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  • 1. Akinsanola, A. A.
    et al.
    Ajayi, V. O.
    Adejare, A. T.
    Adeyeri, O. E.
    Gbode, I. E.
    Ogunjobi, K. O.
    Nikulin, Grigory
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Abolude, A. T.
    Evaluation of rainfall simulations over West Africa in dynamically downscaled CMIP5 global circulation models2018Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 132, nr 1-2, s. 437-450Artikel i tidskrift (Refereegranskat)
  • 2. Iqbal, W.
    et al.
    Syed, F. S.
    Sajjad, H.
    Nikulin, Grigory
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Kjellström, Erik
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Hannachi, A.
    Mean climate and representation of jet streams in the CORDEX South Asia simulations by the regional climate model RCA42017Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 129, nr 1-2, s. 1-19Artikel i tidskrift (Refereegranskat)
  • 3.
    Josefsson, Weine
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    UV-radiation 1983-2003 measured at Norrkoping, Sweden2006Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 83, nr 1-4, s. 59-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Total ozone has been monitored with high accuracy at many sites for a relative long period of time. This is not the case for UV. The main reason is that UV is difficult to measure accurately. Extensive monitoring started first during the 1990s. However, there are some data series still in operation that were initiated at earlier dates. This paper will discuss one such series from Norrkoping, Sweden that began in March 1983. The instruments used to measure UV radiation have some characteristics producing an output signal that is not directly related to the UV. Here, these problems are discussed and corrections are applied. The goal is to produce a homogenous and an accurate set of UV data as is possible. An analysis of the various sources of uncertainty is done and summarised as total uncertainty. This was found to be about 6% for the yearly values of CIE weighted UV. However, the precision is much better at about 0.6%. Finally, some results are shown for yearly and seasonal UV. The trends for the full period 1983-2003 are tested for significance. The spring, summer, autumn and yearly data showed a significant increase in UV of respectively 0.8, 0.3, 0.8 and 0.5% per year. To get some indication of the cause of the variation of global radiation (indicator of cloudiness) and total ozone measured at the same site were also processed. A small, but insignificant, decrease of total ozone was found, whilst global radiation showed an increase. It seems that cloudiness is the major factor for the observed variation in UV for this period. The data are available on the internet.

  • 4.
    Karlsson, Karl-Göran
    SMHI, Forskningsavdelningen, Atmosfärisk fjärranalys.
    Cloud climate investigations in the Nordic region using NOAA AVHRR data1997Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 57, nr 3-4, s. 181-195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to estimate monthly cloud conditions (monthly cloud frequencies) from multispectral satellite imagery is described. The operational cloud classification scheme SCANDIA (the SMHI Cloud ANalysis model using DIgital AVHRR data), based on high resolution imagery from the polar orbiting NOAA-satellites, has been used to produce monthly cloud frequencies for the entire year of 1993 and some additional months in 1991, 1992, 1994 and 1995. Cloud analyses were made for an area covering the Nordic countries with a horizontal resolution of four km. Examples of seasonal, monthly and diurnal variation in cloud conditions are given and an annual mean for 1993 is presented. Comparisons with existing surface observations showed very good agreement for horizontal cloud distributions but approximately 5% smaller cloud amounts were found in the satellite estimations. The most evident problems were encountered in the winter season due to difficulties in identifying low-level cloudiness at very low sun elevations. The underestimation in the summer season was partly fictious and caused by the overestimation of convective cloud cover by surface observers. SCANDIA results were compared to ISCCP (International Satellite Cloud Climatology Project) cloud climatologies for two selected months in 1991 and 1992. ISCCP cloudiness was indicated to be higher, especially during the month with anticyclonic conditions where a cloudiness excess of more than 10% were found. The regional variation of cloud conditions in the area was found to be inadequately described by ISCCP cloud climatologies. An improvement of the horizontal resolution of ISCCP data seems necessary to enable use for regional applications. The SCANDIA model is proposed as a valuable tool for local and regional monitoring of the cloud climatology at high latitudes. More extensive comparisons with ISCCP cloud climatologies are suggested as well as comparisons with modelled cloudiness from atmospheric general circulation models and climate models. Special studies of cloud conditions in the Polar areas are also proposed.

  • 5. Klutse, Nana Ama Browne
    et al.
    Sylla, Mouhamadou Bamba
    Diallo, Ismaila
    Sarr, Abdoulaye
    Dosio, Alessandro
    Diedhiou, Arona
    Kamga, Andre
    Lamptey, Benjamin
    Ali, Abdou
    Gbobaniyi, Emiola O.
    Owusu, Kwadwo
    Lennard, Christopher
    Hewitson, Bruce
    Nikulin, Grigory
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Panitz, Hans-Juergen
    Buechner, Matthias
    Daily characteristics of West African summer monsoon precipitation in CORDEX simulations2016Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 123, nr 1-2, s. 369-386Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyze and intercompare the performance of a set of ten regional climate models (RCMs) along with the ensemble mean of their statistics in simulating daily precipitation characteristics during the West African monsoon (WAM) period (June-July-August-September). The experiments are conducted within the framework of the COordinated Regional Downscaling Experiments for the African domain. We find that the RCMs exhibit substantial differences that are associated with a wide range of estimates of higher-order statistics, such as intensity, frequency, and daily extremes mostly driven by the convective scheme employed. For instance, a number of the RCMs simulate a similar number of wet days compared to observations but greater rainfall intensity, especially in oceanic regions adjacent to the Guinea Highlands because of a larger number of heavy precipitation events. Other models exhibit a higher wet-day frequency but much lower rainfall intensity over West Africa due to the occurrence of less frequent heavy rainfall events. This indicates the existence of large uncertainties related to the simulation of daily rainfall characteristics by the RCMs. The ensemble mean of the indices substantially improves the RCMs' simulated frequency and intensity of precipitation events, moderately outperforms that of the 95th percentile, and provides mixed benefits for the dry and wet spells. Although the ensemble mean improved results cannot be generalized, such an approach produces encouraging results and can help, to some extent, to improve the robustness of the response of the WAM daily precipitation to the anthropogenic greenhouse gas warming.

