322 research outputs found
Extratropical transition and characteristics of storm Mauri in September 1982
An intense storm named Mauri swept over Lapland, Finland on the 22nd of September 1982 causing 3 Mm3 forest damage and two fatalities. There were thoughts that Mauri originated from a category 4 hurricane Debby but the linkage between Debby and Mauri and their connection to climatic conditions have not been investigated before.
In this thesis, a climatic overview of September 1982 in comparison to 1981-2010 Septembers is provided. The calculations are based on ERA-Interim reanalysis data produced by European Centre for Medium-Range Weather Forecasts. The track of the storm is determined from ERA-Interim data from the time Debby occurred until Mauri crossed Finland. The evolution of Debby is also presented with the storm track data by National Oceanic and Atmospheric Administration to comparison. Extratropical transition (ET) and phase diagram of Debby and the synoptic evolution of Mauri are examined. ET is defined to start when the cyclone loses a symmetric hurricane eye feature to form asymmetric fronts, and ET is completed when the warm core of the storm turns cold. A comparison between Mauri and two other intense storms that have affected Europe is briefly presented.
It was discovered, that Debby completed ET before rapidly crossing the North Atlantic. However, near the UK ex-Debby started to lose its cold core and asymmetric structure typical to an extratropical cyclone. Ex-Debby phased back to warm cored while crossing Sweden, and at the same time it was rapidly deepening up to 27 hPa in 24 hours defining the storm as a meteorological bomb. Ex-Debby developed a frontal structure along a pre-existing cold front before hitting Lapland. It merged with the pre-existing low pressure center from the Norwegian Sea and proceeded right ahead of an upper trough, a region for cyclogenesis. These made the storm, now named Mauri, more intense as it crossed Lapland, and led to 30 m/s winds based on Finnish Meteorological Institute. Meanwhile, an occluded bent-back front approached Mauri, wrapped around the storm trapping the warmer air inside it and formed a warm seclusion. Due to that, Mauri regained the symmetric structure before reaching the Barents Sea.
Examining the climatic aspect, positive surface pressure and temperature anomalies over central Europe caused the jet stream to shift northward. Also, positive NAO and AO phases changed the storm track in general to higher latitudes. Hence, climatic conditions favoured the storm track to move more north.
The results of this thesis suggested that Mauri was the remnant of a hurricane Debby. It was shown that ERA-Interim was successful in locating the evolution of a cyclone and analysing its structure whereas it underestimated the surface pressure and wind speed values. Future work is still needed, for instance comparing these results to different reanalyses and collecting a statistic examination of hurricane originated storms in Europe, in order to adapt these methods and climatic indicators to future cases and storm predictions.Raju Mauri-myrsky iski Lappiin 22.9.1982 aiheuttaen 3 Mm3 metsÀvauriot ja kaksi kuolonuhria. Maurin ajateltiin olevan perÀisin 4-luokan Debby-hurrikaanista, mutta Debbyn ja Maurin vÀlistÀ linkkiÀ sekÀ yhteyksiÀ ilmastollisiin olosuhteisiin ei ole tutkittu aiemmin.
TÀssÀ työssÀ verrattiin syyskuun 1982 ilmastollisia oloja vuosien 1981-2010 syyskuihin. Laskelmat perustuvat Euroopan keskipitkien sÀÀennusteiden keskuksen tuottamaan ERA-Interim-uusanalyysiin. ERA-Interimin myrskyrata on tehty Debbyn esiintymisestÀ Maurin Suomen ylitykseen saakka. Vertailun vuoksi Debbyn reitti on esitetty myös Yhdysvaltain liittovaltion sÀÀ- ja valtamerentutkimus-organisaation myrskyradan avulla. TyössÀ tarkasteltiin hurrikaani-Debbyn muuntumista keskileveys-asteiden matalapaineeksi sekÀ Mauri-myrskyn synoptista kehittymistÀ. Muuntuminen mÀÀriteltiin alkamaan myrskyn menettÀessÀ hurrikaanin silmÀn symmetrisyyden muodostaessa rintamarakenteen, ja muuntuminen pÀÀttyy myrskyn ytimen muuttuessa lÀmpimÀstÀ kylmÀksi. Mauria verrattiin myös kahteen muuhun voimakkaaseen, Euroopassa vaikuttaneeseen myrskyyn.
