Accurate satellite-derived estimates of the tropospheric ozone impact on the global radiation budget

Estimates of the radiative forcing due to anthropogenically-produced tropospheric O3 are derived primarily from models. Here, we use tropospheric ozone and cloud data from several instruments in the A-train constellation of satellites as well as information from the GEOS-5 Data Assimilation System to accurately estimate the radiative effect of tropospheric O3 for January and July 2005. Since we cannot distinguish between natural and anthropogenic sources with the satellite data, our derived radiative effect reflects the unadjusted (instantaneous) effect of the total tropospheric O3 rather than the anthropogenic component. We improve upon previous estimates of tropospheric ozone mixing ratios from a residual approach using the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) by incorporating cloud pressure information from OMI. We focus specifically on the magnitude and spatial structure of the cloud effect on both the short- and long-wave radiative budget. The estimates presented here can be used to evaluate the various aspects of model-generated radiative forcing. For example, our derived cloud impact is to reduce the radiative effect of tropospheric ozone by ~16%. This is centered within the published range of model-produced cloud effect on unadjusted ozone radiative forcing

Intra-seasonal variability in tropospheric ozone and water vapor in the tropics

Nearly two years of tropospheric O3 and H2O data from the Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) instruments are analyzed to study the characteristics of intra-seasonal oscillation (ISO) of 20–100 day periods. The analysis shows the presence of ISO signals in O3 and H2O throughout much of the tropics including the north Atlantic not shown in previous studies. ISO variability west of the dateline appears as a manifestation of eastward propagation of the Madden-Julian Oscillation (MJO). Time series of tropospheric O3 and H2O are negatively correlated throughout much of the tropics, and mostly over ocean. This suggests lofting of air from convection as a basic driving mechanism, with convection transporting low amounts of O3 and high amounts of H2O upwards from the boundary layer. ISO/MJO related changes in O3 and H2O are a major source of variability and often exceed 25% of background concentrations

Early data from Aura and continuity from UARS and TOMS

Aura, the last of the large EOS observatories, was launched on July 15, 2004. Aura is designed to make comprehensive stratospheric and tropospheric composition measurements from its four instruments, HIRDLS, MLS, OMI and TES. These four instruments work in synergy to provide data on ozone trends, air quality and climate change. The instruments observe in the nadir and limb and provide the best horizontal and vertical resolution ever achieved from space. After over one year in orbit the instruments are nearly operational and providing data to the scientific community. We summarize the mission, instruments, and initial results and give examples of how Aura will provide continuity to earlier chemistry mission

Dehydration and denitrification in the Arctic polar vortex during the 1995-1996 winter

Geophys. Res. Letts., 25, 501-504.Dehydration of more than 0.5 ppmv water was observed between 18 and 19 km (0~450~465 K) at the edge of the Arctic polar vortex on February 1, 1996. More than half the reactive nitrogen (NOy) had also been removed, with layers of enhanced NOy at lower altitudes..

Ozone mixing ratios inside tropical deep convective clouds from OMI satellite measurements

We have compared spectral ultraviolet overpass irradiances from the Ozone Monitoring Instruments (OMI) against ground-based Brewer measurements at Thessaloniki, Greece from September 2004 to December 2007. It is demonstrated that OMI overestimates UV irradiances by 30%, 17% and 13% for 305 nm, 324 nm, and 380 nm respectively and 20% for erythemally weighted irradiance. The bias between OMI and Brewer increases with increasing aerosol absorption optical thickness. We present methodologies that can be applied for correcting this bias based on experimental results derived from the comparison period and also theoretical approaches using radiative transfer model calculations. All correction approaches minimize the bias and the standard deviation of the ratio OMI versus Brewer ratio. According to the results, the best correction approach suggests that the OMI UV product has to be multiplied by a correction factor CA(¿) of the order of 0.8, 0.88 and 0.9 for 305 nm, 324 nm and 380 nm respectively. Limitations and possibilities for applying such methodologies in a global scale are also discussed

High resolution simulation of recent Arctic and Antarctic stratospheric chemical ozone loss compared to observations

Simulations of polar ozone losses were performed using the three-dimensional high-resolution (1° × 1°) chemical transport model MIMOSA-CHIM. Three Arctic winters 1999–2000, 2001–2002, 2002–2003 and three Antarctic winters 2001, 2002, and 2003 were considered for the study. The cumulative ozone loss in the Arctic winter 2002–2003 reached around 35% at 475K inside the vortex, as compared to more than 60% in 1999–2000. During 1999–2000, denitrification induces a maximum of about 23% extra ozone loss at 475K as compared to 17% in 2002–2003. Unlike these two colder Arctic winters, the 2001–2002 Arctic was warmer and did not experience much ozone loss. Sensitivity tests showed that the chosen resolution of 1° ×1° provides a better evaluation of ozone loss at the edge of the polar vortex in high solar zenith angle conditions. The simulation results for ozone, ClO, HNO3, N2O, and NOy for winters 1999–2000 and 2002–2003 were compared with measurements on board ER-2 and Geophysica aircraft respectively. Sensitivity tests showed that increasing heating rates calculated by the model by 50% and doubling the PSC (Polar Stratospheric Clouds) particle density (from 5 × 10-3 to 10-2 cm-3) refines the agreement with in situ ozone, N2O and NOy levels. In this configuration, simulated ClO levels are increased and are in better agreement with observations in January but are overestimated by about 20% in March. The use of the Burkholder et al. (1990) Cl2O2 absorption cross-sections slightly increases further ClO levels especially in high solar zenith angle conditions. Comparisons of the modelled ozone values with ozonesonde measurement in the Antarctic winter 2003 and with Polar Ozone and Aerosol Measurement III (POAM III) measurements in the Antarctic winters 2001 and 2002, shows that the simulations underestimate the ozone loss rate at the end of the ozone destruction period. A slightly better agreement is obtained with the use of Burkholder et al. (1990) Cl2O2 absorption cross-sections