Long-term variations in the correlation between NAO and solar activity: The importance of north–south solar activity asymmetry for atmospheric circulation (original) (raw)
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Long-Term Correlation Between the Nao and Solar Activity
Solar Physics, 2004
We extend the correlation analysis of solar signals and the North Atlantic Oscillation (NAO) back in time by using the aa index (since 1868) and the PC index (since 1948) as a proxy of the solar wind energy imparted to the magnetosphere. Prior to the 1940s the records of the NAO and the aa index were not closely connected, while after the 1940s their rhythms matched. We compare two distinctive periods with recent results on the long-scale reconstruction of solar activity. The shift in the NAO-aa interconnection can provide the explanation of a significant increase of solar activity after the 1940s. A strengthening of the interplanetary magnetic field leads to more intensive variations of the high-latitude ionospheric electric field that influences the atmospheric circulation.
Solar influences on atmospheric circulation
Journal of Atmospheric and Solar-Terrestrial Physics, 2012
Various atmospheric parameters are in some periods positively and in others negatively correlated with solar activity. Solar activity is a result of the action of solar dynamo transforming solar poloidal field into toroidal field and back. The poloidal and toroidal fields are the two faces of solar magnetism, so they are not independent, but we demonstrate that their long-term variations are not identical, and the periods in which solar activity agents affecting the Earth are predominantly related to solar toroidal or poloidal fields are the periods in which the North Atlantic Oscillation is negatively or positively correlated with solar activity, respectively. We find further that solar poloidal field-related activity increases the NAM index, while solar toroidal field-related activity decreases it. This is a possible explanation of the changing correlation between the North Atlantic Oscillation and solar activity.
Long-term variations of the solar activity-lower atmosphere relationship
Long-term variations of the air temperature in St. Petersburg (ϕ = 60 • N), Stockholm (ϕ = 59 • N), English Midlands (ϕ ∼ 50 • N) and Salzburg (ϕ = 48 • N) are considered. It is shown that in the regions under consideration the air temperature distinctly depends on the intensity of the lower atmosphere zonal circulation (North Atlantic Oscillation (NAO) index). In turn, the NAO index is shown to depend on the solar activity. However, this dependence is rather complicated and exhibits long-period variations. A possible mechanism of this phenomenon is discussed.
Theoretical and Applied Climatology, 2007
Spectral analysis of geomagnetic activity, global air temperature, Earth's rotation rate and zonal circulation, when smoothed from secular trend and periods shorter than 23 years, shows a concentration of energy around the 60-year period explaining more than 80% of the entire variance. This information has enabled the set-up of a cascade physical model that integrates the Sun-atmosphere-Earth system as a single unit and ties solar corpuscular radiation to global warming through Earth's rotation and atmospheric circulation. Our results suggest that changes in geomagnetic activity, and in the Earth's rotation, could be used as long-and shortterm indicators, respectively, of future changes in global air temperature.
Changes in the relationship NAO–Northern hemisphere temperature due to solar activity
Earth and Planetary Science Letters, 2003
The influence of the North Atlantic Oscillation (NAO) on wintertime Northern Hemisphere Temperature (NHT) is investigated. The results suggest that this relationship has different sign according to the phase of the solar cycle. For solar maximum phases NAO and NHT are positively correlated^a result assumed up to the moment^but for solar minimum phases correlations are not significant or even negative. This result is in agreement with the different extension of the NAO for solar cycle phases [Kodera, Geophys. Res. Lett. 29 (2002) 14557^14560]^almost hemispheric for maximum phases and confined to the eastern Atlantic for minimum phases. ß
Solar influence on a major mode of atmospheric variability
Journal of Geophysical Research, 2002
We find that the North Annular Mode (NAM) of the wintertime geopotential height anomalies between 10 and 1000 hPa is influenced by solar changes and that the effect is statistically significant. This evidence suggests that a mechanism of solar influence on climate operates through the excitation of this mode. The influence depends on the phase of the quasi-biennial oscillation (QBO). In early winter for the west QBO and late winter for the east QBO the solar changes affect the NAM in both the stratosphere and the troposphere almost equally. The results are compared with earlier studies of the role of the QBO and solar UV changes on near-polar temperatures and geopotential heights. Thus the late winter effect for the west QBO found by Labitzke and van Loon [1988] is clearly evident in the NAM in the stratosphere but does not appear in the troposphere.
