| 1. |
- Azorin-Molina, Cesar, et al.
(författare)
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Biases in wind speed measurements due to anemometer changes
- 2023
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Ingår i: Atmospheric Research. - 0169-8095. ; 289
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Tidskriftsartikel (refereegranskat)abstract
- This research presents a case study of the biases and discontinuities that were introduced in observed long-term mean wind-speed and gust data-series due to anemometer changes in a meteorological station in northern Spain, operated by the Spanish State Meteorological Agency: San Sebastian-Igueldo. Field and wind-tunnel experiments with predefined conditions have been presented in the literature, however this research uses a real case study to assess the impact of anemometer changes on wind speed measurements due to three factors being: (i) the 3-cup anemometer model (SEAC vs. THIES companies); (ii) sensor height (∼19.95 m vs. ∼20.45 m) and (iii) sensor age (20-years old vs. new). Our results show (a) substantial biases in the measured wind speed and daily peak wind gusts, with the new THIES anemometer reporting stronger surface winds than the old SEAC anemometer; (b) opposing biases under weak (negative) and moderate-strong (positive) winds; and (c) significant breakpoints in the long-term wind data-series, which highlight the importance of data homogenization. National Weather Services and climate assessment groups will benefit from these findings since errors in wind speed and gust measurements can be minimized by implementing systematic observation protocols. Robust anemometer observations provide a basis for accurate quantification of the magnitude of changes and the variability of surface winds.
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| 2. |
- Azorin-Molina, Cesar, et al.
(författare)
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Evaluating anemometer drift: A statistical approach to correct biases in wind speed measurement
- 2018
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Ingår i: Atmospheric research. - : Elsevier BV. - 0169-8095. ; 203, s. 175-188
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies on observed wind variability have revealed a decline (termed “stilling”) of near-surface wind speed during the last 30–50 years over many mid-latitude terrestrial regions, particularly in the Northern Hemisphere. The well-known impact of cup anemometer drift (i.e., wear on the bearings) on the observed weakening of wind speed has been mentioned as a potential contributor to the declining trend. However, to date, no research has quantified its contribution to stilling based on measurements, which is most likely due to lack of quantification of the ageing effect. In this study, a 3-year field experiment (2014–2016) with 10-minute paired wind speed measurements from one new and one malfunctioned (i.e., old bearings) SEAC SV5 cup anemometer which has been used by the Spanish Meteorological Agency in automatic weather stations since mid-1980s, was developed for assessing for the first time the role of anemometer drift on wind speed measurement. The results showed a statistical significant impact of anemometer drift on wind speed measurements, with the old anemometer measuring lower wind speeds than the new one. Biases show a marked temporal pattern and clear dependency on wind speed, with both weak and strong winds causing significant biases. This pioneering quantification of biases has allowed us to define two regression models that correct up to 37% of the artificial bias in wind speed due to measurement with an old anemometer.
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| 3. |
- Azorin-Molina, Cesar, et al.
(författare)
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Recent trends in wind speed across Saudi Arabia, 1978-2013: a break in the stilling
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- We analyse recent trends and variability of observed near-surface wind speed from 19 stations across Saudi Arabia (SA) for 1978-2013. The raw wind speed data set was subject to a robust homogenization protocol, and the stations were then classified under three categories: (1) coast, (2) inland and (3) mountain stations. The results reveal a statistically significant (p<0.05) reduction of wind speed of -0.058m s(-1) dec(-1) at annual scale across SA, with decreases in winter (-0.100m s(-1) dec(-1)) and spring (-0.066m s(-1) dec(-1)) also detected, being non-significant in summer and autumn. The coast, inland and mountain series showed similar magnitude and significance of the declining trends across all SA series, except for summer when a decoupled variability and opposite trends of wind speed between the coast and inland series (significant declines: -0.101m s(-1) dec(-1) and -0.065m s(-1) dec(-1), respectively) and the high-elevation mountain series (significant increase: +0.041m s(-1) dec(-1)) were observed. Even though wind speed declines dominated across much of the country throughout the year, only a small number of stations showed statistically significant negative trends in summer and autumn. Most interestingly, a break in the stilling was observed in the last 12-year (2002-2013) period (+0.057m s(-1) dec(-1); not significant) compared to the significant slowdown detected in the previous 24-year (1978-2001) period (-0.089m s(-1) dec(-1)). This break in the slowdown of winds, even followed by a non-significant recovery trend, occurred in all seasons (and months) except for some winter months. Atmospheric circulation plays a key role in explaining the variability of winds, with the North Atlantic Oscillation positively affecting the annual wind speed, the Southern Oscillation displaying a significant negative relationship with winds in winter, spring and autumn, and the Eastern Atlantic negatively modulating winds in summer.
