scholarly journals How can we understand the solar cycle signal on the Earth's surface?

2016 ◽  
Author(s):  
Kunihiko Kodera ◽  
Rémi Thiéblemont ◽  
Seiji Yukimoto ◽  
Katja Matthes
Keyword(s):  
Solar Cycle ◽  
Surface Temperature ◽  
Zonal Wind ◽  
High Solar Activity ◽  
Late Winter ◽  
Mean Flow ◽  
Central Pacific ◽  
Solar Signal ◽  
The Tropics ◽  
The Impact

Abstract. To understand solar cycle signals on the Earth's surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analyzed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no warming in the tropics. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During Northern Hemisphere winter this is manifested in a modulation of the polar-night jet whereas in the Southern Hemisphere the subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counter balanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. The model results suggest that both tropical and extra-tropical solar surface signals can result from circulation changes in the upper stratosphere through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

scholarly journals How can we understand the global distribution of the solar cycle signal on the Earth's surface?

2016 ◽  
Vol 16 (20) ◽  
pp. 12925-12944 ◽  
Author(s):  
Kunihiko Kodera ◽  
Rémi Thiéblemont ◽  
Seiji Yukimoto ◽  
Katja Matthes
Keyword(s):  
Solar Cycle ◽  
Surface Temperature ◽  
Zonal Wind ◽  
High Solar Activity ◽  
Mean Flow ◽  
Central Pacific ◽  
Solar Signal ◽  
The Tropics ◽  
Solar Influence ◽  
The Impact

Abstract. To understand solar cycle signals on the Earth's surface and identify the physical mechanisms responsible, surface temperature variations from observations as well as climate model data are analysed to characterize their spatial structure. The solar signal in the annual mean surface temperature is characterized by (i) mid-latitude warming and (ii) no overall tropical warming. The mid-latitude warming during solar maxima in both hemispheres is associated with a downward penetration of zonal mean zonal wind anomalies from the upper stratosphere during late winter. During the Northern Hemisphere winter this is manifested by a modulation of the polar-night jet, whereas in the Southern Hemisphere, the upper stratospheric subtropical jet plays the major role. Warming signals are particularly apparent over the Eurasian continent and ocean frontal zones, including a previously reported lagged response over the North Atlantic. In the tropics, local warming occurs over the Indian and central Pacific oceans during high solar activity. However, this warming is counterbalanced by cooling over the cold tongue sectors in the southeastern Pacific and the South Atlantic, and results in a very weak zonally averaged tropical mean signal. The cooling in the ocean basins is associated with stronger cross-equatorial winds resulting from a northward shift of the ascending branch of the Hadley circulation during solar maxima. To understand the complex processes involved in the solar signal transfer, results of an idealized middle atmosphere–ocean coupled model experiment on the impact of stratospheric zonal wind changes are compared with solar signals in observations. Model integration of 100 years of strong or weak stratospheric westerly jet condition in winter may exaggerate long-term ocean feedback. However, the role of ocean in the solar influence on the Earth's surface can be better seen. Although the momentum forcing differs from that of solar radiative forcing, the model results suggest that stratospheric changes can influence the troposphere, not only in the extratropics but also in the tropics through (i) a downward migration of wave–zonal mean flow interactions and (ii) changes in the stratospheric mean meridional circulation. These experiments support earlier evidence of an indirect solar influence from the stratosphere.

scholarly journals On the detection of the solar signal in the tropical stratosphere

2014 ◽  
Vol 14 (11) ◽  
pp. 5251-5269 ◽  
Author(s):  
G. Chiodo ◽  
D. R. Marsh ◽  
R. Garcia-Herrera ◽  
N. Calvo ◽  
J. A. García
Keyword(s):  
Solar Cycle ◽  
Lower Stratosphere ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
High Solar Activity ◽  
Relative Role ◽  
Quasi Biennial Oscillation ◽  
Solar Signal ◽  
The Impact

Abstract. We investigate the relative role of volcanic eruptions, El Niño–Southern Oscillation (ENSO), and the quasi-biennial oscillation (QBO) in the quasi-decadal signal in the tropical stratosphere with regard to temperature and ozone commonly attributed to the 11 yr solar cycle. For this purpose, we perform transient simulations with the Whole Atmosphere Community Climate Model forced from 1960 to 2004 with an 11 yr solar cycle in irradiance and different combinations of other forcings. An improved multiple linear regression technique is used to diagnose the 11 yr solar signal in the simulations. One set of simulations includes all observed forcings, and is thereby aimed at closely reproducing observations. Three idealized sets exclude ENSO variability, volcanic aerosol forcing, and QBO in tropical stratospheric winds, respectively. Differences in the derived solar response in the tropical stratosphere in the four sets quantify the impact of ENSO, volcanic events and the QBO in attributing quasi-decadal changes to the solar cycle in the model simulations. The novel regression approach shows that most of the apparent solar-induced lower-stratospheric temperature and ozone increase diagnosed in the simulations with all observed forcings is due to two major volcanic eruptions (i.e., El Chichón in 1982 and Mt. Pinatubo in 1991). This is caused by the alignment of these eruptions with periods of high solar activity. While it is feasible to detect a robust solar signal in the middle and upper tropical stratosphere, this is not the case in the tropical lower stratosphere, at least in a 45 yr simulation. The present results suggest that in the tropical lower stratosphere, the portion of decadal variability that can be unambiguously linked to the solar cycle may be smaller than previously thought.

