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Creators/Authors contains: "Zhai, Changzhi"

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  1. Abstract

    A thermospheric O and N2column density ratio (∑O/N2) depletion with long‐duration (>16 hr) was observed by the Global‐scale Observations of the Limb and Disk at the Atlantic longitudes (75W–20W) and middle latitudes (20N–50N) during the recovery phase of the 8 June 2019 geomagnetic storm. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations reproduced the ∑O/N2depletion patterns with a similar magnitude, and indicated that the composition recovery at middle latitudes began several hours after the beginning of the recovery phase of the geomagnetic storm. The TIEGCM simulations enable quantitative analysis of the physical mechanisms driving the middle‐latitude composition changes during the storm recovery phase. This analysis indicates that vertical advection and molecular diffusion dominated the initial recovery of composition perturbations at middle latitudes. Horizontal advection was also a main driver in the initial recovery of composition, but its contribution decreased rapidly. In the late recovery phase, the composition recovery was mainly determined by horizontal advection. In comparison, vertical advection and molecular diffusion played a much less important role.

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  2. Abstract

    GPS total electron content (TEC) measurements were used to investigate high‐m ultralow frequency (ULF) waves during the recovery phase of a geomagnetic storm. ULF wave signals in TEC data show high coherence and significant common power in the wavelet coherence and cross wavelet transform analyses with magnetic field radial component data from GOES‐15. They did not cause significant ionospheric scintillation or ground magnetic signatures due to ionospheric screening effects. An automatic identification procedure is developed to identify ULF wave signature in TEC data from 10 GPS receivers on January 25, 2016. The waves were mainly distributed on the dayside and post dusk sector from ∼64° to ∼71° magnetic latitude. This is the first time that the large‐scale 2D spatial structure and temporal evolution of high‐m ULF waves are revealed, which demonstrates TEC measurements as an effective high‐m ULF wave remote sensing tool.

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  3. Abstract

    The three‐dimensional computerized ionospheric tomography (3DCIT) technique is used to reconstruct the spatial distribution of storm‐enhanced density (SED) based on the global positioning system total electron content measurements over the North American area during the 17 March 2013 storm. The reconstruction results are carefully validated with observations from three ionosonde stations, the constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultations, and the Millstone Hill incoherent scatter radar. The electron density profiles from the 3DCIT reconstruction show a good agreement with the ionosonde and COSMIC electron density profiles. The 3DCIT‐derived electron density difference between the storm day of 17 March and the quiet day of 16 March also captures the similar SED plume signature that was observed by the Millstone Hill incoherent scatter radar. The 3DCIT reconstruction allows us for the first time to unveil the 3‐D configuration of the SED plume and its spatiotemporal evolution. It was found that the SED plume first appeared around 400 km and then expanded downward to ~300 km as well as upward to ~500 km over the course of a 3‐hr period from 19 to 22 UT on 17 March. Our study also showed that the density enhancement within the SED plume occurred mostly above the storm timeFlayer peak height.

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