This　study　analyzes　the　geophysical　signals　in　J2　time　series　from　1976　to　2020　by　using　singular　spectrum　analysis　(SSA)　and　the　Lomb-Scargle　(L-S)　periodogram　for　the　first　time.　The　results　of　SSA　indicate　that　the　secular　trend　is　characterized　by　a　superposition　of　the　secular　linear　decrease　with　a　rate　of　approximately　(−5.80　±　0.08)　×　10−11/yr　and　an　obvious　quadratic　rate　of　(2.38　±　0.02)　×　10−13/yr2　.　Besides,　the　annual,　semi-annual,　and　10.6-year　signals　with　determining　for　the　first　time　its　amplitude　of　5.01　×　10−11,　are　also　detected　by　SSA,　where　their　stochastic　behavior　can　be　maintained　to　the　greatest　extent.　The　18.6-year　signal　cannot　be　detected　by　SSA　even　when　the　window　size　of　18.6　years　was　selected,　while　L-S　periodogram　can　detect　the　signal　of　18.6　years　after　removing　the　18.6-year　tidal　theoretical　value　and　the　linear　trend,　proving　the　existence　of　the　tidal　variations　of　18.6　years　in　the　residual　time　series.　Nevertheless,　the　10.6-year　signal　can　be　found　only　after　removing　the　secular　trend.　This　fact　suggests　that　the　advantages　of　different　methods　used　will　lead　to　different　sensitivity　to　the　particular　signals　hard　to　be　detected.　Finally,　the　reconstructed　J2　time　series　through　the　sum　of　the　climate-driven　contributions　from　glacial　isostatic　adjustment　(GIA),　Antarctic　ice　sheets　(ANT),　atmosphere　(ATM),　continental　glaciers　(GLA),　Greenland　ice　sheets　(GRE),　ocean　bottom　pressure　(OBP),　and　terrestrial　water　storage　(TWS)　by　using　GRACE　gravity　field　solution　and　geophysical　models　agrees　very　well　with　that　of　the　observed　J2　from　SLR　in　terms　of　the　amplitude　and　phase.　About　81.5%　of　observed　J2　can　be　explained　by　the　reconstructed　value.　ATM,　TWS,　and　OBP　are　the　most　significant　contributing　sources　for　seasonal　signals　in　J2　time　series,　explaining　up　to　40.1%,　31.9%,　and　26.3%　of　the　variances　of　observed　J2　.　These　three　components　contribute　to　the　annual　and　semi-annual　variations　of　the　observed　J2　up　to　30.1%　and　1.6%,　30.8%　and　1.0%,　as　well　as　25.4%　and　0.7%,　respectively.　GRE,　ANT,　and　GLA　have　~3　to　~7-year　periodic　fluctuations　and　a　positive　linear　trend,　excluding　GIA.　©　2021　by　the　authors.　Licensee　MDPI,　Basel,　Switzerland.