Natural forcing of climate during the last millennium: fingerprint of solar variability
Climate Dynamics, 2010
The variability of the climate during the last millennium is partly forced by changes in total solar irradiance (TSI). Nevertheless, the amplitude of these TSI changes is very small so that recent reconstruction data suggest that low frequency variations in the North Atlantic Oscillation (NAO) and in the thermohaline circulation may have amplified, in the North Atlantic sector and mostly in winter, the radiative changes due to TSI variations. In this study we use a state-of-the-art climate model to simulate the last millennium. We find that modelled variations of surface temperature in the Northern Hemisphere are coherent with existing reconstructions. Moreover, in the model, the low frequency variability of this mean hemispheric temperature is found to be correlated at 0.74 with the solar forcing for the period 1001-1860. Then, we focus on the regional climatic fingerprint of solar forcing in winter and find a significant relationship between the low frequency TSI forcing and the NAO with a time lag of more than 40 years for the response of the NAO. Such a lag is larger than the around 20-year lag suggested in other studies. We argue that this lag is due, in the model, to a northward shift of the tropical atmospheric convection in the Pacific Ocean, which is maximum more than four decades after the solar forcing increase. This shift then forces a positive NAO through an atmospheric wave connection related to the jet-stream wave guide. The shift of the tropical convection is due to the persistence of anomalous warm SST forcing the anomalous precipitation, associated with the advection of warm SST by the North Pacific subtropical gyre in a few decades. Finally, we analyse the response of the Atlantic meridional overturning circulation to solar forcing and find that the former is weakened when the latter increases. Changes in wind stress, notably due to the NAO, modify the barotropic streamfunction in the Atlantic 50 years after solar variations. This implies a wind-driven modification of the oceanic circulation in the Atlantic sector in response to changes in solar forcing, in addition to the variations of the thermohaline circulation.
Interrelationship between the North Atlantic Oscillation and Solar cycle
Understanding the influence of solar variability on the Earth's climate requires knowledge of solar variability, solar interactions, and the mechanisms explain the response of the Earth's climate system. The NAO (North Atlantic oscillation) is one of the most dominant modes of global climate variability. Like El Niño, La Niña, and the Southern Oscillation, it is considered as free internal oscillation of the climate system not subjected to external forcing. It is shown, to be linked to energetic solar eruptions. Surprisingly, it turns out that features of solar activity have been related to El Niño and La Niña, also have an significant impact on the NAO. The climate of the Atlantic sector exhibits considerable variability on a wide range of time scales. A substantial portion is associated with the North Atlantic Oscillation (NAO), a hemispheric meridional oscillation as atmospheric mass with centers of action near Iceland and over the subtropical Atlantic. NAO-has a related impacts on winter climate extend from Florida to Greenland and from northwestern Africa over Europe far into northern Asian region. In the present work solar cycle 22 was implemented via sun spots number and area and there interrelationship with NAO index and discussed their dependency which consequently that could be used to predict the behavior of NAO index in the next solar cycle as an indicator to climatic variability.
Patterns of tropospheric response to solar variability
Geophysical Research Letters, 2003
1] Despite numerous reports of apparent climate responses to the 11-year solar cycle, the Sun's role for weather and climate has remained a matter of controversy. One important reason is the difficulty of reliably attributing the observed atmospheric effects to solar variability, rather than to other forcing factors or intrinsic variability. Here we show that consistent patterns of statistically significant solar signals emerge in all major observables throughout the low-and midlatitude troposphere, when El Niño and volcanic signals are removed from meteorological data. Solar forcing is strongest in the tropics and at mid-latitudes, and the heating and moistening of the troposphere during solar maximum is accompanied by a modulation of the large-scale tropospheric circulation systems. These findings have implications for the question of where and how the Sun exerts its influences in the climate system.
Characteristics of the Recent Eastward Shift of Interannual NAO Variability
Journal of Climate, 2003
Recent observational studies have shown that the centers of action of interannual variability of the North Atlantic Oscillation (NAO) were located farther eastward during winters of the period 1978-97 compared to previous decades of the twentieth century. In this study, which focuses on the winter season (December-March), new diagnostics characterizing this shift are presented. Further, the importance of this shift for NAO-related interannual climate variability in the North Atlantic region is discussed. It is shown that an NAO-related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones, near-surface air temperature, and turbulent surface heat flux throughout the North Atlantic region. By using a near-surface air temperature dataset that is homogenous with respect to the kind of observations used, it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s. Finally, an EOF-based Monte Carlo test is developed to quantify the probability of changes in the spatial structure of interannual NAO variability for a relatively short (20 yr) time series given multivariate ''white noise.'' It is estimated that the likelihood for differences in the spatial structure of the NAO between two independent 20-yr periods, which are similar (as measured by the angle and pattern correlation between two NAO patterns) to the observed differences, to occur just by chance is about 18%. From the above results it is argued that care has to be taken when conclusions about long-term properties of NAO-related climate variability are being drawn from relatively short recent observational data (e.g., 1978-97).