Menu Close

Uncertainty in Aerosol Optical Depth From Modern Aerosol-Climate Models, Reanalyses, and Satellite Products

Despite the impli­ca­tion of aerosols for the radi­a­tion bud­get, there are per­sis­tent dif­fer­ences in data for the aerosol opti­cal depth (τ) for 1998–2019. This study presents a com­pre­hen­sive eval­u­a­tion of the large-scale spa­tio-tem­po­ral pat­terns of mid-vis­i­ble τ from mod­ern data sets. In total, we assessed 94 dif­fer­ent glob­al data sets from eight satel­lite retrievals, four aerosol-cli­mate mod­el ensem­bles, one oper­a­tional ensem­ble prod­uct, two reanaly­ses, one cli­ma­tol­ogy and one merged satel­lite prod­uct. We include the new satel­lite data SLSTR and aerosol-cli­mate sim­u­la­tions from the Cou­pled Mod­el Inter­com­par­i­son Project Phase 6 (CMIP6) and the Aerosol Com­par­isons between Obser­va­tions and Mod­els Phase 3 (Aero­Com-III). Our inter­com­par­i­son high­lights mod­el dif­fer­ences and obser­va­tion­al uncer­tain­ty. Spa­tial mean τ for 60°N – 60°S ranges from 0.124 to 0.164 for indi­vid­ual satel­lites, with a mean of 0.14. Aver­aged τ from aerosol-cli­mate mod­el ensem­bles fall with­in this satel­lite range, but indi­vid­ual mod­els do not. Our assess­ment sug­gests no sys­tem­at­ic improve­ment com­pared to CMIP5 and AeroCom‑I. Although some region­al bias­es have been reduced, τ from both CMIP6 and Aero­Com-III are for instance sub­stan­tial­ly larg­er along extra-trop­i­cal storm tracks com­pared to the satel­lite prod­ucts. The con­sid­er­able uncer­tain­ty in observed τ implies that a mod­el eval­u­a­tion based on a sin­gle satel­lite prod­uct might draw biased con­clu­sions. This under­lines the need for con­tin­ued efforts to improve both mod­el and satel­lite esti­mates of τ, for exam­ple, through mea­sure­ment cam­paigns in areas of par­tic­u­lar­ly uncer­tain satel­lite esti­mates iden­ti­fied in this study, to facil­i­tate a bet­ter under­stand­ing of aerosol effects in the Earth sys­tem.

Anni­ka Vogel, Ghazi Alessa, Robert Scheele, Lisa Weber, Oleg Dubovik, Peter North, Stephanie Fiedler

Pub­lished in JGR Atmos­pheres, Volume127, Issue2, 27 Jan­u­ary 2022

Read the full arti­cle here

News, Publications, Research