| 1. |
- Ades, M., et al.
(författare)
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GLOBAL CLIMATE
- 2020
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Ingår i: BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY. - 0003-0007 .- 1520-0477. ; 101:8
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Corell, D., et al.
(författare)
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Influences of synoptic situation and teleconnections on fog-water collection in the Mediterranean Iberian Peninsula, 2003-2012
- 2020
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 40:7, s. 3297-3317
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Tidskriftsartikel (refereegranskat)abstract
- Fog-water collection has been widely analysed for its quantification and potential uses; however, there are few studies assessing the synoptic conditions and large-scale teleconnection patterns that affect its occurrence. Focusing on the Mediterranean Iberian Peninsula, this work aims to analyse the synoptic patterns, both at surface level and 850 hPa geopotential height, that most likely to favour fog-water collection, and to quantify the relationship between fog-water collection and the NAOi (North Atlantic Oscillation index), MOi (Mediterranean Oscillation index) as well as WeMOi (Western Mediterranean Oscillation index) teleconnection patterns. For this purpose, daily fog-water observations from a dense network of 23 fog-water collectors located along the Mediterranean Iberian Peninsula for 2003-2012 were analysed in relation to synoptic patterns and the three-teleconnection indices. The major findings are: (a) The most favourable synoptic patterns for fog-water collection are maritime advections carrying humidity from the Mediterranean basin, and cyclonic circulations, whereas anti-cyclonic situations generally led to large number of foggy days with low fog-collection rates. (b) In terms of winds at 850 hPa, the most favourable low-level flows for fog-water collection are associated with strong winds (>5.1 m s(-1)) from the Mediterranean. Atlantic winds generally cause a greater number of fog days than Mediterranean winds, with less fog-water collection rates. (c) WeMOi has the greatest influence on fog-water collection, mainly during winter and spring months, with statistically significant negative relationships for most of the stations. MOi also shows a great influence, with a large number of statistically significant negative correlations, mainly during the same months as WeMOi. Lastly, NAOi presented the lowest and no significant negative correlations with fog-water collection.
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| 3. |
- Minola, Lorenzo, et al.
(författare)
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Near-surface mean and gust wind speeds in ERA5 across Sweden: towards an improved gust parametrization
- 2020
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 55:3-4, s. 887-907
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Tidskriftsartikel (refereegranskat)abstract
- The ERA5 reanalysis product has been compared with hourly near-surface wind speed and gust observations across Sweden for 2013-2017. ERA5 shows closer agreement than the previous ERA-Interim reanalysis with regard to both mean wind speed and gust measurements, although significant discrepancies are still found for inland and mountainous regions. Therefore, attempts have been made to improve formulations of the gust parametrization used in ERA5 by adding an elevation-dependency and by adjusting the convective gust contribution. Major improvements, especially over mountain regions, are achieved when the elevation differences among the stations are considered. Closer agreement between the observed and parametrized gusts is reached when the convective gust contribution is also tuned. The newly designed gust parametrization was also tested for Norway, which is characterized by more complex topography. Wind gusts from the selected Norwegian stations are more realistically simulated when both the elevation-dependency and the tuned convective contribution are implemented, although the parametrized gusts are still negatively biased. Such biases are not explained by the different in gust duration in recorded wind gusts between Sweden and Norway.
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| 4. |
- Navarro-Serrano, F., et al.
(författare)
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Maximum and minimum air temperature lapse rates in the Andean region of Ecuador and Peru
- 2020
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418 .- 1097-0088. ; 40:4, s. 6150-68
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Tidskriftsartikel (refereegranskat)abstract
- To know the vertical distribution of air temperature is complex, and this is necessary for different applications. The main explanatory variable of air temperature is elevation above sea level, whose relationship with air temperature is measured by air temperature lapse rates (LRs). LRs can vary considerably spatiotemporally due to a wide spectrum of geographical, environmental, and other atmospheric factors. Our study presents the first comprehensive assessment of spatiotemporal changes of LRs over the Tropical Andes. Our study is focused on the Peruvian and Ecuadorian Andes, divided in two subregions by the parallel 9.5 degrees (i.e., north and south). Maximum and minimum air temperatures were employed from 115 quality checked weather stations, for the period 1994-2011. Maximum (LRmax) and minimum (LRmin) air temperature lapse rates have been calculated for the whole study period. The effects of seasonality, humidity content and ENSO on the variability of LRs have been analysed. Results show that LRs have large spatiotemporal variability, since references values of LRmax range from -3.57 (South, dry season) to -4.77 (North, wet season), and LRmin range from -3.78 (North, dry season) to -4.93 degrees C center dot km(-1) (South, dry season), in function of season and subregion. Results indicate that the ENSO phases contribute significantly to the variability of southern subregion LRs. This study also presents that minimum air temperatures were more unpredictable than maximum air temperatures in terms of error and uncertainty, as a consequence of the larger spatial variability of nocturnal air temperatures, mainly influenced by local topography. In conclusion, this work goes deeper into the need to obtain precise LRs adapted to the study region, and shows that the use of standard LR values can cause significant failures in modelling air temperature in regions of complex terrain, such as the Andes.
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| 5. |
- Pirooz, A. A. S., et al.
