scholarly journals Constraining turbulent heat flux parameterization over a temperate maritime glacier in New Zealand

2013 ◽  
Vol 54 (63) ◽  
pp. 41-51 ◽  
Author(s):  
J.P. Conway ◽  
N.J. Cullen
Keyword(s):  
New Zealand ◽  
Wind Speed ◽  
Mass Balance ◽  
Roughness Length ◽  
Heat Fluxes ◽  
Large Temperature ◽  
Glacier Mass Balance ◽  
Turbulent Heat ◽  
Neutral Atmosphere ◽  
Turbulent Heat Fluxes

AbstractThe turbulent sensible and latent heat fluxes are important components of the surface energy balance over glaciers in the Southern Alps of New Zealand, contributing over half the energy available for ablation during large melt events. To calculate these terms confidently in glacier mass-balance models it is essential to use appropriate parameterizations for surface roughness and atmospheric stability. Eddy covariance measurements at Brewster Glacier were obtained over an ice surface to help facilitate an assessment of the calculation of the turbulent heat fluxes. The roughness length for momentum was found to be 3.6 x 10−3m, while the roughness lengths for temperature and humidity were two orders of magnitude smaller, in agreement with surface renewal theory. A Monte Carlo approach was used to assess the uncertainty in turbulent heat fluxes calculated using the bulk aerodynamic method. It was found that input-data and roughness-length uncertainty could not explain underestimates of observed sensible heat fluxes during periods with low wind speed and large temperature gradients. During these periods a katabatic wind speed maximum alters the formulation of the turbulent exchange coefficient to that typically observed in a neutral atmosphere and this has implications for glacier mass-balance sensitivity.

scholarly journals Climate sensitivity of a high-precipitation glacier in New Zealand

2010 ◽  
Vol 56 (195) ◽  
pp. 114-128 ◽  
Author(s):  
Brian Anderson ◽  
Andrew Mackintosh ◽  
Dorothea Stumm ◽  
Laurel George ◽  
Tim Kerr ◽  
...  
Keyword(s):  
New Zealand ◽  
Mass Balance ◽  
Sea Level ◽  
Temperature Change ◽  
Heat Fluxes ◽  
Balance Model ◽  
Glacier Mass Balance ◽  
Turbulent Heat ◽  
Meltwater Runoff ◽  
Run Off

AbstractThe sensitivity of glaciers to climatic change is key information in assessing the response and sea-level implications of projected future warming. New Zealand glaciers are important globally as an example of how maritime glaciers will contribute to sea-level rise. A spatially distributed energy-balance model is applied to Brewster Glacier, New Zealand, in order to calculate glacier mass balance, run-off and sensitivity to climate change. The model successfully simulates four annual mass-balance cycles. Close to half (52%) of the energy available for melt on the glacier is supplied by turbulent heat fluxes, with radiation less important, except during the winter. Model sensitivity to temperature change is one of the largest reported on Earth, at −2.0 m w.e. a−1 °C−1. In contrast, a 50% change in precipitation is required to offset the mass-balance change resulting from a 1 °C temperature change. Meltwater runoff sensitivity is also very high, increasing 60% with a 1°C warming. The extreme sensitivity of mass balance to temperature change suggests that significant ice loss will occur with even moderate climate warming.

The Importance of Relative Wind Speed in Estimating Air–Sea Turbulent Heat Fluxes in Bulk Formulas: Examples in the Bohai Sea

2020 ◽  
Vol 37 (4) ◽  
pp. 589-603 ◽  
Author(s):  
Xiangzhou Song
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Wind Speed ◽  
Bohai Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Surface Currents ◽  
The Bohai Sea ◽  
Turbulent Heat Fluxes ◽  
Relative Wind

AbstractSea surface currents are commonly neglected when estimating the air–sea turbulent heat fluxes in bulk formulas. Using buoy observations in the Bohai Sea, this paper investigated the effects of near-coast multiscale currents on the quantification of turbulent heat fluxes, namely, latent heat flux (LH) and sensible heat flux (SH). The maximum current reached 1 m s−1 in magnitude, and a steady northeastward current of 0.16 m s−1 appeared in the southern Bohai Strait. The predominant tidal signal was the semidiurnal current, followed by diurnal components. The mean absolute surface wind was from the northeast with a speed of approximately 3 m s−1. The surface winds at a height of 11 m were dominated by the East Asian monsoon. As a result of upwind flow, the monthly mean differences in LH and SH between the estimates with and without surface currents ranged from 1 to 2 W m−2 in July (stable boundary layer) and November (unstable boundary layer). The hourly differences were on average 10 W m−2 and ranged from 0 to 24 W m−2 due to changes in the relative wind speed by high-frequency rotating surface tidal currents. The diurnal variability in LH/SH was demonstrated under stable and unstable boundary conditions. Observations provided an accurate benchmark for flux comparisons. The newly updated atmospheric reanalysis products MERRA-2 and ERA5 were superior to the 1° OAFlux data at this buoy location. However, future efforts in heat flux computation are still needed to, for example, consider surface currents and resolve diurnal variations.

