scholarly journals A multi-season investigation of glacier surface roughness lengths through in situ and remote observation

2018 ◽  
Author(s):  
Noel Fitzpatrick ◽  
Valentina Radic ◽  
Brian Menounos
Keyword(s):  
Eddy Covariance ◽  
Roughness Length ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Glacier Surface ◽  
Mean Values ◽  
Mountain Glaciers ◽  
Roughness Lengths ◽  
Order Of Magnitude ◽  
Remote Estimation

Abstract. The roughness length values for momentum, temperature, and water vapour are key inputs to the bulk aerodynamic method for estimating turbulent heat flux. Measurements of site-specific roughness length are rare for glacier surfaces, and substantial uncertainty remains in the values and ratios commonly assumed when parameterising turbulence. Over three melt seasons, eddy covariance observations were implemented to derive the momentum and scalar roughness lengths at several locations on two mid-latitude mountain glaciers. In addition, two techniques were developed in this study for the remote estimation of momentum roughness length, utilising LiDAR-derived digital elevation models with a 1 × 1 m resolution. Seasonal mean momentum roughness length values derived from eddy covariance observations at each location ranged from 0.7–4.5 mm for ice surfaces, and 0.5–2.4 mm for snow surfaces. From one season to the next, mean momentum roughness length values over ice remained relatively consistent at a given location (0–1 mm difference between seasonal mean values), while within a season, temporal variability in momentum roughness length over melting snow was found to be substantial (> an order of magnitude). The two remote techniques were able to differentiate between ice and snow cover, and return momentum roughness lengths that were within 1–2 mm (

scholarly journals A multi-season investigation of glacier surface roughness lengths through in situ and remote observation

2019 ◽  
Vol 13 (3) ◽  
pp. 1051-1071 ◽  
Author(s):  
Noel Fitzpatrick ◽  
Valentina Radić ◽  
Brian Menounos
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Wind Direction ◽  
Roughness Length ◽  
Turbulent Heat Flux ◽  
Turbulent Heat ◽  
Glacier Surface ◽  
Roughness Lengths ◽  
Order Of Magnitude

Abstract. The roughness length values for momentum, temperature, and water vapour are key inputs to the bulk aerodynamic method for estimating turbulent heat flux. Measurements of site-specific roughness length are rare for glacier surfaces, and substantial uncertainty remains in the values and ratios commonly assumed when parameterising turbulence. Over three melt seasons, eddy covariance observations were implemented to derive the momentum and scalar roughness lengths at several locations on two mid-latitude mountain glaciers. In addition, two techniques were developed in this study for the remote estimation of momentum roughness length, utilising lidar-derived digital elevation models with a 1×1 m resolution. Seasonal mean momentum roughness length values derived from eddy covariance observations at each location ranged from 0.7 to 4.5 mm for ice surfaces and 0.5 to 2.4 mm for snow surfaces. From one season to the next, mean momentum roughness length values over ice remained relatively consistent at a given location (0–1 mm difference between seasonal mean values), while within a season, temporal variability in momentum roughness length over melting snow was found to be substantial (> an order of magnitude). The two remote techniques were able to differentiate between ice and snow cover and return momentum roughness lengths that were within 1–2 mm (≪ an order of magnitude) of the in situ eddy covariance values. Changes in wind direction affected the magnitude of the momentum roughness length due to the anisotropic nature of features on a melting glacier surface. Persistence in downslope wind direction on the glacier surfaces, however, reduced the influence of this variability. Scalar roughness length values showed considerable variation (up to 2.5 orders of magnitude) between locations and seasons and no evidence of a constant ratio with momentum roughness length or each other. Of the tested estimation methods, the Andreas (1987) surface renewal model returned scalar roughness lengths closest to those derived from eddy covariance observations. Combining this scalar method with the remote techniques developed here for estimating momentum roughness length may facilitate the distributed parameterisation of turbulent heat flux over glacier surfaces without in situ measurements.

