scholarly journals Effects of Spatial and Temporal Variations in PBL Depth on a GCM

2007 ◽  
Vol 20 (18) ◽  
pp. 4717-4732 ◽  
Author(s):  
Sun-Hee Shin ◽  
Kyung-Ja Ha
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
East Asian Monsoon ◽  
East Asian ◽  
Sensible Heat Flux ◽  
Lower Troposphere ◽  
Lower Atmosphere ◽  
Convective Boundary ◽  
Stable Conditions ◽  
The Impact

Abstract The effect of variations in planetary boundary layer (PBL) height on a GCM was investigated using the Yonsei University (YONU) AGCM. This GCM assumes a convective boundary layer constrained to the two lowest model levels. As a consequence of this fixed PBL height, the model tends to produce excessive mixing. In this study the authors focuse on the impact of spatially and temporally varying PBL height. In addition to stability-dependent eddy diffusivity, the model adopts both bulk mixing due to the surface heat flux and z-less mixing under stable conditions. The variable-depth PBL strongly suppressed excessive mixing so that the model bias was reduced over stable regions such as the Antarctic continent. On the other hand, vertical mixing over continents in the summer hemisphere was stronger than for the fixed-PBL version, resulting in greater rising motion and warming effects in the lower atmosphere. The variable-PBL height reduces excess precipitation over the western Pacific and East Asian monsoon region. Based on the improved PBL parameterization, widespread decreases in surface sensible heat flux and rising motion in the lower troposphere occurred simultaneously over the East Asian continent. This implies that the precipitation simulation is very sensitive to PBL processes.

scholarly journals Observation of sensible and latent heat flux profiles with lidar

2020 ◽  
Vol 13 (6) ◽  
pp. 3221-3233 ◽  
Author(s):  
Andreas Behrendt ◽  
Volker Wulfmeyer ◽  
Christoph Senff ◽  
Shravan Kumar Muppa ◽  
Florian Späth ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensible Heat Flux ◽  
Ground Level ◽  
Sensible Heat ◽  
Flux Divergence ◽  
Convective Boundary ◽  
The Mean

Abstract. We present the first measurement of the sensible heat flux (H) profile in the convective boundary layer (CBL) derived from the covariance of collocated vertical-pointing temperature rotational Raman lidar and Doppler wind lidar measurements. The uncertainties of the H measurements due to instrumental noise and limited sampling are also derived and discussed. Simultaneous measurements of the latent heat flux profile (L) and other turbulent variables were obtained with the combination of water-vapor differential absorption lidar (WVDIAL) and Doppler lidar. The case study uses a measurement example from the HOPE (HD(CP)2 Observational Prototype Experiment) campaign, which took place in western Germany in 2013 and presents a cloud-free well-developed quasi-stationary CBL. The mean boundary layer height zi was at 1230 m above ground level. The results show – as expected – positive values of H in the middle of the CBL. A maximum of (182±32) W m−2, with the second number for the noise uncertainty, is found at 0.5 zi. At about 0.7 zi, H changes sign to negative values above. The entrainment flux was (-62±27) W m−2. The mean sensible heat flux divergence in the observed part of the CBL above 0.3 zi was −0.28 W m−3, which corresponds to a warming of 0.83 K h−1. The L profile shows a slight positive mean flux divergence of 0.12 W m−3 and an entrainment flux of (214±36) W m−2. The combination of H and L profiles in combination with variance and other turbulent parameters is very valuable for the evaluation of large-eddy simulation (LES) results and the further improvement and validation of turbulence parameterization schemes.

scholarly journals Airborne observation of mixing across the entrainment zone during PARADE 2011

2015 ◽  
Vol 15 (20) ◽  
pp. 29171-29212 ◽  
Author(s):  
F. Berkes ◽  
P. Hoor ◽  
H. Bozem ◽  
D. Kunkel ◽  
M. Sprenger ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Dynamic Properties ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
Correlation Method ◽  
Late Summer ◽  
Lower Atmosphere ◽  
Boundary Layer Height ◽  
Entrainment Zone ◽  
The Impact

Abstract. This study presents the analysis of the structure and air mass characteristics of the lower atmosphere during the field campaign PARADE (PArticles and RAdicals: Diel observations of the impact of urban and biogenic Emissions) on Mount Kleiner Feldberg in southwestern Germany during late summer 2011. We analysed measurements of meteorological variables (temperature, moisture, pressure, wind speed and direction) from radio soundings and of chemical tracers (carbon dioxide, ozone) from aircraft measurements. We focus on the thermodynamic and dynamic properties, that control the chemical distribution of atmospheric constituents in the boundary layer. We show that the evolution of tracer profiles of CO2 and O3 indicate mixing across the inversion layer (or entrainment zone). This finding is supported by the analysis of tracer–tracer correlations which are indicative for mixing and the relation of tracer profiles in relation to the evolution of the boundary layer height deduced from radio soundings. The study shows the relevance of entrainment processes for the lower troposphere in general and specifically that the tracer–tracer correlation method can be used to identify mixing and irreversible exchange processes across the inversion layer.