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| 4. |
- Azorin-Molina, Cesar, et al.
(författare)
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Wind speed variability over the Canary Islands, 1948–2014: focusing on trend differences at the land–ocean interface and below–above the trade-wind inversion layer
- 2018
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 50:11-12, s. 4061-4081
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Tidskriftsartikel (refereegranskat)abstract
- This study simultaneously examines wind speed trends at the land–ocean interface, and below–above the trade-wind inversion layer in the Canary Islands and the surrounding Eastern North Atlantic Ocean: a key region for quantifying the variability of trade-winds and its response to large-scale atmospheric circulation changes. Two homogenized data sources are used: (1) observed wind speed from nine land-based stations (1981–2014), including one mountain weather station (Izaña) located above the trade-wind inversion layer; and (2) simulated wind speed from two atmospheric hindcasts over ocean (i.e., SeaWind I at 30 km for 1948–2014; and SeaWind II at 15 km for 1989–2014). The results revealed a widespread significant negative trend of trade-winds over ocean for 1948–2014, whereas no significant trends were detected for 1989–2014. For this recent period wind speed over land and ocean displayed the same multi-decadal variability and a distinct seasonal trend pattern with a strengthening (late spring and summer; significant in May and August) and weakening (winter–spring–autumn; significant in April and September) of trade-winds. Above the inversion layer at Izaña, we found a predominance of significant positive trends, indicating a decoupled variability and opposite wind speed trends when compared to those reported in boundary layer. The analysis of the Trade Wind Index (TWI), the North Atlantic Oscillation Index (NAOI) and the Eastern Atlantic Index (EAI) demonstrated significant correlations with the wind speed variability, revealing that the correlation patterns of the three indices showed a spatio-temporal complementarity in shaping wind speed trends across the Eastern North Atlantic.
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| 5. |
- Kaiqiang, Deng, et al.
(författare)
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Changes of Southern Hemisphere westerlies in the future warming climate
- 2022
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Ingår i: Atmospheric Research. - : Elsevier BV. - 0169-8095. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- The Southern Hemisphere westerlies (SHWs) play a key role in regulating global climate and ocean circulation, but their future changes under low to high greenhouse gas forcings remain unclear. This study investigates the long-term trends in strength and position of the SHWs and their linkage with human activities, based on the ERA5 reanalysis and model simulations from the Coupled Model Intercomparison Project phase 6 (CMIP6). The results show that the SHWs have intensified and shifted poleward in the recent decades, and are projected to experience divergent trends in strength and position during the 21st century under different Shared Socioeconomic Pathway (SSP) scenarios. Forced by SSP245, 370, and 585, which represent the middle to high greenhouse gas forcings, the SHWs will continue to strengthen and move southward in 2015–2099, with the largest trends induced by SSP585. Nevertheless, forced by SSP126, which implies a low greenhouse gas forcing in the future, the ongoing trends in strength and position of the SHWs will be interrupted and even reversed. Further investigation reveals that the anthropogenic forcing could have affected and will likely influence the SHWs by modulating meridional atmospheric circulation in the Southern Hemisphere. In particular, the Southern Annular Mode and the tropical Pacific convection play crucial roles in the changes of SHWs. This study links human activities to the changes in SHWs, providing important implications for climate change and its mitigation. © 2022 The Authors
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| 6. |
- Kaiqiang, Deng, et al.
