A Climatological Study of the Nocturnal Boundary Layer over a Complex-Terrain Station

AbstractTwo years of Doppler sodar measurements are used to study the time–height structure of the nocturnal boundary layer (NBL), its seasonal variation, and the characteristics of different types of NBL. A total of 220 clear-sky nights during which the inversion layer is clearly visible on a sodar echogram are examined. The NBL depth estimated with sodar data using a wind maxima criterion matches reasonably well with radiosonde-based NBL depth estimates. The NBL exhibits clear seasonal variation with greater depths during the monsoon season. Shallow NBLs are generally observed in winter. The evolution of NBL height shows two distinctly different patterns (called type 1 and type 2), particularly in the second half of the night. Type 1 NBL depth is nearly constant and the wind speed in this type is generally weak and steady throughout the night, while type 2 is characterized by moderate to strong winds with considerable variations in NBL height. The local circulation generated by the complex topography is clearly seen in type 1 throughout the night, whereas it is seen only in the first half of the night in type 2. Type 1 NBLs seem to be more prevalent over Gadanki, India, with nearly 61% of total nights showing type 1 characteristics. Furthermore, type 1 NBL shows large seasonal variability with the majority of type 1 cases in winter. The type 2 cases are mostly observed in monsoon (~60%) followed by summer (39%). The surface meteorological parameters during type 1 and type 2 cases are examined. Differences between type 1 and type 2 NBL patterns are discussed in relation to the surface forcing.

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Boundary layer structure characteristics under objective classification of persistent pollution weather types in the Beijing area

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-8863-2021 ◽

2021 ◽

Vol 21 (11) ◽

pp. 8863-8882

Author(s):

Zhaobin Sun ◽

Xiujuan Zhao ◽

Ziming Li ◽

Guiqian Tang ◽

Shiguang Miao

Keyword(s):

Boundary Layer ◽

Layer Structure ◽

Local Circulation ◽

Weather Types ◽

Beijing Area ◽

Haze Pollution ◽

Type 3 ◽

Pollution Events

Abstract. Different types of pollution boundary layer structures form via the coupling of different synoptic systems and local mesoscale circulation in the boundary layer; this coupling contributes toward the formation and continuation of haze pollution. In this study, we objectively classify the 32 heavy haze pollution events using integrated meteorological and environmental data and ERA-Interim analysis data based on the rotated empirical orthogonal function method. The thermodynamic and dynamic structures of the boundary layer for different pollution weather types are synthesized, and the corresponding three-dimensional boundary layer conceptual models for haze pollution are constructed. The results show that four weather types mainly influence haze pollution events in the Beijing area: (a) type 1 – southerly transport, (b) type 2 – easterly convergence, (c) type 3 – sinking compression, and (d) type 4 – local accumulation. The explained variances in the four pollution weather types are 43.69 % (type 1), 33.68 % (type 2), 16.51 % (type 3), and 3.92 % (type 4). In persistent haze pollution events, type 1 and type 2 surpass 80 % on the first and second days, while the other types are present alternately in later stages. The atmospheric structures of type 1, type 2, and type 3 have typical baroclinic characteristics at mid–high latitudes, indicating that the accumulation and transport of pollutants in the boundary layer are affected by coupled structures in synoptic-scale systems and local circulation. The atmospheric structure of type 4 has typical barotropic characteristics, indicating that the accumulation and transport of pollutants is primarily affected by local circulation. In type 1, southerly winds with a specific thickness and intensity prevail in the boundary layer, which is favorable for the accumulation of pollutants in plain areas along the Yan and Taihang Mountains, whereas haze pollution levels in other areas are relatively low. Due to the interaction between weak easterly winds and the western mountains, pollutants accumulate mainly in the plain areas along the Taihang Mountains in type 2. The atmospheric vertical structure is not conducive to upward pollutant diffusion. In type 3, the heights of the inversion and boundary layers are the lowest due to a weak sinking motion while relative humidity is the highest among the four types. The atmosphere has a small capacity for pollutant dispersion and is favorable to particulate matter hygroscopic growth; as a result, type 3 has the highest PM2.5 concentration. In type 4, the boundary layer is the highest among the four types, the relative humidity is the lowest, and the PM2.5 concentration is relatively lower under the influence of local mountain–plain winds. Different weather types will shape significantly different structures of the pollution boundary layer. The findings of this study allow us to understand the inherent difference among heavy pollution boundary layers; in addition, they reveal the formation mechanism of haze pollution from an integrated synoptic-scale and boundary layer structure perspective. We also provide scientific support for the scientific reduction of emissions and air quality prediction in the Beijing–Tianjin–Hebei region of China.

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Nocturnal Boundary Layer Evolution and Its Impacts on the Vertical Distributions of Pollutant Particulate Matter

Atmosphere ◽

10.3390/atmos12050610 ◽

2021 ◽

Vol 12 (5) ◽

pp. 610

Author(s):

Yu Shi ◽

Lei Liu ◽

Fei Hu ◽

Guangqiang Fan ◽

Juntao Huo

Keyword(s):

