The rapid glaciation of tropical cumulus clouds has been an enigma and has been debated in the literature for over 60 years. Possible mechanisms responsible for the rapid freezing have been ...postulated, but until now direct evidence has been lacking. Recent high-speed photography of electrostatically suspended supercooled drops in the laboratory has shown that freezing events produce small secondary ice particles. Aircraft observations from the Ice in Clouds Experiment-Tropical (ICE-T), strongly suggest that the drop-freezing secondary ice production mechanism is operating in strong, tropical cumulus updraft cores. The result is the production of small ice particles colliding with large supercooled drops (hundreds of microns up to millimeters in diameter), producing a cascading process that results in rapid glaciation of water drops in the updraft. The process was analyzed from data collected using state-of-the-art cloud particle probes during 54 Learjet penetrations of strong cumulus updraft cores over open ocean in a temperature range from 5 degree to -20 degree C. Repeated Learjet penetrations of an updraft core containing 3-5 g m super(-3) supercooled liquid showed an order-of-magnitude decrease in liquid mass concentration 3 min later at an elevation 1-1.5 km higher in the cloud. The aircraft observations were simulated using a one-dimensional cloud model with explicit bin microphysics. The model was initialized with drop and ice particle size distributions observed prior to rapid glaciation. Simulations show that the model can explain the observed rapid glaciation by the drop-freezing secondary ice production process and subsequent riming, which results when large supercooled drops collide with ice particles.
The recent proposal by Lawson and Rainey (2015) to restrict the genus Clostridium to Clostridium butyricum and related species has ramifications for the members of the genera that fall outside this ...clade that should not be considered as Clostridium sensu stricto. One such organism of profound medical importance is C. difficile that is a major cause of hospital-acquired diarrhea and mortality in individuals. Based on 16S rRNA gene sequence analysis, the closest relative of Clostridium difficile is Clostridium mangenotii with a 94.7% similarity value and both are located within the family Peptostreptococcaceae that is phylogenetically far removed from C. butyricum and other members of Clostridium sensu stricto. Clostridium difficile and Clostridium mangenotii each produce abundant H2 gas when grown in PYG broth and also produce a range of straight and branched chain saturated and unsaturated fatty acids with C16:0 as a major product. The cell wall peptidoglycan contains meso-DAP as the diagnostic diamino acid. Based on phenotypic, chemotaxonomic and phylogenetic analyses, novel genus Clostridioides gen. nov. is proposed for Clostridium difficile as Clostridioides difficile gen. nov. comb. nov. and that Clostridium mangenotii be transferred to this genus as Clostridioides mangenotii comb. nov. The type species of Clostridioides is Clostridioides difficile.
•The proposal to restrict the genus Clostridium to C. butyricum and related species has ramifications organisms that fall outside this clade.•The closest relative of C. difficile is C. mangenotii with a 94.7% similarity value; both are located within the family Peptostreptococcaceae.•Clostridium difficile Clostridium mangenotii are transferred to the genus
A strictly anaerobic, cellulolytic strain, designated 18P13(T), was isolated from a human faecal sample. Cells were Gram-positive non-motile cocci. Strain 18P13(T) was able to degrade ...microcrystalline cellulose but the utilization of soluble sugars was restricted to cellobiose. Acetate and succinate were the major end products of cellulose and cellobiose fermentation. 16S rRNA gene sequence analysis revealed that the isolate belonged to the genus Ruminococcus of the family Ruminococcaceae. The closest phylogenetic relative was the ruminal cellulolytic strain Ruminococcus flavefaciens ATCC 19208(T) (<95% 16S rRNA gene sequence similarity). The DNA G+C content of strain 18P13(T) was 53.05±0.7 mol%. On the basis of phylogenetic analysis, and morphological and physiological data, strain 18P13(T) can be differentiated from other members of the genus Ruminococcus with validly published names. The name Ruminococcus champanellensis sp. nov. is proposed, with 18P13(T) (=DSM 18848(T)=JCM 17042(T)) as the type strain.
Significance Polar regions are foci of climate change, because of more-than-expected warming, problematic remote-sensing retrievals, and large uncertainties about cloud effects on radiation budgets. ...Antarctica is the world’s most remote, coldest, and driest location. Until recently, researchers have assumed that low-level clouds over the frozen Antarctic Plateau consist mainly of ice crystals. Now, measurements with a unique tethered balloon system and a ground-based lidar show that nearly 50% of clouds in the austral summer contain supercooled water which has a significant impact on the radiative properties of Antarctic clouds. Modifying a global climate model to relax the freezing below −20 °C results in a strong simulated radiative (cooling) effect, affecting the entire Antarctic Continent and extending out into the Southern Ocean.
Precious little is known about the composition of low-level clouds over the Antarctic Plateau and their effect on climate. In situ measurements at the South Pole using a unique tethered balloon system and ground-based lidar reveal a much higher than anticipated incidence of low-level, mixed-phase clouds (i.e., consisting of supercooled liquid water drops and ice crystals). The high incidence of mixed-phase clouds is currently poorly represented in global climate models (GCMs). As a result, the effects that mixed-phase clouds have on climate predictions are highly uncertain. We modify the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) GCM to align with the new observations and evaluate the radiative effects on a continental scale. The net cloud radiative effects (CREs) over Antarctica are increased by +7.4 Wm ⁻², and although this is a significant change, a much larger effect occurs when the modified model physics are extended beyond the Antarctic continent. The simulations show significant net CRE over the Southern Ocean storm tracks, where recent measurements also indicate substantial regions of supercooled liquid. These sensitivity tests confirm that Southern Ocean CREs are strongly sensitive to mixed-phase clouds colder than −20 °C.
