Search

Lower atmospheric gravity waves (GWs) can significantly impact waves in the middle and upper atmospheres and are vital for turbulence generation. This paper puts the spotlight on the spatial–temporal variability of tropospheric GW total energy (ET) and its potential sources above four regions of interest (ROIs) gathered from high‐resolution radiosonde observations from the China Radiosonde Network during the years 2016–2019. The seasonality of ET above four ROIs shows different characteristics and is dependent on latitudes and underlying terrains, reaching its maximum identified in the winter at middle latitudes. Interestingly, the annual cycles of the maximal ET shift from 35°N in October to 25°N in March of the next year, triggered by the shift in the winter subtropical jet. Based on the random forests regressor, the jet stream between 200 and 125 hPa likely serves as the primary source for the observed GWs above the ROIs with low and middle latitudes, with relative contributions of around 60%. However, the Kelvin–Helmholtz instability between 800 and 125 hPa could be the most recognized source of GWs and contributes around 68.4% to the observed energy. During the rainy season, the ET under scenarios of convective precipitation is around 20% larger than the other. As well, as the near‐surface or low‐level wind interacts with a mountain barrier over the Tibetan Plateau region, 12.4% of the observed ET is attributed to the strength of the low‐level wind. Plain Language Summary: The gravity wave (GW) is one of the most important waves in the atmosphere and acts as a triggering source to turbulence. However, the tropospheric GWs in the context of China has seldomly been investigated by using high‐resolution radiosonde data set. This analysis shows that the GW total energy exhibit obvious seasonal various at low and middle latitudes, with maximal identified in the winter and minimal in the summer. The jet stream in the upper troposphere is the most important source for GW at low and middle latitudes and gives rise to a southward propagation of the maximal GW energy in cold season. In the summer of southern China, the convective precipitation could contribute to the enhancement of GW energy. In addition, 12.4% of the observed GW energy is attributed to the strength of the low‐level wind over the Tibetan Plateau. Key Points: Jet stream is the dominant source for gravity waves (GWs) at low and middle latitudes and triggers southward movement of GW energy core during cold seasonsOver the Tibetan Plateau, Kelvin–Helmholtz instabilities and terrain‐induced flows contribute to the intensive GW activitiesDuring the summertime of southern China, convective precipitation could contribute to the enhancement of energy of about 20% [ABSTRACT FROM AUTHOR]

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]

The planetary boundary layer is crucial for the turbulence mixing and exchange of heat flux, momentum, and atmospheric pollutants between the atmosphere and Earth's surface. Nevertheless, the estimated boundary layer height (BLH) varies greatly by data sources and algorithms. This paper seeks to characterize the convective BLHs from 1‐s radiosonde measurements of China Radiosonde Network (CRN) for the 2012–2020 period at 1400 Beijing time, by using eight well‐known algorithms, wherein the newly established Thorpe method is theoretically fundamental on turbulence analysis and is in remarkable agreement with the parcel and bulk Richardson number methods. BLHs obtained by eight methods, ranging from 1.2 to 2.5 km, strongly vary with methods based on different kinetic or thermodynamic theories. The significant offsets among methods motivate the present study to propose a merged algorithm, to minimize the spread of BLH estimate. The merged BLH contains more physical information than that retrieved from a single method and can significantly lower the uncertainty. The BLH climatology exhibits a spatial pattern of "Southwest‐High Southeast‐Low," ascending from 0.6 km over southeastern China to 2.3 km over southwestern China, which could be largely attributed to the variations in the integrated surface sensible heat flux, soil moisture, total cloud cover, land cover, synoptic forcing, and terrain‐induced flow. Of interest is that land surface properties could be the major driver for the development of CBL. Also noteworthy is that the smallest BLH is expected under the strongest synoptic forcing condition. Plain Language Summary: The planetary boundary layer (PBL), where the exchanges of heat, moisture, momentum, and mass mainly occur with a variety of physical and chemical processes involved, is the lowest part of the troposphere in direct contact with the ground surface. However, the determination of boundary layer height (BLH) tends to be dramatically influenced by the dataset and methods used. Few studies have been conducted to evaluate the discrepancy of nationwide daytime BLH over China originating from the methods used. In particular, eight well‐known methods, including the novel Thorpe method and seven other traditional methods, are applied to estimate BLHs from high‐resolution soundings from the China Radiosonde Network. However, BLH derived by eight methods vary from approximately 1.2 to 2.5 km, strongly depending on the method. Therefore, to compile a more convincing BLH dataset eight methods are selected and composed as a merged BLH. The climatology of the merged BLH for the period 2012–2020 shows a well‐defined "Southwest‐High Southeast‐Low " pattern, which could be attributed to the diversities in sensible heat flux, soil moisture, land cover, total cloud cover, synoptic forcing, and terrain‐induced flow across China. Key Points: The merged boundary layer height (BLH) is synthesized from eight methods and it carries more planetary boundary layer (PBL) information and can considerably lower the uncertaintiesThe "Southwest‐High Southeast‐Low" pattern of BLH could be attributed to land properties, synoptic forcing, and terrain‐induced flowUnder weak synoptic forcing condition the development of convective PBL is more susceptible to the variation of land surface properties [ABSTRACT FROM AUTHOR]

By using 90 radiosonde stations with high vertical resolution data during the period 1998–2011, the latitudinal variation of the tropopause inversion layer (TIL) in different seasons and the interactions with the inertial gravity wave (IGW) activities in the region covering the Northern Hemispheric latitudes from 5° to 75° are studied. For the midlatitudes, the TIL features show obviously seasonal variations. In the Arctic region, TIL is strong and thick. The averaged Arctic TIL intensity peaks in summer. The intense interaction between the TIL and IGW is found in the region of 5°N to 75°N. The TIL could inhibit the upward propagation of IGWs from ~2 km below the tropopause in a larger region (40–75°N). It is found that for the middle‐latitude regions, the enhanced wind shear layer just above the tropopause could lead to instability and finally result in IGW breaking and intensive turbulence, which then leads to strong wave energy dissipation and a downward heat flux. The IGW‐induced cooling around the tropopause, which resulted from the downward heat flux, then makes a colder and sharper tropopause and finally form the TIL. The IGW‐associated strong downward heat flux is also found around the Arctic tropopause. However, there is no corresponding wind shear enhancement above the tropopause. This indicates that this strong heat flux may result from some other processes and then form the strong TIL in the Arctic. Key Points: Intense interaction between the TIL and IGW is confirmed in a larger regionThe TIL could inhibit the upward propagation of IGWs from below mainly for the middle and high latitudesIGW‐induced downward heat flux around the tropopause could cause TIL formation, not only for the middle latitudes but also for the Arctic [ABSTRACT FROM AUTHOR]