J. Tamminen

An adaptive Metropolis algorithm

A proper choice of a proposal distribution for Markov chain Monte Carlo methods, for example for the Metropolis-Hastings algorithm, is well known to be a crucial factor for the convergence of the algorithm. In this paper we introduce an adaptive Metropolis (AM) algorithm, where the Gaussian proposal distribution is updated along the process using the full information cumulated so far. Due to the adaptive nature of the process, the AM algorithm is non-Markovian, but we establish here that it has the correct ergodic properties. We also include the results of our numerical tests, which indicate that the AM algorithm competes well with traditional Metropolis-Hastings algorithms, and demonstrate that the AM algorithm is easy to use in practical computation.

Science objectives of the ozone monitoring instrument

The Ozone Monitoring Instrument (OMI) flies on NASAs Earth Observing System AURA satellite, launched in July 2004. OMI is an ultraviolet/visible (UV/VIS) nadir solar backscatter spectrometer, which provides nearly global coverage in one day, with a spatial resolution of 13 km/spl times/24 km. Trace gases measured include O/sub 3/, NO/sub 2/, SO/sub 2/, HCHO, BrO, and OClO. In addition OMI measures aerosol characteristics, cloud top heights and cloud coverage, and UV irradiance at the surface. OMIs unique capabilities for measuring important trace gases with daily global coverage and a small footprint will make a major contribution to our understanding of stratospheric and tropospheric chemistry and climate change along with Auras other three instruments. OMIs high spatial resolution enables detection of air pollution at urban scales. Total Ozone Mapping Spectrometer and differential optical absorption spectroscopy heritage algorithms, as well as new ones developed by the international (Dutch, Finnish, and U.S.) OMI science team, are used to derive OMIs advanced backscatter data products. In addition to providing data for Auras prime objectives, OMI will provide near-real-time data for operational agencies in Europe and the U.S. Examples of OMIs unique capabilities are presented in this paper.

GOMOS on Envisat: an overview

Abstract GOMOS (Global Ozone Monitoring by Occultation of Stars) on board Envisat measures O 3 , NO 2 , NO 3 , neutral density, aerosols, H 2 O, and O 2 , in the stratosphere and mesosphere by detecting absorption of starlight in ultraviolet, visible and near-infrared wavelengths. During bright limb conditions GOMOS will also observe scattered solar radiation. GOMOS will deliver ozone concentration profiles at altitudes 15–100 km with a vertical sampling better than 1.7 km and with a global coverage. As a self-calibrating method stellar occultation measurements provide a basis for a long-term global monitoring of ozone profiles. We will present here the status of the GOMOS instrument and show samples of first results obtained in 2002.

Componentwise adaptation for high dimensional MCMC

SummaryWe introduce a new adaptive MCMC algorithm, based on the traditional single component Metropolis-Hastings algorithm and on our earlier adaptive Metropolis algorithm (AM). In the new algorithm the adaption is performed component by component. The chain is no more Markovian, but it remains ergodic. The algorithm is demonstrated to work well in varying test cases up to 1000 dimensions.

Validation of daily erythemal doses from Ozone Monitoring Instrument with ground‐based UV measurement data

[1] The Dutch-Finnish Ozone Monitoring Instrument (OMI) on board the NASA EOS Aura spacecraft is a nadir viewing spectrometer that measures solar reflected and backscattered light in a selected range of the ultraviolet and visible spectrum. The instrument has a 2600 km wide viewing swath and it is capable of daily, global contiguous mapping. The Finnish Meteorological Institute and NASA Goddard Space Flight Center have developed a surface ultraviolet irradiance algorithm for OMI that produces noontime surface spectral UV irradiance estimates at four wavelengths, noontime erythemal dose rate (UV index), and the erythemal daily dose. The overpass erythemal daily doses derived from OMI data were compared with the daily doses calculated from the ground-based spectral UV measurements from 18 reference instruments. Two alternative methods for the OMI UV algorithm cloud correction were compared: the plane-parallel cloud model method and the method based on Lambertian equivalent reflectivity. The validation results for the two methods showed some differences, but the results do not imply that one method is categorically superior to the other. For flat, snow-free regions with modest loadings of absorbing aerosols or trace gases, the OMI-derived daily erythemal doses have a median overestimation of 0–10%, and some 60 to 80% of the doses are within ±20% from the ground reference. For sites significantly affected by absorbing aerosols or trace gases one expects, and observes, bigger positive bias up to 50%. For high-latitude sites the satellite-derived doses are occasionally up to 50% too small because of unrealistically small climatological surface albedo.

Arctic and Antarctic polar winter NOx and energetic particle precipitation in 2002-2006

Received 19 February 2007; revised 8 May 2007; accepted 16 May 2007; published 26 June 2007. [1] We report GOMOS nighttime observations of middle atmosphere NO2 and O3 profiles during eight recent polar winters in the Arctic and Antarctic. The NO2 measurements are used to study the effects of energetic particle precipitation and further downward transport of polar NOx. During seven of the eight observed winters NOx enhancements occur in goodcorrelation withlevelsofenhancedhigh-energyparticle precipitation and/or geomagnetic activity as indicated by the Ap index. We find a nearly linear relationship between the average winter time Ap index and upper stratospheric polar winterNO2columndensityinbothhemispheres.IntheArctic winter 2005–2006 the NOx enhancement is higher than expected from the geomagnetic conditions, indicating the importance of changing meteorological conditions.

