Christian von Savigny

Stratospheric profiles of nitrogen dioxide observed by Optical Spectrograph and Infrared Imager System on the Odin satellite

[1] Vertical profiles of nitrogen dioxide in the 19–40 km altitude range are successfully retrieved over the globe from Optical Spectrograph and Infrared Imager System (OSIRIS) limb scatter observations in late 2001 and early 2002. The inclusion of multiple scattering in the radiative transfer model used in the inversion algorithm allows for the retrieval of NO2 down to 19 km. The slant column densities, which represent the observations in the inversion, are obtained by fitting the fine structure in normalized radiance spectra over the 435–449 nm range, where NO2 electronic absorption is readily observable because of long light paths through stratospheric layers rich in this constituent. Details of the spectral fitting and inversion algorithm are discussed, including the discovery of a pseudo-absorber associated with pixelated detectors and a new method to verify altitude registration. Comparisons are made with spatially and temporally coincident profile measurements of this photochemically active trace gas. Better than 20% agreement is obtained with all correlative measurements over the common retrieval altitude range, confirming the validity of OSIRIS NO2 profiles. Systematic biases in the number densities are not observed at any altitude. A ‘‘snapshot’’ meridional cross section between 40� N and 70� S is shown from observations during a fraction of an orbit. INDEX TERMS: 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0394 Atmospheric Composition and Structure: Instruments and techniques; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342); KEYWORDS: optical, Sun-synchronous, polar-orbiting, Fraunhofer, Ring effect, iterative onion peel

Investigation of Solar Irradiance Variations and Their Impact on Middle Atmospheric Ozone

The satellite spectrometer SCIAMACHY aboard ENVISAT is a unique instrument that covers at a moderately high spectral resolution the entire optical range from the near UV (230 nm) to the near IR (2.4 μm) with some gaps above 1.7 μ. This broad spectral range allows not only the retrieval of several atmospheric trace gases (among them ozone), cloud and aerosol parameters, but also regular daily measurements of the spectral solar irradiance (SSI) with an unprecedented spectral coverage. The following studies were carried out with irradiance and ozone data from SCIAMACHY: a) SCIAMACHY SSI was compared to other solar data from space and ground as well as with SIM/SORCE (Solar Irradiance Monitor, the only other satellite instrument daily measuring the visible and near IR), in order to verify the quality of the SCIAMACHY measurements, b) an empirical solar proxy model, in short the SCIA proxy model, was developed that permits expressing the SCIAMACHY SSI variations by fitting solar proxies for faculae brightening and sunspot darkening, which then allows investigation of solar variability on time scales beyond the instrument life time, e.g. 11-year solar cycle, c) solar cycle SSI variations derived from empirical models (Lean2000, SATIRE, SCIA proxy) and different observations (SBUV composite, SUSIM) were compared for the three most recent solar cycles 21–23, and d) SCIAMACHY ozone limb profiles were analyzed to derive signatures of the 27-day solar rotation on stratospheric ozone. Our studies were complemented by investigations of daytime variations in mesospheric ozone (here data from SABER/TIMED), which were compared to results from the HAMMONIA chemistry climate model.

Ten-Year SCIAMACHY Stratospheric Aerosol Data Record: Signature of the Secondary Meridional Circulation Associated with the Quasi-Biennial Oscillation

The ten-year long stratospheric aerosol data record, retrieved from SCIAMACHY limb scattered sunlight measurements, is a continuous data set during the period from 2002 to 2012. As a result of the relatively high vertical resolution (3–4 km) and near global coverage on the sun-facing side of the Earth, the retrieved data set (V1.1) provides global information about the variability of stratospheric aerosol extinction between the tropopause and about 33 km altitude. Stratospheric aerosols are near-spherical droplets mainly comprised of sulfuric acid and water. The background aerosol load in the stratosphere results from the tropical injection of tropospheric air containing precursors of stratospheric aerosols. A sporadic but important source is the injection of gases from volcanic eruptions. These release the precursor gas SO2 into the troposphere or even directly into the stratosphere due to convection induced by volcanic heat. Stratospheric aerosols belong to the essential climate variables, as they influence the Earth’s radiation budget and are involved in the depletion of ozone. In this study, we analyse the time series of SCIAMACHY observed tropical aerosol extinction coefficients at 30 km altitude. A distinct biennial variation has been found. Based on ECMWF ERA-Interim reanalysis data, this variation is explained by the secondary meridional circulation that is induced by the quasi-biennial oscillation of the tropical zonal wind in the stratosphere.

