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Hansson, Ulf
Publications (10 of 18) Show all publications
Strandberg, G., Bärring, L., Hansson, U., Jansson, C., Jones, C., Kjellström, E., . . . Ullerstig, A. (2015). CORDEX scenarios for Europe from the Rossby Centre regional climate model RCA4. SMHI
Open this publication in new window or tab >>CORDEX scenarios for Europe from the Rossby Centre regional climate model RCA4
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2015 (English)Report (Other academic)
Abstract [sv]

Denna rapport dokumenterar klimatmodellsimuleringar på 50 km horisontell upplösning över Europa med Rossby Centres regionala atmosfärsmodell (RCA4) gjorda inom projektet Coordinated Regional Downscaling Experiment (CORDEX) för i) ERAInterim-drivna (ERAINT) simuleringar för att utvärdera förmågan hos RCA4 att simuleraden senaste tidens klimat, ii) historiska simuleringar av de senaste årtiondena med drivning från nio olika globala klimatmodeller (GCM:er) och iii) framtidsscenarierna RCP 4,5 och RCP 8,5 drivna med samma GCM:er. Dessa simuleringar representerar en delmängd av alla CORDEX-simuleringar producerade vid Rossby Centre och en allmän slutsats dragen vid Rossby Centre är att en sådan ensemble inte varit möjlig utan att först etablera den effektiva produktionskedja som beskrivs här. Första delen av rapporten dokumenterar RCA4 och dess förmåga i en simulering där ERAINT skalades ner. RCA4 återskapar till stor del den storskaliga cirkulationen från ERAINT, men några lokala avvikelser förekommer. I allmänhet simuleras säsongscykler för temperatur och nederbörd i överensstämmelse med observationer. Några avvikelser finns, som för mycket nederbörd i norra Europa och för lite i södra. På vintern är det även för mycket nederbörd i östra Europa. Temperaturen är i allmänhet underskattad i norra Europa och i medelhavsområdet på vintern, medan för höga temperaturer ges i sydöstra Europa på vintern och i medelhavsområdet på sommaren. RCA4 presterar i allmänhet bra i simuleringar av den senaste tidens klimat med randvillkor från GCM:er. En stor del av det simulerade klimatet i RCA4 kan tillskrivas den drivande GCM:en, men RCA4 skapar sitt eget klimat inuti modelldomänen och lägger till detaljer på grund av högre upplösning. Alla nio nedskalade GCM:er har gemensamma problem i representationen av den storskaliga cirkulationen på vintern. Denna egenskap förs vidare till RCA4. Avvikelserna i storskalig cirkulation medför avvikelser i temperatur och nederbörd i RCA4. Klimatförändringssignalen som den simuleras av RCA4-ensembler enligt RCP 4,5 och RCP 8,5 är mycket lika tidigare resultat. I både scenario RCP 4,5 och RCP 8,5 beräknas Europa bli varmare i framtiden. På vintern är uppvärmningen störst i norra Europa, och på sommaren i södra Europa. Den högsta dygnsmedeltemperaturen på sommaren ökar på ungefär samma sätt som sommartemperaturen, men något mer i södra Europa. Den lägsta dygnsmedeltemperaturen på vintern i norra Europa är den temperatur som förändras mest. Nederbörden beräknas öka under alla årstider i norra Europa och minska i södra Europa. Den största dygnsnederbörden (och per sjudagarsperiod) beräknas öka i nästan hela Europa och i alla årstider. Samtidigt beräknas den längsta perioden utan nederbörd att bli längre i södra Europa. I allmänhet förutses små förändringar i medelvindhastighet. Det finns emellertid områden med signifikanta förändringar i vind. Att använda ensembler är ett sätt att beskriva osäkerheterna i scenarierna, men det finns andra möjliga ensembler som använder andra modeller och som skulle ge andra resultat. Ändå anses den ensemble som används här vara tillräckligt lik dessa andra ensembler för att vara representativ för den hela mängden GCM:er. Dynamisk nedskalning med RCA4 förändrar klimatförändringssignalen, och spridningen i ensemblen minskar ibland, men ensemblen med nio RCA4 simuleringar med olika GCM:er anses vara representativ för den hela ensemblen. Alla scenarier är överens om mönstret på klimatförändringen, men storleken på förändringen bestäms av valet av scenario. Den relativa betydelsen av valet av scenario ökar med tiden.

