Upper atmosphere radiance data assimilation: A feasibility study for GOLD far ultraviolet observations

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Tuesday, January 7, 2020

Availability of far ultraviolet observations of Earth’s dayglow by the NASA Global-scale Observations of the Limb and Disk (GOLD) mission presents an unparalleled opportunity for upper atmosphere radiance data assimilation.

Graph depicting accuracy of temperature estimates
Accuracy of temperature estimates in the measurement update step for four different assimilated observations.

Assimilation of the observed dayglow emissions can be formulated in a similar fashion to lower atmosphere radiance data assimilation approaches using the sensitivity of the Lyman-Birge-Hopfield (LBH) band emission to thermospheric temperature. To demonstrate such an approach, this paper presents a proof-of-concept implementation of an ensemble filter measurement update step using ensemble simulation of the thermosphere and LBH emission by the NOAA's Whole Atmosphere Model (WAM) and NCAR’s Global Airglow model. Testing the approach with observing system simulation experiments has yielded the following findings: (1) Assimilation of GOLD LBH disk emission data can reduce the error in model temperature specification from forecast to analysis by 97% under geomagnetically quiet conditions and 87% under disturbed conditions, (2) The reduction in model uncertainty from forecast to analysis as a result of GOLD assimilation is ~20% in the lower thermosphere and ~25% in the upper thermosphere, and (3) Ingestion of three prominent LBH features, in comparison to the entire LBH spectrum, into the WAM leads to more accurate assimilation analyses. With the help of a radiance data assimilation approach, the utility of GOLD observations can be extended to reveal global, time-dependent, altitude-resolved thermospheric structure, offering the key to addressing a number of outstanding questions such as those relating to the properties of travelling atmospheric disturbances.

Publication Name: Journal of Geophysical Research Space Physics, 124, 8154, doi:10.1029/2019JA026910.
First HAO Author's Name: Stanley C. Solomon

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