TyössÀ selvitettiin, ettÀ Debby muuntui keskileveysasteiden matalapaineeksi ennen kuin se ylitti nopeasti Pohjois-Atlantin. LÀhellÀ Englantia ex-Debby alkoi kuitenkin menettÀÀ keskileveysasteiden myrskyille tyypillistÀ kylmÀn ytimen ja epÀsymmetrisyyden rakennetta. Ex-Debby muuntui takaisin lÀmminytimiseksi ylittÀessÀÀn Ruotsia samalla nopeasti syventyen jopa 27hPa/vrk mÀÀrittÀen myrskyn meteorologiseksi pommiksi. Ex-Debby muodosti rintamarakenteen jo olemassa olevaan kylmÀÀn rintamaan ennen iskemistÀÀn Lappiin. Se yhdistyi NorjanmerellÀ olevan toisen matalapaineen keskuksen kanssa ja eteni ylÀsolan edelle, joka syventÀÀ pintamatalapainetta. NÀmÀ voimistivat myrskyÀ entisestÀÀn, kun se kulki Lapin yli ja nimettiin Mauriksi, ja johtivat Ilmatieteen laitoksen havaintojen mukaan 30 m/s tuulen nopeuksiin. TÀllöin taaksetaipunut okluusiorintama lÀhestyi Mauria, kiertyi sen ympÀrille vangiten lÀmpimÀmmÀn ilman myrskyn keskuksen sisÀÀn ja muodosti lÀmpimÀn sekluusion. TÀmÀn johdosta Mauri sai takaisin symmetrisen rakenteen ennen ajautumistaan Barentsinmerelle.
Ilmastollista nÀkökulmaa tutkiessa saatiin selville, ettÀ positiiviset pintapaine- ja lÀmpötila-anomaliat keski-Euroopan yllÀ aiheuttivat suihkuvirtauksen siirtymisen pohjoisemmaksi. Myös positiiviset NAO- ja AO-vaiheet muuttivat myrskyrataa yleisesti korkeammille leveys-asteille. NÀin ollen ilmastolliset olosuhteet suosivat myrskyradan siirtymistÀ pohjoisemmaksi.
Työn tulokset viittaavat siihen, ettĂ€ Mauri oli Debby-hurrikaanin jÀÀnne. ERA-Interim onnistui matalapaineen paikantamisessa, sen kehityskulun seuraamisessa ja myrskyn rakenteen tarkastelussa, kun se taas aliarvioi myrskyn pintapaineen ja âtuulen arvot. Tulevaisuudessa tĂ€mĂ€n työn tuloksia voisi verrata eri uusanalyyseihin, ja Euroopan hurrikaaniperĂ€isistĂ€ myrskyistĂ€ olisi hyvĂ€ kerĂ€tĂ€ tilastollinen tarkastelu, jotta tĂ€mĂ€n työn menetelmiĂ€ ja ilmastollisia mittareita voisi soveltaa tulevaisuuden myrskytapauksiin ja sÀÀennusteisiin
The Extratropical Transition of Hurricane Debby (1982) and the Subsequent Development of an Intense Windstorm over Finland
On 22 September 1982, an intense windstorm caused considerable damage in northern Finland. Local forecasters noted that this windstorm potentially was related to Hurricane Debby, a category 4 hurricane that occurred just 5 days earlier. Due to the unique nature of the event and lack of prior research, our aim is to document the synoptic sequence of events related to this storm using ERA-Interim reanalysis data, best track data, and output from OpenIFS simulations. During extratropical transition, the outflow from Debby resulted in a ridge building and an acceleration of the jet. Debby did not reintensify immediately in the midlatitudes despite the presence of an upper-level trough. Instead, ex-Debby propagated rapidly across the Atlantic as a diabatic Rossby wave-like feature. Simultaneously, an upper-level trough approached from the northeast and once ex-Debby moved ahead of this feature near the United Kingdom, rapid reintensification began. All OpenIFS forecasts diverged from reanalysis after only 2 days indicating intrinsic low predictability and strong sensitivities. Phasing between Hurricane Debby and the weak trough, and phasing of the upper- and lower-level potential vorticity anomalies near the United Kingdom was important in the evolution of ex-Debby. In the only OpenIFS simulation to correctly capture the phasing over the United Kingdom, stronger wind gusts were simulated over northern Finland than in any other simulation. Turbulent mixing behind the cold front, and convectively driven downdrafts in the warm sector, enhanced the wind gusts over Finland. To further improve understanding of this case, we suggest conducting research using an ensemble approach.Peer reviewe
Winds and windstorms in northern Europe and Finland
Strong winds can cause large impacts and damage to society. Many sectors, such as wind energy, forestry and insurance, are highly affected by winds. Thus, preparedness and adaptation to winds and windstorms is essential in both weather (days) and climate (decades) time scales. The aim of this thesis is to better understand the near surface mean and extreme wind climate in northern Europe and Finland and the role of extratropical cyclones in contributing to the extreme winds.
