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Kirk A. Fuller - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of Nocturnal Boundary Layer temperature to tropospheric aerosol surface radiative forcing under clear sky conditions
Journal of Geophysical Research, 2011Co-Authors: Udaysankar S. Nair, Richard T. Mcnider, Falguni Patadia, Sundar A. Christopher, Kirk A. FullerAbstract:[1] Since the middle of the last century, global surface air temperature exhibits an increasing trend, with Nocturnal temperatures increasing at a much higher rate. Proposed causative mechanisms include the radiative impact of atmospheric aerosols on the Nocturnal Boundary Layer (NBL) where the temperature response is amplified due to shallow depth and its sensitivity to potential destabilization. A 1-D version of the Regional Atmospheric Modeling System is used to examine the sensitivity of the Nocturnal Boundary Layer temperature to the surface longwave radiative forcing (SLWRF) from urban aerosol loading and doubled atmospheric carbon dioxide concentrations. The analysis is conducted for typical midlatitude Nocturnal Boundary Layer case days from the CASES-99 field experiment and is further extended to urban sites in Pune and New Delhi, India. For the cases studied, locally, the Nocturnal SLWRF from urban atmospheric aerosols (2.7-47 W m -2 ) is comparable or exceeds that caused by doubled atmospheric carbon dioxide (3 W m -2 ), with the surface temperature response ranging from a compensation for daytime cooling to an increase in the Nocturnal minimum temperature. The sensitivity of the NBL to radiative forcing is approximately 4 times higher compared to the daytime Boundary Layer. Nighttime warming or cooling may occur depending on the nature of diurnal variations in aerosol optical depth. Soil moisture also modulates the magnitude of SLWRF, decreasing from 3 to 1 W m -2 when soil saturation increases from 37% to 70%. These results show the importance of aerosols on the radiative balance of the climate system.
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Sensitivity of Nocturnal Boundary Layer temperature to tropospheric aerosol surface radiative forcing under clear‐sky conditions
Journal of Geophysical Research, 2011Co-Authors: Udaysankar S. Nair, Richard T. Mcnider, Falguni Patadia, Sundar A. Christopher, Kirk A. FullerAbstract:[1] Since the middle of the last century, global surface air temperature exhibits an increasing trend, with Nocturnal temperatures increasing at a much higher rate. Proposed causative mechanisms include the radiative impact of atmospheric aerosols on the Nocturnal Boundary Layer (NBL) where the temperature response is amplified due to shallow depth and its sensitivity to potential destabilization. A 1-D version of the Regional Atmospheric Modeling System is used to examine the sensitivity of the Nocturnal Boundary Layer temperature to the surface longwave radiative forcing (SLWRF) from urban aerosol loading and doubled atmospheric carbon dioxide concentrations. The analysis is conducted for typical midlatitude Nocturnal Boundary Layer case days from the CASES-99 field experiment and is further extended to urban sites in Pune and New Delhi, India. For the cases studied, locally, the Nocturnal SLWRF from urban atmospheric aerosols (2.7-47 W m -2 ) is comparable or exceeds that caused by doubled atmospheric carbon dioxide (3 W m -2 ), with the surface temperature response ranging from a compensation for daytime cooling to an increase in the Nocturnal minimum temperature. The sensitivity of the NBL to radiative forcing is approximately 4 times higher compared to the daytime Boundary Layer. Nighttime warming or cooling may occur depending on the nature of diurnal variations in aerosol optical depth. Soil moisture also modulates the magnitude of SLWRF, decreasing from 3 to 1 W m -2 when soil saturation increases from 37% to 70%. These results show the importance of aerosols on the radiative balance of the climate system.
Peter Baas - One of the best experts on this subject based on the ideXlab platform.
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from near neutral to strongly stratified adequately modelling the clear sky Nocturnal Boundary Layer at cabauw
Boundary-Layer Meteorology, 2018Co-Authors: Peter Baas, B J H Van De Wiel, S J A Van Der Linden, F C BosveldAbstract:The performance of an atmospheric single-column model (SCM) is studied systematically for stably-stratified conditions. To this end, 11 years (2005–2015) of daily SCM simulations were compared to observations from the Cabauw observatory, The Netherlands. Each individual clear-sky night was classified in terms of the ambient geostrophic wind speed with a (Formula presented.) bin-width. Nights with overcast conditions were filtered out by selecting only those nights with an average net radiation of less than (Formula presented.). A similar procedure was applied to the observational dataset. A comparison of observed and modelled ensemble-averaged profiles of wind speed and potential temperature and time series of turbulent fluxes showed that the model represents the dynamics of the Nocturnal Boundary Layer (NBL) at Cabauw very well for a broad range of mechanical forcing conditions. No obvious difference in model performance was found between near-neutral and strongly-stratified conditions. Furthermore, observed NBL regime transitions are represented in a natural way. The reference model version performs much better than a model version that applies excessive vertical mixing as is done in several (global) operational models. Model sensitivity runs showed that for weak-wind conditions the inversion strength depends much more on details of the land-atmosphere coupling than on the turbulent mixing. The presented results indicate that in principle the physical parametrizations of large-scale atmospheric models are sufficiently equipped for modelling stably-stratified conditions for a wide range of forcing conditions.
