Conference Agenda

This report provides an overview of the recent progress on the cross-calibration and validation of CSES/Swarm satellite magnetic field and plasma measurements.

(1)High precision magnetometer (HPM) has worked successfully more than 5 years to provide continuous magnetic field measurement since the launch of CSES. After rechecking these years data, it is necessary to make an improvement for fluxgate magnetometer (FGM) orthogonal calibration (to estimate offsets, scale values and non-othogonalities) and alignment (to estimate three Euler angles). The following efforts are made to achieve this goal: For orthogonal calibration, we further considered the FGM sensor temperature correction on offsets and scale values to remove the seasonal effect. Based on these results, Euler angles are estimated along with global geomagnetic field modeling and then the latitudinal effect for east component is improved. After considering above improvement, we can prolong the updating period of all calibration parameters from daily to 10 days, without the separation of dayside and nightside data. These algorithms will be helpful to improve HPM routine data processing efficiency and data quality to support more scientific studies.

(2)The first detailed analysis about the spacecraft potential (Vs) variations of Swarm satellites are provided, which are flying at about 400-500 km. Different to previous studies that investigate the extremely charging events, usually with spacecraft potential as negative as -100 V, we focus on the variation of Swarm Vs varying within a few negative volts. The Swarm observations show that the spacecraft at low Earth orbit (LEO) altitudes are charged slightly negative, varying between -7 V and 0 V, and with the majority around -2 V. Interestingly, a second peak of Vs is found at -5.5 V, though the event number is less by an order than the first peak around -2 V. The two groups show different spatial and temporal distributions. For the slighter negative charged group, at low and middle latitudes the Vs shows relatively larger values above the magnetic equator, and with much more negative values on the dayside at low and middle latitudes; at high latitudes, the Vs shows relatively negative values during local summer. For the deeper negative charged group, Vs at equatorial and low latitudes is slightly lower at the SAA region; and at high latitudes, the valid Vs observations appear mainly during local winter. We found for the first group much negative Vs is observed at regions with higher background plasma density, while for the second group much negative Vs is observed at regions with lower background plasma density.

(3) The high-resolution magnetic field measurements from ESA’s Swarm satellite constellation provide a good opportunity for revisiting the mean properties of ionospheric currents. Among the Swarm Level 2 data products, provided by ESA, are field-aligned current (FAC) estimates based on single-spacecraft (single-SC) and dual-spacecraft (dual-SC) solutions. For the more reliable dual-SC approach only magnetic signatures from currents flowing through the integration loop are considered. In the case of single-SC FAC estimates the magnetic effects of all remote current systems contribute also to the results. A direct comparison between the two FAC products at auroral latitudes reveals that the single-SC estimates systematically overestimate the current density of region 2 (R2) FACs (~15%) while underestimates the region 1 (R1) FACs (~10%). The differences between the two FAC products appear closely related to the location and direction of the horizontal polar electrojet (PEJ) at auroral latitudes. A direct comparison of these two current systems suggests an influence of the PEJ induced magnetic field on the solutions from single-SC FACs.

An IFS125HR has been deployed in Xianghe Integrated Observatory. Long-term operations were carried out for accumulating high quality data, which is significant for validating the satellite greenhouse gases products and for finding the signal of climate change. Methane (CH₄) is the second most important greenhouse gas after carbon dioxide. Accurate monitoring and understanding of its spatiotemporal distribution are crucial for effective mitigation strategies. In this study, the spatiotemporal variations of CH₄ over China were investigated based on the CH₄ products from 4 well-known satellites (GOSAT, TROPOMI, AIRS, and IASI). As we know, the spectrometers on board the 4 satellites are quite different in specifications as well as in the inversion algorithms. GOSAT and TROPOMI CH₄ retrieval use shortwave infrared spectra, having a better sensitivity near the surface, while IASI and AIRS CH₄ retrieval use thermal infrared spectra, showing a good sensitivity in the mid-upper troposphere. Therefore, GOSAT and TROPOMI observed higher CH₄ concentrations in the east and south, and lower concentrations in the west and north, which is highly related to the CH₄ emissions. IASI and AIRS show a more uniform CH₄ distribution over China, which is dominated by the variation of CH₄ at a high altitude. However, a large discrepancy is found among these satellite data. AIRS CH₄ mole fraction is systematically lower than the other 3 satellites. Significant differences in seasonal variations of CH₄ are observed between IASI and AIRS across several regions in China. The highest concentration of CH₄ was observed by AIRS in Inner Mongolia, which is probably due to the dust inferences above the bare soil.

Keywords: CH₄, spatiotemporal variation, methane measuring satellites, intercomparison, FTIR