Patterns of atmospheric excitation functions of polar motion from high‐resolution regional sectors

Abstract

[1] In this paper regional values of equatorial components of the atmospheric excitation function of polar motion, which are proportional to the equatorial components of angular momentum (AAM), were computed at high spatial resolution in 3312 equal-area sectors from the surface pressure fields of the NCEP-NCAR reanalyses in order to improve our knowledge of patterns of atmospheric excitation functions of polar motion. The inverted barometer (IB) model of oceanic isostatic adjustment is applied to readjust the effective atmospheric pressure fields. To identify the influence of different geographic regions of the atmosphere on the excitation of polar motion, correlations and covariances between these regional excitations values and either the global geodetic excitation function, determined from the geodetic observational data, or the atmospheric excitation functions, equivalent to the sum of such excitations in all regions, were computed in different spectral bands, from subseasonal to interannual period ones. The covariances show the regional contribution to the global excitation, whereas the correlations show an overall similar relationship. Furthermore, these analyses determine regional sources of polar motion excitation by surface pressure variations in the atmosphere in different spectral bands. The broad regions over Eurasia and North America were identified as principal atmospheric excitation sources for polar motion. The results revealed that atmospheric excitation over land regions in the northern middle latitudes, especially over Asia, is exceptionally strong, a point generally noted in previous studies, though without identifying detailed features. Over the Himalayan Mountains the covariance of local with global atmospheric excitation in the annual band forms a small minimum surrounded by larger values in a ring-like formation. For other terms, maxima of atmospheric excitation have a longitudinal formation mostly across the Eurasian continent. The atmospheric excitation of polar motion over the ocean is weak when subject to the IB correction, but it contains nevertheless a clear annual signal and is highly correlated with the annual oscillation of the global geodetic excitation function of polar motion.

Earth Rotation Variations – Long Period

“…Abarca del Rio and Cazenave (1994) compared the observed excitation of the Earth's wobbles to atmospheric excitation during 1980-91, finding similar fluctuations both in components on timescales between 1 and 3 years and in the y-component on timescales between 1.2 and 8 years, but only when the atmospheric excitation is computed assuming the oceans fully transmit the imposed atmospheric pressure variations to the floor of the oceans (rigid ocean approximation). Although little agreement was found with the SOI, a significant agreement was found with the NAOI, especially for the x-component of the observed excitation function, indicating a possible meteorologic origin of the interannual wobbles (also see Nastula et al, 2009;Neef and Matthes, 2012;Zhou et al, 1998). Although little agreement was found with the SOI, a significant agreement was found with the NAOI, especially for the x-component of the observed excitation function, indicating a possible meteorologic origin of the interannual wobbles (also see Nastula et al, 2009;Neef and Matthes, 2012;Zhou et al, 1998).…”

“…Chao and Au (1991) showed that during 1980-88, the amplitude of the prograde annual polar motion excitation can be accounted for by atmospheric wind and pressure fluctuations, with equatorial winds contributing about 25% and pressure fluctuations contributing about 75% to the total atmospheric excitation. Discrepancies as large as a factor of two in amplitude were also found by Chao and Au (1991) between observed semiannual polar motion excitation and that due to atmospheric processes (also see Aoyama and Naito, 2000;Barnes et al, 1983;Chao, 1993;Dobslaw et al, 2010;King and Agnew, 1991;Kolaczek et al, 2003;Merriam, 1982;Nastula and Kolaczek, 2002;Nastula et al, , 2009Neef and Matthes, 2012;Stuck et al, 2005;Wahr, 1983;Wilson and Haubrich, 1976;Zhou et al, 2006Zhou et al, , 2008. Furthermore, no agreement was found by Chao and Au (1991) between the observed retrograde annual polar motion excitation and that due to atmospheric processes, with atmospheric excitation being about twice as large as the observed excitation.…”

Regional atmospheric influence on the Chandler wobble

“…Like in Liao et al (2007) and we will determine the regional contribution to EAAM in Chandler band, but after having designed a narrow-band Panteleev filter as in Zotov and Bizouard (2012). Unlike Nastula et al (2009Nastula et al ( , 2014, we do not calculate covariances between regional contribution to EAAM and excitation. We focus our study on filtered AAM fields in Chandler frequency band and their evolution: animated maps permit to track changes of the atmospheric excitation sources and their geographical location, Hovmoeller plots are used to characterise temporal evolution over latitude and longitude bands.…”

Commission 19: Rotation of the Earth

“…During the past triennium, investigations in the U.S. of the Earth's time varying rotation followed a number of themes, including theoretical studies (Gross, 2011), tidal variations (Gross, 2009a(Gross, , 2009b(Gross, , 2009cDickman, 2010;Dickman and Gross, 2010;Gross and Dickman, 2011), glacial isostatic adjustment (Matsuyama et al, 2010;Mitrovica and Wahr, 2011), effects of global geophysical fluids (Dey and Dickman, 2010;Dickey et al, 2010;Landerer et al, 2009;Marcus et al, 2010;Nastula et al, 2009;Schindelegger et al, 2011;), effects of earthquakes (Gross and Chao, 2010), effects of the core (Buffett, 2010a(Buffett, , 2010bBuffett et al, 2009;Dickey and de Viron, 2009;Dickey et al, 2011), comparisons with gravity measurements (Cheng et al, 2011;Gross et al, 2009;Jin et al, 2010Jin et al, , 2011, and improving predictions (Chin et al, 2009;Gambis and Luzum, 2011;42 DIVISION I / COMMISSION 19 Gambis et al, 2011;Kalarus et al, 2010;Luzum and Nothnagel, 2010). Attention has been given to the use of atmospheric models to investigate the changes in Earth rotation that might be expected due to climate variability and possible secular changes The most important IAG meetings held in 2009-2011 were:…”