scholarly journals Energy-balance model validation on the top of Kilimanjaro, Tanzania, using eddy covariance data

2007 ◽  
Vol 46 ◽  
pp. 227-233 ◽  
Author(s):  
Nicolas J. Cullen ◽  
Thomas Mölg ◽  
Georg Kaser ◽  
Konrad Steffen ◽  
Douglas R. Hardy
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Longwave Radiation ◽  
Heat Fluxes ◽  
Balance Model ◽  
Turbulent Heat ◽  
Turbulent Heat Fluxes ◽  
Roughness Lengths ◽  
Order Of Magnitude ◽  
Important Input

AbstractEddy covariance data collected over a horizontal surface on the largest ice body on Kilimanjaro, Tanzania, over 26–29 July 2005 were used to assess the uncertainty of calculating sublimation with a surface energy balance (SEB) model. Data required for input to the SEB model were obtained from an existing automatic weather station. Surface temperatures that were solved iteratively by the SEB model were used to compute emitted longwave radiation, turbulent heat fluxes using the aerodynamic bulk method and the subsurface heat flux. Roughness lengths for momentum and temperature, which were found to be the most important input parameters controlling the magnitude of modelled (bulk method) turbulent heat fluxes, were obtained using eddy covariance data. The roughness length for momentum was estimated to be 1.7×10–3 m, while the length for temperature was one order of magnitude smaller. Modelled sensible and latent heat fluxes (bulk method) compared well to eddy covariance data, with root-mean-square differences between 3.1 and 4.8 Wm–2 for both turbulent heat fluxes. Modelled sublimation accounted for about 90% of observed ablation, confirming that mass loss by melting is much less important than sublimation on the horizontal surfaces of the remaining plateau glaciers on Kilimanjaro.

scholarly journals The use of bulk and profile methods for determining surface heat fluxes in the presence of glacier winds

2000 ◽  
Vol 46 (154) ◽  
pp. 445-452 ◽  
Author(s):  
Bruce Denby ◽  
W. Greuell
Keyword(s):  
Wind Speed ◽  
Turbulent Fluxes ◽  
Turbulent Heat Flux ◽  
Heat Fluxes ◽  
Katabatic Wind ◽  
Turbulent Heat ◽  
Glacier Surface ◽  
Surface Heat Fluxes ◽  
Wind Speed Maximum

AbstractA one-dimensional second-order closure model and in situ observations on a melting glacier surface are used to investigate the suitability of bulk and profile methods for determining turbulent fluxes in the presence of the katabatic wind-speed maximum associated with glacier winds. The results show that profile methods severely underestimate turbulent fluxes when a wind-speed maximum is present. The bulk method, on the other hand, only slightly overestimates the turbulent heat flux in the entire region below the wind-speed maximum and is thus much more appropriate for use on sloping glacier surfaces where katabatic winds dominate and wind-speed maxima are just a few meters above the surface.

scholarly journals Sea waves impact on turbulent heat fluxes in the Barents Sea according to numerical modeling

2020 ◽  
Author(s):  
Stanislav Myslenkov ◽  
Anna Shestakova ◽  
Dmitry Chechin
Keyword(s):  
Roughness Length ◽  
Barents Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Sea Waves ◽  
Cold Air ◽  
Mean Values ◽  
The Barents Sea ◽  
Turbulent Heat Fluxes ◽  
Cold Air Outbreaks

