scholarly journals On polar daily geomagnetic variation

2015 ◽  
Vol 58 (5) ◽  
Author(s):  
Paola De Michelis ◽  
Giuseppe Consolini
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Field ◽  
Empirical Orthogonal Functions ◽  
Activity Level ◽  
Geomagnetic Variation ◽  
Orthogonal Functions ◽  
Equivalent Current ◽  
Dominant Component ◽  
Magnetospheric Currents ◽  
Current Representation

<p style="-qt-block-indent: 0; text-indent: 0px; margin: 0px;">The aim of this work is to investigate the nature of the daily magnetic field perturbations produced by ionospheric and magnetospheric currents at high latitudes. We analyse the hourly means of the X and Y geomagnetic field components recorded by a meridian chain of permanent geomagnetic observatories in the polar region of the Northern Hemisphere during a period of four years (1995-1998) around the solar minimum. We apply a mathematical method, known as natural orthogonal component (NOC), which is capable of characterizing the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). Using the first two modes we reconstruct a two-dimensional equivalent current representation of the ionospheric electric currents, which contribute substantially to the geomagnetic daily variations. The obtained current structures resemble the equivalent current patterns of DP2 and DP1. We characterize these currents by studying their evolution with the geomagnetic activity level and by analysing their dependence on the interplanetary magnetic field. The obtained results support the idea of a coexistence of two main processes during all analysed period although one of them, the directly driven process, represents the dominant component of the geomagnetic daily variation.</p>

scholarly journals On the terms of geomagnetic daily variation in Antarctica

2009 ◽  
Vol 27 (6) ◽  
pp. 2483-2490 ◽  
Author(s):  
P. De Michelis ◽  
R. Tozzi ◽  
A. Meloni
Keyword(s):  
Geomagnetic Field ◽  
Daily Variation ◽  
Empirical Orthogonal Functions ◽  
High Latitudes ◽  
Orthogonal Functions ◽  
Modes Of Variability ◽  
Magnetospheric Currents ◽  
Geomagnetic Data ◽  
Magnetic Perturbations ◽  
The Magnetic Field

Abstract. The target of this work is to investigate the nature of magnetic perturbations produced by ionospheric and magnetospheric currents as recorded at high-latitude geomagnetic stations. In particular, we investigate the effects of these currents on geomagnetic data recorded in Antarctica. To this purpose we apply a mathematical method, known as Natural Orthogonal Composition, to analyze the magnetic field disturbances along the three geomagnetic field components (X, Y and Z) recorded at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7° S, 164.1° E) from 1995 to 1998. Using this type of analysis, we characterize the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, we find that some of them are actually related to well known current patterns located at high latitudes.

Decomposing the geomagnetic field: oscillation modes and characteristics

2020 ◽  
Author(s):  
Cristiana Stefan ◽  
Venera Dobrica ◽  
Crisan Demetrescu
Keyword(s):  
Geomagnetic Field ◽  
Field Model ◽  
Empirical Orthogonal Functions ◽  
Time Span ◽  
Eof Analysis ◽  
Detailed Structure ◽  
Orthogonal Functions ◽  
Oscillation Modes ◽  
Field Oscillation

&lt;p&gt;Using the COV-OBS.x1 (Gillet et al., 2015) main geomagnetic field model, covering the time span 1840&amp;#8211;2020, respectively IGRF-13 (1900-2020), we decomposed the geomagnetic field at Earth&amp;#8217;s surface in oscillation modes by means of empirical orthogonal functions (EOF) as well into a long term and a cyclic component using HP filtering (Hodrick and Prescott, 1997). Further, the long term component is filtered using a Butterworth filter (1930) with different cut-off periods in order to obtain oscillation at inter-centennial (&gt; 100 years) and sub-centennial (60-90 years) timescales. The EOF analysis shows that the first three oscillation modes are characterized by periodicities of &gt;100 years while modes 4 and 5 are characterized by dominant periodicities of 70-90 year. Although the variance of the modes 4 and 5 is rather small compared to that of the first three modes, these two modes are responsible for the detailed structure of the geomagnetic field. A comparison between the results of both methods is done as well.&lt;/p&gt;