This thesis investigated the main characteristics of wind and windstorm climate in northern Europe and Finland over a 40-year period. The wind and windstorm climate was found to have large inter-annual and decadal variability and no significant linear trends. The well-known seasonal cycle was detected: winds in northern Europe are up to 30 % stronger in winter than in summer and while there are on average 5â6 windstorms per month in winter in northern Europe there are none in summer months. A more surprising result was that the number of all extratropical cyclones does not vary between seasons. Windstorms were found to be the most frequent over the Barents Sea whereas weaker extratropical cyclones occur over the land areas in northern Europe.
The development and structure of strong winds in windstorms in northern Europe and Finland were examined. The results show that the strongest wind gusts associated with windstorms shift and extend from the warm sector to behind the cold front during the evolution. The cold-season (OctâMar) windstorms are overall stronger and spatially larger than warm-season (AprâSep) windstorms. For example, the central pressure is on average 9 hPa deeper and the maximum wind gust 2 ms-1 stronger in cold-season windstorms than in warm-season windstorms. Analysing a case study of storm Mauri, a damaging windstorm in Finland in September 1982, shows that an individual windstorm development can vary largely from the climateâs general concept. The case study also found that during storm Mauri the wind speeds over land areas in Finland are underestimated in the weather model by 2â13 ms-1 compared to observations, but the location of strong winds is correctly predicted.
Lastly, this thesis investigated what meteorological factors affect the intensity of windstorms in northern Europe. This was studied by using an ensemble sensitivity method. The sensitivities of windstorm intensity to all studied meteorological factors were 20â75 % higher in the cold season than in the warm season. This implies that cold season windstorms are potentially better predictable than warm-season windstorms. The strongest impact to the intensity of northern Europe windstorms is from the low-level temperature gradient which is therefore an important variable to follow when forecasting windstorms. The results from this thesis highlight the importance of examining long-term inter-annual variations, instead of just linear trends, to get a broader understanding of the climate. Moreover, the results emphasize the need of both general conceptual models and individual case studies to better understand the large variety of windstorm development paths.Voimakkaat tuulet voivat aiheuttaa vaikutuksia ja tuhoja yhteiskunnalle. Tuulisuus vaikuttaa moniin aloihin, kuten tuulienergia-, metsĂ€- ja vakuutussektoreihin. Varautuminen ja sopeutuminen tuuliin ja myrskyihin ovat nĂ€in ollen tĂ€rkeitĂ€ sekĂ€ sÀÀn (pĂ€iviĂ€) ettĂ€ ilmaston (vuosikymmeniĂ€) aikaskaaloissa. TĂ€mĂ€n vĂ€itöskirjan tavoitteena on ymmĂ€rtÀÀ paremmin maanpinnan lĂ€heisten keski- ja ÀÀrituulten ilmastoa Pohjois-Euroopassa ja Suomessa sekĂ€ keskileveysasteiden matalapaineiden roolia ÀÀrituulten aiheuttajana.