scholarly journals Evaluation of different methods to model near-surface turbulent fluxes for a mountain glacier in the Cariboo Mountains, BC, Canada

2017 ◽  
Vol 11 (6) ◽  
pp. 2897-2918 ◽  
Author(s):  
Valentina Radić ◽  
Brian Menounos ◽  
Joseph Shea ◽  
Noel Fitzpatrick ◽  
Mekdes A. Tessema ◽  
...  
Keyword(s):  
Wind Speed ◽  
Friction Velocity ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Katabatic Flow ◽  
Glacier Surface ◽  
Mountain Glacier ◽  
Near Surface ◽  
Wind Speed Maximum ◽  
Turbulent Heat Fluxes

Abstract. As part of surface energy balance models used to simulate glacier melting, choosing parameterizations to adequately estimate turbulent heat fluxes is extremely challenging. This study aims to evaluate a set of four aerodynamic bulk methods (labeled as C methods), commonly used to estimate turbulent heat fluxes for a sloped glacier surface, and two less commonly used bulk methods developed from katabatic flow models. The C methods differ in their parameterizations of the bulk exchange coefficient that relates the fluxes to the near-surface measurements of mean wind speed, air temperature, and humidity. The methods' performance in simulating 30 min sensible- and latent-heat fluxes is evaluated against the measured fluxes from an open-path eddy-covariance (OPEC) method. The evaluation is performed at a point scale of a mountain glacier, using one-level meteorological and OPEC observations from multi-day periods in the 2010 and 2012 summer seasons. The analysis of the two independent seasons yielded the same key findings, which include the following: first, the bulk method, with or without the commonly used Monin–Obukhov (M–O) stability functions, overestimates the turbulent heat fluxes over the observational period, mainly due to a substantial overestimation of the friction velocity. This overestimation is most pronounced during the katabatic flow conditions, corroborating the previous findings that the M–O theory works poorly in the presence of a low wind speed maximum. Second, the method based on a katabatic flow model (labeled as the KInt method) outperforms any C method in simulating the friction velocity; however, the C methods outperform the KInt method in simulating the sensible-heat fluxes. Third, the best overall performance is given by a hybrid method, which combines the KInt approach with the C method; i.e., it parameterizes eddy viscosity differently than eddy diffusivity. An error analysis reveals that the uncertainties in the measured meteorological variables and the roughness lengths produce errors in the modeled fluxes that are smaller than the differences between the modeled and observed fluxes. This implies that further advances will require improvement to model theory rather than better measurements of input variables. Further data from different glaciers are needed to investigate any universality of these findings.

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 The impact of sea waves on turbulent heat fluxes in the Barents Sea according to numerical modeling

2021 ◽  
Vol 21 (7) ◽  
pp. 5575-5595
Author(s):  
Stanislav Myslenkov ◽  
Anna Shestakova ◽  
Dmitry Chechin
Keyword(s):  
Roughness Length ◽  
Barents Sea ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Sea Waves ◽  
Cold Air ◽  
The Barents Sea ◽  
Turbulent Heat Fluxes ◽  
Storm Wave ◽  
Cold Air Outbreaks

Abstract. This paper investigates the impact of sea waves on turbulent heat fluxes in the Barents Sea. The Coupled Ocean–Atmosphere Response Experiment (COARE) algorithm, meteorological data from reanalysis and wave data from the WAVEWATCH III wave model results were used. The turbulent heat fluxes were calculated using the modified Charnock parameterization for the roughness length and several parameterizations that explicitly account for the sea wave 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 between the Barents Sea and the atmosphere is demonstrated. A high correlation was found between the number of cold-air outbreak days and turbulent fluxes of sensible and latent heat, as well as with the net flux of longwave 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. The parameterizations of Taylor and Yelland (2001) and Oost et al. (2002) lead to an increase in the magnitude of the fluxes on average, and the parameterization of Drennan et al. (2003) leads to a decrease in the magnitude of the fluxes over the entire sea compared with 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 explicitly accounting for the wave parameters is, on average, small and multidirectional, depending on the parameterization used for the roughness length. With respect to the climatic aspect, it can be argued that explicitly accounting for sea waves in the calculations of heat fluxes can be neglected. However, during the simultaneously observed storm wave events and cold-air outbreaks, the sensitivity of the calculated values of fluxes to the parameterizations used increases along with the turbulent heat transfer increase. In some extreme cases, during storms and cold-air outbreaks, the difference exceeds 700 W m−2.

