scholarly journals Modeling chemistry in and above snow at Summit, Greenland – Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer

2012 ◽  
Vol 12 (14) ◽  
pp. 6537-6554 ◽  
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
L. G. Huey ◽  
J. Liao ◽  
D. Tanner ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ozone Production ◽  
Ionization Mass ◽  
Peroxy Radicals ◽  
Layer Model ◽  
One Dimensional ◽  
Oxidation Capacity ◽  
Boundary Layer Model ◽  
Boundary Layer Ozone ◽  
The Impact

Abstract. The chemical composition of the boundary layer in snow covered regions is impacted by chemistry in the snowpack via uptake, processing, and emission of atmospheric trace gases. We use the coupled one-dimensional (1-D) snow chemistry and atmospheric boundary layer model MISTRA-SNOW to study the impact of snowpack chemistry on the oxidation capacity of the boundary layer. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. While it is acknowledged that the chemistry occurring at ice surfaces may consist of a true quasi-liquid layer and/or a concentrated brine layer, lack of additional knowledge requires that this chemistry be modeled as primarily aqueous chemistry occurring in a liquid-like layer (LLL) on snow grains. The model has been recently compared with BrO and NO data taken on 10 June–13 June 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). In the present study, we use the same focus period to investigate the influence of snowpack derived chemistry on OH and HOx + RO2 in the boundary layer. We compare model results with chemical ionization mass spectrometry (CIMS) measurements of the hydroxyl radical (OH) and of the hydroperoxyl radical (HO2) plus the sum of all organic peroxy radicals (RO2) taken at Summit during summer 2008. Using sensitivity runs we show that snowpack influenced nitrogen cycling and bromine chemistry both increase the oxidation capacity of the boundary layer and that together they increase the mid-day OH concentrations. Bromine chemistry increases the OH concentration by 10–18% (10% at noon LT), while snow sourced NOx increases OH concentrations by 20–50% (27% at noon LT). We show for the first time, using a coupled one-dimensional snowpack-boundary layer model, that air-snow interactions impact the oxidation capacity of the boundary layer and that it is not possible to match measured OH levels without snowpack NOx and halogen emissions. Model predicted HONO compared with mistchamber measurements suggests there may be an unknown HONO source at Summit. Other model predicted HOx precursors, H2O2 and HCHO, compare well with measurements taken in summer 2000, which had lower levels than other years. Over 3 days, snow sourced NOx contributes an additional 2 ppb to boundary layer ozone production, while snow sourced bromine has the opposite effect and contributes 1 ppb to boundary layer ozone loss.

scholarly journals Modeling chemistry in and above snow at Summit, Greenland − Part 2: Impact of snowpack chemistry on the oxidation capacity of the boundary layer

2012 ◽  
Vol 12 (2) ◽  
pp. 5551-5600 ◽  
Author(s):  
J. L. Thomas ◽  
J. E. Dibb ◽  
L. G. Huey ◽  
J. Liao ◽  
D. Tanner ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ozone Production ◽  
Ionization Mass ◽  
Peroxy Radicals ◽  
Layer Model ◽  
One Dimensional ◽  
Oxidation Capacity ◽  
Boundary Layer Model ◽  
Boundary Layer Ozone ◽  
The Impact

Abstract. The chemical composition of the boundary layer in snow covered regions is impacted by chemistry in the snowpack via uptake, processing, and emission of atmospheric trace gases. We use the coupled one-dimensional (1-D) snow chemistry and atmospheric boundary layer model MISTRA-SNOW to study the impact of snowpack chemistry on the oxidation capacity of the boundary layer. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. Chemistry on snow grains is simulated assuming a liquid-like layer (LLL), treated as an aqueous layer on the snow grain surface. The model has been recently compared with BrO and NO data taken on 10 June–13 June 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). In the present study, we use the same focus period to investigate the influence of snowpack derived chemistry on OH and HOx + RO2 in the boundary layer. We compare model results with chemical ionization mass spectrometry (CIMS) measurements of the hydroxyl radical (OH) and of the hydroperoxyl radical (HO2) plus the sum of all organic peroxy radicals (RO2) taken at Summit during summer 2008. Using sensitivity runs we show that snowpack influenced nitrogen cycling and bromine chemistry both increase the oxidation capacity of the boundary layer and that together they increase the mid-day OH concentrations by approximately a factor of 2. We show for the first time, using an unconstrained coupled one-dimensional snowpack-boundary layer model, that air-snow interactions impact the oxidation capacity of the boundary layer and that it is not possible to match measured OH levels without snowpack NOx and halogen emissions. Model predicted HONO compared with mistchamber measurements suggests there may be an unknown HONO source at Summit. Other model predicted HOx precursors, H2O2 and HCHO, compare well with measurements taken in summer 2000. Over 3 days, snow sourced NOx contributes an additional 2 ppb to boundary layer ozone production, while snow sourced bromine has the opposite effect and contributes 1 ppb to boundary layer ozone loss.