  • 6. Perrin, O.
    et al.
    Rootzen, H.
    Taesler, Roger
    SMHI, Forskningsavdelningen.
    A discussion of statistical methods used to estimate extreme wind speeds2006Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 85, nr 3-4, s. 203-215Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Wind speeds in extra-tropical latitudes are known to be approximately Weibull distributed. Hence a Weibull distribution fitted to all available data is often used to predict extreme winds. The most extreme values then, however, have little influence on the estimated parent Weibull distribution, and the accuracy of the extreme value predictions obtained in this manner may be questioned. In the present paper such a "Weibull method" is compared to a method based on statistical extreme value theory, "the annual maxima method". The comparison is based on 30 years of 10 minute wind speed averages measured hourly at 12 meteorological stations located at airports in Sweden. Results show that the Weibull method generates incorrect estimates of the tails of the distributions of wind speeds and of the distribution of yearly maximum wind speed, and that serial dependence of individual measurements has to be taken into account. In addition, it is inherent in the Weibull method that it does not provide any confidence bounds for the estimates. The annual maxima method avoids these problems. The measurements were rounded, first to entire knots, and then to m/s. A further, "technical", result is that if this rounding were disregarded in the estimation procedure, then the computed standard errors of the parameter estimates would be erroneously low. Hence, if rounding is done, it should be taken into account in the estimation procedure. We also believe this to be a clear indication that rounding of the data decreases estimation accuracy.

  • 7.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Internal variability as a cause of qualitative intermodel disagreement on anthropogenic climate changes1999Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 64, nr 1-2, s. 1-13Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The qualitative agreement of two climate models, HADCM2 and ECHAM3, on the response of surface climate to anthropogenic climate forcing in the period 2020-2049 is studied. Special attention is paid to the role of internal climate variability as a source of intermodel disagreement. After illustrating the methods in an intermodel comparison of simulated changes in June-August mean precipitation, some global statistics are presented. Excluding surface air temperature, the four-season mean proportion of areas in which the two models agree on the sign of the climatic response is only 53-60% both for increases in CO2 alone and for increases in CO2 together with direct radiative forcing by sulphate aerosols, but somewhat larger, 59-70% for the separate aerosol effect. In areas where the response is strong (at least twice the standard error associated with internal variability) in both models, the agreement is better and the contrast between the different forcings becomes more marked. The proportion of agreement in such areas is 57-75% for the response to increases in CO2 alone, 64-84% for the response to combined CO2 and aerosol forcing, and as high as 88-94% for the separate aerosol effect. The relatively good intermodel agreement for aerosol-induced climate changes is suggested to be associated with the uneven horizontal distribution of aerosol forcing.

  • 8.
    Wetterhall, Fredrik
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Bardossy, Andras
    Chen, Deliang
    Halldin, Sven
    Xu, Chong-yu
    Statistical downscaling of daily precipitation over Sweden using GCM output2009Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 96, nr 1-2, s. 95-103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A classification of Swedish weather patterns (SWP) was developed by applying a multi-objective fuzzy-rule-based classification method (MOFRBC) to large-scale-circulation predictors in the context of statistical downscaling of daily precipitation at the station level. The predictor data was mean sea level pressure (MSLP) and geopotential heights at 850 (H850) and 700 hPa (H700) from the NCEP/NCAR reanalysis and from the HadAM3 GCM. The MOFRBC was used to evaluate effects of two future climate scenarios (A2 and B2) on precipitation patterns on two regions in south-central and northern Sweden. The precipitation series were generated with a stochastic, autoregressive model conditioned on SWP. H850 was found to be the optimum predictor for SWP, and SWP could be used instead of local classifications with little information lost. The results in the climate projection indicated an increase in maximum 5-day precipitation and precipitation amount on a wet day for the scenarios A2 and B2 for the period 2070-2100 compared to 1961-1990. The relative increase was largest in the northern region and could be attributed to an increase in the specific humidity rather than to changes in the circulation patterns.

  • 9.
    Yang, Wei
    et al.
    SMHI, Forskningsavdelningen, Hydrologi.
    Bardossy, Andras
    Caspary, Hans-Joachim
    Downscaling daily precipitation time series using a combined circulation- and regression-based approach2010Ingår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 102, nr 3-4, s. 439-454Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this paper is to introduce a new conditional statistical model for generating daily precipitation time series. The generated daily precipitation can thus be used for climate change impact studies, e.g., crop production, rainfall-runoff, and other water-related processes. It is a stochastic model that links local rainfall events to a continuous atmospheric predictor, moisture flux, in addition to classified atmospheric circulation patterns. The coupled moisture flux is proved to be capable of capturing continuous property of climate system and providing extra information to determine rainfall probability and rainfall amount. The application was made to simultaneously downscale daily precipitation at multiple sites within the Rhine River basin. The results show that the model can well reproduce statistical properties of daily precipitation time series. Especially for extreme rainfall events, the model is thought to better reflect rainfall variability compared to the pure CP-based downscaling approach.

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