Intercomparison of Aerosol Optical Thickness Derived from MODIS and <i>in Situ</i> Ground Datasets over Jaipur, a Semi-arid Zone in India

The first detailed seasonal validation has been carried out for the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra and Aqua satellites Level 2.0 Collection Version 5.1 AOT (τ_MODIS) with Aerosol Robotic Network (AERONET) Level 2.0 AOT (τ_AERONET) for the years 2009–2012 over semi-arid region Jaipur, northwestern India. The correlation between τ_MODIS versus τ_AERONET at 550 nm is determined with different spatial and temporal size windows. The τ_MODIS overestimates τ_AERONET within a range of +0.06 ± 0.24 during the pre-monsoon (April–June) season, while it underestimates the τ_AERONET with −0.04 ± 0.12 and −0.05 ± 0.18 during dry (December–March) and post-monsoon (October–November) seasons, respectively. Correlation without (with) error envelope has been found for pre-monsoon at 0.71 (0.89), post-monsoon at 0.76 (0.94), and dry season at 0.78 (0.95). τ_MODIS is compared to τ_AERONET at three more ground AERONET stations in India, i.e., Kanpur, Gual Pahari, and Pune. Furthermore, the performance of MODIS Deep Blue and Aqua AOT_550 nm (τ_DB550 nm and τ_Aqua550 nm) with τ_AERONET is also evaluated for all considered sites over India along with a U.S. desert site at White Sand, Tularosa Basin, NM. The statistical results reveal that τ_Aqua550 nm performs better over Kanpur and Pune, whereas τ_DB550 nm performs better over Jaipur, Gual Pahari, and White Sand High Energy Laser Systems Test Facility (HELSTF) (U.S. site)

A Ferredoxin Disulfide Reductase Delivers Electrons to the <i>Methanosarcina barkeri</i> Class III Ribonucleotide Reductase

Two subtypes of class III anaerobic ribonucleotide reductases (RNRs) studied so far couple the reduction of ribonucleotides to the oxidation of formate, or the oxidation of NADPH via thioredoxin and thioredoxin reductase. Certain methanogenic archaea contain a phylogenetically distinct third subtype of class III RNR, with distinct active-site residues. Here we report the cloning and recombinant expression of the <i>Methanosarcina barkeri</i> class III RNR and show that the electrons required for ribonucleotide reduction can be delivered by a [4Fe-4S] protein ferredoxin disulfide reductase, and a conserved thioredoxin-like protein NrdH present in the RNR operon. The diversity of class III RNRs reflects the diversity of electron carriers used in anaerobic metabolism