Nighttime ozone profiles in the stratosphere and mesosphere by the Global Ozone Monitoring by Occultation of Stars on Envisat

[1] The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European Space Agency’s Envisat satellite measures ozone and a few other trace gases using the stellar occultation method. Global coverage, good vertical resolution and the self-calibrating measurement method make GOMOS observations a promising data set for building various climatologies. In this paper we present the nighttime stratospheric ozone distribution measured by GOMOS in 2003. We show monthly latitudinal distributions of the ozone number density and mixing ratio profiles, as well as the seasonal variations of profiles at several latitudes. The stratospheric profiles are compared with the Fortuin-Kelder daytime ozone climatology. Large differences are found in polar areas and they can be shown to be correlated with large increases of NO2. In the upper stratosphere, ozone values from GOMOS are systematically larger than in the Fortuin-Kelder climatology, which can be explained by the diurnal variation. In the middle and lower stratosphere, GOMOS finds a few percent less ozone than Fortuin-Kelder. In the equatorial area, at heights of around 15–22 km, GOMOS finds much less ozone than Fortuin-Kelder. For the mesosphere and lower thermosphere, there has previously been no comprehensive nighttime ozone climatology. GOMOS is one of the first new instruments able to contribute to such a climatology. We concentrate on the characterization of the ozone distribution in this region. The monthly latitudinal and seasonal distributions of ozone profiles in this altitude region are shown. The altitude of the mesospheric ozone peak and the semiannual oscillation of the number density are determined. GOMOS is also able to determine the magnitude of the ozone minimum around 80 km. The lowest seasonal mean mixing ratio values are around 0.13 ppm. The faint tertiary ozone peak at 72 km in polar regions during wintertime is observed.

First simultaneous global measurements of nighttime stratospheric NO2 and NO3 observed by Global Ozone Monitoring by Occultation of Stars (GOMOS)/Envisat in 2003

The Global Ozone Monitoring by Occultation of Stars (GOMOS) stellar occultation instrument on board the Envisat European satellite provides global coverage of ozone and other stratospheric species with good vertical resolution and a self-calibrating method. In this paper we present the first simultaneous global distribution of stratospheric NO 2 and NO 3 from 1 year of nighttime GOMOS data in 2003. Most previous NO 2 satellite observations have been made using the solar occultation technique. They are difficult to interpret due to the fast photochemical evolution of NO 2 at sunrise and sunset. There are no published observations of NO 3 from space because this constituent is rapidly photodissociated during daytime and is not observable by solar occultation. It is shown that the NO 2 mixing ratio reaches a maximum around 40 km with values between 14 and 16 ppbv at low and middle latitudes. The global distribution of NO 2 observed by GOMOS is very similar to the NO + NO 2 Halogen Occultation Experiment climatology deduced from sunset measurements from 1999 to 2004. At high latitude a high mixing ratio is observed in the north vortex in November 2003 after a strong solar proton event and in the south vortex in July 2003. The NO 3 mixing ratio peaks at 40–45 km. NO 3 follows a semiannual variation at low latitudes with maxima at equinoxes and an annual variation at middle and high latitudes with a maximum in summer. In the upper stratosphere the mixing ratio of NO 3 is strongly correlated with temperature due to the thermal dependence of its formation rate. Citation: Hauchecorne, A., et al. (2005), First simultaneous global measurements of nighttime stratospheric NO 2 and NO 3 observed by Global Ozone Monitoring by Occultation of Stars (GOMOS)/Envisat in 2003

Bayesian solution for nonlinear and non-Gaussian inverse problems by Markov chain Monte Carlo method

In this paper we apply the Bayesian approach for solving retrieval problems encountered in remote sensing measurements of the atmosphere. The approach gives as a solution the posterior probability distribution of the unknown parameters and allows a possibility to combine new measurements with prior knowledge. While the Bayesian solution can easily be computed in the case of linear, Gaussian inverse problems, the characterization of the solution in all other cases is difficult. Here we apply Markov chain Monte Carlo (MCMC) method for computing posterior distributions for inverse problems. The advantage of the MCMC technique is that it can easily be implemented in a great variety of inverse problems including nonlinear problems with various prior or noise structures. The MCMC algorithms are not yet effective enough for operational processing of large amounts of data, but they provide excellent tools for development and validation purposes. We have applied successfully the MCMC technique to the inverse problem arising from the Global Ozone Monitoring by Occultation of Stars instrument.

A global climatology of the mesospheric sodium layer from GOMOS data during the 2002–2008 period

This paper presents a climatology of the mesospheric sodium layer built from the processing of 7 years of GOMOS data. With respect to preliminary results already published for the year 2003, a more careful analysis was applied to the averaging of occultations inside the climatological bins (10 in latitude-1 month). Also, the slant path absorption lines of the Na doublet around 589 nm shows evidence of partial saturation that was responsible for an underestimation of the Na concentration in our previous results. The sodium climatology has been validated with respect to the Fort Collins lidar measurements and, to a lesser extent, to the OSIRIS 2003–2004 data. Despite the important natural sodium variability, we have shown that the Na vertical column has a marked semi-annual oscillation at low latitudes that merges into an annual oscillation in the polar regions,a spatial distribution pattern that was unreported so far. The sodium layer seems to be clearly influenced by the mesospheric global circulation and the altitude of the layer shows clear signs of subsidence during polar winter. The climatology has been parameterized by time-latitude robust fits to alCorrespondence to: D. Fussen (didier.fussen@oma.be) low for easy use. Taking into account the non-linearity of the transmittance due to partial saturation, an experimental approach is proposed to derive mesospheric temperatures from limb remote sounding measurements.