scholarly journals Using Commercial Aircraft Meteorological Data to Assess the Heat Budget of the Convective Boundary Layer Over the Santiago Valley in Central Chile

2022 ◽  
Author(s):  
Ricardo C. Muñoz ◽  
C. David Whiteman ◽  
René D. Garreaud ◽  
José A. Rutllant ◽  
Jacqueline Hidalgo
Keyword(s):  
Boundary Layer ◽  
Convective Boundary Layer ◽  
Heat Budget ◽  
Meteorological Data ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Lower Troposphere ◽  
Commercial Aircraft ◽  
Convective Boundary ◽  
Central Chile

AbstractThe World Meteorological Organization Aircraft Meteorological Data Relay (AMDAR) programme refers to meteorological data gathered by commercial aircraft and made available to weather services. It has become a major source of upper-air observations whose assimilation into global models has greatly improved their performance. Near busy airports, AMDAR data generate semi-continuous vertical profiles of temperature and winds, which have been utilized to produce climatologies of atmospheric-boundary-layer (ABL) heights and general characterizations of specific cases. We analyze 2017–2019 AMDAR data for Santiago airport, located in the centre of a $$40\times 100$$ 40 × 100  km$$^2$$ 2 subtropical semi-arid valley in central Chile, at the foothills of the Andes. Profiles derived from AMDAR data are characterized and validated against occasional radiosondes launched in the valley and compared with routine operational radiosondes and with reanalysis data. The cold-season climatology of AMDAR temperatures reveals a deep nocturnal inversion reaching up to 700 m above ground level (a.g.l.) and daytime warming extending up to 1000 m a.g.l. Convective-boundary-layer (CBL) heights are estimated based on AMDAR profiles and the daytime heat budget of the CBL is assessed. The CBL warming variability is well explained by the surface sensible heat flux estimated with sonic anemometer measurements at one site, provided advection of the cool coastal ABL existing to the west is included. However, the CBL warming accounts for just half of the mean daytime warming of the lower troposphere, suggesting that rather intense climatological diurnal subsidence affects the dynamics of the daytime valley ABL. Possible sources of this subsidence are discussed.

scholarly journals On Boundary Layer Separation in the Lee of Mesoscale Topography

2007 ◽  
Vol 64 (2) ◽  
pp. 401-420 ◽  
Author(s):  
Qingfang Jiang ◽  
James D. Doyle ◽  
Shouping Wang ◽  
Ronald B. Smith
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Surface Wind ◽  
Sensible Heat Flux ◽  
Lower Troposphere ◽  
Boundary Layer Separation ◽  
Surface Wind Speed ◽  
Trapped Waves ◽  
Layer Separation

Abstract The onset of boundary layer separation (BLS) forced by gravity waves in the lee of mesoscale topography is investigated based on a series of numerical simulations and analytical formulations. It is demonstrated that BLS forced by trapped waves is governed by a normalized ratio of the vertical velocity maximum to the surface wind speed; other factors such as the mountain height, mountain slope, or the leeside speedup factor are less relevant. The onset of BLS is sensitive to the surface sensible heat flux—a positive heat flux tends to increase the surface wind speed through enhancing the vertical momentum mixing and accordingly inhibits the occurrence of BLS, and a negative heat flux does the opposite. The wave forcing required to cause BLS decreases with an increase of the aerodynamical roughness zo; a larger zo generates larger surface stress and weaker surface winds and therefore promotes BLS. In addition, BLS shows some sensitivity to the terrain geometry, which modulates the wave characteristics. For a wider ridge, a higher mountain is required to generate trapped waves with a wave amplitude comparable to that generated by a lower but narrower ridge. The stronger hydrostatic waves associated with the wider and higher ridge play only a minor role in the onset of BLS. It has been demonstrated that although hydrostatic waves generally do not directly induce BLS, undular bores may form associated with wave breaking in the lower troposphere, which in turn induce BLS. In addition, BLS could occur underneath undular jump heads or associate with trapped waves downstream of a jump head in the presence of a low-level inversion.

scholarly journals The Effects of Mesoscale Surface Heterogeneity on the Fair-Weather Convective Atmospheric Boundary Layer

2008 ◽  
Vol 65 (10) ◽  
pp. 3197-3213 ◽  
Author(s):  
Song-Lak Kang ◽  
Kenneth J. Davis
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Atmospheric Boundary Layer ◽  
Sensible Heat Flux ◽  
Surface Heterogeneity ◽  
High Amplitude ◽  
Steady Flows ◽  
Heterogeneous Surfaces ◽  
Lower Amplitude ◽  
The Impact

