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Willén, Ulrika
Alternative names
Publications (10 of 24) Show all publications
Bennartz, R., Hoschen, H., Picard, B., Schroder, M., Stengel, M., Sus, O., . . . Willén, U. (2017). An intercalibrated dataset of total column water vapour and wet tropospheric correction based on MWR on board ERS-1, ERS-2, and Envisat. Atmospheric Measurement Techniques, 10(4), 1387-1402.
Open this publication in new window or tab >>An intercalibrated dataset of total column water vapour and wet tropospheric correction based on MWR on board ERS-1, ERS-2, and Envisat
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2017 (English)In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 10, no 4, 1387-1402 p.Article in journal (Refereed) Published
National Category
Meteorology and Atmospheric Sciences
Research subject
Remote sensing
Identifiers
urn:nbn:se:smhi:diva-4093 (URN)10.5194/amt-10-1387-2017 (DOI)000399302900001 ()
Available from: 2017-05-11 Created: 2017-05-11 Last updated: 2017-05-11Bibliographically approved
Lauer, A., Eyring, V., Righi, M., Buchwitz, M., Defourny, P., Evaldsson, M., . . . Willén, U. (2017). Benchmarking CMIP5 models with a subset of ESA CCI Phase 2 data using the ESMValTool. Remote Sensing of Environment, 203, 9-39.
Open this publication in new window or tab >>Benchmarking CMIP5 models with a subset of ESA CCI Phase 2 data using the ESMValTool
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2017 (English)In: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 203, 9-39 p.Article in journal (Refereed) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-4459 (URN)10.1016/j.rse.2017.01.007 (DOI)000418464200003 ()
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-01-09Bibliographically approved
Stengel, M., Stapelberg, S., Sus, O., Schlundt, C., Poulsen, C., Thomas, G., . . . Hollmann, R. (2017). Cloud property datasets retrieved from AVHRR, MODIS, AATSR and MERIS in the framework of the Cloud_cci project. Earth System Science Data, 9(2), 881-904.
Open this publication in new window or tab >>Cloud property datasets retrieved from AVHRR, MODIS, AATSR and MERIS in the framework of the Cloud_cci project
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2017 (English)In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 9, no 2, 881-904 p.Article in journal (Refereed) Published
National Category
Remote Sensing
Research subject
Remote sensing
Identifiers
urn:nbn:se:smhi:diva-4451 (URN)10.5194/essd-9-881-2017 (DOI)000416002500001 ()
Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2017-12-12Bibliographically approved
Koenigk, T., Brodeau, L., Graversen, R. G., Karlsson, J., Svensson, G., Tjernstrom, M., . . . Wyser, K. (2013). Arctic climate change in 21st century CMIP5 simulations with EC-Earth. Climate Dynamics, 40(11-12), 2719-2743.
Open this publication in new window or tab >>Arctic climate change in 21st century CMIP5 simulations with EC-Earth
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2013 (English)In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 40, no 11-12, 2719-2743 p.Article in journal (Refereed) Published
Abstract [en]

The Arctic climate change is analyzed in an ensemble of future projection simulations performed with the global coupled climate model EC-Earth2.3. EC-Earth simulates the twentieth century Arctic climate relatively well but the Arctic is about 2 K too cold and the sea ice thickness and extent are overestimated. In the twenty-first century, the results show a continuation and strengthening of the Arctic trends observed over the recent decades, which leads to a dramatically changed Arctic climate, especially in the high emission scenario RCP8.5. The annually averaged Arctic mean near-surface temperature increases by 12 K in RCP8.5, with largest warming in the Barents Sea region. The warming is most pronounced in winter and autumn and in the lower atmosphere. The Arctic winter temperature inversion is reduced in all scenarios and disappears in RCP8.5. The Arctic becomes ice free in September in all RCP8.5 simulations after a rapid reduction event without recovery around year 2060. Taking into account the overestimation of ice in the twentieth century, our model results indicate a likely ice-free Arctic in September around 2040. Sea ice reductions are most pronounced in the Barents Sea in all RCPs, which lead to the most dramatic changes in this region. Here, surface heat fluxes are strongly enhanced and the cloudiness is substantially decreased. The meridional heat flux into the Arctic is reduced in the atmosphere but increases in the ocean. This oceanic increase is dominated by an enhanced heat flux into the Barents Sea, which strongly contributes to the large sea ice reduction and surface-air warming in this region. Increased precipitation and river runoff lead to more freshwater input into the Arctic Ocean. However, most of the additional freshwater is stored in the Arctic Ocean while the total Arctic freshwater export only slightly increases.

