The Swedish Meteorological and Hydrological Institute is a government agency in Sweden and operates under the Ministry of the Environment. SMHI has expertise within the areas of meteorology, hydrology and oceanography, and has extensive service and business operations within these areas.SMHI's head office is located in Norrköping. Prior to 1975 it was located in Stockholm but after a decision taken in the Riksdag in 1971 it was relocated to Norrköping in 1975. SMHI also has offices in Stockholm, Göteborg, Malmö and Sundsvall. To the Swedish public SMHI is mostly known for the weather forecasts in the public-service radio provided by Sveriges Radio. Many of the other major media companies in Sweden also buy weather forecasts from SMHI. Wikipedia.
Kahnert M.,Swedish Meteorological and Hydrological Institute |
Devasthale A.,Swedish Meteorological and Hydrological Institute
Atmospheric Chemistry and Physics | Year: 2011
We investigate the impact of the morphological properties of freshly emitted black carbon aerosols on optical properties and on radiative forcing. To this end, we model the optical properties of fractal black carbon aggregates by use of numerically exact solutions to Maxwell's equations within a spectral range from the UVC to the mid-IR. The results are coupled to radiative transfer computations, in which we consider six realistic case studies representing different atmospheric pollution conditions and surface albedos. The spectrally integrated radiative impacts of black carbon are compared for two different fractal morphologies, which brace the range of recently reported experimental observations of black carbon fractal structures. We also gauge our results by performing corresponding calculations based on the homogeneous sphere approximation, which is commonly employed in climate models. We find that at top of atmosphere the aggregate models yield radiative impacts that can be as much as 2 times higher than those based on the homogeneous sphere approximation. An aggregate model with a low fractal dimension can predict a radiative impact that is higher than that obtained with a high fractal dimension by a factor ranging between 1.1-1.6. Although the lower end of this scale seems like a rather small effect, a closer analysis reveals that the single scattering optical properties of more compact and more lacy aggregates differ considerably. In radiative flux computations there can be a partial cancellation due to the opposing effects of different error sources. However, this cancellation effect can strongly depend on atmospheric conditions and is therefore quite unpredictable. We conclude that the fractal morphology of black carbon aerosols and their fractal parameters can have a profound impact on their radiative forcing effect, and that the use of the homogeneous sphere model introduces unacceptably high biases in radiative impact studies. We emphasise that there are other potentially important morphological features that have not been addressed in the present study, such as sintering and coating of freshly emitted black carbon by films of organic material. Finally, we found that the spectral variation of the absorption cross section of black carbon significantly deviates from a simple 1/λ scaling law. We therefore discourage the use of single-wavelength absorption measurements in conjunction with a 1/λ scaling relation in broadband radiative forcing simulations of black carbon. © Author(s) 2011.
Kahnert M.,Swedish Meteorological and Hydrological Institute
Atmospheric Chemistry and Physics | Year: 2010
Light absorbing carbon (LAC) aerosols have a complex, fractal-like aggregate structure. Their optical and radiative properties are notoriously difficult to model, and approximate methods may introduce large errors both in the interpretation of aerosol remote sensing observations, and in quantifying the direct radiative forcing effect of LAC. In this paper a numerically exact method for solving Maxwell's equations is employed for computing the optical properties of freshly emitted, externally mixed LAC aggregates. The computations are performed at wavelengths of 440 nm and 870 nm, and they cover the entire size range relevant for modelling these kinds of aerosols. The method for solving the electromagnetic scattering and absorption problem for aggregates proves to be sufficiently stable and fast to make accurate multiple-band computations of LAC optical properties feasible. The results from the electromagnetic computations are processed such that they can readily be integrated into a chemical transport model (CTM), which is a prerequisite for constructing robust observation operators for chemical data assimilation of aerosol optical observations. A case study is performed, in which results obtained with the coupled optics/CTM model are employed as input to detailed radiative transfer computations at a polluted European location. It is found that the still popular homogeneous sphere approximation significantly underestimates the radiative forcing at top of atmosphere as compared to the results obtained with the aggregate model. Notably, the LAC forcing effect predicted with the aggregate model is less than that one obtains by assuming a prescribed mass absorption cross section for LAC.
