Elisa Lindgren

Finnish Meteorological Institute

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Matti Leppäranta

University of Helsinki

Georgiy Kirillin

Leibniz Institute of Freshwater Ecology and Inland Fisheries

Laura Tuomi

Finnish Meteorological Institute

Jan‐Victor Björkqvist

Finnish Meteorological Institute

Victor Alari

Tallinn University of Technology

Siim Pärt

Tallinn University of Technology

Sander Rikka

Tallinn University of Technology

I.A. Aslamov

Siberian Branch of the Russian Academy of Sciences

Martyn Sunter

Exeter Hospital

Jacqueline Sugier

Met Office

Cooperative Institutions

Finnish Meteorological Institute

Tallinn University of Technology

University of Helsinki

Northwest Institute of Eco-Environment and Resources

Chinese Academy of Sciences

Exeter Hospital

Met Office

Helsinki Institute of Physics

Norwegian Meteorological Institute

Leibniz Institute of Freshwater Ecology and Inland Fisheries

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Turbulent mixing and heat fluxes under lake ice: the role of seiche oscillations

Georgiy Kirillin I.A. Aslamov Matti Leppäranta Elisa Lindgren

Abstract. We performed a field study on mixing and vertical heat transport under ice cover of an Arctic lake. Mixing intensities were estimated from small-scale oscillations of water temperature and turbulent kinetic energy dissipation rates derived from current velocity fluctuations. Well-developed turbulent conditions prevailed in the stably stratified interfacial layer separating the ice base from the warmer deep waters. The source of turbulent mixing was identified as whole-lake (barotropic) oscillations of the water body driven by strong wind events over the ice surface. We derive a scaling of ice-water heat flux based on dissipative Kolmogorov scales and successfully tested against measured dissipation rates and under-ice temperature gradients. The results discard the conventional assumption of nearly conductive heat transport within the stratified under-ice layer and suggest contribution of the basal heat flux into the melt of ice cover is higher than commonly assumed. Decline of the seasonal ice cover in the Arctic is currently gaining recognition as a major indicator of climate change. The heat transfer at the ice-water interface remains the least studied among the mechanisms governing the growth and melting of seasonal ice. The outcomes of the study find application in heat budget of seasonal ice on inland and coastal waters.

Ice-albedo feedback

Melt pond

Energy budget

Stratification (seeds)

10.5194/hess-2018-376

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Citations (3)

Ice cover decay and heat balance in Lake Kilpisjärvi in Arctic tundra

Journal of Limnology (2019)

Matti Leppäranta Elisa Lindgren Lijuan Wen Georgiy Kirillin

To gain more understanding of lake ice melting process, field research was carried out in an arctic tundra lake, Kilpisjärvi (surface area 37.1 km2, maximum depth 57 m) in the melting periods of 2013 and 2014. The heat budget of the ice cover was dominated by the radiation balance; turbulent heat fluxes were large in 2013 due to warm air advection but small in 2014. Transmittance of solar radiation through ice was 0.25 in 2013 and 0.10 in 2014, snow-ice was absent in 2013 but in 2014 accounted for 50% of the ice cover. The melting rate was 4.4 cm d-1 in 2013, 1.9 cm d-1 in 2014. The portions of surface, bottom and internal melting were, respectively, 2.9, 1.0 and 0.5 cm d-1 in 2013 and 0.8, 1.0 and 0.1 cm d-1 in 2014. Internal melting was realized in increase of ice porosity. In 2013 a rapid ice breakage event completed the ice breakup in short time when ice porosity had reached 40-50%. A lake ice melting model should include the thickness and porosity of ice, with porosity connected to an ice strength criterion.

Melt pond

Meltwater

Snowmelt

10.4081/jlimnol.2019.1879

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Citations (38)

Observations from Personal Weather Stations—EUMETNET Interests and Experience

Climate (2022)

Claudia Hahn Irene Garcia‐Martí Jacqueline Sugier Fiona Emsley Anne-Lise Beaulant

The number of people owning a private weather station (PWS) and sharing their meteorological measurements online is growing worldwide. This leads to an unprecedented high density of weather observations, which could help monitor and understand small-scale weather phenomena. However, good data quality cannot be assured and thorough quality control is crucial before the data can be utilized. Nevertheless, this type of data can potentially be used to supplement conventional weather station networks operated by National Meteorological & Hydrological Services (NMHS), since the demand for high-resolution meteorological applications is growing. This is why EUMETNET, a community of European NMHS, decided to enhance knowledge exchange about PWS between NMHSs. Within these efforts, we have collected information about the current interest in PWS across NMHSs and their experiences so far. In addition, this paper provides an overview about the data quality challenges of PWS data, the developed quality control (QC) approaches and openly available QC tools. Some NMHS experimented with PWS data, others have already incorporated PWS measurements into their operational workflows. The growing number of studies with promising results and the ongoing development of quality control procedures and software packages increases the interest in PWS data and their usage for specific applications.