Keyword
Arctic climate, Future scenarios, CMIP5, Global coupled atmosphere-ocean modeling, Coupled Arctic climate processes
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-375 (URN)10.1007/s00382-012-1505-y (DOI)000319360800010 ()
Available from: 2015-04-07 Created: 2015-03-31 Last updated: 2017-12-04Bibliographically approved
Ning, T., Elgered, G., Willén, U. & Johansson, J. M. (2013). Evaluation of the atmospheric water vapor content in a regional climate model using ground-based GPS measurements. Journal of Geophysical Research - Atmospheres, 118(2), 329-339.
Open this publication in new window or tab >>Evaluation of the atmospheric water vapor content in a regional climate model using ground-based GPS measurements
2013 (English)In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, no 2, 329-339 p.Article in journal (Refereed) Published
Abstract [en]

Ground-based GPS measurements can provide independent data for the assessment of climate models. We use the atmospheric integrated water vapor (IWV) obtained from GPS measurements at 99 European sites to evaluate the regional Rossby Centre Atmospheric climate model (RCA) driven at the boundaries by the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA Interim). The GPS data were compared to the RCA simulation and the ERA Interim data. The comparison was first made using the monthly mean values. Averaged over the domain and the 14 years covered by the GPS data, IWV differences of about 0.47 kg/m(2) and 0.39 kg/m(2) are obtained for RCA-GPS and ECMWF-GPS, respectively. The RCA-GPS standard deviation is 0.98 kg/m(2) whereas it is 0.35 kg/m(2) for the ECMWF-GPS comparison. The IWV differences for RCA are positively correlated to the differences for ECMWF. However, this is not the case for two sites in Italy where a wet bias is seen for ECMWF, while a dry bias is seen for RCA, the latter being consistent with a cold temperature bias found for RCA in that region by other authors. Comparisons of the estimated diurnal cycle and the spatial structure function of the IWV were made between the GPS data and the RCA simulation. The RCA captures the geographical variation of the diurnal peak in the summer. Averaged over all sites, a peak at 17 local solar time is obtained from the GPS data while it appears later, at 18, in the RCA simulation. The spatial variation of the IWV obtained for an RCA run with a resolution of 11 km gives a better agreement with the GPS results than does the spatial variation from a 50 km resolution run. Citation: Ning, T., G. Elgered, U. Willen, and J. M. Johansson (2013), Evaluation of the atmospheric water vapor content in a regional climate model using ground-based GPS measurements, J. Geophys. Res. Atmos., 118, 329-339, doi: 10.1029/2012JD018053.

National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-392 (URN)10.1029/2012JD018053 (DOI)000317838100007 ()
Available from: 2015-04-02 Created: 2015-03-31 Last updated: 2017-12-04Bibliographically approved
Ning, T., Haas, R., Elgered, G. & Willen, U. (2012). Multi-technique comparisons of 10 years of wet delay estimates on the west coast of Sweden. Journal of Geodesy, 86(7), 565-575.
Open this publication in new window or tab >>Multi-technique comparisons of 10 years of wet delay estimates on the west coast of Sweden
2012 (English)In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 86, no 7, 565-575 p.Article, review/survey (Refereed) Published
Abstract [en]

We present comparisons of 10-year-long time series of the atmospheric zenith wet delay (ZWD), estimated using the global positioning system (GPS), geodetic very long baseline interferometry (VLBI), a water vapour radiometer (WVR), radiosonde (RS) observations, and the reanalysis product of the European Centre for Medium-Range Weather Forecasts (ECMWF). To compare the data sets with each other, a Gaussian filter is applied. The results from 10 GPS-RS comparisons using sites in Sweden and Finland show that the full width at half maximum at which the standard deviation (SD) is a minimum increases with the distance between each pair. Comparisons between three co-located techniques (GPS, VLBI, and WVR) result in mean values of the ZWD differences at a level of a few millimetres and SD of less than 7 mm. The best agreement is seen in the GPS-VLBI comparison with a mean difference of -3.4 mm and an SD of 5.1 mm over the 10-year period. With respect to the ZWD derived from other techniques, a positive bias of up to similar to 7 mm is obtained for the ECMWF reanalysis product. Performing the comparisons on a monthly basis, we find that the SD including RS or ECMWF varies with the season, between 3 and 15 mm. The monthly SD between GPS and WVR does not have a seasonal signature and varies from 3 to 7 mm.

Keyword
Zenith wet delay, GPS, Radiosonde, VLBI, Water vapour radiometer, ECMWF
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-455 (URN)10.1007/s00190-011-0527-2 (DOI)000305466100006 ()
Available from: 2015-04-20 Created: 2015-04-14 Last updated: 2017-12-04Bibliographically approved
Hazeleger, W., Severijns, C., Semmler, T., Stefanescu, S., Yang, S., Wang, X., . . . Willén, U. (2010). EC-Earth A Seamless Earth-System Prediction Approach in Action. Bulletin of The American Meteorological Society - (BAMS), 91(10), 1357-1363.
Open this publication in new window or tab >>EC-Earth A Seamless Earth-System Prediction Approach in Action
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2010 (English)In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 91, no 10, 1357-1363 p.Article in journal, Editorial material (Other academic) Published
National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-555 (URN)10.1175/2010BAMS2877.1 (DOI)000284206300002 ()
Available from: 2015-04-22 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
Soerensson, A. A., Menendez, C. G., Ruscica, R., Alexander, P., Samuelsson, P. & Willén, U. (2010). Projected precipitation changes in South America: a dynamical downscaling within CLARIS. Paper presented at 2nd Lund Regional-Scale Climate Modelling Workshop, MAY 04-08, 2009, Lund, SWEDEN. Meteorologische Zeitschrift, 19(4), 347-355.
Open this publication in new window or tab >>Projected precipitation changes in South America: a dynamical downscaling within CLARIS
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2010 (English)In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 19, no 4, 347-355 p.Article in journal (Refereed) Published
Abstract [en]