scholarly journals Modeling experiments on seasonal lake ice mass and energy balance in Qinghai-Tibet Plateau: A case study

2018 ◽  
Author(s):  
Wenfeng Huang ◽  
Bin Cheng ◽  
Jinrong Zhang ◽  
Zheng Zhang ◽  
Timo Vihma ◽  
...  
Keyword(s):  
Energy Balance ◽  
Mass Balance ◽  
Open Water ◽  
Heat Fluxes ◽  
Tibet Plateau ◽  
Turbulent Heat ◽  
Lake Ice ◽  
Ice Surface ◽  
Turbulent Heat Fluxes ◽  
Ice Mass Balance

Abstract. The lake-rich Qinghai-Tibet Plateau (QTP) has significant impacts on regional and global water cycles and monsoon systems through heat and water vapor exchange. The lake-atmosphere interactions have been quantified over open-water periods, yet little is known about the lake ice thermodynamics and heat and mass balance during ice-covered season due to a lack of field data. Modeling experiments on ice evolution and energy balance were performed in a shallow lake with a high-resolution snow and ice thermodynamic model. The bottom ice growth and decay dominated the seasonal evolution of the thickness of lake ice. Strong surface sublimation was a crucial pattern of ice loss, which was up to 40 % of the maximum ice thickness. Simulation results matched well with the observations with respect to ice mass balance components, net ice thickness, and ice temperature. Strong solar radiation, consistent freezing air temperature, and low air moisture were the major driving forces controlling the seasonal ice mass balance. Energy balance was estimated at the ice surface and bottom, and within the ice interior and under-ice water. Particularly, almost all heat fluxes showed significant diurnal variations including short- and long-wave radiation, turbulent heat fluxes, water heat fluxes at ice bottom, and absorbed and penetrated solar radiation. The calculated ice surface temperature indicated that the atmospheric boundary layer was consistently stable and neutral over the ice-covered period. The turbulent heat fluxes between the lake ice and air and the net heat gain by the lake were much lower than those during open-water period. Ice surface sublimation (vapor flux) was demonstrated to be a vital seasonal water balance component, accounting for 41 % of lake water loss during the ice seasons.

scholarly journals Evaluation of different methods to model near-surface turbulent fluxes for an alpine glacier in the Cariboo Mountains, BC, Canada

2017 ◽  
Author(s):  
Valentina Radić ◽  
Brian Menounos ◽  
Joseph Shea ◽  
Noel Fitzpatrick ◽  
Mekdes A. Tessema ◽  
...  
Keyword(s):  
Wind Speed ◽  
Momentum Flux ◽  
Flow Model ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Exchange Coefficient ◽  
Katabatic Flow ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Turbulent Heat Fluxes

Abstract. As part of surface energy balance models used to simulate glacier melting, choosing parameterizations to adequately estimate turbulent heat fluxes is extremely challenging. This study aims to evaluate a set of bulk methods commonly used to estimate turbulent heat fluxes for a sloped glacier surface. The methods differ in their parameterizations of the bulk exchange coefficient that relates the fluxes to the mean meteorological variables measured 2 m above a glacier surface. The performance of 23 bulk approaches in simulating 30-min sensible and latent heat fluxes is evaluated against the measured fluxes from an open path eddy-covariance (OPEC) method. The evaluation is performed at a point scale of an alpine glacier, using one-level meteorological and OPEC observations from a multi-day periods in the 2010 and 2012 summer season. The analysis of the two independent seasons yielded similar findings, listed as following. The bulk method, with or without the commonly used Monin–Obukhov (M–O) stability functions, overestimates the turbulent heat fluxes over the observational period, mainly due to an overestimation of the momentum flux. In the absence of OPEC-derived M–O stability parameter, no method can successfully predict this parameter, which results in poor performances of the M–O stability corrections and consequently the bulk method. The OPEC-derived 30-min momentum flux is linearly related to the measured wind speed, contrary to the proposed quadratic relation by the commonly used bulk methods. An approach based on a katabatic flow model, which assumes a linear relation between the shear stress and the wind speed, outperforms any other bulk approach that we tested in simulating the momentum flux. In agreement with the katabatic flow model, we show that in a more stable atmosphere the bulk exchange coefficient for momentum is smaller. The sensible heat flux can be more successfully modeled if the bulk exchange coefficients for momentum and heat are allowed to follow different parametrization schemes, rather than assuming equal schemes as is the case in the common bulk methods. Further data from different glaciers are needed to investigate any universality of these findings.

scholarly journals Mass Balance Sensitivity and Future Projections of Rabots Glaciär, Sweden