10.3390/cli10120192

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Citations (13)

Heat balance of supraglacial lakes in the western Dronning Maud Land

Annals of Glaciology (2016)

Matti Leppäranta Elisa Lindgren Лаури Арвола

ABSTRACT Thermodynamics of a seasonal supraglacial lake were examined based on field data from three summers. At maximum, the lake body consisted of an upper layer with thin ice on top, and a lower layer with slush, hard ice and sediment at the bottom. Sublimation from the upper ice surface averaged to 0.7 mm d −1 , and melting in the ice interior averaged to 9.1 mm d −1 during summer. Albedo was on average 0.6 and light attenuation coefficient was ~1 m −1 . Averaged over December and January, and over 3 different years, we found that the net solar heating was 137 W m −2 , while the losses averaged to 62 W m −2 for the longwave radiation, 16 W m −2 for the sensible heat flux, 24 W m −2 for the latent heat flux and 3 W m −2 for the bottom flux. The depth scale is determined by the light attenuation distance and thermal diffusion coefficient, and the net liquid water volume ranged from 0.5 to 1.0 m in different years. The potential winter growth is more than summer melting, and thus the lake freezes up completely in winter in the present climate.

Sublimation

10.1017/aog.2016.12

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Citations (8)

Swell hindcast statistics for the Baltic Sea

Ocean science (2021)

Jan‐Victor Björkqvist Siim Pärt Victor Alari Sander Rikka Elisa Lindgren

Abstract. The classic characterisation of swell as regular, almost monochromatic, wave trains does not necessarily accurately describe swell in water bodies shielded from the oceanic wave climate. In such enclosed areas the locally generated swell waves still contribute to processes at the air and seabed interfaces, and their presence can be quantified by partitioning wave components based on their speed relative to the wind. We present swell statistics for the semi-enclosed Baltic Sea using 20 years of swell-partitioned model data. The swell significant wave height was mostly under 2 m, and in the winter (DJF) the mean significant swell height was typically less than 0.4 m; higher swell was found in limited nearshore areas. Swell waves were typically short (under 5 s), with mean periods over 8 s being rare. In open-sea areas the average ratio of swell energy (to total energy) was mostly below 0.4 – significantly less than in the World Ocean. Certain coastal areas were swell dominated over half the time, mostly because of weak winds (U<5 m s−1) rather than high swell heights. Swell-dominated events with a swell height over 1 m typically lasted under 10 h. A cross-correlation analysis indicates that swell in the open sea is mostly generated from local wind sea when wind decays (dominant time lag roughly 15 h). Near the coast, however, the results suggest that the swell is partially detached from the local wind waves, although not necessarily from the weather system that generates them because the highest swell typically arrives with a roughly 10 h delay after the low-pressure system has already passed.

Swell

Infragravity wave

Hindcast

Significant wave height

10.5194/os-17-1815-2021

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Citations (12)

Swell hindcast statistics for the Baltic Sea

Jan‐Victor Björkqvist Siim Pärt Victor Alari Sander Rikka Elisa Lindgren

Abstract. Swell dominates the global sea state and therefore significantly contributes to processes at the air and seabed interfaces. Nonetheless, smaller enclosed seas are detached from the global swell climate. We present swell statistics for the Baltic Sea using 20 years of swell partitioned model data. The swell significant wave height was mostly under 2 m, and in the winter (DJF) the mean significant swell height was typically less than 0.4 m; higher swell was found at limited nearshore areas. Swell waves were typically short (under 5 s), with mean periods over 8 s being rare. In open-sea areas the average ratio of swell energy (to total energy) was below 0.4 – significantly less than in World Ocean. Certain coastal areas were swell dominated over half the times, mostly because of weak winds (U < 5 ms−1) rather than high swell heights. Swell dominated events with a swell height over 1 m typically lasted under 10 h. A cross-correlation analysis indicates that swell in the open sea is mostly generated from local wind-sea when wind decays (dominant time lag roughly 15 h). Near the coast, however, the results suggests that the swell is partially detached from the local wind-waves, although not necessarily from the weather system that generates them.

