Abstract
For a variational data assimilation (DA) system that assimilates radiance observations, the simulated brightness temperature (BT) at the top of the atmosphere and the corresponding Jacobians carried out by the radiance observation operator are needed information. Previous studies reported that the incorporation of aerosol information into the radiance observation operator leads to cooler simulated infrared (IR) BTs and warmer temperature analyses at low levels of the atmosphere. However, the role of the aerosol-affected Jacobians in the DA system, which not only affect the determination of analysis increments but also influence the quality control and the bias correction algorithm, is yet to be investigated. This study examines the aerosol impacts on the sensitivity of IR radiance simulations, Jacobians, and the analysis increments by conducting two experiments: (i) sensitivity tests to assess how the different aspects of the aerosol profiles (i.e., mass loading, peak aerosol level, aerosol thickness layer, and bin partition) affect the simulated BT and the Jacobians from the Community Radiative Transfer Model (CRTM), which is the radiance observation operator in the Gridpoint Statistical Interpolation (GSI) analysis system; (ii) single IR observation experiments using GSI to investigate how the aerosol-affected atmospheric Jacobians influence the analysis increment. The results show that dust aerosols produce the strongest cooling to simulated BTs under similar aerosol optical depths; simulated BTs and Jacobians are most sensitive to the loading and peak altitude of the aerosol layer; simulated BTs become more sensitive to the temperature of the aerosol layer; aerosol-induced differences in atmospheric Jacobians lead to considerable changes to temperature and moisture increments. These results provide a better understanding of the aerosol impacts on each component involved in radiance DA, which can provide guidance for assimilating aerosol-affected IR observations.
Highlights
Licensee MDPI, Basel, Switzerland.Satellite radiance observations in the units of equivalent brightness temperature (BT)at the top of the atmosphere have been directly assimilated at many operational numerical weather prediction (NWP) centers since the early 1990s [1,2,3,4]
In addition to the sensitivity tests involving the aerosol profiles, we examined the sensitivity of the bin partition for dust and carbonaceous aerosols to address the different impacts on BTs between a fresh and an aged aerosol plume
It should be noted that sea salt aerosols produced comparable BT cooling
Summary
Kim et al [17] and Wei et al [18] incorporated the aerosol information into the BT simulation of the radiance observation operator to assess the aerosol impacts on meteorological analyses To do this, both studies conducted two Gridpoint Statistical Interpolation (GSI) experiments, which utilized CRTM handling the BT simulations. This experiment will better understand how different aerosol profiles influence the simulated BTs and Jacobians These results will provide insights about the uncertainties for assimilating aerosol-affected IR observations, such as the systematic biases. Given identical model states and first-guess departures, this experiment will isolate the impacts of aerosol-affected atmospheric Jacobians on the vertical distribution of analysis increments.
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