scholarly journals Parameterization of fluxes over heterogeneous snow cover for GCMs

1997 ◽  
Vol 25 ◽  
pp. 38-41 ◽  
Author(s):  
Richard Essery
Keyword(s):  
Boundary Layer ◽  
Snow Cover ◽  
Surface Fluxes ◽  
Layer Model ◽  
Boundary Layer Model ◽  
Single Column ◽  
Hadley Centre ◽  
Heat And Moisture ◽  
The Impact ◽  
Tile Model

Fluxes of heat and moisture over heterogeneous snow cover are studied using a boundary-layer model. The performance of a “tile” model, suitable for calculating gridbox-average surface fluxes in a GCM, is assessed in comparison with the boundary-layer model. The impact of using a tile representation for heterogeneous snow cover in a single-column version of the Hadley Centre GCM is discussed.

A Simple, Minimal Parameter Model for Predicting the Influence of Changing Land Cover on the Land–Atmosphere System+

2011 ◽  
Vol 15 (29) ◽  
pp. 1-32 ◽  
Author(s):  
Justin E. Bagley ◽  
Ankur R. Desai ◽  
Paul C. West ◽  
Jonathan A. Foley
Keyword(s):  
Boundary Layer ◽  
Land Cover ◽  
Boreal Forest ◽  
Land Cover Change ◽  
General Circulation ◽  
Surface Model ◽  
Layer Model ◽  
Boundary Layer Model ◽  
Atmosphere System ◽  
The Impact

Abstract The impacts of changing land cover on the soil–vegetation–atmosphere system are numerous. With the fraction of land used for farming and grazing expected to increase, extensive alterations to land cover such as replacing forests with cropland will continue. Therefore, quantifying the impact of global land-cover scenarios on the biosphere is critical. The Predicting Ecosystem Goods and Services Using Scenarios boundary layer (PegBL) model is a new global soil–vegetation–boundary layer model designed to quantify these impacts and act as a complementary tool to computationally expensive general circulation models and large-eddy simulations. PegBL provides high spatial resolution and inexpensive first-order estimates of land-cover change on the surface energy balance and atmospheric boundary layer with limited input requirements. The model uses a climatological-data-driven land surface model that contains only the physics necessary to accurately reproduce observed seasonal cycles of fluxes and state variables for natural and agricultural ecosystems. A bulk boundary layer model was coupled to the land model to estimate the impacts of changing land cover on the lower atmosphere. The model most realistically simulated surface–atmosphere dynamics and impacts of land-cover change at tropical rain forest and northern boreal forest sites. Further, simple indices to measure the potential impact of land-cover change on boundary layer climate were defined and shown to be dependent on boundary layer dynamics and geographically similar to results from previous studies, which highlighted the impacts of land-cover change on the atmosphere in the tropics and boreal forest.

The Impact of Gradient Wind Imbalance on Potential Intensity of Tropical Cyclones in an Unbalanced Slab Boundary Layer Model

2013 ◽  
Vol 70 (7) ◽  
pp. 1874-1890 ◽  
Author(s):  
Thomas Frisius ◽  
Daria Schönemann ◽  
Jonathan Vigh
Keyword(s):  
Boundary Layer ◽  
Model Parameters ◽  
Layer Model ◽  
Noticeable Effect ◽  
Surface Exchange ◽  
Model Driven ◽  
Gradient Wind ◽  
Boundary Layer Model ◽  
Horizontal Momentum ◽  
The Impact

