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A sporadic case of noctilucent clouds (NLCs) was observed unexpectedly on the night of the 6–7 July 2020 in Beijing (40°2′N, 115°30′E). The noticeable wavy structures and observed ambient temperature (135.54K at the mesosphere and lower thermosphere [MLT]), both indicated that the increase in temperature oscillations could be the cold phase of gravity waves (GWs). The reasons for NLC formation were analyzed based on the observations and model data sets in our study. The real‐time synoptic analysis revealed that there were GWs originally generated by a squall line in the troposphere. Due to the blocked effect of a stable tropopause inversion layer (TIL), the GWs broke, leading to strong energy dissipation near the TIL. The reverse ray tracing analysis between the TIL and NLCs' layer revealed the travel distance (206.88 km) and time (49.91 min) of GWs. These findings show that the turbulence over the TIL (at approximately 14.64 km) excited secondary GWs, which propagated upwards toward the mesosphere and probably interacted with diurnal and semi‐diurnal tides. The cold phase of the larger‐amplitude waves can provide optimal conditions for NLCs forming. Our study highlights the significance of dynamic coupling mechanisms regarding the effects from troposphere to MLT thermal conditions and offers a case study for the increasing occurrences of NLCs at midlatitudes. Plain Language Summary: Noctilucent clouds (NLCs) are ice clouds forming at 80–86 km during summertime in the Northern Hemisphere. During the night of 6–7 July 2020, a Chinese photographer captured the occurrence of NLCs in Beijing (40°2′N, 115°30′E). The wavy structures in the photographs revealed that the occurrence of NLCs had a close relation with the atmospheric gravity waves (GWs), the significant transport of momentum and energy in the atmosphere. We used comprehensive data sets and models to locate the source of these GWs. The real‐time synoptic analysis in the troposphere revealed that the GWs were generated by a convective system, a squall line. However, a stable tropopause inversion layer inhibited the waves like a huge lid, resulting in strong energy dissipation and exciting new GWs propagating upwards. The secondary‐generation GWs can interact with large‐scale waves and cause severe cooling in the MLT, providing an ideal condition for the growth of ice particles in NLCs. These particles integrated the wave source at the tropopause and GWs that are visible in the NLCs for the first time at midlatitudes. The results inspired us to further explore the connection between the troposphere and the upper atmosphere in the future studies. Key Points: The mechanism of a sporadic case of formation of midlatitude noctilucent clouds (NLCs) in China is demonstratedThe interaction between gravity waves (GWs) and tidal waves substantially cooled the NLC layerTurbulence of the tropopause inversion layer excited secondary GWs which propagated upwards toward the mesosphere [ABSTRACT FROM AUTHOR]

In this study, a lidar system based on the Fizeau interferometer and photomultiplier tube array is designed to analyze the entire Rayleigh‐Brillouin spectrum aiming at obtaining the atmospheric temperature profiles. The laser wavelength emitted by the lidar is 355 nm with the pulse energy of 20 mJ, and the diameter of the receiving telescope is 0.6 m. We analyze the influence of the cumulative average of different pulse numbers on the accuracy of temperature inversion. The temperature inversion results in different height ranges are calculated and the results show that if the integration time is 100 s, the temperature deviation is less than 3 K in the altitude range below 24 km. [ABSTRACT FROM AUTHOR]

Oceans are widely regarded as major offsets for anthropogenic carbon emissions, leading to an evident lower measured atmospheric CO2 concentration than expected. It is thus of great significance to develop effective means to monitor CO2 fluxes over oceans globally. In this work, we utilized observations obtained by an airborne CO2‐IPDA LIDAR to evaluate the potential of such means in estimating sea‐air CO2 flux. During a flight experiment in 2019, we have estimated the CO2 exchange rate, −1.5 ± 0.18 mmol/m2/h, between the Bohai Bay and the atmosphere using equilibrium atmospheric boundary layer theory. These findings indicated that the forthcoming space‐borne CO2‐IPDA LIDAR is capable of identifying CO2 uptakes over oceans qualitatively, which would be a novel means and a basis for monitoring CO2 fluxes over global oceans. Plain Language Summary: Oceans are regarded as important offsets to anthropogenic CO2 emissions, delaying an increase in atmospheric CO2 concentration. However, there is a lack of understanding of the intensity, distribution, and variability of marine carbon sinks. China is due to launch a space‐borne LIDAR for measuring atmospheric CO2 concentration globally in 2021. In this work, we utilized data collected during a flight test for the forthcoming satellite mission to explore the ability of such a novel means in revealing and estimating CO2 fluxes of oceans quantitatively. Results confirmed an evident CO2 uptake in the Bohai Bay and exhibited a promising prospect for the novel CO2 measuring means. Key Points: We detected XCO2 gradient during a flight campaign in ChinaRetrieve XCO2 in the atmosphere boundary layer by cloud slicing methodProvide a model to retrieve CO2 flux over ocean by CO2‐IPDA system [ABSTRACT FROM AUTHOR]

Abstract: Data from the Cloud Imaging and Particle Size experiment on the Aeronomy of Ice in the Mesosphere (AIM) satellite are employed to study the impact of small‐scale gravity wave (GW) on albedo, ice water content (IWC), and particle radius (PR) of polar mesospheric clouds. Overall, 23,987 eligible GW events, with a horizontal wavelength of 20–150 km are eventually extracted from Cloud Imaging and Particle Size level 2 orbit albedo maps during 2007–2011. The overall statistical results show that when small‐scale GWs travel horizontally in polar mesospheric clouds, they can amplify the albedo and IWC by a rate of 10.0–22.6%, while reducing the PR by as much as −7.01%. Owing to the strong temporal and spatial dependences, the albedo and IWC variations are larger on an average during the core of the season, while they decrease during the initial and final periods of the season. The obvious zonal asymmetries are also found. The albedo variations show a positive linear relation with the GW amplitudes in albedo, as opposed to a negative linear relation with GW horizontal wavelengths. In most of the GW events, the periodic variation in the trend of albedo exhibits an anticorrelation with that of PR. Combining previous research studies with our results, we deduce that the rapid change in particle concentration and the upward movement of water vapor by GWs may be very important aspects for explaining the influence mechanism. [ABSTRACT FROM AUTHOR]