(författare)
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Global Near-Surface Wind Speed Changes over the Last Decades Revealed by Reanalyses and CMIP6 Model Simulations
- 2021
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Ingår i: Journal of Climate. - 0894-8755 .- 1520-0442. ; 34:6, s. 2219-2234
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Tidskriftsartikel (refereegranskat)abstract
- Near-surface (10 m) wind speed (NWS) plays a crucial role in many areas, including hydrological cycles, wind energy production, and air pollution, but what drives its multidecadal changes is still unclear. Using reanalysis datasets and model simulations from phase 6 of the Coupled Model Intercomparison Projection (CMIP6), this study investigates recent trends in the annual mean NWS. The results show that the Northern Hemisphere (NH) terrestrial NWS experienced significant (p < 0.1) decreasing trends during 1980–2010, when the Southern Hemisphere (SH) ocean NWS was characterized by significant (p < 0.1) upward trends. However, during 2010–19, global NWS trends shifted in their sign: NWS trends over the NH land became positive, and trends over the SH tended to be negative. We propose that the strengthening of SH NWS during 1980–2010 was associated with an intensified Hadley cell over the SH, while the declining of NH land NWS could have been caused by changes in atmospheric circulation, alteration of vegetation and/or land use, and the accelerating Arctic warming. The CMIP6 model simulations further demonstrate that the greenhouse gas (GHG) warming plays an important role in triggering the NWS trends over the two hemispheres during 1980–2010 through modulating meridional atmospheric circulation. This study also points at the importance of anthropogenic GHG forcing and the natural Pacific decadal oscillation to the long-term trends and multidecadal variability in global NWS, respectively.
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| 7. |
- Kaiqiang, Deng, et al.
(författare)
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Shifting of summertime weather extremes in Western Europe during the last decade
- 2022
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Ingår i: Advances in Climate Change Research. - : Elsevier BV. - 1674-9278. ; 13:2, s. 218-227
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Tidskriftsartikel (refereegranskat)abstract
- Over the past decades, droughts and heatwaves frequently appeared in Western Europe (45°–65°N, 10°W–20°E) during boreal summer, causing huge impacts on human society and ecosystems. Although these extremes are projected to increase in both frequency and intensity under a warming climate, our knowledge of their interdecadal variations and causes is relatively limited. Here we show that the droughts and heatwaves in Western Europe have shifted in their trends in the last decade: for 1979–2012, wind speed and precipitation have both strengthened in Western Europe; for 2012–2020, however, Western Europe have experienced declined wind speed, decreased precipitation, and higher air temperature, leading to more frequent droughts and heatwaves there. Recent changes in the WE climate and extremes are related to the variations of the North Atlantic westerly jet stream. In 1979–2012 (2012–2020), the westerly jet stream shifted equatorward (poleward), which enhanced (reduced) transportation of water vapor fluxes from the North Atlantic Ocean to the European land areas, resulting in wetter (drier) surface in Western Europe. Further analysis suggests that phase changes in the Pacific Decadal Oscillation could have played a key role in regulating the position of the jet stream, providing important implications for decadal predictions of the Western Europe summertime climate and weather extremes. © 2022 The Authors
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| 8. |
- Kaiqiang, Deng, et al.