scholarly journals On the detection of the solar signal in the tropical stratosphere

2013 ◽  
Vol 13 (11) ◽  
pp. 30097-30142 ◽  
Author(s):  
G. Chiodo ◽  
D. R. Marsh ◽  
R. Garcia-Herrera ◽  
N. Calvo ◽  
J. A. García
Keyword(s):  
Solar Cycle ◽  
Lower Stratosphere ◽  
Climate Model ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
High Solar Activity ◽  
Relative Role ◽  
Solar Signal ◽  
The Impact

Abstract. We investigate the relative role of volcanic eruptions, El-Niño Southern-Oscillation (ENSO) and the Quasi-Biennal-Oscillation (QBO) in the quasi-decadal signal in the tropical stratosphere in temperature and ozone commonly attributed to the 11 yr solar cycle. For this purpose, we perform transient simulations with the Whole Atmosphere Community Climate Model forced from 1960 to 2004 with an 11 yr solar cycle in irradiance and different combinations of other forcings. An improved multiple regression technique is used to diagnose the 11 yr solar signal in the simulations. One set of simulations includes all observed forcings, and is thereby aimed at closely reproducing observations. Three idealized sets exclude ENSO variability, volcanic aerosol forcing, and QBO in tropical stratospheric winds, respectively. Differences in the derived solar response in the tropical stratosphere in the four sets quantify the impact of ENSO, volcanic events and the QBO in attributing quasi-decadal changes to the solar cycle in the model simulations. It is shown that most of the apparent solar-induced lower stratospheric temperature and ozone increase diagnosed in the simulations with all observed forcings is due to two major volcanic eruptions (i.e., El Chichón in 1982 and Mt. Pinatubo in 1991), that are concurrent with periods of high solar activity. While in the middle and upper tropical stratosphere, it is feasible to detect a robust solar signal, this is not the case in the tropical lower stratosphere, at least in a 45 yr record. The present results suggest that in the tropical lower stratosphere, the portion of decadal variability that can be unambigously linked to the solar cycle may be smaller than previously thought.

Future projections of river floods over the European region using EURO-CORDEX simulations

2020 ◽  
Author(s):  
Fabio Di Sante ◽  
Erika Coppola ◽  
Filippo Giorgi
Keyword(s):  
Climate Change ◽  
Hydrological Cycle ◽  
Snow Accumulation ◽  
Late Winter ◽  
European Regions ◽  
Mean Flow ◽  
The North ◽  
North Eastern ◽  
River Floods ◽  
The Impact

<p>In a sick world with fever caused by global warming, the hydrological cycle will experience most certainly large changes in intensity and variability. One of the most intense phenomena that will probably be affected by the climate change is the flood hazard. For a long time the stakeholders have been dedicated resources to assess the risk linked to the floods magnitude and frequencies and shaping the public infrastructures based on the assumption of their immutability. Under the effect of the climate change this assumption can be broken and a different approach should be followed to avoid large disasters and threaten to the population health. In this study the biggest ever ensemble of hydroclimatic  simulations has been used to simulate the river floods over the European regions. A river routing model derived from a distributed hydrological model (CHyM) has been forced with 44 EURO-CORDEX, 5 CMIP5 and 7 CMIP6 simulations to assess the effects of the climate change on the floods magnitude under two different scenarios (RCP2.6 and RCP8.5 for EURO-CORDEX and CMIP5, SSP126 and SSP585 for CMIP6). The impact of the climate change has been evaluated using a 100 year return period discharge indicator (Q100) obtained fitting a Gumbel distribution on the yearly peak discharge values. Results show a decrease of magnitude of flood events over the Mediterranean, Scandinavia and the North Eastern European regions. Over these two last regions the signal appear particularly robust and in contrast to the projected mean flow signal that is shown to increase by the end of the century mainly driven by the related increase of mean precipitations. The reduction of snow accumulation during winter time linked to a large increase of late winter temperatures is the main reason behind the decrease of floods over the North Eastern regions. An opposite signal is projected  instead over Great Britain, Ireland, Northern Italy and Western Europe where a robust signal of floods magnitude increase is evident driven by e the increase of extreme precipitations. All these simulation are meant to feed the impact community and to shade the light on the use of climate information for impact assessment studies.</p>