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The Minimum Wind Speed for Sustainable Turbulence in the Nocturnal Boundary Layer
Journal of the Atmospheric Sciences, 2012Co-Authors: Van De Bjh Bas Wiel, Peter Baas, Arnold F. Moene, H.j.j. Jonker, Sukanta Basu, Jmm Judith Donda, Jielun Sun, A A M HoltslagAbstract:The collapse of turbulence in the Nocturnal Boundary Layer is studied by means of a simple bulk model that describes the basic physical interactions in the surface energy balance. It is shown that for a given mechanical forcing, the amount of turbulent heat that can be transported downward is limited to a certain maximum. In the case of weak winds and clear skies, this maximum can be significantly smaller than the net radiative loss minus soil heat transport. In the case when the surface has low heat capacity, this imbalance generates rapid surface cooling that further suppresses the turbulent heat transport, so that eventually turbulence largely ceases (positive feedback mechanism). The model predicts the minimum wind speed for sustainable turbulence for the so-called crossing level. At this level, some decameters above the surface, the wind is relatively stationary compared to lower and higher levels. The critical speed is predicted in the range of about 5–7 m s21, depending on radiative forcing and surface properties, and is in agreement with observations at Cabauw. The critical value appears not very sensitive to model details or to the exact values of the input parameters. Finally, results are interpreted in terms of external forcings, such as geostrophic wind. As it is generally larger than the speed at crossing height, a 5 m s21 geostrophic wind may be considered as the typical limit below which sustainable, continuous turbulence under clear-sky conditions is unlikely to exist. Below this threshold emergence of the very stable Nocturnal Boundary Layer is anticipated.
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composite hodographs and inertial oscillations in the Nocturnal Boundary Layer
Quarterly Journal of the Royal Meteorological Society, 2012Co-Authors: Peter Baas, B J H Van De Wiel, L Van Den Brink, A A M HoltslagAbstract:In this work the dynamic behaviour of the wind in the Nocturnal Boundary Layer is studied, with a particular focus on systematic behaviour of the near-surface wind. Recently, an extension of the well-known Blackadar model for frictionless inertial oscillations above the Nocturnal Boundary Layer was proposed by Van de Wiel et al., which accounts for frictional effects within the Nocturnal Boundary Layer. It appears that the Nocturnal wind velocity profile tends to perform an inertial oscillation around an equilibrium wind profile, rather than around the geostrophic wind vector (as in the Blackadar model). In the present study we propose the concept of ‘composite hodographs’ to evaluate the ideas and assumptions of the aforementioned analytical model. Composite hodographs are constructed based on a large observational dataset from the Cabauw observatory. For comparison and deeper analysis, this method is also applied to single-column model simulations that represent the same dataset. From this, it is shown that winds in the middle and upper part of the Nocturnal Boundary Layer closely follow the dynamics predicted by the model by Van de Wiel et al. In contrast, the near-surface wind shows more complex behaviour that can be described by two different stages: (1) a decelerating phase where the wind decreases rapidly in magnitude due to enlarged stress divergence in the transition period near sunset (an aspect not included in the analytical model), and (2) a regular type of inertial oscillation, but with relatively small amplitude as compared to the oscillations in the middle and upper parts of the Nocturnal Boundary Layer. Copyright © 2011 Royal Meteorological Society
Jennifer A. Salmond - One of the best experts on this subject based on the ideXlab platform.
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Wavelet analysis of intermittent turbulence in a very stable Nocturnal Boundary Layer: implications for the vertical mixing of ozone
Boundary-Layer Meteorology, 2005Co-Authors: Jennifer A. SalmondAbstract:Turbulence in the very stable Nocturnal Boundary Layer is weak, patchy and intermittent. Near the surface isolated bursts of turbulent activity, characterised by abrupt changes in vertical velocity variance, have been shown to play an important role in determining the vertical transport of pollutants. However, there is little consensus as to the most appropriate methods for identifying or analysing the characteristics of intermittent turbulence that are of direct relevance to air quality studies. This paper presents an original technique, based on wavelet analysis, to objectively isolate intermittent turbulent ‘bursts’ within vertical velocity time series. The technique permits the quantitative description of global intermittency and can be used to assess the duration and strength of turbulence within a time series. The technique is applied to a dataset from a summer field experiment in the Lower Fraser Valley, British Columbia, 1998. A very stable Nocturnal Boundary Layer was observed in this region of complex terrain during anticyclonic synoptic conditions. During the 11 nights studied turbulent activity was characterised (within each 30-min time series) by three to four individual bursts persisting for less than 10 min in total. The implications of these results for air quality studies are discussed within the context of the vertical mixing of ozone (stored within the residual Layer) to the surface. Results show that, despite the complexity of the processes determining Nocturnal surface ozone concentration, the strength and duration of turbulent bursts can play an important role in determining local surface concentrations.
