Change search
Refine search result
1 - 8 of 8
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Holtslag, A. A. M.
    et al.
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Baas, P.
    Basu, S.
    Beare, B.
    Beljaars, A. C. M.
    Bosveld, F. C.
    Cuxart, J.
    Lindvall, Jenny
    Stockholm University, Faculty of Science, Department of Meteorology .
    Steeneveld, G. J.
    Tjernström, Michael
    Stockholm University, Faculty of Science, Department of Meteorology .
    Van de Wiel, B. J. H.
    STABLE ATMOSPHERIC BOUNDARY LAYERS AND DIURNAL CYCLES: Challenges for Weather and Climate Models2013In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 94, no 11, p. 1691-1706Article in journal (Refereed)
    Abstract [en]

    The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For this purpose, single-column versions of weather and climate models have been compared with observations, research models, and large-eddy simulations. The intercomparison cases are based on observations taken in the Arctic, Kansas, and Cabauw in the Netherlands. From these studies, we find that even for the noncloudy boundary layer important parameterization challenges remain.

  • 2.
    Lindvall, Jenny
    Stockholm University, Faculty of Science, Department of Meteorology .
    The Representation of Atmospheric Boundary Layer Processes in Global Climate Models2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The atmospheric boundary layer is the lowest part of the atmosphere, which is in direct contact with the surface. It is here, in this turbulent layer, that the exchange of heat, moisture and momentum between the surface and the atmosphere takes place. This thesis examines how well the boundary layer is described in global climate models with particular focus on the representation of the diurnal cycle. Two versions of the Community Atmosphere Model (CAM) that employ different turbulence parameterizations are evaluated in the same model framework. It is found that both overestimate the amplitude of the diurnal cycles of near-surface variables compared to observations from flux tower sites. The 10-m wind is much lower in CAM5 than in CAM4 due to the Turbulent Mountain Stress (TMS) parameterization of subgrid orography in CAM5. Additionally, the diurnal temperature range (DTR) is studied in a large set of models participating in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The model discrepancies are large both in simulations of the present day and in projections of the future. A correlative approach is used to assess which parameters are important for the model differences in DTR. No single parameter is found to be responsible, but clouds play an important role in all seasons and so do the evaporative fraction in summer. The diurnal cycles of these CMIP5 models are also evaluated against flux tower observations. The diurnal cycle of temperature is well captured, while most variables show a large inter-model spread. A subset of the models are analyzed deeper regarding their vertical boundary layer structure for a flux site in Oklahoma. A substantial warm summer bias is revealed in the models. Finally, the impact of TMS and changes in the vertical diffusion in CAM5 is studied. It is found that, although the inclusion of TMS leads to an improved large-scale circulation, the wind turning becomes too strong, which adds to the overestimation of the ageostrophic flow in the boundary layer. Instead, increasing the diffusivity in stable conditions tends to both degrade the large-scale circulation and cause an underestimated wind turning in the boundary layer.

  • 3.
    Lindvall, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    The diurnal temperature range in the CMIP5 models2015In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 44, no 1-2, p. 405-421Article in journal (Refereed)
    Abstract [en]

    This paper analyzes the diurnal temperature range (DTR) over land in simulations of the recent past and in future projections by 20 models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). The annually averaged DTR is evaluated for the present-day climate using two gridded datasets (HadGHCND and CRU). The DTR varies substantially between different CMIP5 models, particularly in the subtropics, and is generally underestimated. In future projections of the high emission scenario RCP8.5, the models disagree on both the sign and the magnitude of the change in DTR. Still, a majority of the models project a globally averaged reduction in the DTR, with an increase over Europe, a decrease over the Sahara desert and a substantial decrease in DTR at high latitudes in winter. The general DTR reduction is partly linked to the enhancement of the downwelling clear sky longwave radiation due to greenhouse gases. At high latitudes in winter, the decrease in DTR seems to be enforced by an increase in cloudiness, but in most other regions counteracted by decreases in cloud fraction. Changes in the hydrological cycle and in the clear sky shortwave radiation also impact the DTR. The DTR integrates many processes and neither the model differences in the DTR nor in the change in DTR can be attributed to a single parameter. Which variables that impact the model discrepancies vary both regionally and seasonally. However, clouds seem to matter in most regions and seasons and the evaporative fraction is important in summer.

  • 4.
    Lindvall, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology .
    The impact of changes in parameterizations of surface drag and vertical diffusion on the large- scale circulation in the Community Atmosphere Model (CAM5)Manuscript (preprint) (Other academic)
  • 5.
    Lindvall, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish e-Science Research Centre, Sweden.
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish e-Science Research Centre, Sweden.
    Caballero, Rodrigo
    Stockholm University, Faculty of Science, Department of Meteorology . Swedish e-Science Research Centre, Sweden.
    The impact of changes in parameterizations of surface drag and vertical diffusion on the large-scale circulation in the Community Atmosphere Model (CAM5)2017In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 48, no 11, p. 3741-3758Article in journal (Refereed)
    Abstract [en]