Nine years of atmospheric remote sensing with sciamachy - atmospheric parameters and data products

The SCIAMACHY instrument on-board ENVISAT measures since 2002 trace gas constituents of the atmosphere in nadir, limb and occultation configuration. It is an imaging spectrometer with q spectral range from the UV/VIS to SWIR (212 nm – 2384nm). In this paper we describe shortly the current status of the operational processing chains from Level 0-1b and Level 1b-2 that deliver Earth radiances, solar irradiance, trace gas total columns and profiles as well as cloud characteristics on an orbital basis. An outlook for future operational products is also given.

Airglow in the Earth atmosphere: basic characteristics and excitation mechanisms

The Earth’s middle and upper atmosphere is a region exhibiting non-thermal emissions of electromagnetic radiation generally known as airglow. Airglow is a ubiquitous phenomenon and comprises a large number of atomic and molecular emissions in the ultraviolet, the visible and the near-infrared spectral regions. The main purpose of this article is to provide an overview of the basic characteristics of the airglow, the most important airglow emissions occurring in the terrestrial atmosphere—with a focus on nighttime or nightglow emissions—as well as the current scientific understanding of their excitation mechanisms.

Impact of Short-Term Solar Variability on the Polar Summer Mesopause and Noctilucent Clouds

The Earth’s middle atmosphere is affected by short-term solar variability in a variety of ways. This chapter focuses on the investigation of two different short-term solar effects on the polar summer mesopause region and on noctilucent clouds (NLCs). First, the effect of solar proton events (SPEs) on the thermal conditions near the polar summer mesopause and consequently on NLCs is discussed. An analysis of the SBUV(/2) time series to identify examples of NLC depletion due to SPEs shows that NLCs are probably frequently affected during strong SPEs. As part of this study a physical mechanism explaining a dynamically induced warming at the polar summer mesopause during and after SPEs is investigated using model simulations with the Kuhlungsborn Mechanistic General Circulation Model (KMCM). A second aspect related to the effect of SPEs on NLCs is on the SPE-induced ion-chemical conversion of H2O to HO x , leading to a possible sublimation of NLCs. However, this effect was found to be of minor importance compared to the dynamically induced temperature effect. Second, we discuss the recently discovered 27-day solar cycle signature in NLCs, which was identified in SCIAMACHY as well as SBUV satellite observations of NLCs using cross correlation analysis and the superposed epoch method. NLC occurrence rate and albedo anomalies are anti-correlated with Lyman-α anomalies with a time-lag of 1 day at most. The sensitivities of the NLC albedo anomalies to Lyman-α forcing in terms of the 27-day and the 11-year solar cycle were found to agree within their uncertainties. This finding suggests that the same underlying physical mechanism drives the 27-day as well as the 11-year solar cycle signature in NLCs. The exact mechanism is still unknown, however.

Nine years of atmospheric remote sensing with SCIAMACHY - instrument performance

SCIAMACHY on ENVISAT has meanwhile explored the Earths atmosphere for more than 9 years. All subsystems perform well which is a precondition for maintaining a high optical and operational performance. Even the unavoidable in-orbit degradation due to the harsh space environment is lower than expected and can be largely compensated by sophisticated calibration and monitoring means. Because of the excellent status of both the platform and the instruments the ENVISAT mission has been extended until the end of 2013. Associated with this extension was a change of the orbit in late October 2010 and reconfiguring SCIAMACHY for achieving successful operations in the coming years.