(författare)
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Terrestrial Stilling Projected to Continue in the Northern Hemisphere Mid-Latitudes
- 2022
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Ingår i: Earths Future. - : American Geophysical Union (AGU). - 2328-4277. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- The near-surface wind speed over land has declined in recent decades, a trend known as terrestrial stilling (TS). However, recent studies have indicated a reversal of the TS during the last decade, triggering renovated interest in the future wind speed changes. This study examines the TS over the Northern Hemisphere (NH) land areas and explores its future changes under Model Inter-comparison Projection Phase 6 Shared Socioeconomic Pathways (SSP) scenarios. The results show that the NH mid-latitude TS will likely continue during the whole 21st century under mid-to-high greenhouse warmings (SSPs-245, 370, and 585). Nevertheless, if the world reduces carbon emissions substantially (SSP-126), the TS will be interrupted and likely reversed after the mid-21st century. The projected TS shows seasonal differences, with the largest (smallest) decreasing trends of wind speed in boreal summer (winter). Moreover, the TS reversal during the last decade is suggested as a multi-decadal fluctuation related to the Pacific and Atlantic multi-decadal oscillations. In addition, this study proposes that increased upper-air warming in the future climate could play a key role in reducing the NH mid-latitude surface wind speed. The continuing TS provides strong implications for the near-surface environment and wind energy development, particularly for countries in the NH mid-latitudes.
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| 9. |
- Minola, Lorenzo
(författare)
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Changes in near-surface winds across Sweden over the past decades - Observations and simulations
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Driven by a combination of anthropogenic activities and climate changes, near- surface terrestrial winds displayed a large decrease in their magnitude in the past decades, named “stilling”, and a recent recovery in their slowdown. Understanding how wind has changed and identifying the factors behind the observed variabilities is crucial so that reasonable future wind scenarios can be constructed. In this way, adaptation strategies can be developed to increase society’s resilience to the plausible future wind climate. This is particularly important for Sweden, which is largely vulnerable to changes in mean wind speed conditions and to the occurrence of extreme winds. Therefore, this thesis investigates past variations in near-surface winds across Sweden and explores the mechanisms behind their variabilities and changes. This is done by using the first homogenized dataset of in-situ observations and by analyzing current simulations of wind gusts. Results show that, during the past decades, both observed mean and gust wind speed underwent nonlinear changes, driven by the dominant winter variability. In particular, consistent with the stilling-reversal phenomena, the significant stilling ceased in 2003, followed by no clear trend afterwards. The detected stilling-reversal is linked to large- scale atmospheric circulation changes, in particular to the North Atlantic Oscillation, and the intensity changes of extratropical cyclones passing across Sweden. The comparison with reanalysis outputs reveals that, in addition to the large-scale interannual variability, changes in surface roughness (e.g. changes in forest cover) have most likely contributed to the observed wind change across Sweden. Moreover, this thesis finds that current regional climate models and reanalyses do not have adequate skills in simulating past wind gusts across inland and mountain regions. Major improvements are achieved when the elevation differences are considered in the formulation of the gust parametrization and the convective gust contribution is adjusted according to the observed climatology. The presented work advances the understanding of how surface winds change in a warmer climate at high midlatitudes and improves the model forecasting of wind gustiness over Sweden.
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| 10. |
- Minola, Lorenzo, et al.
(författare)
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Climatology of Near-Surface Daily Peak Wind Gusts Across Scandinavia: Observations and Model Simulations
- 2021
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Ingår i: Journal of Geophysical Research: Atmospheres. - 2169-897X. ; 126:7
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Tidskriftsartikel (refereegranskat)abstract
- An observed daily peak wind gusts (DPWG) dataset over Scandinavia, consisting of time series from 127 meteorological stations across Finland, Norway and Sweden, has been created. This dataset provides high-quality and homogenized near-surface DPWG series for Scandinavia, spanning the longest available time period (1996–2016). The aim of this study is to evaluate the ability of two regional climate models (RCMs) in simulating DPWG winds. According to the observed DPWG climatology, meteorological stations are classified into three regions for which wind conditions are influenced by similar physical processes: coast, inland and mountain. Smaller-scale DPWG features of the three regions are only captured when coarser general circulation models or reanalyses are downscaled by a RCM. Dynamic downscaling is thus needed to achieve more realistic simulations of DPWG when compared to their driving models. The performances of the RCMs are found to be more dependent on model dynamics and physics (such as gust parametrization) than on the boundary conditions provided by the driving models. We also found that the RCMs cannot accurately simulate observed DPWG in inland and mountainous areas, suggesting the need for higher horizontal resolution and/or better representation of relevant boundary-layer processes. © 2021. The Authors.
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