Responses of precipitation seasonal means and extremes over South America in a downscaling of a Climate change scenario are assessed with the Rossby Centre Regional Atmospheric Model (RCA). The anthropogenic warming under A1B scenario influences more on the likelihood of occurrence of severe extreme events like heavy precipitation and dry spells than on the mean seasonal precipitation. The risk of extreme precipitation increases in the La Plata Basin with a factor of 1.5-2.5 during all seasons and in the northwestern part of the continent with a factor 1.5-3 in summer, while it decreases in central and northeastern Brazil during winter and spring. The maximum amount of 5-days precipitation increases by up to 50% in La Plata Basin, indicating risks of flooding. Over central Brazil and the Bolivian lowland, where present 5-days precipitation is higher, the increases are similar in magnitude and could cause less impacts. In southern Amazonia, northeastern Brazil and the Amazon basin, the maximum number of consecutive dry days increases and mean winter and spring precipitation decreases, indicating a longer dry season. In the La Plata Basin, there is no clear pattern of change for the dry spell duration.

National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-565 (URN)10.1127/0941-2948/2010/0467 (DOI)000283202700004 ()
Conference
2nd Lund Regional-Scale Climate Modelling Workshop, MAY 04-08, 2009, Lund, SWEDEN
Available from: 2015-04-22 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
Devasthale, A., Willén, U., Karlsson, K.-G. & Jones, C. (2010). Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles. Atmospheric Chemistry And Physics, 10(12), 5565-5572.
Open this publication in new window or tab >>Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles
2010 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 12, 5565-5572 p.Article in journal (Refereed) Published
Abstract [en]

Temperature inversions are one of the dominant features of the Arctic atmosphere and play a crucial role in various processes by controlling the transfer of mass and moisture fluxes through the lower troposphere. It is therefore essential that they are accurately quantified, monitored and simulated as realistically as possible over the Arctic regions. In the present study, the characteristics of inversions in terms of frequency and strength are quantified for the entire Arctic Ocean for summer and winter seasons of 2003 to 2008 using the AIRS data for the clear-sky conditions. The probability density functions (PDFs) of the inversion strength are also presented for every summer and winter month. Our analysis shows that although the inversion frequency along the coastal regions of Arctic decreases from June to August, inversions are still seen in almost each profile retrieved over the inner Arctic region. In winter, inversions are ubiquitous and are also present in every profile analysed over the inner Arctic region. When averaged over the entire study area (70 degrees N-90 degrees N), the inversion frequency in summer ranges from 69 to 86% for the ascending passes and 72-86% for the descending passes. For winter, the frequency values are 88-91% for the ascending passes and 89-92% for the descending passes of AIRS/AQUA. The PDFs of inversion strength for the summer months are narrow and right-skewed (or positively skewed), while in winter, they are much broader. In summer months, the mean values of inversion strength for the entire study area range from 2.5 to 3.9 K, while in winter, they range from 7.8 to 8.9 K. The standard deviation of the inversion strength is double in winter compared to summer. The inversions in the summer months of 2007 were very strong compared to other years. The warming in the troposphere of about 1.5-3.0K vertically extending up to 400 hPa was observed in the summer months of 2007.

National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology; Remote sensing
Identifiers
urn:nbn:se:smhi:diva-583 (URN)10.5194/acp-10-5565-2010 (DOI)000279391100018 ()
Available from: 2015-04-21 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
Soerensson, A. A., Menendez, C. G., Samuelsson, P., Willén, U. & Hansson, U. (2010). Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model. Climatic Change, 98(3-4), 429-447.
Open this publication in new window or tab >>Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model
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2010 (English)In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 98, no 3-4, 429-447 p.Article in journal (Refereed) Published
Abstract [en]

We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993-92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously in subtropical South America as well. Finally, we calculated the soil moisture-precipitation coupling strength through comparing a ten member ensemble forced by the same space-time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture-precipitation coupling strength through comparing a ten member ensemble forced by the same space-time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development.

National Category
Climate Research
Research subject
Climate
Identifiers
urn:nbn:se:smhi:diva-574 (URN)10.1007/s10584-009-9740-x (DOI)000275319100006 ()
Available from: 2015-04-22 Created: 2015-04-20 Last updated: 2017-12-04Bibliographically approved
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