TĂ€ssĂ€ vĂ€itöskirjassa tutkittiin Pohjois-Euroopan ja Suomen tuuli- ja myrskyilmaston tyypillisiĂ€ piirteitĂ€ 40 vuoden jaksolta. Tuuli- ja myrskyilmastolle havaittiin tyypilliseksi suuri vuosien ja vuosikymmenien vĂ€linen vaihtelu ilman merkitseviĂ€ pitkĂ€najan trendejĂ€. Tutkimuksessa osoitettiin tiedetty kausivaihtelu: tuulet ovat Pohjois Euroopassa jopa 30 % voimakkaampia talvella kuin kesĂ€llĂ€, ja talvikuukausina Pohjois-Euroopassa esiintyy keskimÀÀrin 5â6 myrskyĂ€ kuukaudessa kun taas kesĂ€kuukausina ei yhtÀÀn. YllĂ€ttĂ€vĂ€mpi tulos oli, ettĂ€ kaikkien matalapaineiden mÀÀrĂ€ssĂ€ ei löydetty kausittaista vaihtelua. MyrskyjĂ€ havaittiin esiintyvĂ€n eniten Barentsin meren yllĂ€ kun taas heikommat matalapaineet esiintyvĂ€t Pohjois-Euroopan maa-alueilla.
TyössĂ€ tutkittiin Pohjois-Euroopan myrskyihin liittyvien voimakkaiden tuulten kehittymistĂ€ ja rakennetta. Tulokset osoittavat, ettĂ€ voimakkaimmat myrskyihin liittyvĂ€t puuskat siirtyvĂ€t ja leviĂ€vĂ€t lĂ€mpimĂ€stĂ€ sektorista kylmĂ€n rintaman taakse myrskyn kehittymisen aikana. KylmĂ€n vuodenajan (lokaâmaaliskuu) myrskyt ovat yleisesti voimakkaampia ja alueellisesti laajempia kuin lĂ€mpimĂ€n vuodenajan (huhtiâsyyskuu) myrskyt. Esimerkiksi myrskyn minimipaine on keskimÀÀrin 9 hPa matalampi ja maksimipuuska 2 ms-1 voimakkaampi kylmĂ€nĂ€ kuin lĂ€mpimĂ€nĂ€ vuodenaikana. Tapaustutkimus Mauri-myrskystĂ€, tuhoisasta myrskystĂ€ Suomessa 22.9.1982, osoittaa, ettĂ€ yksittĂ€isen myrskyn kehitys voi poiketa suuresti ilmaston yleisestĂ€ kehitysmallista. Tapaustutkimuksessa selvisi myös, ettĂ€ sÀÀmalli aliarvioi Suomen maa-alueilla Mauri-myrskyn tuulennopeuksia 2â13 ms-1 havaintoihin verrattuna, mutta voimakkaiden tuulten sijainnit on ennustettu oikein.
ViimeisimpĂ€nĂ€ vĂ€itöskirjassa tutkittiin mitkĂ€ meteorologiset tekijĂ€t vaikuttavat myrskyn voimakkuuteen Pohjois Euroopassa. TĂ€tĂ€ tutkittiin kĂ€yttĂ€mĂ€llĂ€ nk. parviherkkyysmenetelmÀÀ. Myrskyn voimakkuuden herkkyydet kaikkiin tutkittuihin meteorologisiin tekijöihin olivat 20â75 % korkeampia kylmĂ€nĂ€ kuin lĂ€mpimĂ€nĂ€ vuodenaikana. TĂ€mĂ€ viittaa siihen, ettĂ€ kylmĂ€n vuodenajan myrskyt ovat potentiaalisesti paremmin ennustettavissa kuin lĂ€mpimĂ€n vuodenajan myrskyt. Pohjois-Euroopan myrskyjen voimakkuuteen vaikuttaa eniten alailmakehĂ€n vaakasuuntainen lĂ€mpötilaero, joka tĂ€ten on tĂ€rkeĂ€ seurattava muuttuja myrskyjĂ€ ennustettaessa.
TÀmÀn vÀitöskirjan tulokset korostavat tÀrkeyttÀ tarkastella pitkÀnajan vuosien vÀlistÀ vaihtelua pelkkien lineaaristen trendien sijaan, jotta ilmastoa ymmÀrrettÀisiin laajemmin. LisÀksi tulokset korostavat tarvetta sekÀ yleisille kÀsitemalleille ettÀ yksitÀisille tapaustutkimuksille, jotta myrskyjen moninaisia kehityspolkuja ymmÀrrettÀisiin paremmin
Winds and windstorms in northern Europe and Finland
Strong winds can cause large impacts and damage to society. Many sectors, such as wind energy, forestry and insurance, are highly affected by winds. Thus, preparedness and adaptation to winds and windstorms is essential in both weather (days) and climate (decades) time scales. The aim of this thesis is to better understand the near surface mean and extreme wind climate in northern Europe and Finland and the role of extratropical cyclones in contributing to the extreme winds.
