Search for: All records

Single- and multi-layer clouds are commonly observed over the Southern Ocean in varying synoptic settings, yet few studies have characterized and contrasted their properties. This study provides a statistical analysis of the microphysical properties of single- and multi-layer clouds using in-situ observations acquired during the Southern Ocean Cloud-Radiation Aerosol Transport Experimental Study. The relative frequencies of ice-containing samples (i.e., mixed and ice phase) for multi-layer clouds are 0.05–0.25 greater than for single-layer clouds, depending on cloud layer height. In multi-layer clouds, the lowest cloud layers have the highest ice-containing sample frequencies, which decrease with increasing cloud layer height up to the third highest cloud layer. This suggests a prominent seeder-feeder mechanism over the region. Ice nucleating particle (cloud condensation nuclei) concentrations are positively (negatively) correlated with ice-containing sample frequencies in select cases. Differences in microphysical properties are observed for single- and multi-layer clouds. Drop concentrations (size distributions) are greater (narrower) for single-layer clouds compared with the lowest multi-layer clouds. When differentiating cloud layers by top (single- and highest multi-layer clouds) and non-top layers (underlying multi-layer clouds), total particle size distributions (including liquid and ice) are similarly broader for non-top cloud layers. Additionally, drop concentrations in coupled environments are approximately double those in decoupled environments. 

Understanding the influence of spatiotemporal variation in environmental factors on phenology is crucial for determining the effects of climate change on amphibian populations. Here we quantify the relative influence of temperature and precipitation on surface activity of a terrestrial salamander, the Eastern Red-Backed Salamander (Plethodon cinereus) in Richmond, Virginia, USA. Specifically, we used spatial capture recapture methods to test the influence of different metrics for temperature and precipitation on baseline detection probability. We found that soil temperature, particularly at 30 cm below the surface, is a better predictor of detection than air temperature or cumulative precipitation; however, greater cumulative precipitation resulted in a higher detection probability. We also show that a quadratic effect was favored in all scenarios suggesting this species has an optimal soil temperature and cumulative precipitation for surface activity during a particular year. The highest detection probability was associated with 12.6º C at 30-cm below the surface and 0.75 cm of cumulative precipitation during the 2-d period prior to the survey occasion. In addition to contributing knowledge on the specific environmental metrics that best predict surface activity for P. cinereus, this work illustrates the importance of incorporating soil temperature measurements in capture mark-recapture studies of terrestrial salamanders. For projects with limited resources, our work indicates which fine-scale environmental measurements associated with terrestrial salamander activity in the southern portion of the range are best. 

Long-range transport of biogenic emissions from the coast of Antarctica, precipitation scavenging, and cloud processing are the main processes that influence the observed variability in Southern Ocean (SO) marine boundary layer (MBL) condensation nuclei (CN) and cloud condensation nuclei (CCN) concentrations during the austral summer. Airborne particle measurements on the HIAPER GV from north-south transects between Hobart, Tasmania and 62°S during the Southern Ocean Clouds, Radiation Aerosol Transport Experimental Study (SOCRATES) were separated into four regimes comprising combinations of high and low concentrations of CCN and CN. In 5-day HYSPLIT back trajectories, air parcels with elevated CCN concentrations were almost always shown to have crossed the Antarctic coast, a location with elevated phytoplankton emissions relative to the rest of the SO in the region south of Australia. The presence of high CCN concentrations was also consistent with high cloud fractions over their trajectory, suggesting there was substantial growth of biogenically formed particles through cloud processing. Cases with low cloud fraction, due to the presence of cumulus clouds, had high CN concentrations, consistent with previously reported new particle formation in cumulus outflow regions. Measurements associated with elevated precipitation during the previous 1.5-days of their trajectory had low CCN concentrations indicating CCN were effectively scavenged by precipitation. A coarse-mode fitting algorithm was used to determine the primary marine aerosol (PMA) contribution which accounted for < 20% of CCN (at 0.3% supersaturation) and cloud droplet number concentrations. Vertical profiles of CN and large particle concentrations (Dp > 0.07µm) indicated that particle formation occurs more frequently above the MBL; however, the growth of recently formed particles typically occurs in the MBL, consistent with cloud processing and the condensation of volatile compound oxidation products. 

Stratocumulus clouds over the Southern Ocean have fewer droplets and are more likely to exist in the predominately supercooled phase than clouds at similar temperatures over northern oceans. One likely reason is that this region has few continental and anthropogenic sources of cloud-nucleating particles that can form droplets and ice. In this work, we present an overview of aerosol particle types over the Southern Ocean, including new measurements made below, in and above clouds in this region. These measurements and others indicate that biogenic sulfur-based particles >0.1 μm diameter contribute the majority of cloud condensation nuclei number concentrations in summer. Ice nucleating particles tend to have more organic components, likely from sea-spray. Both types of cloud nucleating particles may increase in a warming climate likely to have less sea ice, more phytoplankton activity, and stronger winds over the Southern Ocean near Antarctica. Taken together, clouds over the Southern Ocean may become more reflective and partially counter the region’s expected albedo decrease due to diminishing sea ice. However, detailed modeling studies are needed to test this hypothesis due to the complexity of ocean-cloud-climate feedbacks in the region. 

Abstract Stratocumulus cloud top entrainment has a significant effect on cloud properties, but there are few observations quantifying its impact. Using explicit 0‐D parcel model simulations, initialized with below‐cloud in situ measurements, and validated with in situ measurements of cloud properties, the shortwave cloud radiative forcing (SWCF) was reduced by up to 100 W m⁻²by cloud top entrainment in the Southern Ocean. The impact of entrainment‐corrected SWCF is between 2 and 20 times that of changes in the aerosol particle concentration or updraft at cloud base. The variability in entrainment‐corrected SWCF accounts for up to 50 W m⁻²uncertainty in estimating cloud forcing. Measurements necessary for estimating the impact of entrainment on cloud properties can be constrained from existing airborne platforms and provide a first‐order approximation for cloud radiative properties of nonprecipitating stratocumulus clouds. These measurement‐derived estimates of entrainment can be used to validate and improve parameterizations of entrainment in Global Climate Models.