    Simulations with the Community Atmosphere Model version 5 (CAM5) are used to analyze the sensitivity of the large-scale circulation to changes in parameterizations of orographic surface drag and vertical diffusion. Many GCMs and NWP models use enhanced turbulent mixing in stable conditions to improve simulations, while CAM5 cuts off all turbulence at high stabilities and instead employs a strong orographic surface stress parameterization, known as turbulent mountain stress (TMS). TMS completely dominates the surface stress over land and reduces the near-surface wind speeds compared to simulations without TMS. It is found that TMS is generally beneficial for the large-scale circulation as it improves zonal wind speeds, Arctic sea level pressure and zonal anomalies of the 500-hPa stream function, compared to ERA-Interim. It also alleviates atmospheric blocking frequency biases in the Northern Hemisphere. Using a scheme that instead allows for a modest increase of turbulent diffusion at higher stabilities only in the planetary boundary layer (PBL) appears to in some aspects have a similar, although much smaller, beneficial effect as TMS. Enhanced mixing throughout the atmospheric column, however, degrades the CAM5 simulation. Evaluating the simulations in comparison with detailed measurements at two locations reveals that TMS is detrimental for the PBL at the flat grassland ARM Southern Great Plains site, giving too strong wind turning and too deep PBLs. At the Sodankyla forest site, the effect of TMS is smaller due to the larger local vegetation roughness. At both sites, all simulations substantially overestimate the boundary layer ageostrophic flow.

  • 6.
    Lindvall, Jenny
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hannay, Cecile
    Evaluation of near surface parameters in the two versions of the atmospheric model in cesm1 using flux station observations2013In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 26, no 1, p. 26-44Article in journal (Refereed)
    Abstract [en]

    This paper describes the performance of the Community Atmosphere Model (CAM) versions 4 and 5 in simulating near-surface parameters. CAM is the atmospheric component of the Community Earth System Model (CESM). Most of the parameterizations in the two versions are substantially different, and that is also true for the boundary layer scheme: CAM4 employs a nonlocal K-profile scheme, whereas CAM5 uses a turbulent kinetic energy (TKE) scheme. The evaluation focuses on the diurnal cycle and global observational and reanalysis datasets are used together with multiyear observations from 35 flux tower sites, providing high-frequency measurements in a range of different climate zones. It is found that both model versions capture the timing of the diurnal cycle but considerably overestimate the diurnal amplitude of net radiation, temperature, wind, and turbulent heat fluxes. The seasonal temperature range at mid-and high latitudes is also overestimated with too warm summer temperatures and too cold winter temperatures. The diagnosed boundary layer is deeper in CAM5 over ocean in regions with low-level marine clouds as a result of the turbulence generated by cloud-top cooling. Elsewhere, the boundary layer is in general shallower in CAM5. The two model versions differ substantially in their representation of near-surface wind speeds over land. The low-level wind speed in CAM5 is about half as strong as in CAM4, and the difference is even larger in areas where the subgrid-scale terrain is significant. The reason is the turbulent mountain stress parameterization, only applied in CAM5, which acts to increase the surface stress and thereby reduce the wind speed.

  • 7.
    Pausata, Francesco S. R.
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lindvall, Jenny
    Stockholm University, Faculty of Science, Department of Meteorology .
    Ekman, Annica M. L.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Svensson, Gunilla
    Stockholm University, Faculty of Science, Department of Meteorology .
    Climate effects of a hypothetical regional nuclear war: Sensitivity to emission duration and particle composition2016In: Earth's Future, ISSN 1384-5160, E-ISSN 2328-4277, Vol. 4, no 11, p. 498-511Article in journal (Refereed)
    Abstract [en]

    Here, we use a coupled atmospheric-ocean-aerosol model to investigate the plume development and climate effects of the smoke generated by fires following a regional nuclear war between emerging third-world nuclear powers. We simulate a standard scenario where 5 Tg of black carbon (BC) is emitted over 1 day in the upper troposphere-lower stratosphere. However, it is likely that the emissions from the fires ignited by bomb detonations include a substantial amount of particulate organic matter (POM) and that they last more than 1 day. We therefore test the sensitivity of the aerosol plume and climate system to the BC/POM ratio (1:3, 1:9) and to the emission length (1 day, 1 week, 1 month). We find that in general, an emission length of 1 month substantially reduces the cooling compared to the 1-day case, whereas taking into account POM emissions notably increases the cooling and the reduction of precipitation associated with the nuclear war during the first year following the detonation. Accounting for POM emissions increases the particle size in the short-emission-length scenarios (1 day/1week), reducing the residence time of the injected particle. While the initial cooling is more intense when including POM emission, the long-lasting effects, while still large, may be less extreme compared to the BC-only case. Our study highlights that the emission altitude reached by the plume is sensitive to both the particle type emitted by the fires and the emission duration. Consequently, the climate effects of a nuclear war are strongly dependent on these parameters.

  • 8.
    Svensson, Gunilla
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lindvall, Jenny
    Stockholm University, Faculty of Science, Department of Meteorology .
    Evaluation of near-surface variables and the vertical structure of the boundary layer in CMIP5 modelsManuscript (preprint) (Other academic)
1 - 8 of 8
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf