A Re‐Examination of the Reversal in Vertical Velocity Profiles at 12 km Altitude Measured by the Middle and Upper Atmosphere Radar Over a 38‐Year Period (1987–2024)

Abstract Vertical air motion is a key factor in many meteorological phenomena, yet measuring it remains challenging. VHF Stratosphere‐Troposphere radars, however, provide methods to measure vertical air velocities ( in the tropo‐stratosphere. From Middle and Upper (MU) atmosphere radar data spanning 38 years (1987–2024), we found that the well‐known reversal in mean profiles at the height of the jet stream maximum, with negative below 12 km and positive above occurs almost every month, not just in winter as previously reported. We developed a refined model, complementary to the ad‐hoc model by Muschinski (1996), https://doi.org/10.1175/1520‐0450(1996)035%3C2210:PEOKHI%3E2.0.CO;2 , which accounts for power imbalance between symmetric oblique beams. This model confirms that the monthly mean profiles above ∼4.0 km are primarily influenced by contamination from a slight tilt in the scatter diagram, induced by horizontal wind shear. Additionally, our analysis of 30 years of ERA5 reanalysis data indicates that adiabatic ascent/descent along potential temperature surfaces can also cause a reversal in winter, consistent with earlier studies. However, the climatological mean vertical velocities are much weaker than those observed by the MU radar, suggesting that wind shear‐induced layer tilt dominates the long‐term effect.