Kuttippurath J.,University Pierre and Marie Curie |
Nikulin G.,Swedish Meteorological and Hydrological Institute
Atmospheric Chemistry and Physics | Year: 2012
We present an analysis of the major sudden stratospheric warmings (SSWs) in the Arctic winters 2003/04-2009/10. There were 6 major SSWs (major warmings [MWs]) in 6 out of the 7 winters, in which the MWs of 2003/04, 2005/06, and 2008/09 were in January and those of 2006/07, 2007/08, and 2009/10 were in February. Although the winter 2009/10 was relatively cold from mid-December to mid-January, strong wave 1 activity led to a MW in early February, for which the largest momentum flux among the winters was estimated at 60° N/10 hPa, about 450 m 2 s -2. The strongest MW, however, was observed in 2008/09 and the weakest in 2006/07. The MW in 2008/09 was triggered by intense wave 2 activity and was a vortex split event. In contrast, strong wave 1 activity led to the MWs of other winters and were vortex displacement events. Large amounts of Eliassen-Palm (EP) and wave 1/2 EP fluxes (about 2-4 ×10 5 kg s -2) are estimated shortly before the MWs at 100 hPa averaged over 45-75° N in all winters, suggesting profound tropospheric forcing for the MWs. We observe an increase in the occurrence of MWs (∼1.1 MWs/winter) in recent years (1998/99-2009/10), as there were 13 MWs in the 12 Arctic winters, although the long-term average (1957/58-2009/10) of the frequency stays around its historical value (∼0.7 MWs/winter), consistent with the findings of previous studies. An analysis of the chemical ozone loss in the past 17 Arctic winters (1993/94-2009/10) suggests that the loss is inversely proportional to the intensity and timing of MWs in each winter, where early (December-January) MWs lead to minimal ozone loss. Therefore, this high frequency of MWs in recent Arctic winters has significant implications for stratospheric ozone trends in the northern hemisphere. © 2012 Author(s).
Kahnert M.,Swedish Meteorological and Hydrological Institute
Aerosol Science and Technology | Year: 2010
Recent modeling studies based on the Rayleigh-Debye-Gans (RDG) approximation have revealed a discrepancy between modeled and measured mass absorption cross sections (MAC) for atmospheric light absorbing carbon (LAC) aerosols. One plausible explanation is that this discrepancy is due to errors introduced by neglecting electromagnetic interactions among monomers in LAC aggregates within the RDG approximation. Here we compute MAC by use of numerically exact solutions to Maxwell's equations and investigate the sensitivity of the results to a variation in the aggregates' physical properties and refractive index. The results do confirm that approximate methods can introduce large errors in the results for the optical properties. However, these errors alone cannot explain the discrepancy between measured and modeled values of MAC. An agreement between observations and theoretical results can only be attained when assuming a fairly high value of the real and imaginary parts of the refractive index along the void-fraction curve and a mass density not exceeding 1.5-1.7 g/cm3. Copyright © American Association for Aerosol Research.
Norin L.,Swedish Meteorological and Hydrological Institute
Atmospheric Measurement Techniques | Year: 2015
In many countries wind turbines are rapidly growing in numbers as the demand for energy from renewable sources increases. The continued deployment of wind turbines can, however, be problematic for many radar systems, which are easily disturbed by turbines located in the radar line of sight. Wind turbines situated in the vicinity of Doppler weather radars can lead to erroneous precipitation estimates as well as to inaccurate wind and turbulence measurements. This paper presents a quantitative analysis of the impact of a wind farm, located in southeastern Sweden, on measurements from a nearby Doppler weather radar. The analysis is based on 6 years of operational radar data. In order to evaluate the impact of the wind farm, average values of all three spectral moments (the radar reflectivity factor, absolute radial velocity, and spectrum width) of the nearby Doppler weather radar were calculated, using data before and after the construction of the wind farm. It is shown that all spectral moments, from a large area at and downrange from the wind farm, were impacted by the wind turbines. It was also found that data from radar cells far above the wind farm (near 3 km altitude) were affected by the wind farm. It is shown that this in part can be explained by detection by the radar sidelobes and by scattering off increased levels of dust and turbulence. In a detailed analysis, using data from a single radar cell, frequency distributions of all spectral moments were used to study the competition between the weather signal and wind turbine clutter. It is shown that, when weather echoes give rise to higher reflectivity values than those of the wind farm, the negative impact of the wind turbines is greatly reduced for all spectral moments. © Author(s) 2015.
