Secular Variation of Atmospheric Turbidity over Japan

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.

Download Full-text

Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites

Earth Planets and Space ◽

10.1186/s40623-021-01357-9 ◽

2021 ◽

Vol 73 (1) ◽

Cited By ~ 1

Author(s):

Magnus D. Hammer ◽

Grace A. Cox ◽

William J. Brown ◽

Ciarán D. Beggan ◽

Christopher C. Finlay

Keyword(s):

Time Series ◽

Secular Variation ◽

Geomagnetic Field ◽

Time Windows ◽

Low Earth Orbit ◽

Data Selection ◽

Spherical Harmonic Analysis ◽

Core Field ◽

The Core ◽

Swarm Satellites

AbstractWe present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

Download Full-text

Excursions and secular variation of the Brunhes epoch geomagnetic field in the Indian Ocean region

Journal of Geophysical Research Atmospheres ◽

10.1029/jb078i026p06060 ◽

1973 ◽

Vol 78 (26) ◽

pp. 6060-6068 ◽

Cited By ~ 29

Author(s):

N. D. Watkins ◽

J. Nougier

Keyword(s):

Indian Ocean ◽

Secular Variation ◽

Geomagnetic Field ◽

Indian Ocean Region ◽

Ocean Region ◽

The Indian Ocean

Download Full-text

Geomagnetic Core Field Secular Variation Models

Space Science Reviews ◽

10.1007/s11214-009-9586-6 ◽

2009 ◽

Vol 155 (1-4) ◽

pp. 129-145 ◽

Cited By ~ 34

Author(s):

N. Gillet ◽

V. Lesur ◽

N. Olsen

Keyword(s):

Secular Variation ◽

Core Field

Download Full-text

Rock-magnetic changes with reduction diagenesis in Japan Sea sediments and preservation of geomagnetic secular variation in inclination during the last 30,000 years

Earth Planets and Space ◽

10.1186/bf03351766 ◽

2003 ◽

Vol 55 (6) ◽

pp. 327-340 ◽

Cited By ~ 76

Author(s):

Toshitsugu Yamazaki ◽

Abdelaziz L. Abdeldayem ◽

Ken Ikehara

Keyword(s):

Secular Variation ◽

Japan Sea ◽

Geomagnetic Secular Variation

Download Full-text

Dating Late Pleistocene Pluvial Events and Tephras by Correlating Paleomagnetic Secular Variation Records from the Western Great Basin

Quaternary Research ◽

10.1016/0033-5894(92)90029-i ◽

1992 ◽

Vol 38 (1) ◽

pp. 46-59 ◽

Cited By ~ 17

Author(s):

Robert M. Negrini ◽

Jonathan O. Davis

Keyword(s):

Great Basin ◽

Secular Variation ◽

Hot Springs ◽

Time Interval ◽

Lake Basin ◽

Lake Surface ◽

Surface Level ◽

Sedimentary Sequences ◽

Tephra Layers ◽

Geologic Record

AbstractPaleomagnetic records are used to correlate sedimentary sequences from pluvial Lakes Chewaucan and Russell in the western Great Basin. This correlation is the basis for age control in the relatively poorly dated sequence from Lake Chewaucan. The resulting chronology supports a lack of sedimentation in Lake Chewaucan during the interval 27,400 to 23,200 yr B.P., an assertion supported by the presence of a lag deposit at the corresponding stratigraphic horizon. Because the Lake Chewaucan outcrop (near Summer Lake, Oregon) is near the bottom of the lake basin, we conclude that Lake Chewaucan was at a lowstand during this time interval. The Chewaucan lowstand is coeval with the lowstand accompanying the Wizard's Beach Recession (isotope stage 3) previously seen in the geologic record from nearby pluvial Lake Lahontan. The ages of six tephra layers, including the Trego Hot Springs tephra, were also estimated using the paleomagnetic correlation. Together, the new age of the Trego Hot Springs tephra (21,800 yr B.P.) and the lake surface level prehistory of Lake Chewaucan imply a revised model for the lake surface level prehistory of Lake Lahontan. The revised model includes a longer duration for the Wizard's Beach Recession and the occurrence of a younger lowstand of short duration soon after the lowstand corresponding to the Wizard's Beach Recession.

Download Full-text