Large-eddy simulation (LES) is used to examine the impact of heterogeneity in the surface energy balance on the mesoscale and microscale structure of the convective atmospheric boundary layer (ABL). A long (16 or 32 km) and narrow (5 km) domain of the convective ABL is forced with an imposed surface heat flux consisting of a constant background flux of 0.20 K m s−1 (250 W m−2) added to a sinusoidal perturbation of 16 or 32 km and whose amplitude varies from 0.02 to 0.20 K m s−1 (25–250 W m−2). The output is analyzed using a spatial filter, spectral analyses, and a wave-cutoff filter to show how the mesoscale and microscale components of the ABL respond to surface heterogeneity. The ABL response is divided by amplitude of heterogeneity into oscillatory and nonoscillatory mesoscale flows, with amplitudes of 0.08 K m s−1 (100 W m−2) and greater being oscillatory. Although mean ABL structure is disturbed relative to the homogeneous case for all heterogeneous cases, the microscale structure of the ABL in the quasi-steady flows retains characteristics of mixed-layer similarity. The vertical sensible heat flux is dominated in all cases by the microscale flux, with an interscale term becoming significant for high-amplitude cases and the mesoscale flux remaining small in all cases. Prior observations of ABLs over heterogeneous surfaces are consistent with the lower-amplitude cases. These results contradict past studies that suggest that heterogeneous surfaces lead to large mesoscale fluxes. The interscale flux and oscillatory microscale structures raise questions about the ability of mesoscale models to properly simulate the ABL in high-amplitude heterogeneity.

scholarly journals Observation of sensible and latent heat flux profiles with lidar

2019 ◽  
Author(s):  
Andreas Behrendt ◽  
Volker Wulfmeyer ◽  
Christoph Senff ◽  
Shravan Kumar Muppa ◽  
Florian Späth ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Sensible Heat Flux ◽  
Ground Level ◽  
Sensible Heat ◽  
Flux Divergence ◽  
Convective Boundary ◽  
The Mean

Abstract. We present the first measurement of the sensible heat flux (H) profile in the convective boundary layer (CBL) derived from the covariance of collocated vertical-pointing temperature rotational Raman lidar and Doppler wind lidar measurements. The uncertainties of the H measurements due to instrumental noise and limited sampling are also derived and discussed. Simultaneous measurements of the latent heat flux profile (L) and other turbulent variables were obtained with the combination of water-vapor DIAL and Doppler lidar. The measurement example is from the HOPE campaign, which took place in western Germany in 2013 and presents a cloud-free well-developed quasi-stationary CBL. The mean boundary layer height z_i was at 1230 m above ground level. The results show – as expected – positive values of H in the middle of the CBL. A maximum of (182 ± 32) W/m2, with the second number for the noise uncertainty, is found at 0.5 z_i. At about 0.7 z_i, H changes sign to negative values above. The entrainment flux was (−62 ± 27) W/m2. The mean sensible heat flux divergence in the observed part of the CBL above 0.3 z_i was −0.28 W/m3, which corresponds to a warming of 0.83 K/h. The L profile shows a slight positive mean flux divergence of 0.12 W/m3 and an entrainment flux of (214 ± 36) W/m2. The combination of H and L profiles in combination with variance and other turbulent parameters is very valuable for the evaluation of large-eddy simulation (LES) results and the further improvement and validation of turbulence parameterization schemes.

scholarly journals Surface Turbulent Fluxes during Persistent Cold-Air Pool Events in the Salt Lake Valley, Utah. Part II: Simulations

2020 ◽  
Vol 59 (6) ◽  
pp. 1029-1050
Author(s):  
Xia Sun ◽  
Heather A. Holmes ◽  
Hui Xiao
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Sensible Heat Flux ◽  
Wrf Model ◽  
Turbulent Fluxes ◽  
Radiative Energy ◽  
Net Radiation ◽  
Energy Fluxes ◽  
Cold Air ◽  
Stable Conditions

AbstractRealistically representing the land–atmosphere interactions during persistent cold-air pools (PCAPs) is critical in simulating the strength of PCAPs, where uncertainties in simulating the PCAP strength will impact the ability to model the poor air quality. To quantify the model performance for land–atmosphere exchange, measurements of surface turbulent and radiative energy fluxes during two PCAPs, one weak and one strong, in Utah were compared with simulations from the Weather Research and Forecasting (WRF) Model. The results show that the WRF Model simulated the surface energy fluxes well in the weak PCAP case and that the performance degraded in the strong PCAP case. The significantly overestimated surface sensible heat flux H and latent heat flux (LE) in the strong PCAP were related, in part, to the overestimated net radiation and soil moisture and unsuitable turbulence parameterizations. The simulation using the Mellor–Yamada–Nakanishi–Niino planetary boundary layer scheme produced the least bias in both net radiation and surface turbulent fluxes for the strong PCAP case, which is expected because of the local higher-order (2.5) turbulence closure scheme. The surface exchange coefficient (CH), a crucial variable used to calculate H, was overall overestimated by the WRF Model. The underestimation of the nondimensional vertical temperature gradient in the Monin–Obukhov stability function was responsible for the overestimated CH, where the stability functions deviate significantly from expected values from observations for the stable atmospheric boundary layer. Our study highlights the need to improve the flux–profile parameterizations under stable conditions over complex terrain by including impacts due to mountainous terrain, such as surface radiative flux divergence and the diurnal mountain wind system.