Abstract The assumption of gradient wind balance is customarily made so as to derive the theoretical upper-bound intensity of a mature tropical cyclone. Emanuel's theory of hurricane potential intensity (E-PI) makes use of this assumption, whereas more recent studies by Bryan and Rotunno demonstrate that the effect of unbalanced flow can result in maximum winds that are well in excess of E-PI (superintensity). The existence of supergradient winds has been verified in a slab boundary layer model developed by Smith. Here, the authors apply the slab boundary layer model within the framework of classical E-PI theory to investigate the sensitivity of supergradient winds to the radius of maximum gradient wind (RMGW) and four nondimensional model parameters. The authors find that the Rossby number, the drag coefficient, and the modified Rankine decay parameter all have a considerable influence on the strength of the unbalanced flow. In contrast, the ratio of surface exchange coefficients has little noticeable effect on superintensity. The inclusion of horizontal momentum diffusion leads to a weaker superintensity, but the qualitative features of the model remain similar. To further elucidate these findings, the authors use the boundary layer model to examine the modified E-PI theory proposed by Emanuel and Rotunno. They assume a constant Richardson number for the outflow. The boundary layer model driven by the modified E-PI solution depends on just three model parameters rather than the four parameters used in the classical E-PI framework. Despite this apparent advantage, the results obtained in the framework of the modified E-PI are less realistic than those computed with the classical E-PI approach.

scholarly journals The Impact of Gradient Wind Imbalance on Tropical Cyclone Intensification within Ooyama’s Three-Layer Model

2016 ◽  
Vol 73 (9) ◽  
pp. 3659-3679 ◽  
Author(s):  
Thomas Frisius ◽  
Marguerite Lee
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Layer Model ◽  
Free Atmosphere ◽  
Gradient Wind ◽  
Maximum Gradient ◽  
Boundary Layer Model ◽  
Advection Term ◽  
Boundary Layer Dynamics ◽  
The Impact

Abstract This paper addresses the validity of the gradient wind balance approximation during the intensification phase of a tropical cyclone in Ooyama’s three-layer model. For this purpose, the sensitivity to various model modifications is examined, given by the inclusion of (i) unbalanced dynamics in the free atmosphere, (ii) unbalanced dynamics in the slab boundary layer, (iii) a height-parameterized boundary layer model, and (iv) a rigid lid. The most rapid intensification occurs when the model employs the unbalanced slab boundary layer, while the simulation with the balanced boundary layer reveals the slowest intensification. The simulation with the realistic height-parameterized boundary layer model exhibits an intensification rate that lies in between. Intensification is induced by a convective ring in all experiments, but a distinct contraction of the radius of maximum gradient wind only takes place with unbalanced boundary layer dynamics. In all experiments the rigid lid and the balance approximation for the free atmosphere have no crucial impact on intensification, and a linear stability analysis cannot explain the found sensitivity to intensification. Most likely the nonlinear momentum advection term plays an important role in the boundary layer. It is found on the basis of a diagnostic radial mass flux equation that the source term for latent heat provides the largest contribution to intensification and contraction. Furthermore, it turns out that the position of the convective ring inside or outside of the radius of maximum gradient wind (RMGW) is of vital importance for intensification and most likely explains the large impact of boundary layer imbalance.

scholarly journals Wave boundary layer model in SWAN revisited

Ocean Science ◽  
2019 ◽  
Vol 15 (2) ◽  
pp. 361-377 ◽  
Author(s):  
Jianting Du ◽  
Rodolfo Bolaños ◽  
Xiaoli Guo Larsén ◽  
Mark Kelly
Keyword(s):  
Boundary Layer ◽  
Source Function ◽  
Source Terms ◽  
Layer Model ◽  
Wave Boundary Layer ◽  
Boundary Layer Model ◽  
Wind Input ◽  
Wave Induced ◽  
The Impact ◽  
Wave Boundary

Abstract. In this study, we extend the work presented in Du et al. (2017) to make the wave boundary layer model (WBLM) applicable for real cases by improving the wind-input and white-capping dissipation source functions. Improvement via the new source terms includes three aspects. First, the WBLM wind-input source function is developed by considering the impact of wave-induced wind profile variation on the estimation of wave growth rate. Second, the white-capping dissipation source function is revised to be not explicitly dependent on wind speed for real wave simulations. Third, several improvements are made to the numerical WBLM algorithm, which increase the model's numerical stability and computational efficiency. The improved WBLM wind-input and white-capping dissipation source functions are calibrated through idealized fetch-limited and depth-limited studies, and validated in real wave simulations during two North Sea storms. The new WBLM source terms show better performance in the simulation of significant wave height and mean wave period than the original source terms.

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