Search Results (6)

The atmospheric boundary layer (ABL) has strong diurnal variability, but routine radiosonde launches at 00:00 and 12:00 UTC cannot fully resolve its daily evolution. This study develops and evaluates a 13-year (2007–2019) hourly ABL profile dataset using Aircraft Meteorological Data Relay (AMDAR) observations from 42 selected European airports, and applies it to characterize airport-scale diurnal, seasonal, and regional variations in ABL structure. AMDAR-derived temperature and wind profiles were validated against collocated radiosonde observations by season, pressure layer, and airport–radiosonde distance. Errors decrease for shorter separation distances and lower-tropospheric layers. For separations < 50 km and pressures > 850 hPa, spring, summer, autumn, and winter RMSEs are 0.9/1.0/1.4/1.2 K for temperature, 1.7/2.0/1.9/1.9 m/s for zonal wind, and 1.4/1.6/1.9/1.6 m/s for meridional wind. Hourly AMDAR profiles reveal distinct diurnal ABL evolution at airport scale. Seasonal ABL height (ABLH) composites are mainly 250–900 m, with available nighttime and early-morning values of about 300–450 m and spring–summer afternoon maxima of 800–900 m at far-inland airports. Coastal airports show weaker daytime growth, mostly below 600–650 m. These results demonstrate AMDAR’s value as a supplementary profile dataset for characterizing European airport-scale ABL structure and diurnal variability. Full article

The thermosphere serves as a pivotal region for Sun–Earth interactions, and thermospheric winds are of great scientific importance for deepening insights into atmospheric dynamics, climate formation mechanisms, and space environment evolution. This study designed and developed a Ground-based Doppler Asymmetric Spatial Heterodyne Interferometer (GDASHI). Targeting the nightglow of the oxygen atomic red line (OI 630.0 nm), this instrument enables high-precision observation of thermospheric winds. The GDASHI was deployed at Gemini Astronomical Manor (26.7°N, 100.0°E), and has obtained one year of nighttime meridional and zonal wind data. To verify the reliability of GDASHI-derived winds, a collocated observation comparison was performed against the Dual-Channel Optical Interferometer stationed at Binchuan Station (25.6°N, 100.6°E), Yunnan. The winds of the two instruments are basically consistent in both their diurnal variation trends and amplitudes. Further Deming regression and correlation analysis were conducted for the two datasets, with the meridional and zonal winds yielding fitting slopes of 0.808 and 0.875 and correlation coefficients of 0.754 and 0.771, respectively. An uncertainty analysis of the inter-instrument comparison was also carried out, incorporating instrumental measurement uncertainties, instrumental parameter errors, and small-scale perturbations induced by observational site differences; the synthesized total uncertainties of zonal and meridional winds are determined to be 20.24 m/s and 20.77 m/s, respectively. This study not only verifies the feasibility and reliability of GDASHI for ground-based thermospheric wind detection but also provides critical observational support for analyzing the spatiotemporal variation characteristics of mid-low latitude thermospheric wind fields and exploring their underlying physical mechanisms. Full article

This study presents a comprehensive statistical analysis of ionospheric midnight collapse events over Arecibo, based on incoherent scatter radar (ISR) observations collected between 1971 and 2019. A total of 224 nights with valid measurements were examined to characterize the timing, intensity, and seasonal variation of these collapse events. The results showed that midnight collapses occurred on 94.6% of the nights, with the highest occurrence rate observed during spring and winter. The first collapse typically began between 22:00 and 00:00 LT, lasted for 1–4 h, initiated at altitudes between 350 and 400 km, and involved a vertical collapse of 50–100 km. A second collapse was identified on 18.8% of nights, occurring predominantly between 01:00 and 02:00 LT, with a notably higher frequency during winter. Compared to the first collapse, the second collapse tended to originate at lower altitudes and exhibited faster collapse rates. Seasonal patterns in the vertical ion drift ($V_z$) were also identified, with winter events characterized by a persistently downward $V_z$ throughout the night. Further decomposition of $V_z$ into field-aligned ($V_{ap}$) and perpendicular ($V_{pn}$) components indicated that $V_{ap}$ played a dominant role in modulating $V_z$, particularly on nights with double collapses. Analysis of meridional wind variations revealed that nighttime changes in $V_{ap}$ were largely controlled by meridional wind, suggesting a strong coupling between thermospheric wind dynamics and field-aligned ion motion. These findings suggest that variations in $V_z$, primarily driven by meridional-wind-controlled changes in $V_{ap}$, are a key driver of ionospheric midnight collapse events at Arecibo. Full article

