One-year observations of particle lidar ratio over the tropical Indian Ocean with Raman lidar

Observations of the extinction-to-backscatter ratio (lidar ratio) of South and Southeast Asian aerosol particles are presented for the wavelength of 532 nm. Raman lidar measurements were performed in the Maldives (4.1 degrees N, 73.3 degrees E) in the framework of the Indian Ocean Experiment (INDOEX) in 1999/2000. These observations in the tropics axe an important contribution to a growing global lidar-ratio climatology which is needed for an improved determination of the particle optical depth with ground-based and spaceborne lidars. The lidar ratio was found to be a useful quantity to trace back different pollution sources and to identify less and considerably light-absorbing particles. During the winter/spring seasons heavily polluted air from India and Southeast Asia was advected to the lidar site. Under these conditions lidar ratios up to 110 sr were observed in the lofted pollution plumes above 1000 m height. According to backward trajectories the highest lidar ratios were found for airmasses which crossed the eastern and northeastern parts of India. Large lidar ratios > 70 sr indicate small, considerably absorbing aerosol particles. Below 1000 in height, the lidar ratio typically ranged from 30-60 sr. The marine boundary layer contained a mixture of marine and anthropogenic particles. Under clean, marine conditions in October 1999, lidar ratios <30 sr were found.Peer reviewe

Global Chemistry Simulations in the AMMA Multimodel Intercomparison Project

International audienceThe authors present results obtained during the chemistry-transport modeling (CTM) component of the African Monsoon Multi-disciplinary Analysis Multimodel Intercomparison Project (AMMA-MIP) using the recently developed L3JRCv2 emission dataset for Af-rica, where emphasis is placed on the summer of 2006. With the use of passive tracers, the authors show that the application of different parameterizations to describe advection, vertical diffusion, and convective mixing in a suite of state-of-the-art global CTMs results in significantly different transport mechanisms westward of the African continent. Moreover, the authors identify that the atmospheric composition over the southern Atlantic is governed by air masses originating from southern Africa for this period, resulting in maximal concentrations around 5°S. Comparisons with ozonesonde measurements at Cotonou (6.2°N, 2.2°E) indicate that the models generally overpredict surface ozone and underpredict ozone in the upper troposphere. Moreover, using recent aircraft measurements, the authors show that the high ozone concentrations that occur around 700 hPa around 5°N are not captured by any of the models, indicating shortcomings in the description of transport, the magnitude and/or location of emissions, or the in situ chemical ozone production by the various chemical mechanisms employed

Validation of 10-year SAO OMI Ozone Profile (PROFOZ) Product Using Ozonesonde Observations

We validate the Ozone Monitoring Instrument (OMI) ozone-profile (PROFOZ) product from October 2004 through December 2014 retrieved by the Smithsonian Astrophysical Observatory (SAO) algorithm against ozonesonde observations. We also evaluate the effects of OMI Row anomaly (RA) on the retrieval by dividing the data set into before and after the occurrence of serious OMI RA, i.e., pre-RA (2004-2008) and post-RA (2009-2014). The retrieval shows good agreement with ozonesondes in the tropics and mid-latitudes and for pressure ~50 hPa after applying OMI averaging kernels to ozonesonde data. The MBs of the stratospheric ozone column (SOC) are within 2% with SDs of ~50 hPa. The SOC MBs increase up to 3% with SDs as great as 6% and the TOC SDs increase up to 30%. The comparison generally degrades at larger solarzenith angles (SZA) due to weaker signals and additional sources of error, leading to worse performance at high latitudes and during the mid-latitude winter. Agreement also degrades with increasing cloudiness for pressure > ~100 hPa and varies with cross-track position, especially with large MBs and SDs at extreme off-nadir positions. In the tropics and mid-latitudes, the post-RA comparison is considerably worse with larger SDs reaching 2% in the stratosphere and 8% in the troposphere and up to 6% in TOC. There are systematic differences that vary with latitude compared to the pre-RA comparison. The retrieval comparison demonstrates good long-term stability during the pre-RA period, but exhibits a statistically significant trend of 0.14-0.7%/year for pressure < ~ 80 hPa, 0.7 DU/year in SOC and -0.33 DU/year in TOC during the post-RA period. The spatiotemporal variation of retrieval performance suggests the need to improve OMI’s radiometric calibration especially during the post-RA period to maintain the long-term stability and reduce the latitude/season/SZA and cross-track dependence of retrieval quality.Astronom