Falguni Patadia - One of the best experts on this subject based on the ideXlab platform.
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sensitivity of Nocturnal Boundary Layer temperature to tropospheric aerosol surface radiative forcing under clear sky conditions
Journal of Geophysical Research, 2011Co-Authors: Udaysankar S. Nair, Richard T. Mcnider, Falguni Patadia, Sundar A. Christopher, Kirk A. FullerAbstract:[1] Since the middle of the last century, global surface air temperature exhibits an increasing trend, with Nocturnal temperatures increasing at a much higher rate. Proposed causative mechanisms include the radiative impact of atmospheric aerosols on the Nocturnal Boundary Layer (NBL) where the temperature response is amplified due to shallow depth and its sensitivity to potential destabilization. A 1-D version of the Regional Atmospheric Modeling System is used to examine the sensitivity of the Nocturnal Boundary Layer temperature to the surface longwave radiative forcing (SLWRF) from urban aerosol loading and doubled atmospheric carbon dioxide concentrations. The analysis is conducted for typical midlatitude Nocturnal Boundary Layer case days from the CASES-99 field experiment and is further extended to urban sites in Pune and New Delhi, India. For the cases studied, locally, the Nocturnal SLWRF from urban atmospheric aerosols (2.7-47 W m -2 ) is comparable or exceeds that caused by doubled atmospheric carbon dioxide (3 W m -2 ), with the surface temperature response ranging from a compensation for daytime cooling to an increase in the Nocturnal minimum temperature. The sensitivity of the NBL to radiative forcing is approximately 4 times higher compared to the daytime Boundary Layer. Nighttime warming or cooling may occur depending on the nature of diurnal variations in aerosol optical depth. Soil moisture also modulates the magnitude of SLWRF, decreasing from 3 to 1 W m -2 when soil saturation increases from 37% to 70%. These results show the importance of aerosols on the radiative balance of the climate system.
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Sensitivity of Nocturnal Boundary Layer temperature to tropospheric aerosol surface radiative forcing under clear‐sky conditions
Journal of Geophysical Research, 2011Co-Authors: Udaysankar S. Nair, Richard T. Mcnider, Falguni Patadia, Sundar A. Christopher, Kirk A. FullerAbstract:[1] Since the middle of the last century, global surface air temperature exhibits an increasing trend, with Nocturnal temperatures increasing at a much higher rate. Proposed causative mechanisms include the radiative impact of atmospheric aerosols on the Nocturnal Boundary Layer (NBL) where the temperature response is amplified due to shallow depth and its sensitivity to potential destabilization. A 1-D version of the Regional Atmospheric Modeling System is used to examine the sensitivity of the Nocturnal Boundary Layer temperature to the surface longwave radiative forcing (SLWRF) from urban aerosol loading and doubled atmospheric carbon dioxide concentrations. The analysis is conducted for typical midlatitude Nocturnal Boundary Layer case days from the CASES-99 field experiment and is further extended to urban sites in Pune and New Delhi, India. For the cases studied, locally, the Nocturnal SLWRF from urban atmospheric aerosols (2.7-47 W m -2 ) is comparable or exceeds that caused by doubled atmospheric carbon dioxide (3 W m -2 ), with the surface temperature response ranging from a compensation for daytime cooling to an increase in the Nocturnal minimum temperature. The sensitivity of the NBL to radiative forcing is approximately 4 times higher compared to the daytime Boundary Layer. Nighttime warming or cooling may occur depending on the nature of diurnal variations in aerosol optical depth. Soil moisture also modulates the magnitude of SLWRF, decreasing from 3 to 1 W m -2 when soil saturation increases from 37% to 70%. These results show the importance of aerosols on the radiative balance of the climate system.
B. Morley - One of the best experts on this subject based on the ideXlab platform.
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Coevolution of Down-Valley Flow and the Nocturnal Boundary Layer in Complex Terrain
Journal of Applied Meteorology and Climatology, 2006Co-Authors: James O. Pinto, David B. Parsons, William O. J. Brown, Stephen A. Cohn, N. Chamberlain, B. MorleyAbstract: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 wit...
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coevolution of down valley flow and the Nocturnal Boundary Layer in complex terrain
Journal of Applied Meteorology and Climatology, 2006Co-Authors: James O. Pinto, David B. Parsons, William O. J. Brown, Stephen A. Cohn, N. Chamberlain, B. MorleyAbstract: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.