scholarly journals Surface sensible and latent heat fluxes over the Tibetan Plateau from ground measurements, reanalysis, and satellite data

2013 ◽  
Vol 13 (11) ◽  
pp. 30349-30405 ◽  
Author(s):  
Q. Shi ◽  
S. Liang
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Asian Monsoon ◽  
East Asian Monsoon ◽  
East Asian ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
The Tibetan Plateau ◽  
Sensible Heat

Abstract. Estimations from meteorological stations indicate that the surface sensible heat flux over the Tibetan Plateau (TP) has been decreasing continuously since 1980s, and modeling studies suggest that such changes are likely linked to the weakening of the East Asian Monsoon through exciting Rossby wave trains. However, the spatial and temporal variations in the surface sensible and latent heat fluxes over the entire TP remain unknown. This study aims to characterize the monthly surface sensible and latent heat fluxes at 0.5° over the TP from 1984 to 2007 by synthesizing multiple data sources including ground measurements, reanalysis products, and remote sensing products. The root mean square errors (RMSEs) from cross-validation are 11.1 W m−2 and 17.8 W m−2 for the monthly fused sensible and latent heat fluxes, respectively. The fused sensible and latent heat flux anomalies are consistent with those estimated from meteorological stations, and the uncertainties of the fused data are also discussed. The annual sensible heat flux over the TP is shown to be decreasing by −1.1 W m−2 deacade−1 with dominant decreasing in summer (−3.9 W m−2 deacade−1), while the latent heat flux shows a decrease (increase) in spring (autumn) but at a magnitude less than that of the sensible heat flux. Such decreased tendency of the fused sensible and latent heat flux over the TP is consistent to the weakened East Asian Monsoon as well as the solar dimming. The associations among sensible and latent heat fluxes and the related surface anomalies such as mean temperature, temperature range, snow cover, and Normalized Difference Vegetation Index (NDVI) in addition to atmospheric anomalies such as cloud cover and water vapor show seasonal dependence, suggest that the land–biosphere–atmosphere interactions over the TP could display nonuniform feedbacks to the climate changes. It would be interesting to disentangle the drivers and responses of the surface sensible and latent heat flux anomalies over the TP in future research from evidences of modeling results.

The Impact of Horizontal Model Grid Resolution on the Boundary Layer Structure over an Idealized Valley

2014 ◽  
Vol 142 (9) ◽  
pp. 3446-3465 ◽  
Author(s):  
Johannes S. Wagner ◽  
Alexander Gohm ◽  
Mathias W. Rotach
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Layer Structure ◽  
Thermal Structure ◽  
Inversion Layer ◽  
Lower Boundary ◽  
Grid Resolution ◽  
Convective Boundary ◽  
Boundary Layer Structure ◽  
The Impact

The role of horizontal model grid resolution on the development of the daytime boundary layer over mountainous terrain is studied. A simple idealized valley topography with a cross-valley width of 20 km, a valley depth of 1.5 km, and a constant surface heat flux forcing is used to generate upslope flows in a warming valley boundary layer. The goal of this study is to investigate differences in the boundary layer structure of the valley when its topography is either fully resolved, smoothed, or not resolved by the numerical model. This is done by performing both large-eddy (LES) and kilometer-scale simulations with horizontal mesh sizes of 50, 1000, 2000, 4000, 5000, and 10 000 m. In LES mode a valley inversion layer develops, which separates two vertically stacked circulation cells in an upper and lower boundary layer. These structures weaken with decreasing horizontal model grid resolution and change to a convective boundary layer over an elevated plain when the valley is no longer resolved. Mean profiles of the LES run, which are obtained by horizontal averaging over the valley show a three-layer thermal structure and a secondary heat flux maximum at ridge height. Strong smoothing of the valley topography prevents the development of a valley inversion layer with stacked circulation cells and leads to higher valley temperatures due to smaller valley volumes. Additional LES and “1 km” runs over corresponding smoothed valleys reveal that differences occur mainly because of unresolved topography and not because of unresolved turbulence processes. Furthermore, the deactivation of horizontal diffusion improved simulations with 1- and 2-km horizontal resolution.

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