Boundary Layer ◽

Nitrate Concentration ◽

Inversion Layer ◽

Mixing Layer ◽

Early Morning ◽

Nocturnal Boundary Layer ◽

Atmospheric Environment ◽

Considerable Proportion ◽

Surface Inversion ◽

Vertical Distributions

To investigate the evolution of the nocturnal boundary layer (NBL) and its impacts on the vertical distributions of pollutant particulates, a combination of in situ observations from a large tethered balloon, remote sensing instruments (aerosol lidar and Doppler wind lidar) and an atmospheric environment-monitoring vehicle were utilized. The observation site was approximately 100 km southwest of Beijing, the capital of China. Results show that a considerable proportion of pollutant particulates were still suspended in the residual layer (RL) (e.g., the nitrate concentration reached 30 μg m−3) after sunset. The NBL height calculated by the aerosol lidar was closer to the top of the RL before midnight because of the pollutants stored aloft in the RL and the shallow surface inversion layer; after midnight, the NBL height was more consistent with the top of the surface inversion layer. As the convective mixing layer gradually became established after sunrise the following day, the pollutants stored in the nocturnal RL of the preceding night were entrained downward into the mixing layer. The early morning PM2.5 concentration near 700 m in the RL on 20 December decreased by 83% compared with the concentration at 13:34 on 20 December at the same height. The nitrate concentration also decreased significantly in the RL, and the mixing down of nitrate from the RL could contribute about 37% to the nitrate in the mixing layer. Turbulence activities still existed in the RL with the bulk Richardson number (Rb) below the threshold value. The corresponding increase in PM2.5 was likely to be correlated with the weak turbulence in the RL in the early morning.

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Seasonal Variation in Blood Pressure in 162,135 Patients With Type 1 or Type 2 Diabetes Mellitus

Journal of Clinical Hypertension ◽

10.1111/jch.12743 ◽

2015 ◽

Vol 18 (4) ◽

pp. 270-278 ◽

Cited By ~ 12

Author(s):

Julia M. Hermann ◽

Joachim Rosenbauer ◽

Axel Dost ◽

Claudia Steigleder-Schweiger ◽

Wieland Kiess ◽

...

Keyword(s):

Diabetes Mellitus ◽

Blood Pressure ◽

Type 2 Diabetes ◽

Type 2 Diabetes Mellitus ◽

Seasonal Variation

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Coevolution of Down-Valley Flow and the Nocturnal Boundary Layer in Complex Terrain

Journal of Applied Meteorology and Climatology ◽

10.1175/jam2412.1 ◽

2006 ◽

Vol 45 (10) ◽

pp. 1429-1449 ◽

Cited By ~ 22

Author(s):

J. O. Pinto ◽

D. B. Parsons ◽

W. O. J. Brown ◽

S. Cohn ◽

N. Chamberlain ◽

...

Keyword(s):

Boundary Layer ◽

Complex Terrain ◽

Salt Lake ◽

Similarity Theory ◽

Inversion Layer ◽

Great Salt Lake ◽

Nocturnal Boundary Layer ◽

Vertical Transport ◽

Low Level ◽

Transport And Mixing

Abstract An enhanced National Center for Atmospheric Research (NCAR) integrated sounding system (ISS) was deployed as part of the Vertical Transport and Mixing (VTMX) field experiment, which took place in October of 2000. The enhanced ISS was set up at the southern terminus of the Great Salt Lake Valley just north of a gap in the Traverse Range (TR), which separates the Great Salt Lake and Utah Lake basins. This location was chosen to sample the dynamic and thermodynamic properties of the flow as it passes over the TR separating the two basins. The enhanced ISS allowed for near-continuous sampling of the nocturnal boundary layer (NBL) and low-level winds associated with drainage flow through the gap in the TR. Diurnally varying winds were observed at the NCAR site on days characterized by weak synoptic forcing and limited cloud cover. A down-valley jet (DVJ) was observed on about 50% of the nights during VTMX, with the maximum winds usually occurring within 150 m of the surface. The DVJ was associated with abrupt warming at low levels as a result of downward mixing and vertical transport of warm air from the inversion layer above. Several processes were observed to contribute to vertical transport and mixing at the NCAR site. Pulses in the strength of the DVJ contributed to vertical transport by creating localized areas of low-level convergence. Gravity waves and Kelvin–Helmholtz waves, which facilitated vertical mixing near the surface and atop the DVJ, were observed with a sodar and an aerosol backscatter lidar that were deployed as part of the enhanced ISS. The nonlocal nature of the processes responsible for generating turbulence in strongly stratified surface layers in complex terrain confounds surface flux parameterizations typically used in mesoscale models that rely on Monin–Obukhov similarity theory. This finding has major implications for modeling NBL structure and drainage flows in regions of complex terrain.

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Intra-seasonal variation of surface air temperature in Nepal Himalayas

MAUSAM ◽

10.54302/mausam.v53i3.1645 ◽

2022 ◽

Vol 53 (3) ◽

pp. 281-288

Author(s):

KENICHI UENO ◽

ADARSHA P. POKHREL

Keyword(s):

Seasonal Variation ◽

Air Temperature ◽

Monsoon Season ◽

Surface Air Temperature ◽

Circulation Pattern ◽

Synoptic Scale ◽

Local Circulation ◽

Pressure System ◽

Surface Temperature Variation ◽

Unique Surface

Intra-seasonal variation of surface air temperature observed by the automatic weather station at Syangpoche in Khumbu region, Nepal Himalayas, is analyzed. In the monsoon season, temperature was nearly constant with large decrease in insolation due to monsoon clouds. On the other hand, large intra-seasonal variation existed in the winter with increase in temperature associated with passing synoptic scale high-pressure system which disturb local circulation pattern as well as decrease in temperature due to the nighttime strong radiative cooling under the condition of snow covers. Monsoon clouds and deep valley system caused unique surface temperature variation.

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