <mi mathvariant="italic">NS</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>, and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${W}_{EW}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>W</mi> <mrow> <mi mathvariant="italic">EW</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> show minimal differences, whereas above 10 km, slight variations appear, potentially related to increased static stability. A notable kurtosis dependence on horizontal wind speed confirms data integrity. Numerical simulations, based on the observed characteristics of <i>W</i> frequency spectra from MU radar, suggest that this relationship is due to filtering effects from horizontal wind advection, rather than gravity wave properties. This effect, however, does not align with the expected properties of gravity waves.</p>

Statistics of vertical wind velocity measured by MU radar over a 38-year period (1987–2024) in the 2–20 km altitude range

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2026年1月1日

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Hubert Luce,
Noriyuki Nishi,
Hiroyuki Hashiguchi

摘要

Accurate measurement of vertical air motion is essential for improving weather forecasts and climate models. VHF stratosphere–troposphere radars, like the 46.5 MHz Middle and Upper atmosphere (MU) radar at the Shigaraki MU Observatory in Japan, are possible tools for quantifying vertical air velocities in the tropo-stratosphere. This study examines vertical air velocity measurements taken over 38 years (1987–2024) using the MU radar at altitudes ranging from ~ 2 to ~ 20 km. The analysis uses three methods: direct vertical measurements ( ${\mathit{W}}$ $W$ ), and calculations derived from two pairs of oblique beams ( ${W}_{NS}$ $W_{NS}$ and ${W}_{EW}$ $W_{EW}$ ), each oriented 10 degrees off zenith in the North–South and East–West directions. Statistical parameters, such as mean, standard deviation, skewness, kurtosis, percentiles, and Gini coefficient, were computed. Except for the average vertical velocity, the higher-order moments show consistent patterns across all three estimates and altitudes. Below 10 km, the profiles of ${W, W}_{NS}$ ${W, W}_{NS}$ , and ${W}_{EW}$ $W_{EW}$ show minimal differences, whereas above 10 km, slight variations appear, potentially related to increased static stability. A notable kurtosis dependence on horizontal wind speed confirms data integrity. Numerical simulations, based on the observed characteristics of W frequency spectra from MU radar, suggest that this relationship is due to filtering effects from horizontal wind advection, rather than gravity wave properties. This effect, however, does not align with the expected properties of gravity waves.