Solar Influences on Stratospheric Circulation Patterns

2020 ◽  
Author(s):  
Yonatan Givon ◽  
Chaim Garfinkel
Keyword(s):  
Zonal Wind ◽  
Wind Anomaly ◽  
Zonal Wind Anomaly ◽  
Circulation Patterns ◽  
Downward Propagation ◽  
P Flux ◽  
Stratospheric Circulation ◽  
The Tropics ◽  
The Impact ◽  
Transformed Eulerian Mean

<p>The impact of the solar cycle on the NH winter stratospheric circulation is analyzed using<br>simulations of a Model of an idealized Moist Atmosphere (MiMA). By comparing solar minimum<br>periods to solar maximum periods, the solar impact on the stratosphere is evaluated: Solar<br>maximum periods are accompanied by warming of the tropics that extends into the midlatitudes<br>due to an altered Brewer Dobson Circulation. This warming of the subtropics and the altered<br>Brewer Dobson Circulation leads to an increase in zonal wind in midlatitudes, which is then<br>followed by a decrease in E-P flux convergence near the winter pole which extends the enhanced<br>westerlies to subpolar latitudes.<br>We use the transformed Eulerian mean framework to reveal the processes that lead to the<br>formation of this sub-polar zonal wind anomaly and its downward propagation from the top of the<br>stratosphere to the tropopause.</p>

scholarly journals The 11-Yr Solar Cycle in ERA-40 Data: An Update to 2008

2010 ◽  
Vol 23 (8) ◽  
pp. 2213-2222 ◽  
Author(s):  
Thomas H. A. Frame ◽  
Lesley J. Gray
Keyword(s):  
Solar Cycle ◽  
Linear Regression ◽  
Zonal Wind ◽  
Volcanic Aerosol ◽  
Mount Pinatubo ◽  
Aerosol Forcing ◽  
Stratospheric Temperature ◽  
Temperature Trends ◽  
Solar Signal ◽  
Using Data

Abstract Multiple linear regression is used to diagnose the signal of the 11-yr solar cycle in zonal-mean zonal wind and temperature in the 40-yr ECMWF Re-Analysis (ERA-40) dataset. The results of previous studies are extended to 2008 using data from ECMWF operational analyses. This analysis confirms that the solar signal found in previous studies is distinct from that of volcanic aerosol forcing resulting from the eruptions of El Chichón and Mount Pinatubo, but it highlights the potential for confusion of the solar signal and lower-stratospheric temperature trends. A correction to an error that is present in previous results of Crooks and Gray, stemming from the use of a single daily analysis field rather than monthly averaged data, is also presented.

Stable channel flow with spanwise heterogeneous surface temperature

2022 ◽  
Vol 933 ◽  
Author(s):  
T. Bon ◽  
J. Meyers
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Friction Coefficient ◽  
Surface Temperature ◽  
Channel Flow ◽  
Secondary Flows ◽  
Heterogeneous Surface ◽  
Length Scale ◽  
Mean Flow ◽  
The Impact

Recent studies have demonstrated that large secondary motions are excited by surface roughness with dominant spanwise length scales of the order of the flow's outer length scale. Inspired by this, we explore the effect of spanwise heterogeneous surface temperature in weakly to strongly stratified closed channel flow (at $Ri_\tau =120$ , 960; $Re_\tau = 180$ , 550) with direct numerical simulations. The configuration consists of equally sized strips of high and low temperature at the lower and upper boundaries, while an overall stable stratification is induced by imposing an average temperature difference between the top and bottom. We consider the influence of the width of the strips ( ${\rm \pi} /8 \leq \lambda /h \leq 4{\rm \pi} $ ), Reynolds number, stability and upper boundary condition on the mean flow structure, skin friction and heat transfer. Results indicate that secondary flows are excited, with alternating high- and low-momentum pathways and vortices, similar to the patterns induced by spanwise heterogeneous surface roughness. We find that the impact of the surface heterogeneity on the outer layer depends strongly on the spanwise heterogeneity length scale of the surface temperature. Comparison to stable channel flow with uniform temperature reveals that the heterogeneous surface temperature increases the global friction coefficient and reduces the global Nusselt number in most cases. However, for the high-Reynolds cases with $\lambda /h \geq {\rm \pi} /2$ , we find a reduction of the friction coefficient. At stronger stability, the vertical extent of the vortices is reduced and the impact of the heterogeneous temperature on momentum and heat transfer is smaller.