This thesis investigated the main characteristics of wind and windstorm climate in northern Europe and Finland over a 40-year period. The wind and windstorm climate was found to have large inter-annual and decadal variability and no significant linear trends. The well-known seasonal cycle was detected: winds in northern Europe are up to 30 % stronger in winter than in summer and while there are on average 5â6 windstorms per month in winter in northern Europe there are none in summer months. A more surprising result was that the number of all extratropical cyclones does not vary between seasons. Windstorms were found to be the most frequent over the Barents Sea whereas weaker extratropical cyclones occur over the land areas in northern Europe.
The development and structure of strong winds in windstorms in northern Europe and Finland were examined. The results show that the strongest wind gusts associated with windstorms shift and extend from the warm sector to behind the cold front during the evolution. The cold-season (OctâMar) windstorms are overall stronger and spatially larger than warm-season (AprâSep) windstorms. For example, the central pressure is on average 9 hPa deeper and the maximum wind gust 2 ms-1 stronger in cold-season windstorms than in warm-season windstorms. Analysing a case study of storm Mauri, a damaging windstorm in Finland in September 1982, shows that an individual windstorm development can vary largely from the climateâs general concept. The case study also found that during storm Mauri the wind speeds over land areas in Finland are underestimated in the weather model by 2â13 ms-1 compared to observations, but the location of strong winds is correctly predicted.
Lastly, this thesis investigated what meteorological factors affect the intensity of windstorms in northern Europe. This was studied by using an ensemble sensitivity method. The sensitivities of windstorm intensity to all studied meteorological factors were 20â75 % higher in the cold season than in the warm season. This implies that cold season windstorms are potentially better predictable than warm-season windstorms. The strongest impact to the intensity of northern Europe windstorms is from the low-level temperature gradient which is therefore an important variable to follow when forecasting windstorms. The results from this thesis highlight the importance of examining long-term inter-annual variations, instead of just linear trends, to get a broader understanding of the climate. Moreover, the results emphasize the need of both general conceptual models and individual case studies to better understand the large variety of windstorm development paths.Voimakkaat tuulet voivat aiheuttaa vaikutuksia ja tuhoja yhteiskunnalle. Tuulisuus vaikuttaa moniin aloihin, kuten tuulienergia-, metsĂ€- ja vakuutussektoreihin. Varautuminen ja sopeutuminen tuuliin ja myrskyihin ovat nĂ€in ollen tĂ€rkeitĂ€ sekĂ€ sÀÀn (pĂ€iviĂ€) ettĂ€ ilmaston (vuosikymmeniĂ€) aikaskaaloissa. TĂ€mĂ€n vĂ€itöskirjan tavoitteena on ymmĂ€rtÀÀ paremmin maanpinnan lĂ€heisten keski- ja ÀÀrituulten ilmastoa Pohjois-Euroopassa ja Suomessa sekĂ€ keskileveysasteiden matalapaineiden roolia ÀÀrituulten aiheuttajana.
TĂ€ssĂ€ vĂ€itöskirjassa tutkittiin Pohjois-Euroopan ja Suomen tuuli- ja myrskyilmaston tyypillisiĂ€ piirteitĂ€ 40 vuoden jaksolta. Tuuli- ja myrskyilmastolle havaittiin tyypilliseksi suuri vuosien ja vuosikymmenien vĂ€linen vaihtelu ilman merkitseviĂ€ pitkĂ€najan trendejĂ€. Tutkimuksessa osoitettiin tiedetty kausivaihtelu: tuulet ovat Pohjois Euroopassa jopa 30 % voimakkaampia talvella kuin kesĂ€llĂ€, ja talvikuukausina Pohjois-Euroopassa esiintyy keskimÀÀrin 5â6 myrskyĂ€ kuukaudessa kun taas kesĂ€kuukausina ei yhtÀÀn. YllĂ€ttĂ€vĂ€mpi tulos oli, ettĂ€ kaikkien matalapaineiden mÀÀrĂ€ssĂ€ ei löydetty kausittaista vaihtelua. MyrskyjĂ€ havaittiin esiintyvĂ€n eniten Barentsin meren yllĂ€ kun taas heikommat matalapaineet esiintyvĂ€t Pohjois-Euroopan maa-alueilla.