Abstract [en]

This report documents Coordinated Regional Downscaling Experiment (CORDEX) climate model simulations at 50 km horizontal resolution over Europe with the Rossby Centre regional atmospheric model (RCA4) for i) a ERA-Interim-driven (ERAINT) simulation used to evaluate model performance in the recent past climate, ii) historical simulations of the recent decades with forcing from nine different global climate models (GCMs) and iii) future scenarios RCP 4.5 and RCP 8.5 forced by the same nine different GCMs. Those simulations represent a subset of all CORDEX simulations produced at the Rossby Centre and a general conclusion drawn at the Rossby Centre is that such large ensembles could not have been produced without the establishment of an efficient production chain as outlined here. The first part of this report documents RCA4 and its performance in a perfect boundary simulation where ERAINT was downscaled. RCA4 is to a large extent replicating the large-scale circulation in ERAINT, but some local biases in mean sea level pressure appear. In general the seasonal cycles of temperature and precipitation are simulated in relatively close agreement to observations. Some biases occur, such as too much precipitation in northern Europe and too little in the south. In winter, there is also too much precipitation in eastern Europe. Temperatures are generally biased low in northern Europe and in the Mediterranean region in winter while overestimated temperatures are seen in southeastern Europe in winter and in the Mediterranean area in summer. RCA4 performs generally well when simulating the recent past climate taking boundary conditions from the GCMs. A large part of the RCA4 simulated climate is attributed to the driving GCMs, but RCA4 creates its own climate inside the model domain and adds details due to higher resolution. All nine downscaled GCMs share problems in their representation of the large-scale circulation in winter. This feature is inherited in RCA4. The biases in large-scale circulation induce some biases in temperature and precipitation in RCA4. The climate change signal in the RCP 4.5 and RCP 8.5 ensembles simulated by RCA4 is very similar to what has been presented previously. Both scenarios RCP 4.5 and RCP 8.5 project Europe to be warmer in the future. In winter the warming is largest in northern Europe and in summer in southern Europe. The summer maximum daily temperature increases in a way similar to summer temperature, but somewhat more in southern Europe. The winter minimum daily temperature in northern Europe is the temperature that changes the most. Precipitation is projected to increase in all seasons in northern Europe and decrease in southern Europe. The largest amount of rainfall per day (and per seven day period) is projected to increase in almost all of Europe and in all seasons. At the same time the longest period without precipitation is projected to be longer in southern Europe. Small changes in mean wind speed are generally projected. There are, however, regions with significant changes in wind. The ensemble approach is a way to describe the uncertainties in the scenarios, but there are other possible ensembles using other models which would give other results. Still, the ensemble used here is found to be similar enough to these other possible ensembles to be representative of the whole set of GCMs. Dynamical downscaling using RCA4 changes the climate change signal, and the ensemble spread is sometimes reduced, but the ensemble of nine RCA4 simulations, using different GCMs, is considered to be representative of the full ensemble. All scenarios agree on a climate change pattern; the amplitude of the change is determined by the choice of scenario. The relative importance of the chosen scenario increases with time.