Swell

Hindcast

Infragravity wave

10.5194/os-2021-62

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Citations (1)

Use of Webcams in Support of Operational Snow Monitoring

Geosciences (2023)

Cemal Melih Taniş Elisa Lindgren Anna Frey Lasse Latva Ali Nadir Arslan

Ultrasonic sensors are one of the most common automatic monitoring methods in operational snow depth monitoring with reliable results. On the other hand, there is significant uncertainty when measuring small snow depths (<2 cm), thus it cannot provide binary snow presence (on/off) information. The use of webcams in monitoring snow cover has proven to be successful in recent studies and applications. In this study, we applied an adaptive thresholding technique on images from webcams to obtain reliable snow on/off information to complement the ultrasonic snow depth measurements. Camera and ultrasonic sensor data from two weather stations in Finland were studied. The webcam data was processed using FMIPROT (Finnish Meteorological Institute Image Processing Tool) software, operating in a cloud computing environment, which can generate near real-time data. Our results indicate that webcam-derived data can be successfully used for quality control or as auxiliary data to support operational ultrasonic sensor measurements and provide a cost-effective improvement to operational monitoring capabilities. Webcam monitoring is especially useful during the melting season when the snow depth is below 15 mm, with accuracy values between 72% and 94%.

Real-time data

10.3390/geosciences13030092

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Citations (2)

Turbulent mixing and heat fluxes under lake ice: the role of seiche oscillations

Hydrology and earth system sciences (2018)

Georgiy Kirillin I.A. Aslamov Matti Leppäranta Elisa Lindgren

Abstract. We performed a field study on mixing and vertical heat transport under the ice cover of an Arctic lake. Mixing intensities were estimated from small-scale oscillations of water temperature and turbulent kinetic energy dissipation rates derived from current velocity fluctuations. Well-developed turbulent conditions prevailed in the stably stratified interfacial layer separating the ice base from the warmer deep waters. The source of turbulent mixing was identified as whole-lake (barotropic) oscillations of the water body driven by strong wind events over the ice surface. We derive a scaling of ice–water heat flux based on dissipative Kolmogorov scales and successfully tested against measured dissipation rates and under-ice temperature gradients. The results discard the conventional assumption of nearly conductive heat transport within the stratified under-ice layer and suggest contribution of the basal heat flux into the melt of ice cover is higher than commonly assumed. Decline of the seasonal ice cover in the Arctic is currently gaining recognition as a major indicator of climate change. The heat transfer at the ice–water interface remains the least studied among the mechanisms governing the growth and melting of seasonal ice. The outcomes of the study find application in the heat budget of seasonal ice on inland and coastal waters.

Ice-albedo feedback

Melt pond

Stratification (seeds)

10.5194/hess-22-6493-2018

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Citations (43)

The heat budget of Lake Kilpisjärvi in the Arctic tundra

Hydrology Research (2016)

Matti Leppäranta Elisa Lindgren Kunio Shirasawa

An extensive research programme has been carried through in 2007–2009 on the ice cover geophysics in Lake Kilpisjärvi, located at 69 °03′N 20 °50′E, 473 m above sea level, and about 60 km from the shore of the Norwegian Sea. The surface area of the lake is 37.1 km2, and the maximum depth is 57 m. Data were collected of ice, snow and weather conditions with an automatic ice station in the lake. The heat budget together with ice structure, growth and melting was analysed. It was dominated by the radiation balance, down to −50 W m−2 in fall and up to 100 W m−2 in summer. Turbulent heat fluxes were significant before freeze-up in fall (absolute values up to 30 W m−2), but in the ice season they were small except for an occasional sensible heat flux which was large due to warm air advection. The evolution of ice thickness served as a very good condition for the total surface heat flux, and was found to be consistent with the ice station time series of air–ice heat fluxes.

Melt pond

10.2166/nh.2016.171

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Citations (26)

Mass and heat balance of snowpatches in Basen nunatak, Dronning Maud Land, Antarctica, in summer

Journal of Glaciology (2013)

Matti Leppäranta Onni Järvinen Elisa Lindgren

Abstract An experimental study concerning the mass and heat balance of snowpatches was performed during the Finnish Antarctic Research Programme (FINNARP) 2004 and 2010 summer expeditions to Basen nunatak (73°03′ S, 13°25′ W). Data were collected from a snow stake line, snow pits and automated weather and snow recording systems. One 100 m perennial snowpatch and several smaller seasonal patches (<10 m) were monitored. Snow thickness decreased by 4.0–6.3 mm d −1 due to sublimation, compression and, close to lateral boundaries, meltwater runoff. The vertical mass loss was 1–2 mm snow water equivalent (SWE) d −1 and the lateral decay was −10 cm d −1 . The net radiation was 20.2 W m −2 and the mean latent heat flux was −15.5 W m −2 .The mean surface energy flux was 4.9 W m −2 and the heat loss to the ground was 1.5 W m −2 . Thin snow decayed faster due to surface thermomechanical erosion and melt from the bottom where the soil was heated by the solar radiation. Between the summers of 2004 and 2010, the thickness of the perennial snowpatch decreased by 230 mm.

Meltwater

Snowmelt

Sublimation

Snow field

10.3189/2013jog12j236

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Citations (7)