Modeling 2 m air temperatures over mountain glaciers: Exploring the influence of katabatic cooling and external warming

Ayala, Álvaro; Pellicciotti, Francesca; Shea, J. M.

doi:10.1002/2015jd023137

Cited by 48 publications

(131 citation statements)

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“…During daytime, turbulent mixing of the glacier boundary layer with the up-valley anabatic winds may erode the shallow katabatic layer of a small glacier (Ayala et al, 2015), and glacier boundary layer temperatures have been found to be higher than expected (Carturan et al, 2015). This effect is exacerbated by solar heating of the unglaciated terrain surrounding the glacier, which causes instability in the overlying boundary layer.…”

Section: Distributing Model Input Variables Over the Glacier Surfacementioning

confidence: 93%

“…1). The limited aerial and vertical extent of the modern glacier favours the steep vertical air temperature gradient along the glacier surface, but on larger glaciers such as LG during its L19 extent, the air temperature gradient over the glacier surface is strongly modified by the katabatic wind field (Ayala et al, 2015;Greuell and Böhm, 1998;Shea and Moore, 2010); and the influence of long-wave emissions from surrounding terrain is drastically reduced as the glacier fills the cirque (Fig. 1).…”

Section: The Impact Of Glacier Extent On the Proxy Potential Of Lewismentioning

confidence: 99%

“…During the night, the vertical air temperature gradient over the glacier was taken to be the moist adiabatic lapse rate of −0.0065 • C m −1 . As the available observed and modelled data do not allow for a quantified partitioning of potential dynamic processes that cause strong daytime gradients observed at the margins of glaciers (Ayala et al, 2015;Carturan et al, 2015;Petersen and Pellicciotti, 2011), the daytime gradient of −0.015 • C m −1 was found through optimization using the spatially distributed stake mass balances of 2011/12. As the component of LWI that is parameterized for terrestrial irradiance from the surroundings is not constrained by measurements, the optimized daytime vertical air temperature gradient will also compensate for shortcomings in the LWI parameterization.…”

Section: Distributing Model Input Variables Over the Glacier Surfacementioning

confidence: 99%

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Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

et al. 2016

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Abstract. The Lewis Glacier on Mt. Kenya is one of the best studied tropical glaciers and has experienced considerable retreat since a maximum extent in the late 19th century (L19). From distributed mass and energy balance modelling, this study evaluates the current sensitivity of the surface mass and energy balance to climatic drivers, explores climate conditions under which the L19 maximum extent might have been sustained, and discusses the potential for using the glacier retreat to quantify climate change. Multi-year meteorological measurements at 4828 m provide data for input, optimization, and evaluation of a spatially distributed glacier mass balance model to quantify the exchanges of energy and mass at the glacier-atmosphere interface. Currently the glacier loses mass due to the imbalance between insufficient accumulation and enhanced melt, because radiative energy gains cannot be compensated by turbulent energy sinks. Exchanging model input data with synthetic climate scenarios, which were sampled from the meteorological measurements and account for coupled climatic variable perturbations, reveals that the current mass balance is most sensitive to changes in atmospheric moisture (via its impact on solid precipitation, cloudiness, and surface albedo). Positive mass balances result from scenarios with an increase of annual (seasonal) accumulation of 30 % (100 %), compared to values observed today, without significant changes in air temperature required. Scenarios with lower air temperatures are drier and associated with lower accumulation and increased net radiation due to reduced cloudiness and albedo. If the scenarios currently producing positive mass balances are applied to the L19 extent, negative mass balances are the result, meaning that the conditions required to sustain the glacier in its L19 extent are not reflected in today's meteorological observations using model parameters optimized for the present-day glacier. Alternatively, a balanced mass budget for the L19 extent can be achieved by changing both climate and optimized gradients (used to extrapolate the meteorological measurements over the glacier) in a manner that implies a distinctly different coupling between the glacier's local surface-air layer and its surrounding boundary layer. This result underlines the difficulty of deriving palaeoclimates for larger glacier extents on the basis of modern measurements of small glaciers.

