Performance of the Ionospheric Kappa-Correction of Radio Occultation Profiles Under Diverse Ionization and Solar Activity Conditions.

The kappa-correction is an easy-to-use method to correct for residual ionospheric errors in radio occultation (RO) data. It is a simple empirical model term that only depends on readily available data. While its basic utility was well proven in previous studies, including a recent predecessor study on RO climatologies under solar cycle variations, its performance for individual RO profile correction under diverse and extreme ionization conditions is unclear so far. Here we tackle this gap and focus on investigating (extremely) low and high solar activity and ionization conditions of individual RO events, including inspection of ionospheric symmetry between inbound and outbound raypaths. Using a global multi-year ensemble of MetOp-A and GRACE-A RO events over 2008-2015 as basis, we applied a sampling approach leading to six characteristic condition cases. These cases also relate to day and night time variations and geographic variations from the equatorial to the high latitude region. We inspected the kappa-correction and its performance relative to the standard bending angle correction for RO-retrieved stratospheric profiles and found mean deviations in temperature of near -0.3 K in the upper stratosphere (40-45 km) for high ionization conditions, with extreme deviations exceeding -2 K for strong inbound/outbound asymmetry. The kappa-correction term itself reaches a mean value near 0.05 µrad under these high conditions. Low solar activity and ionization conditions lead to a mean correction smaller than 0.005 µrad and mean temperature deviations smaller than 0.02 K. An intercomparison to other quality datasets, predominantly showed a decrease in mean temperature difference when applying the kappa-correction.

Sensitivity Analysis and Impact of the Kappa-Correction of Residual Ionospheric Biases on Radio Occultation Climatologies.

A new model was recently introduced to correct for higher-order ionospheric residual biases in radio occultation (RO) data. The model depends on the α 1 and α 2 dual-frequency bending angle difference squared, and a factor κ, which varies with time, season, solar activity, and height, needing only the F10.7 solar radio flux index as additional background information. To date, this kappa-correction was analyzed in simulation studies. In this study, we test it on real observed Metop-A RO data. The goal is to improve the accuracy of monthly mean RO climate records, potentially raising the accuracy of RO data toward higher stratospheric altitudes. We performed a thorough analysis of the kappa-correction, evaluating its ionospheric sensitivity during the solar cycle for monthly RO climatologies and comparing the kappa-corrected RO stratospheric climatologies to three other data sets from reanalysis and passive infrared sounding. We find a clear dependence of the kappa-correction on solar activity, geographic location, and altitude; hence, it reduces systematic errors that vary with the solar cycle. From low to high solar activity conditions, the correction can increase from values of about 0.2 K to more than 2.0 K at altitudes between 40 to 45 km. The correction shifts RO climatologies toward warmer temperatures. With respect to other data sets, however, we found it difficult to draw firm conclusions, because the biases in the other data sets appear to be at similar magnitude as the size of the kappa-correction. Further validation with more accurate data will be useful.

Ethanol radical-induced protein-DNA crosslinking. A radiolysis study.

Aqueous solutions of double-stranded DNA from calf thymus and bovine serum albumin (BSA) were irradiated at pH 7 under N2O and N2 in the presence of 10(-1) mol dm-3 ethanol, which was partly 14C-labelled. Ethanol protects DNA from strand breakage by scavenging OH radicals, but ethanol radicals induce protein-DNA crosslinks. Ethanol radicals react readily with BSA mainly by addition. They react also with double-stranded DNA, but produce crosslinking only very slowly. Based on these results the following mechanism is proposed: ethanol radicals bind to BSA producing protein radicals which become crosslinked to DNA.

Isolation and properties of an H2O-forming NADH oxidase from Streptococcus faecalis.

An H2O-forming NADH oxidase from Streptococcus faecalis, recently described [Hoskins, D. D., Whiteley, H. R. and Mackler, B. (1962) J. Biol. Chem. 237, 2647-2651], has been isolated as a uniform protein with specific activity 690 U/mg in a total yield of 50% by a two-step affinity chromatography procedure. The enzyme is metal-free and has a molecular mass of about 51 000 Da and probably consists of a single polypeptide chain. As shown by fluorimetric titration, the prosthetic group is 1 mol FAD/mol protein. The affinity behaviour of the enzyme gives evidence for the existence of a dinucleotide-binding domain capable of binding NADH or FAD. The enzyme is specific for NADH (Km = 4.1 X 10(-5) M), NADPH is not oxidized. O2 is the preferred electron acceptor, in addition FAD and, very slowly, one-electron acceptors are reduced. It is not clear whether the reduction of FAD proceeds through the dinucleotide-binding site or by exchange of the prosthetic group. The stoichiometry of the reaction with O2 corresponds to the consumption of 2 mol NADH/mol O2, and only H2O is formed (2 NADH + 2 H+ + O2----2 NAD+ + 2 H2O). Neither H2O2 nor O2.- is detected as intermediate and H2O2 cannot replace O2 as an oxidant. The enzyme can, mainly in its reduced state, be inhibited by -SH reagents. Spectral data give no evidence for the existence of radical intermediates during reduction. The enzyme can obviously accept more than two electrons/mol. On the basis of these data two possible reaction mechanisms are discussed. A proposal for the biological purpose of the reaction is made.