Climate ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 126
Author(s):  
Moon Taveirne ◽  
Laura Ekemar ◽  
Berta González Sánchez ◽  
Josefine Axelsson ◽  
Qiong Zhang
Keyword(s):  
Wind Speed ◽  
Mass Balance ◽  
Climate Scenario ◽  
Summer Temperature ◽  
Glacier Mass Balance ◽  
Northern Sweden ◽  
Dramatic Decrease ◽  
Future Projections ◽  
Modelling Studies ◽  
The Relationship

Glacier mass balance is heavily influenced by climate, with responses of individual glaciers to various climate parameters varying greatly. In northern Sweden, Rabots Glaciär’s mass balance has decreased since it started being monitored in 1982. To relate Rabots Glaciär’s mass balance to changes in climate, the sensitivity to a range of parameters is computed. Through linear regression of mass balance with temperature, precipitation, humidity, wind speed and incoming radiation the climate sensitivity is established and projections for future summer mass balance are made. Summer mass balance is primarily sensitive to temperature at −0.31 m w.e. per °C change, while winter mass balance is mainly sensitive to precipitation at 0.94 m w.e. per % change. An estimate using summer temperature sensitivity projects a dramatic decrease in summer mass balance to −3.89 m w.e. for the 2091–2100 period under climate scenario RCP8.5. With large increases in temperature anticipated for the next century, more complex modelling studies of the relationship between climate and glacier mass balance is key to understanding the future development of Rabots Glaciär.

Estimation of turbulent heat fluxes and exchange coefficients for heat at Dumont d'Urville, East Antarctica

1999 ◽  
Vol 11 (1) ◽  
pp. 93-99 ◽  
Author(s):  
S. Argentini ◽  
G. Mastrantonio ◽  
A. Viola
Keyword(s):  
Boundary Layer ◽  
Heat Fluxes ◽  
East Antarctica ◽  
Turbulent Heat ◽  
Convective Boundary ◽  
Doppler Sodar ◽  
Turbulent Heat Fluxes ◽  
Unstable Boundary Layer ◽  
Sodar Measurements ◽  
The Antarctic

Simultaneous acoustic Doppler sodar and tethersonde measurements were used to study some of the characteristics of the unstable boundary layer at Dumont d'Urville, Adélie Land, East Antarctica during the summer 1993–94. A description of the convective boundary layer and its behaviour in connection with the wind regime is given along with the frequency distribution of free convection episodes. The surface heat flux has been evaluated using the vertical velocity variance derived from sodar measurements. The turbulent exchange coefficients, estimated by coupling sodar and tethered balloon measurements, are in strong agreement with those present in literature for the Antarctic regions.

Searching for new physics: Using explainable AI to understand deep learned parameterizations of turbulent heat fluxes

2021 ◽  
Author(s):  
Andrew Bennett ◽  
Bart Nijssen
Keyword(s):  
Neural Network ◽  
Neural Networks ◽  
Deep Learning ◽  
Coupled System ◽  
Hydrologic Model ◽  
Heat Fluxes ◽  
Turbulent Heat ◽  
Phase Lag ◽  
Geophysical Research ◽  
Turbulent Heat Fluxes

<p>Machine learning (ML), and particularly deep learning (DL), for geophysical research has shown dramatic successes in recent years. However, these models are primarily geared towards better predictive capabilities, and are generally treated as black box models, limiting researchers’ ability to interpret and understand how these predictions are made. As these models are incorporated into larger models and pushed to be used in more areas it will be important to build methods that allow us to reason about how these models operate. This will have implications for scientific discovery that will ensure that these models are robust and reliable for their respective applications. Recent work in explainable artificial intelligence (XAI) has been used to interpret and explain the behavior of machine learned models.</p><p>Here, we apply new tools from the field of XAI to provide physical interpretations of a system that couples a deep-learning based parameterization for turbulent heat fluxes to a process based hydrologic model. To develop this coupling we have trained a neural network to predict turbulent heat fluxes using FluxNet data from a large number of hydroclimatically diverse sites. This neural network is coupled to the SUMMA hydrologic model, taking imodel derived states as additional inputs to improve predictions. We have shown that this coupled system provides highly accurate simulations of turbulent heat fluxes at 30 minute timesteps, accurately predicts the long-term observed water balance, and reproduces other signatures such as the phase lag with shortwave radiation. Because of these features, it seems this coupled system is learning physically accurate relationships between inputs and outputs. </p><p>We probe the relative importance of which input features are used to make predictions during wet and dry conditions to better understand what the neural network has learned. Further, we conduct controlled experiments to understand how the neural networks are able to learn to regionalize between different hydroclimates. By understanding how these neural networks make their predictions as well as how they learn to make predictions we can gain scientific insights and use them to further improve our models of the Earth system.</p>

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