Abstract. This paper investigates the impact of sea waves on turbulent heat fluxes in the Barents Sea. The COARE algorithm, meteorological data from reanalysis and wave data from the WW3 wave model results were used. The turbulent heat fluxes were calculated using the modified Charnock parameterization for the roughness length and several parameterizations, which explicitly account for the sea waves parameters. A catalog of storm wave events and a catalog of extreme cold-air outbreaks over the Barents Sea were created and used to calculate heat fluxes during extreme events. The important role of cold-air outbreaks in the energy exchange of the Barents Sea and the atmosphere is demonstrated. A high correlation was found between the number of cold-air outbreaks days and turbulent fluxes of sensible and latent heat, as well as with the net flux of long-wave radiation averaged over the ice-free surface of the Barents Sea during a cold season. The differences in the long-term mean values of heat fluxes calculated using different parameterizations for the roughness length are small and are on average 1–3 % of the flux magnitude. Parameterizations of Taylor and Yelland and Oost et al. on average lead to an increase of the magnitude of the fluxes, and the parameterization of Drennan et al. leads to a decrease of the magnitude of the fluxes over the entire sea compared to the Charnock parameterization. The magnitude of heat fluxes and their differences during the storm wave events exceed the mean values by a factor of 2. However, the effect of explicit accounting for the wave parameters is, on average, small and multidirectional, depending on the used parameterization for the roughness length. In the climatic aspect, it can be argued that the explicit accounting for sea waves in the calculations of heat fluxes can be neglected. However, during the simultaneously observed storm waves and cold-air outbreaks, the sensitivity of the calculated values of fluxes to the used parameterizations increase along with the turbulent heat transfer increase. In some extreme cases, during storms and cold-air outbreaks, the difference reaches 700 W m−2.

scholarly journals Aerodynamic roughness length of crevassed tidewater glaciers from UAV mapping

2021 ◽  
Author(s):  
Armin Dachauer ◽  
Richard Hann ◽  
Andrew J. Hodson
Keyword(s):  
Wind Direction ◽  
Roughness Length ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Aerodynamic Roughness Length ◽  
Tidewater Glaciers ◽  
Ice Melt ◽  
Order Of Magnitude ◽  
Aerodynamic Roughness

Abstract. The aerodynamic roughness length (z0) is an important parameter in the bulk approach for calculating turbulent fluxes and their contribution to ice melt. However, for heavily crevassed tidewater glaciers z0 estimations are rare or only generalized. This study used unmanned aerial vehicles (UAVs) to map inaccessible tidewater glacier front areas. The high-resolution images were used in a structure-from-motion photogrammetry approach to build digital elevation models (DEMs). These DEMs were applied to five different models (split across transect and raster methods) to estimate z0 values of the mapped area. The results point out that the range of z0 values across a glacier is large, with up to three (locally even four) orders of magnitude. The division of the mapped area into sub-grids (50 m x 50 m), each producing one z0 value, best accounts for the high spatial variability of z0 across the glacier. The z0 estimations from the transect method are in general higher (up to one order of magnitude) than the raster method estimations. Furthermore, wind direction (values parallel to the ice flow direction are larger than perpendicular) and the chosen sub-grid size turned out to have a large impact on the z0 values, again presenting a range of up to one order of magnitude each. On average, z0 values between 0.08 m and 0.88 m for a down-glacier wind direction were found. The UAV approach proved to be an ideal tool to provide distributed z0 estimations of crevassed glaciers, which can be incorporated by models to improve the prediction of turbulent heat fluxes and ice melt rates.

scholarly journals Assessment of radiative heating errors in Tropical Atmosphere Ocean array marine air temperature measurements

2022 ◽  
Vol 17 (1) ◽  
pp. 014040
Author(s):  
Francesco De Rovere ◽  
Davide Zanchettin ◽  
Michael J McPhaden ◽  
Angelo Rubino
Keyword(s):  
Air Temperature ◽  
Turbulent Heat Flux ◽  
Radiative Heating ◽  
Turbulent Heat ◽  
Tropical Atmosphere ◽  
Night Time ◽  
Mean Values ◽  
Impact Surface ◽  
Marine Air ◽  
Lower Limits

Abstract We assess the radiative heating error affecting marine air temperature (MAT) measurements in the Tropical Atmosphere Ocean array. The error in historical observations is found to be ubiquitous across the array, spatially variable and approximately stationary in time. The error induces spurious warming during daytime hours, but does not affect night-time temperatures. The range encompassing the real, unknown daily- and monthly-mean values is determined using daytime and night-time mean temperatures as upper and lower limits. The uncertainty in MAT is less than or equal to 0.5 °C and 0.2 °C for 95% of daily and monthly estimates, respectively. Uncertainties impact surface turbulent heat flux estimates, with potentially significant influences on the quantification of coupled ocean-atmosphere processes.

