Barbara Kolaczek

Oceanic excitation of polar motion from intraseasonal to decadal periods

We study the oceanic excitation of polar motion by using six different time series of the non-tidal oceanic angular momentum which are either publicly available or more experimental in nature. The oceanic excitation series are compared to each other and to the difference between the excitation inferred from the polar motion data and the corresponding atmospheric contributions. Comparisons show good agreement between the observed residual excitation and most of the ocean series. By performing computations separately for the seasonal sinusoids and four non-overlapping spectral components decadall, interannual, seasonal and intraseasonal) we demonstrate that the quality of the ocean products depends on the considered frequency band. We also discuss the importance of using data-constrained ocean models in future efforts to improve ocean angular momentum estimates.

El Nino-related variations in atmosphere–polar motion interactions

Abstract The influence of El Nino phenomena on the correlation between atmospheric and geodetic excitation functions of polar motion during four decades, from 1962 to 2000, is studied. These correlations are computed in three different spectral ranges of polar motion variations, namely 90–150, 150–230 and 230–450 days, which include the 120-day, semiannual, and annual oscillations, respectively. These correlation coefficients are variable in all spectra ranges. They are the most stable in the case of the annual oscillation, reaching maxima of about 0.9. In the case of the semiannual oscillation they are more variable, especially before 1970, and they reach maximum values of 0.8–0.9. In the case of the 120-day oscillation, correlation coefficients are the most variable, though more stable after 1980. The disturbances of correlation coefficients between atmospheric and geodetic excitation functions of polar motion are highly correlated with the epochs of El Nino/La Nina phenomena in the most cases, suggesting that during these events, non-atmospheric effects, such as those in the ocean, also have an influence on polar motion.

Assessment of the Global and Regional Land Hydrosphere and Its Impact on the Balance of the Geophysical Excitation Function of Polar Motion

The impact of continental hydrological loading from land water, snow and ice on polar motion excitation, calculated as hydrological angular momentum (HAM), is difficult to estimate, and not as much is known about it as about atmospheric angular momentum (AAM) and oceanic angular momentum (OAM). In this paper, regional hydrological excitations to polar motion are investigated using monthly terrestrial water storage data derived from the Gravity Recovery and Climate Experiment (GRACE) mission and from the five models of land hydrology. The results show that the areas where the variance shows large variability are similar for the different models of land hydrology and for the GRACE data. Areas which have a small amplitude on the maps make an important contribution to the global hydrological excitation function of polar motion. The comparison of geodetic residuals and global hydrological excitation functions of polar motion shows that none of the hydrological excitation has enough energy to significantly improve the agreement between the observed geodetic excitation and geophysical ones.

Excitations of Polar Motion from an Ensemble of Global Atmospheric Models

We study how atmospheric models can be best used to understand excitations of polar motion. The set of models consists of those contributed worldwide by meteorological centers participating in the Atmospheric Model Intercomparison Project, which are forced solely by a prescribed distribution of sea surface temperatures. We have calculated the monthly mean values of excitations from the resulting surface pressure fields over the 17-year study period. With such historical variability and with the spread inherent in the suite of models, a measure of the excitations of polar motion can be obtained, including variability at intraseasonal and seasonal scales; from these models we can also view the resulting interannual variability, including the impact of El Nino events. We compare the results with the excitations determined by atmospheric analyses, as well as with the geodetic excitation functions themselves, determined from analysis of observations. Based on the suite of atmospheric models we estimate the spread in the polar motion excitation from the ensemble of 19 different models.