Analysis of Geomagnetic Variability by Empirical Orthogonal Functions

2020 ◽  
Author(s):  
Chi-Hua Chung ◽  
Benjamin Fong Chao
Keyword(s):  
Geomagnetic Field ◽  
Empirical Orthogonal Functions ◽  
Spatial Structures ◽  
Orthogonal Functions ◽  
Core Mantle Boundary ◽  
The Core ◽  
Orthogonal Function ◽  
Secular Variations ◽  
Complex Eof ◽  
Westward Drift

&lt;p&gt;We examine the secular variations of global geomagnetic field on long temporal scales using the IGRF model given in Gauss coefficients for 1900 - 2020. We apply the Empirical Orthogonal Function (EOF) analysis to the geomagnetic field truncated at degree 6 and downward continue it to the core-mantle boundary (CMB) under the assumption of an insulating mantle. The first three EOF modes show the periods around 120, 75 and 60 years with corresponding spatial structures. These oscillational modes potentially support the manifestation of magnetic, Archimedes and Coriolis (MAC) waves in the stably stratified layer near CMB (Buffett, 2016). We also model and decompose the geomagnetic field to standing and drifting components according to trajectories of the Gauss coefficients similarly to Yukutake (2015). We then use the Complex EOF (CEOF) analysis on the drifting field. The results indicate the presence of the westward drift phenomenon but only weakly given the fact that the westward drift has only completed a fraction of a cycle during this time.&lt;/p&gt;

Empirical Methods in Short-Term Climate Prediction

2006 ◽  
Author(s):  
Huug van den Dool
Keyword(s):  
Climate Prediction ◽  
Empirical Orthogonal Functions ◽  
Data Sets ◽  
Seasonal Forecasts ◽  
Short Term ◽  
Orthogonal Functions ◽  
Ocean Atmosphere Interaction ◽  
Global Coverage ◽  
Atmosphere Interaction ◽  
Global Data

This clear and accessible text describes the methods underlying short-term climate prediction at time scales of 2 weeks to a year. Although a difficult range to forecast accurately, there have been several important advances in the last ten years, most notably in understanding ocean-atmosphere interaction (El Nino for example), the release of global coverage data sets, and in prediction methods themselves. With an emphasis on the empirical approach, the text covers in detail empirical wave propagation, teleconnections, empirical orthogonal functions, and constructed analogue. It also provides a detailed description of nearly all methods used operationally in long-lead seasonal forecasts, with new examples and illustrations. The challenges of making a real time forecast are discussed, including protocol, format, and perceptions about users. Based where possible on global data sets, illustrations are not limited to the Northern Hemisphere, but include several examples from the Southern Hemisphere.

scholarly journals Predictions of the geomagnetic secular variation based on the ensemble sequential assimilation of geomagnetic field models by dynamo simulations

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Sabrina Sanchez ◽  
Johannes Wicht ◽  
Julien Bärenzung
Keyword(s):  
Magnetic Field ◽  
Secular Variation ◽  
Geomagnetic Field ◽  
Wave Number ◽  
Main Magnetic Field ◽  
Candidate Model ◽  
Uncertainty Estimates ◽  
Geomagnetic Field Models ◽  
Dipole Configuration

Abstract The IGRF offers an important incentive for testing algorithms predicting the Earth’s magnetic field changes, known as secular variation (SV), in a 5-year range. Here, we present a SV candidate model for the 13th IGRF that stems from a sequential ensemble data assimilation approach (EnKF). The ensemble consists of a number of parallel-running 3D-dynamo simulations. The assimilated data are geomagnetic field snapshots covering the years 1840 to 2000 from the COV-OBS.x1 model and for 2001 to 2020 from the Kalmag model. A spectral covariance localization method, considering the couplings between spherical harmonics of the same equatorial symmetry and same azimuthal wave number, allows decreasing the ensemble size to about a 100 while maintaining the stability of the assimilation. The quality of 5-year predictions is tested for the past two decades. These tests show that the assimilation scheme is able to reconstruct the overall SV evolution. They also suggest that a better 5-year forecast is obtained keeping the SV constant compared to the dynamically evolving SV. However, the quality of the dynamical forecast steadily improves over the full assimilation window (180 years). We therefore propose the instantaneous SV estimate for 2020 from our assimilation as a candidate model for the IGRF-13. The ensemble approach provides uncertainty estimates, which closely match the residual differences with respect to the IGRF-13. Longer term predictions for the evolution of the main magnetic field features over a 50-year range are also presented. We observe the further decrease of the axial dipole at a mean rate of 8 nT/year as well as a deepening and broadening of the South Atlantic Anomaly. The magnetic dip poles are seen to approach an eccentric dipole configuration.