TyössĂ€ tutkittiin Pohjois-Euroopan myrskyihin liittyvien voimakkaiden tuulten kehittymistĂ€ ja rakennetta. Tulokset osoittavat, ettĂ€ voimakkaimmat myrskyihin liittyvĂ€t puuskat siirtyvĂ€t ja leviĂ€vĂ€t lĂ€mpimĂ€stĂ€ sektorista kylmĂ€n rintaman taakse myrskyn kehittymisen aikana. KylmĂ€n vuodenajan (lokaâmaaliskuu) myrskyt ovat yleisesti voimakkaampia ja alueellisesti laajempia kuin lĂ€mpimĂ€n vuodenajan (huhtiâsyyskuu) myrskyt. Esimerkiksi myrskyn minimipaine on keskimÀÀrin 9 hPa matalampi ja maksimipuuska 2 ms-1 voimakkaampi kylmĂ€nĂ€ kuin lĂ€mpimĂ€nĂ€ vuodenaikana. Tapaustutkimus Mauri-myrskystĂ€, tuhoisasta myrskystĂ€ Suomessa 22.9.1982, osoittaa, ettĂ€ yksittĂ€isen myrskyn kehitys voi poiketa suuresti ilmaston yleisestĂ€ kehitysmallista. Tapaustutkimuksessa selvisi myös, ettĂ€ sÀÀmalli aliarvioi Suomen maa-alueilla Mauri-myrskyn tuulennopeuksia 2â13 ms-1 havaintoihin verrattuna, mutta voimakkaiden tuulten sijainnit on ennustettu oikein.
ViimeisimpĂ€nĂ€ vĂ€itöskirjassa tutkittiin mitkĂ€ meteorologiset tekijĂ€t vaikuttavat myrskyn voimakkuuteen Pohjois Euroopassa. TĂ€tĂ€ tutkittiin kĂ€yttĂ€mĂ€llĂ€ nk. parviherkkyysmenetelmÀÀ. Myrskyn voimakkuuden herkkyydet kaikkiin tutkittuihin meteorologisiin tekijöihin olivat 20â75 % korkeampia kylmĂ€nĂ€ kuin lĂ€mpimĂ€nĂ€ vuodenaikana. TĂ€mĂ€ viittaa siihen, ettĂ€ kylmĂ€n vuodenajan myrskyt ovat potentiaalisesti paremmin ennustettavissa kuin lĂ€mpimĂ€n vuodenajan myrskyt. Pohjois-Euroopan myrskyjen voimakkuuteen vaikuttaa eniten alailmakehĂ€n vaakasuuntainen lĂ€mpötilaero, joka tĂ€ten on tĂ€rkeĂ€ seurattava muuttuja myrskyjĂ€ ennustettaessa.
TÀmÀn vÀitöskirjan tulokset korostavat tÀrkeyttÀ tarkastella pitkÀnajan vuosien vÀlistÀ vaihtelua pelkkien lineaaristen trendien sijaan, jotta ilmastoa ymmÀrrettÀisiin laajemmin. LisÀksi tulokset korostavat tarvetta sekÀ yleisille kÀsitemalleille ettÀ yksitÀisille tapaustutkimuksille, jotta myrskyjen moninaisia kehityspolkuja ymmÀrrettÀisiin paremmin
Climatology, variability, and trends in near-surface wind speeds over the North Atlantic and Europe during 1979-2018 based on ERA5
This study presents the monthly 10âm wind speed climatology, decadal variability and possible trends in the North Atlantic and Europe from ERA5 reanalysis from 1979 to 2018 and investigates the physical reasons for the decadal variability. Additionally, temporal time series are examined in three locations: the central North Atlantic, Finland and Iberian Peninsula. The 40âyear mean and the 98th percentile wind speeds emphasize a distinct landâsea contrast and a seasonal variation with the strongest winds over the ocean and during winter. The strongest winds and the highest variability are associated with the storm tracks and local wind phenomena such as the mistral. The extremeness of the winds is examined with an extreme wind factor (the 98th percentile divided by mean wind speeds) which in all months is higher in southern Europe than in northern Europe. Mostly no linear trends in 10âm wind speeds are identified in the three locations but large annual and decadal variability is evident. The decadal 10âm wind speeds were stronger than average in the 1990s in northern Europe and in the 1980s and 2010s in southern Europe. These decadal changes were largely explained by the positioning of the jet stream and storm tracks and the strength of the northâsouth pressure gradient in the North Atlantic. The 10âm winds have a positive correlation with the North Atlantic Oscillation in the central North Atlantic and Finland on annual scales and during cold season months and a negative correlation in Iberian Peninsula mostly from July to March. The Atlantic Multiâdecadal Oscillation has