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Is there an influence of solar activity on the North Atlantic Oscillation? : a literature study of the forcing factors behind the North Atlantic Oscillation

Johansson, Ida LU (2015) In Dissertations in Geology at Lund University GEOL01 20151
Department of Geology
Abstract (Swedish)
Nordatlantiska Oscillationen (NAO) är ett atmosfäriskt cirkulationsfenomen som kännetecknas av skillnader i havsnivåtryck mellan högtrycksområdet vid Azorerna och lågtrycksområdet över Island. NAO varierar mellan en positiv och negativ fas beroende på hur väl utvecklade dessa högtrycksområden är. NAO har visat sig ha stor påverkan på vinterklimatet på norra halvklotet eftersom den påverkar temperaturer, stormar och nederbörd över Atlantområdet. På senare år har flera studier publicerats med teorier angående vilka bakomliggande faktorer som driver NAO. Denna kandidatuppsats är en litteraturstudie med syfte att sammanfatta de mest framstående teorierna kring de pådrivande mekanismerna bakom NAO, med främsta fokus inriktat på effekterna av... (More)
Nordatlantiska Oscillationen (NAO) är ett atmosfäriskt cirkulationsfenomen som kännetecknas av skillnader i havsnivåtryck mellan högtrycksområdet vid Azorerna och lågtrycksområdet över Island. NAO varierar mellan en positiv och negativ fas beroende på hur väl utvecklade dessa högtrycksområden är. NAO har visat sig ha stor påverkan på vinterklimatet på norra halvklotet eftersom den påverkar temperaturer, stormar och nederbörd över Atlantområdet. På senare år har flera studier publicerats med teorier angående vilka bakomliggande faktorer som driver NAO. Denna kandidatuppsats är en litteraturstudie med syfte att sammanfatta de mest framstående teorierna kring de pådrivande mekanismerna bakom NAO, med främsta fokus inriktat på effekterna av variationer i solaktivitet. Det är debatterat huruvida NAO drivs av variationer i solaktivitet. NAO har visat sig korrelera med variationer i solaktivitet under den senare halvan av 1900-talet men under första halvan av 1900-talet syns ingen korrelation. Studier visar att variationer i solaktivitet kan leda till uppvärmning av stratosfären. På grund av ökade temperaturer i stratosfären förstärks de stratosfäriska vindar vilka sedan kan spridas ner till troposfären. Detta leder till ökade västvindar och en positiv NAO-fas. Forskning visar även att variationer i solinstrålning leder till blockerande högtryck. Dessa förändrar vind- och stormriktningen över Atlanten, vilket leder till en negativ NAO-fas. Förutom variationer i solaktivitet har det föreslagits att NAO drivs av skillnader i havsytetemperaturer, havsis och vulkanisk aktivitet. (Less)
Abstract
The North Atlantic Oscillation (NAO) is an atmospheric circulation phenomenon, characterized by differences in sea level pressure between the Azores high- and the Icelandic low pressure systems. The NAO fluc-tuates between a positive and a negative phase depending on how well developed these pressure systems are. The NAO has a great impact on northern hemisphere winter climate since it affects temperatures, storms and precipita-tion over the Atlantic area. In recent years various studies have investigated the underlying mechanisms which cause the NAO to oscillate. This paper is a literature study with the aim to summarize the most prominent theories of the forcing mechanisms behind the NAO, with a main focus on the effects of variations in... (More)
The North Atlantic Oscillation (NAO) is an atmospheric circulation phenomenon, characterized by differences in sea level pressure between the Azores high- and the Icelandic low pressure systems. The NAO fluc-tuates between a positive and a negative phase depending on how well developed these pressure systems are. The NAO has a great impact on northern hemisphere winter climate since it affects temperatures, storms and precipita-tion over the Atlantic area. In recent years various studies have investigated the underlying mechanisms which cause the NAO to oscillate. This paper is a literature study with the aim to summarize the most prominent theories of the forcing mechanisms behind the NAO, with a main focus on the effects of variations in solar activity. Differ-ent studies disagree on whether the NAO is forced by solar activity variations or not. While the NAO has been shown to correlate with variations in solar activity in the second half of the 20th century, this correlation is less clear during the first half of the 20th century. Several studies indicate that variations in solar activity might affect the NAO by inducing stratospheric circulation changes which are propagated down on the troposphere. During high solar activity years this enhances the westerly winds and causes a positive NAO. It is also suggested that the varia-tions in solar irradiance cause atmospheric blockings to occur. These blockings, that interrupt winds and storm tracks over the Atlantic, is more persistent during low solar activity years and is associated with a negative NAO. Except variations in solar activity, it has been suggested that the NAO varies due to variations in sea surface tem-peratures, sea ice and volcanic activity. (Less)
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author
Johansson, Ida LU
supervisor
organization
course
GEOL01 20151
year
type
M2 - Bachelor Degree
subject
keywords
stratospheric-tropospheric couplings, solar activiy, The North Atlantic Oscillation, blockings, climatic variations
publication/series
Dissertations in Geology at Lund University
report number
447
language
English
id
5469871
date added to LUP
2015-06-16 15:11:52
date last changed
2015-06-18 14:04:26
@misc{5469871,
  abstract     = {The North Atlantic Oscillation (NAO) is an atmospheric circulation phenomenon, characterized by differences in sea level pressure between the Azores high- and the Icelandic low pressure systems. The NAO fluc-tuates between a positive and a negative phase depending on how well developed these pressure systems are. The NAO has a great impact on northern hemisphere winter climate since it affects temperatures, storms and precipita-tion over the Atlantic area. In recent years various studies have investigated the underlying mechanisms which cause the NAO to oscillate. This paper is a literature study with the aim to summarize the most prominent theories of the forcing mechanisms behind the NAO, with a main focus on the effects of variations in solar activity. Differ-ent studies disagree on whether the NAO is forced by solar activity variations or not. While the NAO has been shown to correlate with variations in solar activity in the second half of the 20th century, this correlation is less clear during the first half of the 20th century. Several studies indicate that variations in solar activity might affect the NAO by inducing stratospheric circulation changes which are propagated down on the troposphere. During high solar activity years this enhances the westerly winds and causes a positive NAO. It is also suggested that the varia-tions in solar irradiance cause atmospheric blockings to occur. These blockings, that interrupt winds and storm tracks over the Atlantic, is more persistent during low solar activity years and is associated with a negative NAO. Except variations in solar activity, it has been suggested that the NAO varies due to variations in sea surface tem-peratures, sea ice and volcanic activity.},
  author       = {Johansson, Ida},
  keyword      = {stratospheric-tropospheric couplings,solar activiy,The North Atlantic Oscillation,blockings,climatic variations},
  language     = {eng},
  note         = {Student Paper},
  series       = {Dissertations in Geology at Lund University},
  title        = {Is there an influence of solar activity on the North Atlantic Oscillation? : a literature study of the forcing factors behind the North Atlantic Oscillation},
  year         = {2015},
}