Place, publisher, year, edition, pages
SMHI, 2015. p. 75
Series
RMK: Report Meteorology and Climatology, ISSN 0347-2116 ; 116
Identifiers
urn:nbn:se:smhi:diva-2839 (URN)Meteorologi, Klimat, Rapporter, Serie RMK (Local ID)Meteorologi, Klimat, Rapporter, Serie RMK (Archive number)Meteorologi, Klimat, Rapporter, Serie RMK (OAI)
Available from: 2015-06-16 Created: 2016-07-08 Last updated: 2016-07-08Bibliographically approved
Thomas, M. A., Kahnert, M., Andersson, C., Kokkola, H., Hansson, U., Jones, C., . . . Devasthale, A. (2015). Integration of prognostic aerosol-cloud interactions in a chemistry transport model coupled offline to a regional climate model. Geoscientific Model Development, 8(6), 1885-1898
Open this publication in new window or tab >>Integration of prognostic aerosol-cloud interactions in a chemistry transport model coupled offline to a regional climate model
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2015 (English)In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 6, p. 1885-1898Article in journal (Refereed) Published
Abstract [en]

To reduce uncertainties and hence to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol-cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model (RCA4) with ERA-Interim lateral boundaries and sea surface temperature (SST) using the standard cloud droplet number concentration (CDNC) formulation (hereafter, referred to as the 'stand-alone RCA4 version' or 'CTRL' simulation). In the stand-alone RCA4 version, CDNCs are constants distinguishing only between land and ocean surface. The meteorology from this simulation is then used to drive the chemistry transport model, Multiple-scale Atmospheric Transport and Chemistry (MATCH), which is coupled online with the aerosol dynamics model, Sectional Aerosol module for Large Scale Applications (SALSA). CDNC fields obtained from MATCH-SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as 'MOD' simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH-SALSA. Simulations are carried out with this model setup for the period 2005-2012 over Europe, and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analysed. Our study shows substantial improvements in cloud microphysical properties with the input of the MATCH-SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model setup improves the spatial, seasonal and vertical distribution of CDNCs with a higher concentration observed over central Europe during boreal summer (JJA) and over eastern Europe and Russia during winter (DJF). Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 mu m, whereas in the stand-alone version the values reached only 5 mu m. A substantial improvement in the distribution of the cloud liquid-water paths (CLWP) was observed when compared to the satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the boreal summer months. The median and standard deviation values from the 'MOD' simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by -5 W m(-2) over the domain selected in the study. The TOA net fluxes from the 'MOD' simulation show a better agreement with the retrievals from the Clouds and the Earth's Radiant Energy System (CERES) instrument. The aerosol indirect effects are estimated in the 'MOD' simulation in comparison to the pre-industrial aerosol emissions (1900). Our simulations estimated the domain averaged annual mean total radiative forcing of -0.64 W m(-2) with a larger contribution from the first indirect aerosol effect (-0.57 W m(-2)) than from the second indirect aerosol effect (-0.14 W m(-2)).

National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-1972 (URN)10.5194/gmd-8-1885-2015 (DOI)000357125000019 ()
Available from: 2016-04-26 Created: 2016-03-03 Last updated: 2017-11-30Bibliographically approved
Kjellström, E., Nikulin, G., Hansson, U., Strandberg, G. & Ullerstig, A. (2011). 21st century changes in the European climate: uncertainties derived from an ensemble of regional climate model simulations. Tellus. Series A, Dynamic meteorology and oceanography, 63(1), 24-40
Open this publication in new window or tab >>21st century changes in the European climate: uncertainties derived from an ensemble of regional climate model simulations
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2011 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 24-40Article in journal (Refereed) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-3807 (URN)10.1111/j.1600-0870.2010.00475.x (DOI)000285309200003 ()
Available from: 2016-12-09 Created: 2016-12-09 Last updated: 2017-11-29Bibliographically approved
Nikulin, G., Kjellström, E., Hansson, U., Strandberg, G. & Ullerstig, A. (2011). Evaluation and future projections of temperature, precipitation and wind extremes over Europe in an ensemble of regional climate simulations. Tellus. Series A, Dynamic meteorology and oceanography, 63(1), 41-55
Open this publication in new window or tab >>Evaluation and future projections of temperature, precipitation and wind extremes over Europe in an ensemble of regional climate simulations
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2011 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 41-55Article in journal (Refereed) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-3808 (URN)10.1111/j.1600-0870.2010.00466.x (DOI)000285309200004 ()