a moderate negative correlation with the winds in the central North Atlantic but no correlation in Finland and Iberian Peninsula. Overall, our results emphasize that while linear trends in wind speeds may show a general longâterm trend, more information on the changes is obtained by analysing longâterm variability.This study presents the monthly 10-m wind speed climatology, decadal variability and possible trends in the North Atlantic and Europe from ERA5 reanalysis from 1979 to 2018 and investigates the physical reasons for the decadal variability. Additionally, temporal time series are examined in three locations: the central North Atlantic, Finland and Iberian Peninsula. The 40-year mean and the 98th percentile wind speeds emphasize a distinct land-sea contrast and a seasonal variation with the strongest winds over the ocean and during winter. The strongest winds and the highest variability are associated with the storm tracks and local wind phenomena such as the mistral. The extremeness of the winds is examined with an extreme wind factor (the 98th percentile divided by mean wind speeds) which in all months is higher in southern Europe than in northern Europe. Mostly no linear trends in 10-m wind speeds are identified in the three locations but large annual and decadal variability is evident. The decadal 10-m wind speeds were stronger than average in the 1990s in northern Europe and in the 1980s and 2010s in southern Europe. These decadal changes were largely explained by the positioning of the jet stream and storm tracks and the strength of the north-south pressure gradient in the North Atlantic. The 10-m winds have a positive correlation with the North Atlantic Oscillation in the central North Atlantic and Finland on annual scales and during cold season months and a negative correlation in Iberian Peninsula mostly from July to March. The Atlantic Multi-decadal Oscillation has a moderate negative correlation with the winds in the central North Atlantic but no correlation in Finland and Iberian Peninsula. Overall, our results emphasize that while linear trends in wind speeds may show a general long-term trend, more information on the changes is obtained by analysing long-term variability.Peer reviewe
Characteristics of extratropical cyclones and precursors to windstorms in northern Europe
Peer reviewe
Lightning observations in Finland 2015
Ilmatieteen laitos on koonnut ja julkaissut salamanlaskijoiden havainnot vuosilta 1960â1997. Vuodesta 1998 lĂ€htien kaikki jĂ€rjestelmĂ€lliset maasalamahavainnot perustuvat salamanpaikantimeen, jonka nykyinen malli aloitti toimintansa elokuussa 1997. Se kĂ€sitti 2015 kahdeksan anturia, pohjoisin Lokassa. Vuodesta 2002 mukana ovat olleet lisĂ€ksi Norjan ja Ruotsin anturit, joiden ansiosta koko Lappi on katettu ja suorituskyky on parantunut myös muualla Suomessa, sekĂ€ yksi anturi Virossa (mukaan vuonna 2005) ja kolme anturia Liettuassa (mukaan 2014). Laitteisto paikantaa maasalamoista erikseen jokaisen osaiskun ja ryhmittelee ne kokonaisiksi salamoiksi. Paikannettu salama voi sisĂ€ltÀÀ 1-15 iskua; keskiarvo Suomessa on vajaa kaksi iskua/salama. Tilastoinnin pohjana kĂ€ytetÀÀn salama- eikĂ€ iskumÀÀriĂ€, koska salama on ilmastollisesti edustavampi suure. KesĂ€n 2015 aikana paikannettiin Suomen alueella ennĂ€tyksellisen vĂ€hĂ€n maasalamoita, noin 30 000, joka on vain viidennes keskimÀÀrĂ€isestĂ€ (139 000). Suomen kesÀÀ pitkÀÀn hallinnut viileĂ€ sÀÀtyyppi ei suosinut rajuja ukkosia, ja elokuun lĂ€mmin ilmamassa estyi tuottamasta ukkospilviĂ€ korkeapainevoittoisen sÀÀn
vuoksi. Kuukausista ainoastaan syyskuu ylsi hieman yli keskimÀÀrÀisen
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