(författare)
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Effects of sensor response and moving average filter duration on maximum wind gust measurements
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 206
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Tidskriftsartikel (refereegranskat)abstract
- The use of wind speed data recorded using different measuring equipment (i.e. anemometers with different response characteristics) and different signal-processing procedures can introduce errors in the characterisation of surface wind speeds. This study aims to assess the effects of a set of various moving average filter durations and turbulence intensities on the recorded maximum gust wind speeds. For this purpose, a series of wind-tunnel experiments was carried out on the widely-used Vaisala WAA151 cup anemometer. The variations of gust and peak factors, and turbulence intensities measured by the cup anemometer as a function of the averaging duration and turbulence intensity are presented. The wind-tunnel results are compared with values computed from a theoretical approach, namely random process and linear system theory, and the results were also validated against values reported in the literature where possible. The results show that the maximum gust wind speeds measured using large averaging durations (e.g. 3 s or 5 s) lead to up to 25%-30% negative biases compared to high frequency measurements (e.g. 4 Hz unfiltered gust measurements). This result can strongly impact subsequent meteorological, climatological and wind engineering studies, as different gust definitions have been adopted by National Weather Services and institutions around the world. Lastly, a set of correction factors (i.e. gust factor ratios) have been proposed that allows measurements at a specific gust duration to be converted to equivalent measurements at specified particular gust durations of interest.
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| 6. |
- Vicente-Serrano, S. M., et al.
(författare)
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Vegetation greening in Spain detected from long term data (1981-2015)
- 2020
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 41:5, s. 1709-1740
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Tidskriftsartikel (refereegranskat)abstract
- This study describes a newly developed high-resolution (1.1 km) Normalized Difference Vegetation Index dataset for the peninsular Spain and the Balearic Islands (Sp_1km_NDVI). This dataset is developed based on National Oceanic and Atmospheric Administration–Advanced Very High Resolution Radiometer (NOAA–AVHRR) afternoon images, spanning the past three decades (1981–2015). After a careful pre-processing procedure, including calibration with post-launch calibration coefficients, geometric and topographic corrections, cloud removal, temporal filtering, and bi-weekly composites by maximum NDVI-value, we assessed changes in vegetation greening over the study domain using Mann-Kendall and Theil-Sen statistics. Our trend results were compared with those derived from some widely recognized global NDVI datasets [e.g. the Global Inventory Modelling and Mapping Studies 3rd generation (GIMMS3g), Smoothed NDVI (SMN) and Moderate-Resolution Imaging Spectroradiometer (MODIS)]. Results demonstrate that there is a good agreement between the annual trends based on Sp_1km_NDVI product and other datasets. Nonetheless, we found some differences in the spatial patterns of the NDVI trends at the seasonal scale. Overall, in comparison to the available global NDVI datasets, Sp_1km_NDVI allows for characterizing changes in vegetation greening at a more-detailed spatial and temporal scale. In specific, our dataset provides relatively long-term corrected satellite time series (>30 years), which are crucial to understand the response of vegetation to climate change and human-induced activities. Also, given the complex spatial structure of NDVI changes over the study domain, particularly due to the rapid land intensification processes, the spatial resolution (1.1 km) of our dataset can provide detailed spatial information on the inter-annual variability of vegetation greening in this Mediterranean region and assess its links to climate change and variability.
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| 7. |
- Zhang, Gangfeng, et al.
(författare)
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Variability of Daily Maximum Wind Speed across China, 1975–2016: An Examination of Likely Causes
- 2020
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 33:7, s. 2793-2816
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Tidskriftsartikel (refereegranskat)abstract
- Assessing change in daily maximum wind speed and its likely causes is crucial for many applications such as wind power generation and wind disaster risk governance. Multidecadal variability of observed near-surface daily maximum wind speed (DMWS) from 778 stations over China is analyzed for 1975–2016. A robust homogenization protocol using the R package Climatol was applied to the DMWS observations. The homogenized dataset displayed a significant (p < 0.05) declining trend of −0.038 m s−1 decade−1 for all China annually, with decreases in winter (−0.355 m s−1 decade−1, p < 0.05) and autumn (−0.108 m s−1 decade−1; p < 0.05) and increases in summer (+0.272 m s−1 decade−1, p < 0.05) along with a weak recovery in spring (+0.032 m s−1 decade−1; p > 0.10); that is, DMWS declined during the cold semester (October–March) and increased during the warm semester (April–September). Correlation analysis of the Arctic Oscillation, the Southern Oscillation, and the west Pacific modes exhibited significant correlation with DMWS variability, unveiling their complementarity in modulating DMWS. Further, we explored potential physical processes relating to the atmospheric circulation changes and their impacts on DMWS and found that 1) overall weakened horizontal airflow [large-scale mean horizontal pressure gradient (from −0.24 to +0.02 hPa decade−1) and geostrophic wind speed (from −0.6 to +0.6 m s−1 decade−1)], 2) widely decreased atmospheric vertical momentum transport [atmospheric stratification thermal instability (from −3 to +1.5 decade−1) and vertical wind shear (from −0.4 to +0.2 m s−1 decade−1)], and 3) decreased extratropical cyclones frequency (from −0.3 to 0 month decade−1) are likely causes of DMWS change.
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