Simple Parameterization of Aerodynamic Roughness Lengths and the Turbulent Heat Fluxes at the Top of Midlatitude August‐One Glacier, Qilian Mountains, China

Abstract

The fluxes of sensible heat (H) and latent heat (LE), which are generally the important parts of the energy and mass balances over glacier surfaces, are widely quantified by the bulk method. However, due to the difficulty of determining the aerodynamic roughness length z 0m in this method, H and LE values may still have large uncertainties with significant inaccuracy. To acquire reliable varying and intrinsic z 0m values, new simpler parameterizations for z 0m values at different ranges of the friction velocity u *b were fitted in this study. The method was implemented using the related meteorological data and glacial sublimation/condensation measured at the top of the August-one glacier (4817 m asl) in the Qilian Mountains from 1 July 2016 to 15 August 2017. The parameterization shows that z 0m increased sharply when u *b exceeded 0.43 m/s (the approximate threshold value) and that the effect of snowdrift was slight for the hourly z 0m values in the range 0.15 ≤ u *b ≤ 0.43 m/s, which could thus be used to calculate the daily z 0m . During the wet period (, the turbulent fluxes calculated by the bulk method showed that net radiation R net was the primary source of surface energy (60.7 w/m 2 ), whereas during the dry period (25 September 2016 to 4 May 2017), the main heat sink was the positive H (28.5 w/m 2 ) rather than the negative R net (À10.0 w/m 2 ). Plain Language SummaryThe profile method and the bulk method have been applied to quantify turbulent fluxes and sublimation/condensation, and the bulk method is more widely used because it is insensitive to observation errors. However, determination of the aerodynamic roughness lengths in the bulk method remains a large challenge. So we tried to acquire reliable varying and intrinsic roughness length for momentum through its parametric analysis. The related meteorological data and glacial sublimation/ condensation were measured over a mountain glacier. Hourly roughness lengths in the transitional range affected slightly by snowdrift were found with the approximate threshold value. The comparison provided here verifies that these values are reliable, although this method is relatively rough. The z 0m parameterization can be regarded as an important basis of turbulent heat flux research. Therefore, in addition to z 0m parameterization, it can also be very meaningful to further discuss the temporal variation of meteorology and turbulent heat fluxes. Further research is needed and very important to improve our understanding of energy and mass exchange between the glacier surface and atmosphere, especially in arid and semiarid regions.

Spatial and temporal variations in glacier aerodynamic surface roughness during the melting season, as estimated at the August-one ice cap, Qilian mountains, China

“…Ice surface z 0 was generally larger than snow surface and smaller than patch snow-covered surface. Our results match values reported in studies reporting results ranging from 0.1 to 6.9 mm in Qilian mountain glaciers (Guo et al, 2018;Sun et al, 2018). Our results showed that z 0 reached its maximum at the end of the summer melt, which matched wind profile measurements by Smeets and Broeke (2008).…”

“…Micro-topography, wind profile and eddy covariance methods generate a wide range of z 0 values for snow and ice surfaces (Grainger and Lister, 1966;Munro, 1989;Bintanja and Broeke, 1995;Schneider, 1999;Hock and Holmgren, 2005;Brock et al, 2006;Andreas et al, 2010;Gromke et al, 2011). In this study, z 0_profile , z 0_DEM and z 0_DEM showed similar variation pattern during the melting season.…”

“…It ranges in elevation from 4550 to 4820 m a.s.l. (Guo et al, 2015). This study was conducted during the melting season of 2018, a season characterized by high precipitation.…”

“…The roughness of ice surfaces is an important control on air-ice heat transfer, on the ice surface albedo, and thus on the surface energy balance (Greuell and Smeets, 2001;Hock and Holmgren, 2005;Irvine-Fynn et al, 2014;Steiner et al, 2018). The snow and ice surface roughness at centimeter and millimeter scales is also an important parameter in studies of wind transport, snowdrifts, snowfall, snow grain size and ice surface melt (Denby and Smeets, 2000;Brock et al, 2006;McClung and Schaerer, 2006;Fassnacht et al, 2009a, b).…”

An Improved Spatial–Temporal Downscaling Method for TRMM Precipitation Datasets in Alpine Regions: A Case Study in Northwestern China’s Qilian Mountains

“…The average RMSE of CFDAP decreased about 66.48 and 83.07 mm than that of FDAP and original TRMM data from 2006 to 2015. Additionally, the distribution of precipitation also changed, with the main trend still showing a gradual increase from southwest to northeast, but exhibiting a notable increase in precipitation in the high-elevation area, where the total amount of precipitation is roughly the same as some observed points in Laohugou No.12 Glacier [41], August-one Glacier [42]. To verify the effectiveness of the improved method, we used the original NDVI instead of PNDVI in the statistical model (4), and the parameters were obtained with statistical relationships.…”