English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We assess the major factors contributing to local biases in thehydroxyl radical (OH) as simulated by a global chemistry–climate model, usinga single-column photochemical model (SCM) analysis. The SCM has beenconstructed to represent atmospheric chemistry at Lauder, New Zealand, whichis representative of the background atmosphere of the Southern Hemisphere(SH) mid-latitudes. We use long-term observations of variables essential totropospheric OH chemistry, i.e. ozone (O3), water vapour(H2O), methane (CH4), carbon monoxide (CO), andtemperature, and assess how using these measurements affect OHcalculated in the SCM, relative to a reference simulation only using modelledfields. The analysis spans 1994 to 2010. Results show that OH respondsapproximately linearly to correcting biases in O3, H2O, CO, CH4,and temperature. The biggest impact on OH is due to correcting anoverestimation by approximately 20 to 60 % of H2O, usingradiosonde observations. Correcting this moist bias leads to a reduction ofOH by around 5 to 35 %. This is followed by correcting predominantlyoverestimated O3. In the troposphere, the model biases are mostlyin the range of −10 to 30 %. The impact of changing O3 onOH is due to two pathways; the OH responses to both are ofsimilar magnitude but different seasonality: correcting in situ troposphericozone leads to changes in OH in the range −14 to 4 %, whereascorrecting the photolysis rate of O3 in accordance with overheadcolumn ozone changes leads to increases of OH of 8 to 16 %. TheOH sensitivities to correcting CH4, CO, andtemperature biases are all minor effects. The work demonstrates thefeasibility of quantitatively assessing OH sensitivity to biases inlonger-lived species, which can help explain differences in simulated OHbetween global chemistry models and relative to observations. In addition toclear-sky simulations, we have performed idealized sensitivity simulations toassess the impact of clouds (ice and liquid) on OH. The resultsindicate that the impacts on the ozone photolysis rate and OH aresubstantial, with a general decrease of OH below the clouds of up to 30 %relative to the clear-skies situation, and an increase of up to 15 % above.Using the SCM simulation we calculate recent OH trends at Lauder. For theperiod of 1994 to 2010, all trends are insignificant, in agreement withprevious studies. For example, the trend in total-column OH is0.5 ± 1.3 % over this period

atmospheric chemistry and physics

Assessing the sensitivity of the hydroxyl radical to model biases in composition and temperature using a single-column photochemical model for Lauder, New Zealand