Temporal oscillations in the IMF Bz associated with Alfvén waves occur frequently in solar wind, with a duration ranging from minutes to hours. Using Swarm observations, Fabry–Pérot interferometer measurements at Mohe station, and Thermosphere–Ionosphere–Electrodynamic General Circulation Model simulations, the perturbations of zonal (ΔUN) and meridional (ΔVN) winds due to temporal oscillations in the IMF Bz on 23–24 April 2023 are explored in the following work. ΔUN is strong westward with a speed of greater than 100 m/s at pre-midnight on 23–24 April. This phenomenon is primarily driven by the pressure gradient, offsetting by the ion drag and Coriolis force. On 23 April, ΔVN is weak northward at the pre-midnight and strong southward at a speed of ~200 m/s at pre-dawn. On 24 April, ΔVN is strong (weak) northward at pre-midnight (pre-dawn). It is mainly controlled by a balance between the pressure gradient, ion drag, and Coriolis force. Full article

The formation and localization of sporadic E (Es) layers predicted by the ion vertical drift velocity and its vertical change in the lower thermosphere during nighttime are shown analytically and by numerical simulations. The consideration of the existence of a minimum negative value of the vertical change of the ion vertical drift velocity as a necessary condition of formation of the Es layer and determining ion convergence rate into this layer is extended in case of the presence of vertical wind. Upward vertical wind can shift the convergence regions upward, while downward vertical wind shifts them downward, unlike the cases of the presence of only meridional and zonal winds. It also changes the ion convergence rate compared to the one with just a horizontal wind. It is shown for the first time that the upward constant wind also causes the convergence of ions with the maximum rate in the region where the ion-neutral collision frequency is equal to their cyclotron frequency. While demonstrating the presented theory by numerical simulations, HWM14 data is used for the meridional and zonal wind velocity profiles and the presence of its vertical component is assumed. In this case, in addition to the estimated ion drift velocity and its vertical changes, their initial distribution and ambipolar diffusion also determine the development of ion convergence/divergence processes. For a small magnitude of vertical wind velocity, its significant influence on the ions/electrons behavior is demonstrated, which shows the importance of both tidal wind and wind changes caused by the propagation of atmospheric gravity waves on the formation of the Es layer. In this theoretical research, it is shown that the realistic profile of the wind velocity, which takes into account the vertical component along with its zonal and meridional ones, is important for the prediction of the Es layers formation, as well as regions of ion depletion. Full article

Due to rapid urbanization, the near-surface meteorological conditions over urban areas are greatly modulated. To capture such modulations, sophisticated urban parameterizations with enhanced hydrological processes have been developed. In this study, we use the single-layer urban canopy model (SLUCM) available within the Weather Research and Forecasting (WRF) model to assess the response of near-surface temperature, wind, and moisture to advection under the impact of the green roof. An ensemble of simulations with different planetary boundary layer (PBL) schemes is conducted in the presence (green roof (GR)) and absence (control (CTL)) of green roof systems. Our results indicate that the near-surface temperature is found to be driven primarily by the surface heat flux with a minor influence from the zonal advection of temperature. The momentum budget analysis shows that both zonal and meridional momentum advection during the evening and early nighttime plays an important role in modulating winds over urban areas. The near-surface humidity remains nearly unchanged in GR compared to CTL, although the physical processes that determine the changes in humidity were different, in particular during the evening when the GR tends to have less moisture advection due to the reduced temperature gradient between the urban areas and the surroundings. Implications of our results are discussed. Full article