Seasonal and intraseasonal polar motion variability as deduced from atmospheric torques

Abstract

The main objective of this paper is to investigate the atmospheric excitation of seasonal and intraseasonal polar motion based on the so-called torque approach. For the period 2009–2011, we calculate the comprehensive set of equatorial torques acting on the solid Earth, which arise from pressure gradients at topographic features, frictional wind stresses, and mass-induced forces on the Earth’s equatorial bulge. The particular innovation of the study is to use the most recent and accurate meteorological reanalysis data of the ECMWF European Centre for Medium-Range Weather Forecasts and the NASA Global Modeling and Assimilation Office for reassessing the ability of atmospheric torques to explain geophysical signals in observed polar motion. Time domain and statistical comparisons suggest that the torque results are of the same quality as the corresponding values from the traditionally applied angular momentum approach. It is shown that the y component of polar motion variability is particularly well accounted for by torques that act over land areas, while the x component also strongly depends on oceanic excitation. A remarkable result is the excellent agreement of the two utilized atmospheric models in terms of torques on all time scales.

Keywords

• Earth rotation,Seasonal and intraseasonal polar motion,Geophysical excitation,Atmospheric torques

Atmosferik torklardan elde edilen mevsimsel ve mevsim-içi kutup gezinmesi değişimleri

Abstract

Bu makalenin temel amacı mevsimsel ve mevsim-içi kutup gezinmesinin atmosferik eksitasyonunu tork yaklaşımı temelinde incelemektir. Bu çalışmada, 2009-2011 süresince, katı Yer’e etkiyen: topoğrafya üzerindeki atmosfer basınç gradyanlarını, rüzgar sürtünme gerilimlerini ve Yer’in ekvatoral bölgesine etkiyen atmosfer kitlesinin oluşturduğu kuvvetleri içeren bir dizi ekvatoral tork seti hesapladık. Bu çalışmanın kendine özgü yeniliği ise güncel ve duyarlığı yüksek ECMWF European Center for Medium-Range Weather Forecasts ve NASA Global Modeling and Assimilation Office meteorolojik analiz verileri kullanılarak ölçülen kutup gezinmeleri içerisindeki jeofizik sinyallerin atmosferik torklar ile açıklanabilme kabiliyetini ortaya koymaktır. Zaman uzayı ve istatistiksel karşılaştırmalar tork sonuçlarının geleneksel açısal momentum yaklaşımından elde edilen ilgili değerleri ile aynı kalitede olduğunu göstermektedir. Kutup gezinmesinin y bileşenindeki değişimlerin karalara etkiyen torklar ile iyi açıklanabildiği, x bileşeninin ise ayrıca okyanussal eksitasyona güçlü bir şekilde bağlı olduğu ortaya konulmuştur. Dikkate değer diğer bir sonuç ise faydalanılan iki atmosfer modelinden tüm zaman ölçekleri için elde edilen torkların mükemmel uyumudur

Keywords

• Yer dönüklüğü,Mevsimsel ve mevsim-i̇çi kutup gezinmesi,Jeofizik eksitasyon,Atmosferik torklar

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