Turbulent heat fluxes by profile and inertial dissipation methods: analysis of the atmospheric surface layer from shipboard measurements during the SOFIA/ASTEX and SEMAPHORE experiments

1995 ◽  
Vol 13 (10) ◽  
pp. 1065-1074 ◽  
Author(s):  
H. Dupuis ◽  
A. Weill ◽  
K. Katsaros ◽  
P. K. Taylor
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Heat Fluxes ◽  
Specific Humidity ◽  
Radiosonde Data ◽  
Reliable Estimate ◽  
Turbulent Heat ◽  
Profile Method ◽  
Roughness Lengths ◽  
Inertial Dissipation Method

Abstract. Heat flux estimates obtained using the inertial dissipation method, and the profile method applied to radiosonde soundings, are assessed with emphasis on the parameterization of the roughness lengths for temperature and specific humidity. Results from the inertial dissipation method show a decrease of the temperature and humidity roughness lengths for increasing neutral wind speed, in agreement with previous studies. The sensible heat flux estimates were obtained using the temperature estimated from the speed of sound determined by a sonic anemometer. This method seems very attractive for estimating heat fluxes over the ocean. However allowance must be made in the inertial dissipation method for non-neutral stratification. The SOFIA/ASTEX and SEMAPHORE results show that, in unstable stratification, a term due to the transport terms in the turbulent kinetic energy budget, has to be included in order to determine the friction velocity with better accuracy. Using the profile method with radiosonde data, the roughness length values showed large scatter. A reliable estimate of the temperature roughness length could not be obtained. The humidity roughness length values were compatible with those found using the inertial dissipation method.

scholarly journals Aerodynamic roughness length of crevassed tidewater glaciers from UAV mapping

2021 ◽  
Vol 15 (12) ◽  
pp. 5513-5528
Author(s):  
Armin Dachauer ◽  
Richard Hann ◽  
Andrew J. Hodson
Keyword(s):  
Wind Direction ◽  
Roughness Length ◽  
Flow Direction ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Aerodynamic Roughness Length ◽  
Tidewater Glaciers ◽  
Ice Melt ◽  
Order Of Magnitude ◽  
Aerodynamic Roughness

Abstract. The aerodynamic roughness length (z0) is an important parameter in the bulk approach for calculating turbulent fluxes and their contribution to ice melt. However, z0 estimates for heavily crevassed tidewater glaciers are rare or only generalised. This study used uncrewed aerial vehicles (UAVs) to map inaccessible tidewater glacier front areas. The high-resolution images were utilised in a structure-from-motion photogrammetry approach to build digital elevation models (DEMs). These DEMs were applied to five models (split across transect and raster methods) to estimate z0 values of the mapped area. The results point out that the range of z0 values across a crevassed glacier is large, by up to 3 orders of magnitude. The division of the mapped area into sub-grids (50 m × 50 m), each producing one z0 value, accounts for the high spatial variability in z0 across the glacier. The z0 estimates from the transect method are in general greater (up to 1 order of magnitude) than the raster method estimates. Furthermore, wind direction (values parallel to the ice flow direction are greater than perpendicular values) and the chosen sub-grid size turned out to have a large impact on the z0 values, again presenting a range of up to 1 order of magnitude each. On average, z0 values between 0.08 and 0.88 m for a down-glacier wind direction were found. The UAV approach proved to be an ideal tool to provide distributed z0 estimates of crevassed glaciers, which can be incorporated by models to improve the prediction of turbulent heat fluxes and ice melt rates.

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