Yavor Chapanov

Solar-terrestrial energy transfer during sunspot cycles and mechanism of Earth rotation excitation

The solar-terrestrial energy transfer, due to the total solar irradiance (TSI), solar wind and interplanetary magnetic field, has 11-year modulation during the sunspot cycles. Other oscillations of solar-terrestrial energy transfer are with periods of 22 and 45 year due to the magnetic reversal and equatorial solar asymmetry, which cause corresponding oscillations of all Earth systems, including climate and weather, atmosphere and ocean circulations, geomagnetic field and core processes. A part of this energy variation is transformed to oscillations of the Earth rotation. A model of indirect mechanism of Earth rotation excitation during sunspot cycles is proposed, which is based on global water circulation and periodical mass transfer between oceans and polar ice caps. The oscillations of the mean sea level (MSL) with periods 11, 22 and 45 years are determined by sea level data for the last two centuries from 13 maregraph stations. The necessary energy of water evaporation, corresponding to the observed MSL variations is provided by TSI oscillations with amplitudes between 0.2-0.5W/m 2 , determined by means of reconstructed time series of the TSI since 1610. The determined mean Universal Time (UT1) amplitudes, corresponding to the 22-year and 45-year cycles of the solar activity are 185ms and 310ms.

Common 22-year cycles of Earth rotation and solar activity

Astronomical Institute, Academy of Sciences of Czech RepublicBoˇcn´i II, 141 31 Prague, Czech Republicemail: vondrak@ig.cas.cz, ron@ig.cas.czAbstract.The 22-year oscillations of the Earth rotation due to several geophysical processesin the core-mantle system, oceans, atmosphere and geomagnetic field are excited mainly by 22-year cycles of the solar activity. These geophysical processes produce their own oscillations ofthe Earth rotation with different periods around 22 years. The direct and indirect influence ofthe solar activity on 22-year cycles of the Earth rotation are separated from the core effects andcorresponding amplitudes are estimated by means of two approaches. The first, direct approachuses extended time series of Wolf’s numbers with22-year cycles, determined by sign alternationof even sunspot cycles. A linear regression between 22-year cycles of UT1 and solar activityis determined and this regression model is used to calculate the UT1 response to the 22-yearcycles of the solar activity. The second, indirect approach uses 22-year oscillation of the mean sealevel, caused by water evaporation due to variations of the total solar irradiance. The influenceof the mean sea level variations on the Earth rotation is calculated by means of an empiricalmodel of global water redistribution. The core-mantle effects on the 22-year UT1 variations aredetermined by excluding the UT1 response to the solar activity and core angular momentumdue to the geomagnetic field variations, according to the solutions from the Special Bureau oftheCore(SBC).Keywords.Sun: activity, sunspots, solar-terrestrial relations, time

Influence of AAM and OAM on the Universal Time Variations

Atmospheric Angular Momentum (AAM) and Ocean Angular Momentum (OAM) function excite Length of Day (LOD) variations and affect Universal Time (UT1) variations at wide frequency band also, which appear as parasitical noise in some problems of parameters estimation. The influences of AAM and OAM on UT1 are determined by an integrating of the AAM and OAM excitation functions of LOD, after removing of their constant parts. The resulting series still contain significant linear trends for some intervals, due to relatively small systematic deviations from the total mean value of LOD excitation (less than 80 μs). The final UT1 corrections for AAM and OAM influences are determined by removing of the residual trends. The maximal AAM effect on UT1 variations is about 100 ms and 1–2ms for OAM series. The obtained time series have good consistency and their application yield more precise estimation of the periodical terms of the Earth rotation.

Decadal Oscillations of The Earth Rotation

The aim of the paper is to create a model of decadal variations of the universal time UT1 for the period 1623.5–2005.5. This model includes polynomial terms of power 2 and Fourier approximation of the periodical part using 100 harmonics, where some of them represent the intrinsic periods of natural phenomena: solar equatorial asymmetry—45a, solar magnetic cycle—22a, lunar node—18.6a and sunspot variations—11a. The coefficients of this model are determined by the Least Squares Method with amplitude estimation accuracy about 11 ms. A separation between the UT1 responses to the sunspots cycles and 12‐year core signals is made.

Earth rotation response to ENSO events

The Earth rotation response to El‐Nino/Southern Oscillation (ENSO) events is investigated by means of Fourier approximation of the universal time (UT1‐TAI) variations according solution C04 of the IERS. The UT1 variations at ENSO frequencies are approximated by 21 oscillations with periods between 1.5 and 5.4 years, whose superposition yields time series with behavior rather similar to the variations of ENSO Index. The delay of the UT1 response to the ENSO events is about 0.5a. The correlation between the variations of ENSO Index and UT1 is negative and with coefficients between −0.59 and −0.68 for some periods. A linear regression UT1−TAI = −73.78EI−8.53 [ms] between UT1 variations and ENSO Index EI is determined. The comparisons between the EI variations for the past epochs and the UT1‐TAI backward extrapolation shows that the model of UT1, based on Fourier approximation, has weak prediction ability.