A Mechanism for the Poleward Propagation of Zonal Mean Flow Anomalies

2007 ◽  
Vol 64 (3) ◽  
pp. 849-868 ◽  
Author(s):  
Sukyoung Lee ◽  
Seok-Woo Son ◽  
Kevin Grise ◽  
Steven B. Feldstein
Keyword(s):  
Wave Propagation ◽  
Zonal Wind ◽  
Wave Breaking ◽  
Observational Studies ◽  
Mean Flow ◽  
Radiative Relaxation ◽  
Meridional Overturning ◽  
Rossby Wave Propagation ◽  
The Tropics ◽  
Pv Gradient

Abstract Observational studies have shown that tropospheric zonal mean flow anomalies frequently undergo quasi-periodic poleward propagation. A set of idealized numerical model runs is examined to investigate the physical mechanism behind this poleward propagation. This study finds that the initiation of the poleward propagation is marked by the formation of negative zonal wind anomalies in the Tropics. These negative anomalies arise from meridional overturning/breaking of waves that originate in midlatitudes. This wave breaking homogenizes the potential vorticity (PV) within the region of negative zonal wind anomalies, and also leads to the formation of positive zonal wind anomalies in the subtropics. Subsequent equatorward radiation of midlatitude waves is halted, which results in wave breaking at the poleward end of the homogenized PV region. This in turn generates new positive and negative zonal wind anomalies, which enables a continuation of the poleward propagation. The shielding of the homogenized PV region from equatorward wave propagation allows the model’s radiative relaxation to reestablish undisturbed westerlies in the Tropics, while extratropical westerly anomalies arise from eddy vorticity fluxes. The above process indicates that the poleward zonal mean anomaly propagation is caused by an orchestrated combination of linear Rossby wave propagation, nonlinear wave breaking, and radiative relaxation. The importance of the meridional wave propagation and breaking is consistent with the fact that the poleward propagation occurs only in the parameter space of the model where the PV gradient is of moderate strength. Implications for predictability are briefly discussed.

scholarly journals Influence of solar variability on the occurrence of central European weather types from 1763 to 2009

2017 ◽  
Vol 13 (9) ◽  
pp. 1199-1212 ◽  
Author(s):  
Mikhaël Schwander ◽  
Marco Rohrer ◽  
Stefan Brönnimann ◽  
Abdul Malik
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Central Europe ◽  
Reanalysis Data ◽  
Activity Level ◽  
Solar Variability ◽  
High Solar Activity ◽  
Weather Types ◽  
Daily Weather ◽  
The Impact

Abstract. The impact of solar variability on weather and climate in central Europe is still not well understood. In this paper we use a new time series of daily weather types to analyse the influence of the 11-year solar cycle on the tropospheric weather of central Europe. We employ a novel, daily weather type classification over the period 1763–2009 and investigate the occurrence frequency of weather types under low, moderate, and high solar activity level. Results show a tendency towards fewer days with westerly and west-southwesterly flow over central Europe under low solar activity. In parallel, the occurrence of northerly and easterly types increases. For the 1958–2009 period, a more detailed view can be gained from reanalysis data. Mean sea level pressure composites under low solar activity also show a reduced zonal flow, with an increase of the mean blocking frequency between Iceland and Scandinavia. Weather types and reanalysis data show that the 11-year solar cycle influences the late winter atmospheric circulation over central Europe with colder (warmer) conditions under low (high) solar activity.

scholarly journals Influence of solar variability on the occurrence of Central European weather types from 1763 to 2009

2017 ◽  
Author(s):  
Mikhaël Schwander ◽  
Marco Rohrer ◽  
Stefan Brönnimann ◽  
Abdul Malik
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Central Europe ◽  
Reanalysis Data ◽  
Activity Level ◽  
Solar Variability ◽  
High Solar Activity ◽  
Weather Types ◽  
Daily Weather ◽  
The Impact

Abstract. The impact of solar variability on weather and climate in Central Europe is still not well understood. In this paper we use a new time series of daily weather types to analyse the influence of the 11-year solar cycle on the tropospheric weather of Central Europe. We employ a novel, daily weather type classification over the period 1763–2009 and investigate the occurrence frequency of weather types under low, moderate and high solar activity level. Results show a tendency towards fewer days with westerly and west south-westerly flow over Central Europe under low solar activity. In parallel, the occurrence of northerly and easterly types increases. Changes are consistent across different sub-periods. For the 1958–2009 period, a more detailed view can be gained from reanalysis data. Mean sea level pressure composites under low solar activity also show a reduced zonal flow, with an increase of the mean blocking frequency between Iceland and Scandinavia. Weather types and reanalysis data show that the 11-year solar cycle influences the late winter atmospheric circulation over Central Europe with colder (warmer) conditions under low (high) solar activity. Model simulations used for a comparison do not reproduce the imprint of the 11-year solar cycle found in the reanalyses data.

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