On A Low Cloud Phenomenon At The Breidamerkurjökull Glacier, Iceland

Kaltenböck, Rudolf; Obleitner, Friedrich

doi:10.1023/a:1001878013148

Cited by 5 publications

(1 citation statement)

References 11 publications

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“…Two mesoscale cyclonic vortices can be seen at the northeast and southwest corners of Iceland, resulting from the convergence between the environmental circulation and the local katabatic wind. In the afternoon, the near-surface winds feature an upslope pattern because of the higher temperature over land; the observational study by Kaltenböck and Obleitner (1999) suggests that coastal sea breezes are a frequent occurrence in summer. The exception is over the Vatnajökull ice cap where downslope winds persist (cf.…”

Section: A Near-surface Wind Climate Over Icelandmentioning

confidence: 99%

High-Resolution Regional Climate Simulations over Iceland Using Polar MM5*

Bromwich

Bai

Bjarnason³

2005

Monthly Weather Review

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High-resolution regional climate simulations of Iceland for 1991-2000 have been performed using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesocale Model (MM5) modified for use in polar regions (Polar MM5) with three nested domains and short-duration integrations. The simulated results are compared with monthly mean surface observations from Iceland for 1991-2000 to demonstrate the high level of model performance; correlation coefficients exceed 0.9 for most variables considered.The simulation results are used to analyze the near-surface climate over Iceland. The simulated nearsurface winds in winter are primarily katabatic. The land-sea-breeze circulation is clearly evident in summer. The land is colder than the ocean during winter, with a strong (weak) temperature gradient along the southern (northern) coast. This temperature pattern over the sloping terrain forces the katabatic wind. The diurnal cycle of near-surface air temperature is marked in summer over the land areas, which drives the land-sea breeze. The near-surface climate variations for extremes of the North Atlantic Oscillation (NAO) index during winter and summer result from the large-scale atmospheric advection conditions.The time-averaged mesoscale precipitation distribution over Iceland is reasonably well simulated by Polar MM5. Winter precipitation rates are double those during the summer, reflecting the much greater winter cyclonic activity. The simulated interannual precipitation variations during winter for 1991-2000 agree with those observed from snow accumulation measurements on the Vatnajökull ice cap. The winter precipitation decrease for 1991-2000 dominates the annual signal for all of Iceland except the northeastern and eastern parts where the precipitation increases. The large precipitation trends (decadal decrease of up to 50%) are caused by the eastward shift and weakening of the Icelandic low during the 1990s, as a result of changes in the NAO modulation of regional climate.

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Section: A Near-surface Wind Climate Over Icelandmentioning

confidence: 99%

High-Resolution Regional Climate Simulations over Iceland Using Polar MM5*

Bromwich

Bai

Bjarnason³

2005

Monthly Weather Review

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HIRLAM experiments on surface energy balance across Vatnajökull, Iceland

Rontu

Obleitner

Gollvik

et al. 2009

Meteorol Atmos Phys

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Numerical Modelling of Katabatic Flow Over a Melting Outflow Glacier

Söderberg

Parmhed

2006

Boundary-Layer Meteorol

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A realistic simulation of katabatic flows is not a straightforward task for numerical models. One complicating factor is that katabatic flows develop within a stably stratified boundary layer, which is poorly resolved and described in many numerical models. To capture the jet-shaped shallow flow a model set-up with high vertical resolution is also required. In this study, 'a state of the art' mesoscale numerical model is applied in a simulation of katabatic flow over a melting glacier. A basic agreement between observations and model results is found. From scale analysis, it is concluded that the simulated flow can be classified as katabatic. Although the background flow varies in strength and direction, the simulated katabatic flow over Breidamerkurjökull is persistent. Two factors vital for this persistence are identified. First, the melting snow maintains the surface temperature close to 0 • C while the air temperature warms adiabatically as it descends the slope. This provides a 'self enhanced' negative buoyancy that drives the flow to a balance with local friction. Second, the jet-like shape of the resulting flow gives rise to a large 'curvature term' in the Scorer parameter, which becomes negative in the upper jet. This prevents vertical wave propagation and isolates the katabatic layer of the influence from the free troposphere aloft. Our results suggest that the formation of local microclimates dominated by katabatic flow is a general feature over melting glaciers. The modelled turbulence structure illustrates the importance of nonlocal processes. Neglecting the vertical transport of turbulence in katabatic flows is not a valid assumption. It is also found that the local friction velocity remains larger than zero through the katabatic jet, due to directional shear where the scalar wind speed approaches its maximum.

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On A Low Cloud Phenomenon At The Breidamerkurjökull Glacier, Iceland

Cited by 5 publications

References 11 publications

High-Resolution Regional Climate Simulations over Iceland Using Polar MM5*

High-Resolution Regional Climate Simulations over Iceland Using Polar MM5*

HIRLAM experiments on surface energy balance across Vatnajökull, Iceland

Numerical Modelling of Katabatic Flow Over a Melting Outflow Glacier

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