scholarly journals Spatio-Temporal Patterns of Mass Changes in Himalayan Glaciated Region from EOF Analyses of GRACE Data

2021 ◽  
Vol 13 (2) ◽  
pp. 265
Author(s):  
Harika Munagapati ◽  
Virendra M. Tiwari
Keyword(s):  
Temperature Anomaly ◽  
Mass Gain ◽  
Snow Accumulation ◽  
Empirical Orthogonal Functions ◽  
Total Water ◽  
Orthogonal Functions ◽  
Grace Data ◽  
Grace Satellite ◽  
Spatio Temporal ◽  
Gravity Recovery

The nature of hydrological seasonality over the Himalayan Glaciated Region (HGR) is complex due to varied precipitation patterns. The present study attempts to exemplify the spatio-temporal variation of hydrological mass over the HGR using time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) satellite for the period of 2002–2016 on seasonal and interannual timescales. The mass signal derived from GRACE data is decomposed using empirical orthogonal functions (EOFs), allowing us to identify the three broad divisions of HGR, i.e., western, central, and eastern, based on the seasonal mass gain or loss that corresponds to prevailing climatic changes. Further, causative relationships between climatic variables and the EOF decomposed signals are explored using the Granger causality algorithm. It appears that a causal relationship exists between total precipitation and total water storage from GRACE. EOF modes also indicate certain regional anomalies such as the Karakoram mass gain, which represents ongoing snow accumulation. Our causality result suggests that the excessive snowfall in 2005–2008 has initiated this mass gain. However, as our results indicate, despite the dampening of snowfall rates after 2008, mass has been steadily increasing in the Karakorum, which is attributed to the flattening of the temperature anomaly curve and subsequent lower melting after 2008.

scholarly journals Survival of molecular gas in a stellar feedback-driven outflow witnessed with the MUSE TIMER project and ALMA

2019 ◽  
Vol 488 (3) ◽  
pp. 3904-3928 ◽  
Author(s):  
Ryan Leaman ◽  
Francesca Fragkoudi ◽  
Miguel Querejeta ◽  
Gigi Y C Leung ◽  
Dimitri A Gadotti ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Mechanical Energy ◽  
Molecular Gas ◽  
Ionized Gas ◽  
Star Forming ◽  
Stellar Feedback ◽  
Dominant Component ◽  
The Galaxy ◽  
Field Lines

ABSTRACT Stellar feedback plays a significant role in modulating star formation, redistributing metals, and shaping the baryonic and dark structure of galaxies – however, the efficiency of its energy deposition to the interstellar medium is challenging to constrain observationally. Here we leverage HST and ALMA imaging of a molecular gas and dust shell ($M_{\mathrm{ H}_2} \sim 2\times 10^{5}\, {\rm M}_{\odot }$) in an outflow from the nuclear star-forming ring of the galaxy NGC 3351, to serve as a boundary condition for a dynamical and energetic analysis of the outflowing ionized gas seen in our MUSE TIMER survey. We use starburst99 models and prescriptions for feedback from simulations to demonstrate that the observed star formation energetics can reproduce the ionized and molecular gas dynamics – provided a dominant component of the momentum injection comes from direct photon pressure from young stars, on top of supernovae, photoionization heating, and stellar winds. The mechanical energy budget from these sources is comparable to low luminosity active galactic neuclei, suggesting that stellar feedback can be a relevant driver of bulk gas motions in galaxy centres – although here ≲10−3 of the ionized gas mass is escaping the galaxy. We test several scenarios for the survival/formation of the cold gas in the outflow, including in situ condensation and cooling. Interestingly, the geometry of the molecular gas shell, observed magnetic field strengths and emission line diagnostics are consistent with a scenario where magnetic field lines aided survival of the dusty ISM as it was initially launched (with mass-loading factor ≲1) from the ring by stellar feedback. This system’s unique feedback-driven morphology can hopefully serve as a useful litmus test for feedback prescriptions in magnetohydrodynamical galaxy simulations.

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