Importance of Wind for the Excitation of Chandler Wobble as Inferred from Wobble Domain Analysis.

Abstract

We explored the atmospheric contribution to the excitation of Chandler wobble (CW), which has spanned about 11 years beginning from September 1983. The atmospheric angular momentum (AAM) function presented by the Japan Meteorological Agency (JMA) and the wobble data set (SPACE93) are employed. We devised a wobble domain method of analysis which enables us to quantify the narrow band power of AAM. The AAM-induced wobble closely resembles the observed wobble, and wind contribution turns out to dominate over atmospheric pressure contribution in the vicinity of the Chandler frequency. When only pressure contribution is taken into account, it is insufficient, as shown in previous studies.

Three-Dimensional Atmospheric Angular Momentum Simulated by the Japan Meteorological Agency Model for the Period of 1955-1994

“…This disagreement arises not only from the difference in the method of computation of the wind terms mentioned in Section 3 but also from differences in the data assimilation system of the two meteorological centers (see Aoyama and Naito 2000, for detail). Also, the different wobbles simulated by the wind terms from the above two analysis data (Furuya et al 1996(Furuya et al , 1997 could be attributed to the same reasons above. These discrepancies will not be resolved without a further advancement of AMIP (see Gates 1992, for example).…”

“…the annual variation of the polar motion), suggesting differences in their data assimilation systems (for details, see Aoyama and Naito 2000). The same equatorial wind AAM functions on time scales near 14 months were found to excite considerably different Chandler wobbles (Furuya et al 1996(Furuya et al , 1997. These are enigmatic results if we take into account that the meteorological centers acquire similar observed meteorological data in their numerical weather prediction systems.…”

Earth Rotation Variations – Long Period

“…The 1s confidence interval for the Q estimates is given in parentheses. 2011), earthquakes (Gross, 1986;Souriau and Cazenave, 1985), continental water storage Hinnov and Wilson, 1987;Jin et al, 2010;Kuehne and Wilson, 1991;Liao et al, 2004), atmospheric wind and surface pressure variations (Aoyama, 2005;Aoyama and Naito, 2001;Aoyama et al, 2003;Furuya et al, , 1997Liao et al, 2007;Stuck et al, 2005;Wahr, 1983;Wilson and Haubrich, 1976), and oceanic current and bottom pressure variations Brzezinski and Nastula, 2002;Brzezinski et al, 2002b;Gross, 2000b;Gross et al, 2003;Liao, 2005;Liao et al, 2003;Ponte, 2005;Ponte and Stammer, 1999;Seitz and Schmidt, 2005;Seitz et al, 2004Thomas et al, 2005;Zotov and Bizouard, 2012). 2011), earthquakes (Gross, 1986;Souriau and Cazenave, 1985), continental water storage Hinnov and Wilson, 1987;Jin et al, 2010;Kuehne and Wilson, 1991;Liao et al, 2004), atmospheric wind and surface pressure variations (Aoyama, 2005;Aoyama and Naito, 2001;Aoyama et al, 2003;Furuya et al, , 1997Liao et al, 2007;Stuck et al, 2005;...…”

“…For example, Gross et al (2003) studied the excitation of the Chandler wobble during 1980-2000, finding that atmospheric winds and surface pressure and oceanic currents and bottom pressure combined are significantly coherent with and have enough power to excite the Chandler wobble. However, other studies have concluded that atmospheric processes alone have enough power to excite the Chandler wobble (Aoyama, 2005;Aoyama and Naito, 2001;Aoyama et al, 2003;Furuya et al, , 1997. Ocean-bottom pressure variations were found to be the single most effective process exciting the Chandler wobble, with atmospheric surface pressure variations having about 2/3 as much power as ocean-bottom pressure variations and with the power of winds and currents combined being less than 1/3 the power of the combined effects of surface and bottom pressure.…”

Oceanic and atmospheric excitation of the Chandler wobble

“…Since the CW was discovered in 1891, its period, amplitude and damping factor have been estimated by many authors (Munk & MacDonald 1960; Currie 1974; Wilson & Haubrich 1976; Smith & Dahlen 1981; Okubo 1982a,b; Dong 1986; Wilson & Vicente 1990; Zhu 1991, 1992; Gao 1993; Furuya et al 1996; Kuehne et al 1996; Vicente & Wilson 1997). As for the excitation sources, many authors have estimated contributions from the atmosphere (Wilson & Haubrich 1976; Wahr 1983; Furuya et al 1996, 1997; Celaya et al 1999; Aoyama & Naito 2001), continental water storage (Chao et al 1987; Hinnov & Wilson 1987; Kuehne & Wilson 1991), and some other possible excitation sources such as earthquakes (Munk & MacDonald 1960; Lambeck 1980; Gross 1985, 1986; Gross & Chao 1985, 1990; Souriau & Cazenave 1985; Chao & Gross 1987; Gu 1996), core–mantle coupling (Gire & Le Mouel 1986; Hinderer et al 1987; Jault & Le Mouel 1993) and oceanic processes (Ponte et al 1998; Celaya et al 1999; Chao & Zhou 1999; Gross 2000a), etc. Among these excitation mechanisms, the seismic excitation is found to have little effect on the Chandler wobble because their contributions are two to five orders of magnitude smaller than the required Chandler wobble excitation power (Souriau & Cazenave 1985; Gross 1986; Chao & Gross 1987).…”