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Section: Distributing Model Input Variables Over the Glacier Surfacementioning

confidence: 93%

Section: The Impact Of Glacier Extent On the Proxy Potential Of Lewismentioning

confidence: 99%

Section: Distributing Model Input Variables Over the Glacier Surfacementioning

confidence: 99%

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Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

et al. 2016

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“…On the one hand, a prevailing up-glacier wind was recognized, but it cannot be attributed unequivocally to valley winds because the direction roughly corresponds to prevailing synoptic winds in the Ortles-Cevedale area (Gabrieli et al, 2011). The occurrence of weaker local winds and more relevant entrainment of synoptic winds have been hypothesized, for example, by Ayala et al (2015), for glaciers without a well-defined tongue. On the other hand, although katabatic flows were generally absent, this site was the coldest in summer 2011, exhibiting a mean depression of 1 • C compared to the ambient temperature (Table 4).…”

Section: Discussionmentioning

confidence: 99%

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

et al. 2015

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Abstract.Glacier mass balance models rely on accurate spatial calculation of input data, in particular air temperature. Lower temperatures (the so-called glacier cooling effect) and lower temperature variability (the so-called glacier damping effect) generally occur over glaciers compared to ambient conditions. These effects, which depend on the geometric characteristics of glaciers and display a high spatial and temporal variability, have been mostly investigated on medium to large glaciers so far, while observations on smaller ice bodies ( < 0.5 km 2 ) are scarce. Using a data set from eight on-glacier and four off-glacier weather stations, collected in the summers of 2010 and 2011, we analyzed the air temperature variability and wind regime over three different glaciers in the Ortles-Cevedale. The magnitude of the cooling effect and the occurrence of katabatic boundary layer (KBL) processes showed remarkable differences among the three ice bodies, suggesting the likely existence of important reinforcing mechanisms during glacier decay and fragmentation. The methods proposed by Greuell and Böhm (1998) and Shea and Moore (2010) for calculating on-glacier temperature from off-glacier data did not fully reproduce our observations. Among them, the more physically based procedure of Greuell and Böhm (1998) provided the best overall results where the KBL prevails, but it was not effective elsewhere (i.e., on smaller ice bodies and close to the glacier margins). The accuracy of air temperature estimations strongly impacted the results from a mass balance model which was applied to the three investigated glaciers. Most importantly, even small temperature deviations caused distortions in parameter calibration, thus compromising the model generalizability.

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“…During the day the LR has two cycles with minima in magnitude close to −0.005 • C m −1 at 11:00 and −0.004 • C m −1 at 19:00, separated by a maximum of −0.007 • C m −1 at 16:00. While the LR minima are likely to be related to the strengthening of katabatic flow during daytime (Petersen and Pellicciotti, 2011), the afternoon maximum is potentially caused by the erosion of the katabatic boundary layer on the lower glacier tongue, due to warm air advection from bare rock surfaces at the glacier sides and proglacial area (van de Broeke, 1997;Ayala et al, 2015). Using the hourly LR, we distribute air temperatures over the entire glacier surface on a 30 m grid at an hourly time step, using the ASTER GDEM V2 and the glacier outline which was digitized from an ASTER image of 27 March 2010.…”

Section: Distributed Degree-hour Model (Ddhm)mentioning

confidence: 99%

Assessing glacier melt contribution to streamflow at Universidad Glacier, central Andes of Chile

Bravo

Loriaux

Rivera

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. Glacier melt is an important source of water for high Andean rivers in central Chile, especially in dry years, when it can be an important contributor to flows during late summer and autumn. However, few studies have quantified glacier melt contribution to streamflow in this region. To address this shortcoming, we present an analysis of meteorological conditions and ablation for Universidad Glacier, one of the largest valley glaciers in the central Andes of Chile at the head of the Tinguiririca River, for the 2009-2010 ablation season. We used meteorological measurements from two automatic weather stations installed on the glacier to drive a distributed temperature-index and runoff routing model. The temperature-index model was calibrated at the lower weather station site and showed good agreement with melt estimates from an ablation stake and sonic ranger, and with a physically based energy balance model. Total modelled glacier melt is compared with river flow measurements at three sites located between 0.5 and 50 km downstream. Universidad Glacier shows extremely high melt rates over the ablation season which may exceed 10 m water equivalent in the lower ablation area, representing between 10 and 13 % of the mean monthly streamflow at the outlet of the Tinguiririca River Basin between December 2009 and March 2010. This contribution rises to a monthly maximum of almost 20 % in March 2010, demonstrating the importance of glacier runoff to streamflow, particularly in dry years such as 2009-2010. The temperature-index approach benefits from the availability of on-glacier meteorological data, enabling the calculation of the local hourly variable lapse rate, and is suited to high melt regimes, but would not be easily applicable to glaciers further north in Chile where sublimation is more significant.

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Modeling 2 m air temperatures over mountain glaciers: Exploring the influence of katabatic cooling and external warming

Cited by 48 publications

References 50 publications

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

Climatic controls and climate proxy potential of Lewis Glacier, Mt. Kenya

Air temperature variability over three glaciers in the Ortles–Cevedale (Italian Alps): effects of glacier fragmentation, comparison of calculation methods, and impacts on mass balance modeling

Assessing glacier melt contribution to streamflow at Universidad Glacier, central Andes of Chile

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