Kahnert M.,Swedish Meteorological and Hydrological Institute
Atmospheric Chemistry and Physics | Year: 2010
The optical properties of externally mixed light absorbing carbon (LAC) aggregates are computed over the spectral range from 200 nmg-12.2 μ/4m by use of the numerically exact superposition T-matrix method. The spectral computations are tailored to the 14-band radiation model employed in the Integrated Forecasting System operated at the European Centre for Medium Range Weather Forecast. The size- and wavelength dependence of the optical properties obtained with the fractal aggregate model differs significantly from corresponding results based on the homogeneous sphere approximation, which is still commonly employed in climate models. The computational results are integrated into the chemical transport model MATCH (Multiple-scale Atmospheric Transport and CHemistry modelling system) to compute 3-D fields of size-averaged aerosol optical properties. Computational results obtained with MATCH are coupled to a radiative transfer model to compute the shortwave radiative impact of LAC. It is found that the fractal aggregate model gives a shortwave forcing estimate that is twice as high as that obtained with the homogeneous sphere approximation. Thus previous estimates based on the homogeneous sphere model may have substantially underestimated the shortwave radiative impact of freshly emitted LAC. © Author(s) 2010.
Hordoir R.,Swedish Meteorological and Hydrological Institute |
Meier H.E.M.,Swedish Meteorological and Hydrological Institute
Climate Dynamics | Year: 2012
The evolution in time of the thermal vertical stratification of the Baltic Sea in future climate is studied using a 3D ocean model. Comparing periods at the end of the twentieth and twenty first centuries we found a strong increase in stratification at the bottom of the mixed layer in the northern Baltic Sea. In order to understand the causes of this increase, a sensitivity analysis is performed. We found that the increased vertical stratification is explained by a major change in re-stratification during spring solely caused by the increase of the mean temperature. As in present climate winter temperatures in the Baltic are often below the temperature of maximum density, warming causes thermal convection. Re-stratification during the beginning of spring is then triggered by the spreading of freshwater. This process is believed to be important for the onset of the spring bloom. In future climate, temperatures are expected to be usually higher than the temperature of maximum density and thermally induced stratification will start without prior thermal convection. Thus, freshwater controlled re-stratification during spring is not an important process anymore. We employed a simple box model and used sensitivity experiments with the 3D ocean model to delineate the processes involved and to quantify the impact of changing freshwater supply on the thermal stratification in the Baltic Sea. It is suggested that these stratification changes may have an important impact on vertical nutrient fluxes and the intensity of the spring bloom in future climate of the Baltic Sea. © 2011 The Author(s).
Koenigk T.,Swedish Meteorological and Hydrological Institute |
Brodeau L.,University of Stockholm
Climate Dynamics | Year: 2014
The ocean heat transport into the Arctic and the heat budget of the Barents Sea are analyzed in an ensemble of historical and future climate simulations performed with the global coupled climate model EC-Earth. The zonally integrated northward heat flux in the ocean at 70°N is strongly enhanced and compensates for a reduction of its atmospheric counterpart in the twenty first century. Although an increase in the northward heat transport occurs through all of Fram Strait, Canadian Archipelago, Bering Strait and Barents Sea Opening, it is the latter which dominates the increase in ocean heat transport into the Arctic. Increased temperature of the northward transported Atlantic water masses are the main reason for the enhancement of the ocean heat transport. The natural variability in the heat transport into the Barents Sea is caused to the same extent by variations in temperature and volume transport. Large ocean heat transports lead to reduced ice and higher atmospheric temperature in the Barents Sea area and are related to the positive phase of the North Atlantic Oscillation. The net ocean heat transport into the Barents Sea grows until about year 2050. Thereafter, both heat and volume fluxes out of the Barents Sea through the section between Franz Josef Land and Novaya Zemlya are strongly enhanced and compensate for all further increase in the inflow through the Barents Sea Opening. Most of the heat transported by the ocean into the Barents Sea is passed to the atmosphere and contributes to warming of the atmosphere and Arctic temperature amplification. Latent and sensible heat fluxes are enhanced. Net surface long-wave and solar radiation are enhanced upward and downward, respectively and are almost compensating each other. We find that the changes in the surface heat fluxes are mainly caused by the vanishing sea ice in the twenty first century. The increasing ocean heat transport leads to enhanced bottom ice melt and to an extension of the area with bottom ice melt further northward. However, no indication for a substantial impact of the increased heat transport on ice melt in the Central Arctic is found. Most of the heat that is not passed to the atmosphere in the Barents Sea is stored in the Arctic intermediate layer of Atlantic water, which is increasingly pronounced in the twenty first century. © 2013 The Author(s).