A strictly anaerobic, Gram-stain-negative rod-shaped bacterium, designated A1-XYC3
, was isolated from the faeces of an alpaca (
). On the basis of the results of a comparative 16S rRNA gene sequence ...analysis, the isolate was assigned to the genus
with the highest sequence similarities to
DSM 2767
(96.8 %),
P7
(96.3 %) and
JW/YJL-B3
(96.1 %). The average nucleotide identity between A1-XYC3
,
and
.
was 77.4, 76.1 and 76.6 %, respectively. The predominant components of the cellular fatty acids of A1-XYC3
were C
, C
and summed feature 10, containing C
/C
cyclo. The DNA G+C content was 32.4 mol%. On the basis of biochemical, phylogenetic, genotypic and chemotaxonomic criteria, this isolate represents a novel species within
for which the name
sp. nov. is proposed. The type strain of this species is strain A1-XYC3
(=CCM 9376
=NRRL B-65691
).
In this study several ice cloud retrieval products that utilize active and passive A-Train measurements are evaluated using in situ data collected during the Small Particles in Cirrus (SPARTICUS) ...field campaign. The retrieval datasets include ice water content (IWC), effective radiusrₑ, and visible extinctionσfromCloudSatlevel-2C ice cloud property product (2C-ICE),CloudSatlevel-2B radar-visible optical depth cloud water content product (2B-CWC-RVOD), radar–lidar(DARDAR), andσfromCloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). When the discrepancies between the radar reflectivityZₑderived from 2D stereo probe (2D-S) in situ measurements andZₑmeasured by theCloudSatradar are less than 10 dBZₑ, the flight mean ratios of the retrieved IWC to the IWC estimated from in situ data are 1.12, 1.59, and 1.02, respectively for 2C-ICE, DARDAR, and 2B-CWC-RVOD. Forrₑ, the flight mean ratios are 1.05, 1.18, and 1.61, respectively. Forσ, the flight mean ratios for 2C-ICE, DARDAR, andCALIPSOare 1.03, 1.42, and 0.97, respectively. TheCloudSat2C-ICE and DARDAR retrieval products are typically in close agreement. However, the use of parameterized radar signals in ice cloud volumes that are below the detection threshold of theCloudSatradar in the 2C-ICE algorithm provides an extra constraint that leads to slightly better agreement with in situ data. The differences in assumed mass–size and area–size relations betweenCloudSat2C-ICE and DARDAR also contribute to some subtle difference between the datasets:rₑfrom the 2B-CWC-RVOD dataset is biased more than the other retrieval products and in situ measurements by about 40%. A slight low (negative) bias inCALIPSOs
may be due to 5-km averaging in situations in which the cirrus layers have significant horizontal gradients inσ.
Abstract In situ data collected by three research aircraft in four geographical locations are analyzed to determine the relationship between cloud-base temperature, drop size distribution, and the ...development of supercooled water drops and ice in strong updraft cores of convective clouds. Data were collected in towering cumulus and feeder cells in the Caribbean, over the Gulf of Mexico, over land near the Gulf Coast, over land in the southeastern United States, and the high plains in Colorado and Wyoming. Convective clouds in the Caribbean, over the Gulf of Mexico and its coast, and over the southeastern United States all develop millimeter-diameter supercooled drops in updraft cores. Clouds over the high plains do not generate supercooled large drops, and rarely are drops >70 μm observed in updraft cores. Commensurate with the production of supercooled large drops, ice is generated and rapidly glaciates updraft cores through a hypothesized secondary ice process that is based on laboratory observations of large drops freezing and emitting tiny ice particles. Clouds over the high plains do not experience the secondary ice process and significant concentrations of supercooled liquid in the form of small drops are carried much higher (up to −35.5°C) in the updraft cores. An empirical relationship that estimates the maximum level to which supercooled liquid water will be transported, based on cloud-base drop size distribution and temperature, is developed. Implications have applications for modeling the transport of water vapor and particles into the upper troposphere and hygroscopic seeding of cumulus clouds.
The genus
is phenotypically and genotypically diverse, with many species phylogenetically located outside
. One such group consists of the species
and
(formally clostridial rRNA cluster XVIII) 1. ...Sequencing of the 16S rRNA and, more recently, the results of genomic analyses have demonstrated that these species represent a coherent cluster separated from other closely related genera located in the family
within the order
2. In addition to phenotypic, phylogenetic and genomic comparisons, chemotaxonomic features were consistent between all four species, the predominant fatty acids were C
and C
ω9
, while glucose and ribose were the whole cell sugars present in the cell walls. Furthermore, he results of peptidoglycan analysis indicated that
-2,6-diaminopimelic acid was present as the diagnostic diamino acid in all four species. Biochemical profiles were also concordant with them being closely related species. Therefore, on the basis of phylogenetic, genomic, phenotypic and chemotaxonomic information, a novel genus,
gen. nov., is proposed. It is suggested that
and
be transferred to this genus as
comb. nov.,
comb. nov.,
comb. nov. and
comb. nov. The type species of the genus is
CCUG 24038
(=ATCC 25582
=DSM 1402
).
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