| 1. |
- Bengtsson, Lars, et al.
(författare)
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Field investigation of winter thermo‐ and hydrodynamics in a small Karelian lake
- 1996
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 41:7, s. 1502-1502
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Tidskriftsartikel (refereegranskat)abstract
- During late winter (18 March–7 April 1994), temperature and current measurements were made in Lake Vendyurskoe, Russia, including three surveys at six cross sections of the lake. Also, the temperature profile evolution was registered with two thermistor chains at two stations (bottom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperature gradients were measured just below the ice cover and in the upper 10‐cm layer of the bottom sediments.The isotherms were found to be almost horizontal and evenly spaced vertically, so no conditions for large‐scale, density‐induced currents existed. The heat flux from sediments to water ranged from 0.6 to 2.0 W m−2. These values were inversely related to the depth. The heat flux from water to ice ranged from 0.7 to 1.2 W m−2. When water heating from solar radiation penetration became apparent, this flux increased by a factor of two. When solar radiation increased, convection occurred in the upper layers of the water column. When solar radiation heating became significant at the beginning of spring, the average net heat flux at the ice‐water interface during daytime was 7.7 W m−2. Weak currents (few mm s−1) with a seiche‐like character were observed, which most likely resulted from ice‐cover oscillations.
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| 2. |
- Lappalainen, Hanna K., et al.
(författare)
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Pan-Eurasian Experiment (PEEX) : towards a holistic understanding of the feedbacks and interactions in the land-atmosphere-ocean-society continuum in the northern Eurasian region
- 2016
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 16:22, s. 14421-14461
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Tidskriftsartikel (refereegranskat)abstract
- The northern Eurasian regions and Arctic Ocean will very likely undergo substantial changes during the next decades. The Arctic-boreal natural environments play a crucial role in the global climate via albedo change, carbon sources and sinks as well as atmospheric aerosol production from biogenic volatile organic compounds. Furthermore, it is expected that global trade activities, demographic movement, and use of natural resources will be increasing in the Arctic regions. There is a need for a novel research approach, which not only identifies and tackles the relevant multi-disciplinary research questions, but also is able to make a holistic system analysis of the expected feedbacks. In this paper, we introduce the research agenda of the Pan-Eurasian Experiment (PEEX), a multi-scale, multi-disciplinary and international program started in 2012 (https://www.atm.helsinki.fi/peex/). PEEX sets a research approach by which large-scale research topics are investigated from a system perspective and which aims to fill the key gaps in our understanding of the feedbacks and interactions between the land-atmosphereaquatic-society continuum in the northern Eurasian region. We introduce here the state of the art for the key topics in the PEEX research agenda and present the future prospects of the research, which we see relevant in this context.
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| 3. |
- Malm, Joakim, et al.
(författare)
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Field Investigation of the Thermal Bar in Lake Ladoga, Spring 1991
- 1993
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Ingår i: Hydrology Research. - : IWA Publishing. - 1998-9563 .- 0029-1277 .- 2224-7955. ; 24:5, s. 339-358
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Tidskriftsartikel (refereegranskat)abstract
- The thermal bar in Lake Ladoga was studied during one week in May 1991. Temperature and current velocity distributions were measured. The movement of the thermal bar and the horizontal heat transport were examined.The temperature off-shore the thermal bar was found to be constant within a vertical. The velocity distributions were complex and dependent on wind conditions. Calculations of changes in heat content showed that there was a horizontal heat transport from the near-shore warm zone towards the thermal bar. The observed off-shore progression of the thermal bar was compared with analytically computed progression rates. The progression rate is underestimated if it is assumed that surface heating and vertical mixing are the only mechanisms contributing to the thermal bar progression. Better agreement is obtained if mixing of warm and cold water near the thermal bar zone is considered.
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| 4. |
- Malm, Joakim, et al.
(författare)
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Field study on currents in a shallow, ice‐covered lake
- 1998
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 43:7, s. 1669-1679
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Tidskriftsartikel (refereegranskat)abstract
- A field study on current structure and circulation characteristics in Lake Vendyurskoe, a small, shallow, icecovered lake in Karelia, Russia, is presented. The current velocity magnitudes were generally found to be small. The most pronounced currents had an oscillating character, with velocity amplitudes on the order of millimeters per second. The oscillation period, obtained from spectral density calculations, corresponded to that of a barotropic uninodal seiche. The seichelike nature of the current oscillations was supported by the results from analysis of icelevel fluctuations, giving identical periods and a phase shift of one‐fourth the period between the two types of oscillations. Mean currents measured during the winter were on the order of millimeters per second. Because Lake Vendyurskoe does not have any significant river inflow or outflow during winter, the most probable cause of these currents is horizontal temperature (pressure) gradients. Scaling analysis indicated that these currents are geostrophic. This was supported by theoretical estimates, based on observed horizontal temperature gradients, being of the same order as the observed currents. The mean current velocities increased considerably after spring convection from <1 to several millimeters per second.
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| 5. |
- Malm, Joakim, et al.
(författare)
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Investigation of the spring thermal regime in Lake Ladoga using field and satellite data
- 1994
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Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 39:6, s. 1333-1333
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Tidskriftsartikel (refereegranskat)abstract
- We use a combination of field and satellite data to investigate the thermal regime in Lake Ladoga in spring 1992. The analysis concentrates mainly on the temperature structure in the convectively mixed region and the dynamics of a special thermo‐hydrodynamic phenomenon called “thermal bar” (a zone of descending water with the temperature of maximum density equal to ∼4°C). A theoretical model of the temperature distribution in the convectively mixed region (temperatures <4°C) and the thermal bar progression is also applied and compared with satellite data. The study shows that the temperature offshore the 4°C isotherm in the convectively mixed region of the lake is almost depth‐constant because of strong convective mixing and that the horizontal heat flux seems to be of minor importance in this region. The comparison between predictions from the simple theoretical model describing the temperature evolution and movement of the thermal bar with observations showed a fairly good agreement. However, calculations of the change of heat content in water columns along sections indicate heat transport from the nearshore, stably stratified region toward the 4°C isotherm which will affect the movement of the thermal bar. This effect has been incorporated in an improved model of the thermal bar progression. A better agreement between predictions and observations was also obtained with this model.
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| 6. |
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