A New Exospheric Temperature Model Based on CHAMP and GRACE Measurements

In this study, the effective exospheric temperature, derived from CHAMP and GRACE density measurements during 2002–2010, was utilized to develop a new exospheric temperature model (ETM) with the aid of the NRLMSIS 2.0 empirical model. We characterized the dominant modes of global exospheric temperature using the principal component analysis (PCA) method, and the first five derived empirical orthogonal functions (EOFs) captured 98.2% of the total variability. The obtained mean field, first five EOFs and the corresponding amplitudes were applied to build ETM using the polynomial method. The ETM and NRLMSIS 2.0 models were independently validated by the SWARM-C and GRACE Follow-On (GRACE-FO) density measurements. ETM can reproduce thermospheric density much better than the NRLMSIS 2.0 model, and the Root Mean Square Errors (RMSE) of ETM predictions were approximately 26.45% and 26.17% for the SWARM-C and GRACE-FO tests, respectively, while they were 39.52% and 44.41% for the NRLMSIS 2.0 model. In addition, ETM can accurately capture the equatorial thermospheric anomaly feature, seasonal variation and hemispheric asymmetry in the thermosphere

A new empirical model of NmF2 based on CHAMP, 3 GRACE and COSMIC radio occultation

To facilitate F2-layer peak density (NmF2) modeling, a nonlinear polynomial model approach based on global NmF2 observational data from ionospheric radio occultation (IRO) measurements onboard the CHAMP, GRACE, and COSMIC satellites, is presented in this paper. We divided the globe into 63 slices from 80°S to 80°N according to geomagnetic latitude. A Nonlinear Polynomial Peak Density Model (NPPDM) was constructed by a multivariable least squares fitting to NmF2 measurements in each latitude slice and the dependencies of NmF2 on solar activity, geographical longitude, universal time, and day of year were described. The model was designed for quiet and moderate geomagnetic conditions (Ap ≤ 32). Using independent radio occultation data, quantitative analysis was made. The correlation coefficients between NPPDM predictions and IRO data were 0.91 in 2002 and 0.82 in 2005. The results show that NPPDM performs better than IRI2016 and Neustrelitz Peak Density Model (NPDM) under low solar activity, while it undergoes performance degradation under high solar activity. Using data from twelve ionosonde stations, the accuracy of NPPDM was found to be better than that of NPDM and comparable to that of IRI2016. Additionally, NPPDM can well simulate the variations and distributions of NmF2 and describe some ionospheric features, including the equatorial ionization anomaly, the mid-latitude trough, and the wavenumber-four longitudinal structure

Magnetic characteristics of LaMnO3+δ thin films deposited by RF magnetron sputtering in an O2/Ar mixture gas

In this work, LaMnO _3+ _δ thin films have been successfully fabricated by RF magnetron sputtering using different O _2 /Ar flux ratios. The crystal structures, morphologies, stoichiometry, surface chemical states and magnetic properties of films are thoroughly characterized by x-ray powder diffraction (XRD), Raman spectrometer, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The magnetic characteristics of LaMnO _3+ _δ films are systematically studied with the transformation from Mn ^3+ to Mn ^4+ , which is strongly controlled by the deposited O _2 /Ar flux ratios. We demonstrate that LaMnO _3+ _δ films undergo an antiferromagnet, the coexistence of ferromagnetism and antiferromagnetism and a robust ferromagnetism ordering by the variation of Mn ^3+ /Mn ^4+ ratios. The LMO film deposited in pure argon atmosphere shows negligible FM signal and an inconspicuous T _C . With the increase of deposited O _2 /Ar flux ratios, the Curie temperature of LMO films increases from 100 K to 224 K and then decreases to 140 K and meanwhile the irreversibility temperature fluctuates between 24 K and 100 K. The appearance of cluster glass state and the unexpected exchange bias phenomenon where the film deposited at highest O _2 /Ar flux ratio has a H _EB  ∼ 115 Oe is observed. All these evolutions of magnetization characteristics are discussed in terms of the strength of ferromagnetic interactions and the degree of competition between ferromagnetic and antiferromagnetic interactions in LaMnO _3+ _δ films. Our work serves as prerequisites for LaMnO _3 -based magnetic heterostructures grown by RF magnetron sputtering