The Nature of Ozone in Deep Convective Clouds

As Inferred from Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) Data

Ozone within deep convective clouds is controlled by several factors involving photochemical reactions and transport. Gas-phase photochemical reactions and heterogeneous surface chemical reactions involving ice, water particles, and aerosols inside the clouds all contribute to the distribution and net production and loss of ozone.

OMI-Derived Mean HCHO in Surface Air with Cancer Risk
    Top: Time series of Aura OMI/MLS clear-sky tropospheric ozone (red curve), thick-cloud ozone (black asterisk curve), and OMI Aerosol Index (blue dotted curve) for a region of India / east Asia. Units for ozone are ppbv. Thick-cloud ozone represents mean volume mixing ratio for deep convective cloud pixels (radiative cloud fractions = 100%) while clear-sky ozone represents mean volume mixing ratio for pixels with radiative cloud fractions < 30%. Black regions in the contour plot denote regions where there are not sufficient number of deep convective clouds for deriving thick-cloud ozone measurements.

  • The first ever long-record data product of ozone concentrations in deep convective clouds is derived from satellite remote sensing

  • This data product is important for quantifying relationships of ozone with tropospheric H2O, OH production, pollution, cloud microphysics/transport and convective properties, evaluation of chemical transport models, and characterizing basic variability from monthly to ENSO/decadal timescales

  • Ozone in thick clouds (i.e., "Thick-Cloud Ozone") is largely a manifestation of boundarylayer / low tropospheric ozone injected upward via deep convection

  • The measurements reveal ozone concentrations in thick clouds as low as 10 ppbv or less over pristine oceanic regions and concentrations of 60 ppbv or greater over more polluted regions such as southern Africa and India/East Asia. The seasonal variability of both clear-sky and thick-cloud ozone over India/East Asia is shown to be linked to changes in pollution over this broad region

Scientific significance, societal relevance, and relationships to future missions:

Characterizing ozone in thick clouds is an important step for quantifying relationships of ozone with tropospheric H2O, OH production, and cloud microphysics/transport properties

Measuring ozone in deep convective clouds from either aircraft or balloon ozonesondes is largely not possible due to extreme meteorological conditions associated with these clouds; however, it is possible to determine ozone in thick clouds using backscattered solar UV radiation measured by satellite instruments such as OMI.

The cloud-ozone measurements reveal many key features including: persistent low ozone concentrations in the tropical Indian Ocean and Pacific Ocean of ~10 ppbv or less; concentrations of up to 60 pphv or greater over landmass regions of South America, southern Africa, Australia, and India/east Asia; connections with tropical ENSO events; and intra-seasonal/Madden-Julian Oscillation (MJO) variability. Analysis of co-incident OMI aerosol measurements further suggests a direct cause and effect relation between boundary-layer pollution and elevated ozone inside thick clouds over land-mass regions including southern Africa and India/east Asia

References: Ziemke, J. R., S. A. Strode, A. R. Douglass, J. Joiner, A. Vasilkov, L. D. Oman, J. Liu, S. E. Strahan, P. K. Bhartia, D. P. Haffner (2017), A Cloud-Ozone Data Product from Aura OMI and MLS Satellite Measurements, Atmos. Meas. Tech., 10, 4067-4078,https://doi.org/10.5194/amt-10-4067-2017.

Data Sources: Our cloud-ozone data product is generated by combining profile ozone from the Aura Microwave Limb Sounder (MLS) with both column ozone and cloud parameter measurements from the Aura Ozone Monitoring Instrument (OMI). These "cloud-ozone" measurements represent the mean ozone concentration (in units ppbv) of ozone lying in the upper levels of deep convective clouds between 550 hPa and cloud top. The time period covered for this first version of the cloud-ozone data is October 2004 through April 2016 with spatial coverage from 30°S to 30°N. This cloud-ozone data product is the first of its kind and is made available and free for the public via ftp://jwocky.gsfc.nasa.gov/. We acknowledge greatly the Aura MLS and OMI instrument and algorithm teams for their extensive satellite data included in our study. OMI is a Dutch-Finnish contribution to the Aura mission.


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