Available from: 2016-12-09 Created: 2016-12-09 Last updated: 2017-11-29Bibliographically approved
Samuelsson, P., Jones, C., Willén, U., Ullerstig, A., Gollvik, S., Hansson, U., . . . Wyser, K. (2011). The Rossby Centre Regional Climate Model RCA3: Model description and performance. Tellus. Series A, Dynamic meteorology and oceanography, 63A(1), 4-23
Open this publication in new window or tab >>The Rossby Centre Regional Climate Model RCA3: Model description and performance
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2011 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63A, no 1, p. 4-23Article in journal (Refereed) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4521 (URN)10.1111/j.1600-0870.2010.00478.x (DOI)
Available from: 2018-03-16 Created: 2018-03-16 Last updated: 2018-03-16Bibliographically approved
Samuelsson, P., Jones, C., Willén, U., Ullerstig, A., Gollvik, S., Hansson, U., . . . Wyser, K. (2011). The Rossby Centre Regional Climate model RCA3: model description and performance. Tellus. Series A, Dynamic meteorology and oceanography (1), 4-23
Open this publication in new window or tab >>The Rossby Centre Regional Climate model RCA3: model description and performance
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2011 (English)In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, no 1, p. 4-23Article in journal (Refereed) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4543 (URN)10.1111/j.1600-0870.2010.00478.x (DOI)
Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-03-20Bibliographically approved
Kjellström, E., Nikulin, G., Hansson, U., Strandberg, G. & Ullerstig, A. (2010). 21st century changes in the Nordic climate: 8ncertainties derived from an ensemble of regional climate model simulations. In: : . Paper presented at Conference on Future climate and renewable energy:Impacts, risks and adaptation, Oslo, 31 May – 2 June 2010. (pp. 72-73).
Open this publication in new window or tab >>21st century changes in the Nordic climate: 8ncertainties derived from an ensemble of regional climate model simulations
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2010 (English)Conference paper, Published paper (Other academic)
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4568 (URN)
Conference
Conference on Future climate and renewable energy:Impacts, risks and adaptation, Oslo, 31 May – 2 June 2010.
Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2018-04-19Bibliographically approved
Nikulin, G., Kjellström, E., Hansson, U., Strandberg, G. & Ullerstig, A. (2010). European weather extremes as simulated by the Rossby Centre Regional Climate Model. In: Geophysical Research Abstracts: . Paper presented at EGU General Assembly 2010. , 12, Article ID EGU2010-4204.
Open this publication in new window or tab >>European weather extremes as simulated by the Rossby Centre Regional Climate Model
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2010 (English)In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-4204Conference paper, Published paper (Refereed)
National Category
Climate Research
Research subject
Climate; Climate
Identifiers
urn:nbn:se:smhi:diva-4574 (URN)
Conference
EGU General Assembly 2010
Available from: 2018-04-23 Created: 2018-04-23 Last updated: 2018-04-23Bibliographically approved
Nikulin, G., Kjellström, E., Hansson, U., Jones, C., Strandberg, G. & Ullerstig, A. (2010). Nordic weather extremes as simulated by the Rossby Centre Regional Climate Model: model evaluation and future projections. In: : . Paper presented at Conference of Future climate and renewable energy Impacts, risks and adaptation, Oslo, 31 May – 2 June 2010.  (pp. 24-25).
Open this publication in new window or tab >>Nordic weather extremes as simulated by the Rossby Centre Regional Climate Model: model evaluation and future projections
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2010 (English)Conference paper, Published paper (Other academic)
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4566 (URN)
Conference
Conference of Future climate and renewable energy Impacts, risks and adaptation, Oslo, 31 May – 2 June 2010. 
Available from: 2018-04-10 Created: 2018-04-10 Last updated: 2018-04-19Bibliographically approved
Kjellström, E., Nikulin, G., Hansson, U., Strandberg, G. & Ullerstig, A. (2010). Seasonal mean temperature, precipitation and wind speed in Europe from an ensemble of 16 transient RCM simulations for 1961-2100. In: Geophysical Research Abstracts: . Paper presented at EGU General Assembly 2010. , 12, Article ID EGU2010-10229.
Open this publication in new window or tab >>Seasonal mean temperature, precipitation and wind speed in Europe from an ensemble of 16 transient RCM simulations for 1961-2100
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2010 (English)In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-10229Conference paper, Published paper (Refereed)
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4573 (URN)
Conference
EGU General Assembly 2010
Available from: 2018-04-23 Created: 2018-04-23 Last updated: 2018-04-23Bibliographically approved
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