Passive ground-based remote sensing of radiation fog

Accurate boundary layer temperature and humidity profiles are crucial for successful forecasting of fog, and accurate retrievals of liquid water path are important for understanding the climatological significance of fog. Passive ground-based remote sensing systems such as microwave radiometers (MWRs) and infrared spectrometers like the Atmospheric Emitted Radiance Interferometer (AERI), which measures spectrally resolved infrared radiation (3.3 to 19.2 µm), can retrieve both thermodynamic profiles and liquid water path. Both instruments are capable of long-term unattended operation and have the potential to support operational forecasting. Here we compare physical retrievals of boundary layer thermodynamic profiles and liquid water path during 12 cases of thin (LWP<40 g m−2) supercooled radiation fog from an MWR and an AERI collocated in central Greenland. We compare both sets of retrievals to in-situ measurements from radiosondes and surface-based temperature and humidity sensors. The retrievals based on AERI observations accurately capture shallow surface-based temperature inversions (0–10 m a.g.l.) with lapse rates of up to −1.2 ∘C m−1, whereas the strength of the surface-based temperature inversions retrieved from MWR observations alone are uncorrelated with in-situ measurements, highlighting the importance of constraining MWR thermodynamic profile retrievals with accurate surface meteorological data. The retrievals based on AERI observations detect fog onset (defined by a threshold in liquid water path) earlier than those based on MWR observations by 25 to 185 min. We propose that, due to the high sensitivity of the AERI instrument to near-surface temperature and small changes in liquid water path, the AERI (or an equivalent infrared spectrometer) could be a useful instrument for improving fog monitoring and nowcasting, particularly for cases of thin radiation fog under otherwise clear skies, which can have important radiative impacts at the surface

Loss of a Conserved tRNA Anticodon Modification Perturbs Plant Immunity

[EN] tRNA is the most highly modified class of RNA species, and modifications are found in tRNAs from all organisms that have been examined. Despite their vastly different chemical structures and their presence in different tRNAs, occurring in different locations in tRNA, the biosynthetic pathways of the majority of tRNA modifications include a methylation step(s). Recent discoveries have revealed unprecedented complexity in the modification patterns of tRNA, their regulation and function, suggesting that each modified nucleoside in tRNA may have its own specific function. However, in plants, our knowledge on the role of individual tRNA modifications and how they are regulated is very limited. In a genetic screen designed to identify factors regulating disease resistance and activation of defenses in Arabidopsis, we identified SUPPRESSOR OF CSB3 9 (SCS9). Our results reveal SCS9 encodes a tRNA methyltransferase that mediates the 2'-O-ribose methylation of selected tRNA species in the anticodon loop. These SCS9-mediated tRNA modifications enhance during the course of infection with the bacterial pathogen Pseudomonas syringae DC3000, and lack of such tRNA modification, as observed in scs9 mutants, severely compromise plant immunity against the same pathogen without affecting the salicylic acid (SA) signaling pathway which regulates plant immune responses. Our results support a model that gives importance to the control of certain tRNA modifications for mounting an effective immune response in Arabidopsis, and therefore expands the repertoire of molecular components essential for an efficient disease resistance response.This work was supported by the National Science Foundation of China (grant 31100268 to PC) and the Spanish MINECO (BFU2012 to PV) and Generalitat Valenciana (Prometeo2014/020 to PV). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ramirez Garcia, V.; González-García, B.; López Sánchez, A.; Castelló Llopis, MJ.; Gil, M.; Zheng, B.; Cheng, P.... (2015). Loss of a Conserved tRNA Anticodon Modification Perturbs Plant Immunity. PLoS Genetics. 11(10):1-27. https://doi.org/10.1371/journal.pgen.1005586S127111

Radiative Influence of Horizontally Oriented Ice Crystals over Summit, Greenland

Ice crystals commonly adopt a horizontal orientation under certain aerodynamic and electrodynamic conditions that occur in the atmosphere. While the radiative impact of horizontally oriented ice crystals (HOIC) has been theoretically studied with respect to their impact on shortwave cloud albedo, the longwave impact remains unexplored. This work analyzes the occurrence of HOIC at Summit, Greenland, from July 2015 to June 2017. Using polarization lidar and ancillary atmospheric sensors, ice crystal orientations are identified and used to interpret cloud radiative impact on the surface radiation budget. We find HOIC occur in at least 25.6% of all ice-only column observations. We find that the shortwave impact of HOIC is to increase cloud radiative effect by approximately 22% for a given solar zenith angle. We also find that the longwave impact of HOIC compared to randomly oriented ice crystals are statistically different at the p < 0.01 significance level, increasing the surface radiative effect by approximately 8% for clouds with infrared optical depths < ~1. We suggest that the observed difference between the surface radiative effect for clouds containing randomly oriented ice crystals and HOIC may be due to enhanced scattering, but this hypothesis needs to be further explored with more detailed observations and modeling

High and Dry: New Observations of Tropospheric and Cloud Properties above the Greenland Ice Sheet

Cloud and atmospheric properties strongly influence the mass and energy budgets of the Greenland Ice Sheet (GIS). To address critical gaps in the understanding of these systems, a new suite of cloud- and atmosphere-observing instruments has been installed on the central GIS as part of the Integrated Characterization of Energy, Clouds, Atmospheric State, and Precipitation at Summit (ICECAPS) project. During the first 20 months in operation, this complementary suite of active and passive ground-based sensors and radiosondes has provided new and unique perspectives on important cloud?atmosphere properties. High atop the GIS, the atmosphere is extremely dry and cold with strong near-surface static stability predominating throughout the year, particularly in winter. This low-level thermodynamic structure, coupled with frequent moisture inversions, conveys the importance of advection for local cloud and precipitation formation. Cloud liquid water is observed in all months of the year, even the particularly cold and dry winter, while annual cycle observations indicate that the largest atmospheric moisture amounts, cloud water contents, and snowfall occur in summer and under southwesterly flow. Many of the basic structural properties of clouds observed at Summit, Greenland, particularly for low-level stratiform clouds, are similar to their counterparts in other Arctic regions. The ICECAPS observations and accompanying analyses will be used to improve the understanding of key cloud?atmosphere processes and the manner in which they interact with the GIS. Furthermore, they will facilitate model evaluation and development in this data-sparse but environmentally unique region

Lack of prominent peptide–major histocompatibility complex features limits repertoire diversity in virus-specific CD8+ T cell populations

Using both 'reverse genetics' and structural analysis, we have examined the in vivo relationship between antigenicity and T cell receptor (TCR) repertoire diversity. Influenza A virus infection of C57BL/6 mice induces profoundly different TCR repertoires specific for the nucleoprotein peptide of amino acids 366−374 (NP366) and the acid polymerase peptide of amino acids 224−233 (PA224) presented by H-2Db. Here we show the H-2Db−NP366 complex with a 'featureless' structure selected a limited TCR repertoire characterized by 'public' TCR usage. In contrast, the prominent H-2Db−PA224 complex selected diverse, individually 'private' TCR repertoires. Substitution of the arginine at position 7 of PA224 with an alanine reduced the accessible side chains of the epitope. Infection with an engineered virus containing a mutation at the site encoding the exposed arginine at position 7 of PA224 selected a restricted TCR repertoire similar in diversity to that of the H-2Db−NP366−specific response. Thus, the lack of prominent features in an antigenic complex of peptide and major histocompatibility complex class I is associated with a diminished spectrum of TCR usage