Estimates of lightning NOsubx/sub production from GOME satellite observations

摘要

Tropospheric NO₂ column retrievals from the Global Ozone MonitoringExperiment (GOME) satellite spectrometer are used to quantify the sourcestrength and 3-D distribution of lightning produced nitrogen oxides(NO_x=NO+NO₂). A sharp increase of NO₂ isobserved at convective cloud tops with increasing cloud top height,consistent with a power-law behaviour with power 5±2. Convectiveproduction of clouds with the same cloud height are found to produceNO₂ with a ratio 1.6/1 for continents compared to oceans. Thisrelation between cloud properties and NO₂ is used to construct a10:30 local time global lightning NO₂ production map for 1997. Anextensive statistical comparison is conducted to investigate the capabilityof the TM3 chemistry transport model to reproduce observed patterns oflightning NO₂ in time and space. This comparison uses the averagingkernel to relate modelled profiles of NO₂ to observed NO₂columns. It exploits a masking scheme to minimise the interference of otherNO_x sources on the observed total columns. Simulations are performedwith two lightning parameterizations, one relating convective preciptation(CP scheme) to lightning flash distributions, and the other relating thefifth power of the cloud top height (H5 scheme) to lightning distributions.The satellite-retrieved NO₂ fields show significant correlations withthe simulated lightning contribution to the NO₂ concentrations forboth parameterizations. Over tropical continents modelled lightningNO₂ shows remarkable quantitative agreement with observations. Overthe oceans however, the two model lightning parameterizations overestimatethe retrieved NO₂ attributed to lightning. Possible explanations forthese overestimations are discussed. The ratio between satellite-retrievedNO₂ and modelled lightning NO₂ is used to rescale theoriginal modelled lightning NO_x production. Eight estimates of thelightning NO_x production in 1997 are obtained from spatial andtemporal correlation methods, from cloud-free and cloud-covered observations,and from two different lightning parameterizations. Accounting for a widevariety of random and possible systematic errors, we estimate the globalNO_x production from lightning to be in the range 1.1–6.4 Tg Nin 1997.