on the influence of total solar irradiance on global land temperature albert varonov, yavor shopov

8/10/2019 ON THE INFLUENCE OF TOTAL SOLAR IRRADIANCE ON GLOBAL LAND TEMPERATURE Albert Varonov, Yavor Shopov

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Comptes rendus de lAcademie bulgare des Sciences

Tome 67, No 9, 2014

GEOPHYSIQUE

Relations helio-terrestres

ON THE INFLUENCE OF TOTAL SOLAR IRRADIANCE

ON GLOBAL LAND TEMPERATURE

Albert Varonov, Yavor Shopov

(Submitted by Corresponding Member P. Velinov on July 8, 2014 )

Abstract

Using statistical analysis, correlation between the variations of the totalsolar irradiance and of the annual-mean land temperatures was found. Anunknown time lag between both data sets was expected to be present due tothe complexity of the Earths climate system leading to a delayed response tochanges in influencing factors. We found the best correlation with coefficient

over 90% for a 14-year shift of the annual mean land temperature record aheadwith data until 1970, while the same comparison with data until 2006 yields61% correlation. These results show substantially higher influence of total solarirradiance on global land temperatures until 1970. The decline of this influenceduring the last 40 years could be attributed to the increasing concentration ofanthropogenic greenhouse gases in the Earths atmosphere.

Key words: total solar irradiance, solar variations, solar forcing, climatechange

Introduction. The Sun is the most important energy source for planetEarth. The first satellite observations of the total solar irradiance (TSI) in thelate 1970s showed that the solar energy flux varies. Measurements of the TSI from

the Nimbus-7 satellite between November 1978 and July 1991 show an apparenteleven year variation that can be related to solar activity and annual mean ampli-tude of the variation of 0.15% [1]. Although very small in intensity, the variationsof the TSI produce changes in the global climate system of the Earth accordingto recent studies. Correlation of the solar indices and modelled solar irradiancewith the Earths temperature are significant at better than the 99% confidencelevel [2]. Solar forcing explains well over 75% of the variance for the decadally-smoothed Arctic annual-mean or spring surface air temperature in the Arctic,while time-frequency characteristics for the annual-mean or seasonally-averaged

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Fig. 1. Real-space periodogram of annual-mean land temperature record

mean land temperature record with 6 years on both of its sides and the smoothedrecord comprises the period 18862006.

The first minimum of both Hoyt index and land temperature anomaly (Fig. 2)are displaced by about 17 years. This is to be expected, since some time delay isnecessary for the land temperature changes to respond to the TSI variations. Weshift the graph of the Hoyt index forward in time to align these minimums, as thereis available smoothed Hoyt index data prior to 1880. The best correlation is foundto be at 14-year shift (Fig. 3) with a correlation coefficient 0.615. The comparisonnow includes the periods 18852006 for the annual-mean land temperature recordand 18711992 for the Hoyt index. The introduction of the 14-year shift leadsto a decrease of the correlation coefficient. The cause of this effect is differentbehaviour of the Hoyt index and the annual-mean land temperature record afterthe year 1970 (Fig. 3). Gradually eliminating the data after 1970 from thecomparison, we get to the maximum value of the correlation coefficient of 0.9363(Fig. 4). The maximum correlation coefficient is achieved when removing 36points from the comparison, which corresponds to the removal of the same numberof years of both data sets. Therefore, the maximum correlation between the Hoytindex and the annual-mean land temperature is within the periods 18711956 forthe former and 18851970 for the latter.

A part of the correlation coefficient increase should be due to the eliminationof the data for comparison. The whole number of values is 121 (years 18862006),while the number of the values for the comparison until 1970 is 85 (years 18861970). Although the less dependent values are excluded, a linear regression withfewer values would generally give a better correlation.

The linear regression equations of the smoothed Hoyt index and annual-meanland temperature record with 13-year window size and a 14-year shift are (1) withthe whole set of data until 2006 and (2) with the reduced set of data until 1970.

(1) y = 0.2408x 328.8

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Fig. 2. Smoothed Hoyt index and annual-mean land temperature with 13-year window

size

(2) y = 0.15265x 208.6 .

Conclusions. Based on the presented results here, one can make the fol-lowing conclusions:

1. There is clear evidence of TSI influence on the global land temperatures.

2. Most of the variations of the annual-mean land temperature before 1970

were produced by variations of the TSI.3. The TSI impact on the global land temperature was substantially higher

until the year 1970.

The decrease of the solar influence on the global land temperatures during the


size and a 14-year shift

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size and a 14-year shift until 1970

last 3040 years could be explained by another phenomenon, namely the anthro-pogenic GHG in the atmosphere, which trap heat and prevent the surface landfrom effective cooling. Similar results are reported in other studies [5, 6, 14, 15].

Presently, there are numerous arguments suggesting that the solar variabilityaffects the global climate in different aspects and on different timescales [16]. Sev-eral possible mechanisms have been suggested, which can be responsible for the

observed relation between the solar variability and the climate: via the changingsolar irradiance or by cosmic rays affecting the cloud formation [ 17]. Energetic cos-mic rays initiate a nucleonic-electromagnetic cascade in the atmosphere, affectingits physical-chemical properties [16, 18]. This is a dominant source of ionizationof the atmosphere. Therefore, the detailed models of the cosmic ray ionizationmake a solid basis for a quantitative study of the mechanism presumably affectingcloud formation [19, 20].

The presented results in this study are based on data from reconstructionsand measurements whose precision is constantly increasing. We expect to obtainmore accurate statistical analysis with the use of enhanced datasets in the nearfuture.

REFERENCES

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[2] Hoyt D. V., K. H. Schatten. J. Geophys. Res., 98(A11), 1993, 18 89518 906.[3] Soon W. H. Geophys. Res. Lett., 32, 2005, L16712, doi:10.1029/2005GL023429.

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[15] Krivova N. A., S. K. Solanki. J. Adv. Space Res., 34, 2004, 361364.[16] Usoskin I., G. Kovaltsov.J. Geophys. Res., 111, 2006, D21206, doi: 10.1029/

2006JD007150.[17] Marsh N., H. Svensmark. Space Sci. Rev., 107, 2003, 317325.[18] Mishev A., P. I. Y. Velinov. Compt. rend. Acad. bulg. Sci., 66, 2013, No 10,

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on the influence of total solar irradiance on global land temperature albert varonov, yavor shopov

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