Rummukainen M.,Swedish Meteorological and Hydrological Institute
Wiley Interdisciplinary Reviews: Climate Change | Year: 2010
Regional climate models are used by a large number of groups, for more or less all regions of the world. Regional climate models are complementary to global climate models. A typical use of regional climate models is to add further detail to global climate analyses or simulations, or to study climate processes in more detail than global models allow. The relationship between global and regional climate models is much akin to that of global and regional weather forecasting models. Over the past 20 years, the development of regional climate models has led to increased resolution, longer model runs, and steps towards regional climate system models. During recent years, community efforts have started to emerge in earnest, which can be expected to further advance the state-of-the-art in regional climate modeling. Applications of regional climate models span both the past and possible future climates, facilitating climate impact studies, information and support to climate policy, and adaptation. © 2010 John Wiley & Sons, Ltd.
News Article | January 26, 2017
Next time you hear "winter is coming," get ready with your vaccine and vitamin C, because that means the flu season will follow shortly. Armed with scientific data from 20,000 virus samples and weather statistics, researchers from Sweden explained the connection between outdoor temperature and influenza outbreaks. The study compared the respiratory incidence from the medical record of patients in the Gothenburg area for three years against the weather reports from the Swedish Meteorological and Hydrological Institute. The researchers discovered that influenza outbreaks consistently begin a week after the first cold spell of winter, when outdoor temperature and humidity are low. "We believe that this sudden drop in temperature contributes to 'kick-start' the epidemic. Once the epidemic has started, it continues even if temperatures rise. Once people are sick and contagious, many more may become infected," said Nicklas Sundell, a researcher at Sahlgrenska Academy and infectious diseases specialist at Sahlgrenska University Hospital. Published in the Journal of Clinical Virology, the results of this study back up the long-standing theory that viruses attached to aerosol particles spread more rapidly during cold and dry season. In dry air, viruses absorb moisture and remain airborne. The weather condition clues can also be used to predict and prevent other known viruses aside from the seasonal flu, such as RS-virus and coronavirus. With this new information, health officials can launch flu vaccine campaigns in advance and prepare emergency wards and hospital staff for a sudden influx of patients affected with the virus. One can experience influenza at different severities. It is usually mild, but can also progress into a serious disease that may lead to death. The most common telltale signs of flu include a fever (although not all who have a flu will have a fever), cough, sore throat, runny nose, stuffy nose, muscle pain, and excessive fatigue. In some cases, especially in children, vomiting and diarrhea are also possible. Typically, recovery from influenza usually takes only a few days to a couple of weeks. However, if the person's flu has led to complications like pneumonia or bronchitis, advanced medical attention is required. Last year, the Centers for Disease Control and Prevention noted a slow but steady rise in reported flu cases for the months of November and early December. Aside from getting your regular flu shots, strengthen your immune system so you don't make an easy target for the flu virus is also a logical strategy. Vitamin C and zinc are some supplements that may help boost your body's flu-fighting ability. "Eat a healthy diet, take regular exercise, and drink plenty of warm drinks in the winter months," Dr. Hasmukh Joshi, vice chair of the Royal College of GPs, recommended. © 2017 Tech Times, All rights reserved. Do not reproduce without permission.