1. |
|
|
2. |
- Chiacchio, Marc, et al.
(författare)
-
Evaluation of the radiation budget with a regional climate model over Europe and inspection of dimming and brightening
- 2015
-
Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 120:5, s. 1951-1971
-
Tidskriftsartikel (refereegranskat)abstract
- Shortwave (SW) and longwave (LW) components of the radiation budget at the surface and top of atmosphere (TOA) are evaluated in the regional climate model RegCM version 4 driven by European Centre for Medium-Range Weather Forecasts Reanalysis over Europe. The simulated radiative components were evaluated with those from satellite-based products and reanalysis. At the surface the model overestimated the absorbed solar radiation but was compensated by a greater loss of thermal energy while both SW and LW TOA net fluxes were underestimated representing too little solar energy absorbed and too little outgoing thermal energy. Averaged biases in radiative parameters were generally within 25 Wm(-2), were dependent on differences by as much as 0.2 in cloud fraction, surface, and planetary albedo and less dependent on surface temperature associated with the surface longwave parameters, and are in line with other studies. Clear-sky fluxes showed better results when cloud cover differences had no influence. We also found a clear distinction between land versus water with smaller biases over land at the surface and over water at the TOA due to differences in cloud fraction and albedo. Finally, we inspected dimming and brightening for the period 1979-2010 with an indication for dimming early in the time series (i.e., 1979-1987) and brightening after, which agrees with surface-based observations. After 2000, however, a decrease in the brightening by more than 1 order of magnitude was evident which is in contrast to the continued brightening found in surface records and satellite-derived estimates.
|
|
3. |
- Fuentes-Franco, Ramón, et al.
(författare)
-
Winter heavy precipitation events over Northern Europe modulated by a weaker NAO variability by the end of the 21st century
- 2023
-
Ingår i: npj Climate and Atmospheric Science. - 2397-3722. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use an ensemble of models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) to analyse the number of days with extreme winter precipitation over Northern Europe and its relationship to the North Atlantic Oscillation (NAO), for the historical period 1950-2014 and two future 21st-century scenarios. Here we find that over Northern Europe, the models project twice more extreme precipitation days by the end of the 21st century under the high-emission scenario compared to the historical period. We also find a weakening of the NAO variability in the second half of the 21st century in the high greenhouse gas emission scenario compared to the historical period, as well as an increasing correlation between extreme winter precipitation events and the NAO index in both future scenarios. Models with a projected decrease in the NAO variability across the 21st century show a positive trend in the number of days with extreme winter precipitation over Northern Europe. These results highlight the role played by NAO in modulating extreme winter precipitation events.
|
|
4. |
- Hesselbjerg Christensen, Jens, et al.
(författare)
-
Weight assignment in regional climate models
- 2010
-
Ingår i: Climate Research. - : Inter-Research Science Center. - 1616-1572 .- 0936-577X. ; 44:2-3, s. 179-194
-
Tidskriftsartikel (refereegranskat)abstract
- An important new development within the European ENSEMBLES project has been to explore performance-based weighting of regional climate models (RCMs). Until now, although no weighting has been applied in multi-RCM analyses, one could claim that an assumption of ‘equal weight’ was implicitly adopted. At the same time, different RCMs generate different results, e.g. for various types of extremes, and these results need to be combined when using the full RCM ensemble. The process of constructing, assigning and combining metrics of model performance is not straightforward. Rather, there is a considerable degree of subjectivity both in the choice of metrics and on how these may be combined into weights. We explore the applicability of combining a set of 6 specifically designed RCM performance metrics to produce one aggregated model weight with the purpose of combining climate change information from the range of RCMs used within ENSEMBLES. These metrics capture aspects of model performance in reproducing large-scale circulation patterns, meso-scale signals, daily temperature and precipitation distributions and extremes, trends and the annual cycle. We examine different aggregation procedures that generate different inter-model spreads of weights. The use of model weights is sensitive to the aggregation procedure and shows different sensitivities to the selected metrics. Generally, however, we do not find compelling evidence of an improved description of mean climate states using performance-based weights in comparison to the use of equal weights. We suggest that model weighting adds another level of uncertainty to the generation of ensemble-based climate projections, which should be suitably explored, although our results indicate that this uncertainty remains relatively small for the weighting procedures examined.
|
|
5. |
- Paeth, Heiko, et al.
(författare)
-
Progress in regional downscaling of west African precipitation
- 2011
-
Ingår i: Atmospheric Science Letters. - : Wiley. - 1530-261X. ; 12:1, s. 75-82
-
Tidskriftsartikel (refereegranskat)abstract
- We review the recent progress in dynamical and statistical downscaling approaches for west African precipitation and perform a regional climate model (RCM) intercomparison using the novel multi-model RCM data set from the Ensembles-based Predictions of Climate Changes and Their Impacts (ENSEMBLES) and African Monsoon Multidisciplinary Analyses (AMMA) projects. Present RCMs have distinct systematic errors in terms of west African precipitation varying in amplitude and pattern across models. This is also reflected in a relatively large spread in projected future precipitation trends. Altogether, the ENSEMBLES RCMs indicate a prevailing drying tendency in sub-Saharan Africa. Statistical post-processing of simulated precipitation is a promising tool to reduce systematic model errors before application in impact studies.
|
|
6. |
- Wu, Jia, et al.
(författare)
-
Changes of effective temperature and cold/hot days in late decades over China based on a high resolution gridded observation dataset
- 2017
-
Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 37:S1, s. 788-800
-
Tidskriftsartikel (refereegranskat)abstract
- © 2017 Royal Meteorological Society The effective temperature (ET) is employed to investigate observed changes of thermal comfort conditions over China during the late decades of the historical observational period. ET considers the aggregate effects of temperature, relative humidity, and wind speed to describe the human thermal sensitivity to weather and climate. The data used in the study is the recently produced gridded daily scale dataset CN05.1, which covers the period of 1961–2014 at a resolution of 0.25° latitude by 0.25° longitude. Results show a general increase of ET in both December-January-February (DJF) and June-July-August (JJA). The increase is mostly caused by an increase of temperature and a decrease of wind speed, while the contribution from relative humidity is small. As measured by ET, China is a cold country with many more cold days than hot days. Large decreases of cold days and increases of hot days are found following the increase of ET. The number of comfortable days shows larger values in the warm areas and during the warm seasons. During the analysis period, the number of annual comfortable days shows an increasing trend when considering the China-wide average. However, the number of annual comfortable days during JJA decreases over warm areas.
|
|