The “Goldilocks Zoneâ€? from a redox perspectiveâ€â€�Adaptive vs. deleterious responses to oxidative stress in striated muscle

Consequences of oxidative stress may be beneficial or detrimental in physiological systems. An organ system's position on the “hormetic curve� is governed by the source and temporality of reactive oxygen species (ROS) production, proximity of ROS to moieties most susceptible to damage, and the capacity of the endogenous cellular ROS scavenging mechanisms. Most importantly, the resilience of the tissue (the capacity to recover from damage) is a decisive factor, and this is reflected in the disparate response to ROS in cardiac and skeletal muscle. In myocytes, a high oxidative capacity invariably results in a significant ROS burden which in homeostasis, is rapidly neutralized by the robust antioxidant network. The up-regulation of key pathways in the antioxidant network is a central component of the hormetic response to ROS. Despite such adaptations, persistent oxidative stress over an extended time-frame (e.g., months to years) inevitably leads to cumulative damages, maladaptation and ultimately the pathogenesis of chronic diseases. Indeed, persistent oxidative stress in heart and skeletal muscle has been repeatedly demonstrated to have causal roles in the etiology of heart disease and insulin resistance, respectively. Deciphering the mechanisms that underlie the divergence between adaptive and maladaptive responses to oxidative stress remains an active area of research for basic scientists and clinicians alike, as this would undoubtedly lead to novel therapeutic approaches. Here, we provide an overview of major types of ROS in striated muscle and the divergent adaptations that occur in response to them. Emphasis is placed on highlighting newly uncovered areas of research on this topic, with particular focus on the mitochondria, and the diverging roles that ROS play in muscle health (e.g., exercise or preconditioning) and disease (e.g., cardiomyopathy, ischemia, metabolic syndrome)

Wintertime In Situ Cloud Microphysical Properties of Mixed-Phase Clouds Over the Southern Ocean

Abstract In situ observations made over 20 flights during three Austral winters (June to October 2013–2015) were analyzed to characterize the cloud microphysical properties and natural variability of mid‐latitude shallow convective clouds over the Southern Ocean (SO), with a focus on pristine conditions and the mixed‐phase temperature range (MPTR, 0°C to −31°C). Liquid, mixed‐phase, and ice cloud fractions were observed 39%, 44%, and 17% of the time, respectively, under various meteorological settings. Liquid phase clouds were typically characterized by low droplet number concentrations and the common presence of drizzle. Supercooled liquid water was prevalent in the MPTR, while freezing of supercooled raindrops likely formed the primary ice nucleation mechanism in these shallow clouds. Ice particles of various habits were present in the mature/maturing convective cloud cells, suggesting the operation of multiple particle growth regimes. Increased ice particle concentrations (exceeding 100 L−1), well in excess of the expected ice nuclei concentrations, were measured at temperature warmer than approximately −12°C, signaling the operation of secondary ice production mechanisms. However, these cloud segments were spatiotemporally inhomogeneous, suggesting the chaotic and turbulent nature of the secondary ice‐forming processes. Accurately representing these processes in global models, while necessary, is likely a challenge. Our analysis also found marked inconsistencies between several satellite‐based cloud phase products that have underpinned recent developments of model parameterization frameworks. Understanding and addressing these inconsistencies are critical toward improving the representation of SO clouds and their radiative properties in climate models

A Comparison of Cloud Microphysical Properties Derived From MODIS and CALIPSO With In Situ Measurements Over the Wintertime Southern Ocean

Abstract In situ observations of cloud effective radius (reff), droplet number concentration (Nd), and thermodynamic phase from 11 wintertime flights over the Southern Ocean (43–45°S, 145–148°E) are compared to products from MODerate‐resolution Imaging Spectroradiometer (MODIS) and Cloud‐Aerosol Lidar with Orthogonal Polarization. The in situ observations were in close alignment with A‐train overpasses for a 30‐min window. For open mesoscale cellular convection, which was predominantly observed, clouds were commonly found to be intermittently drizzling, patchy, and mixed phase. Compared to the in situ observations of the cloud thermodynamic phase, the Cloud‐Aerosol Lidar with Orthogonal Polarization and MODIS cloud phase optical property products consistently underestimated the occurrence of mixed‐phase clouds, whereas the MODIS infrared‐based phase product showed a better qualitative agreement despite a frequent classification of uncertainty. The MODIS reff_2.1 overestimated the in situ reff for nondrizzling clouds (by ~13 μm on average) and, to a lesser extent, for lightly drizzling cases. Conversely, MODIS reff_2.1 underestimated the in situ reff for heavily drizzling cases by ~10 μm on average. The overestimation of reff is much greater than that for the stratocumulus over the Southeast Pacific shown in other studies. An examination on subpixel heterogeneity, droplet size variability, a bimodal distribution, and solar zenith angle suggests that all of these factors have measurable impacts on the MODIS reff bias. The MODIS Nd is largely consistent with the in situ observations. However, the Nd of the two high Nd cases (closed mesoscale cellular convection) are highly underestimated. An error analysis suggests that the Nd biases are likely a result of a compensating error effect

A Characterization of Clouds and Precipitation Over the Southern Ocean From Synoptic to Micro Scales During the CAPRICORN Field Campaigns

Abstract The persistent Southern Ocean (SO) shortwave radiation biases in climate models and reanalyses have been associated with the poor representation of clouds, precipitation, aerosols, the atmospheric boundary layer, and their intrinsic interactions. Capitalizing on shipborne observations collected during the Clouds Aerosols Precipitation Radiation and atmospheric Composition Over the Southern Ocean 2016 and 2018 field campaigns, this research investigates and characterizes cloud and precipitation processes from synoptic to micro scales. Distinct cloud and precipitation regimes are found to correspond to the seven thermodynamic clusters established using a K‐means clustering technique, while less distinctions are evident using the cyclone and (cold) front compositing methods. Cloud radar and disdrometer data reveal that light precipitation is common over the SO with higher intensities associated with cyclonic and warm frontal regions. Multiple lines of evidence suggest the presence of diverse microphysical features in several cloud regimes, including the likely dominance of ice aggregation in deep precipitating clouds. Signatures of mixed phase, and in some cases, riming were detected in shallow convective clouds away from the frontal conditions. Two of the K‐means clusters with contrasting cloud and precipitation properties are observed over the high‐latitude SO and coastal Antarctica, suggesting distinct physical processes therein. Through a single case study, in‐situ and remote‐sensing data collected by an overflight of the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study were also evaluated and complement the ship‐based analysis

A climatology of open and closed mesoscale cellular convection over the Southern Ocean derived from Himawari-8 observations

Abstract. Marine atmospheric boundary layer clouds cover vast areas of the Southern Ocean (SO), where they are commonly organized into mesoscale cellular convection (MCC). Using 3 years of Himawari-8 geostationary satellite observations, open and closed MCC structures are identified using a hybrid convolutional neural network. The results of the climatology show that open MCC clouds are roughly uniformly distributed over the SO storm track across midlatitudes, while closed MCC clouds are most predominant in the southeast Indian Ocean, with a second maximum along the storm track. The ocean polar front, derived from ECMWF-ERA5 sea surface temperature gradients, is found to be aligned with the southern boundaries for both MCC types. Along the storm track, both closed and open MCCs are commonly located in post-frontal, cold air masses. The hourly classification of closed MCC reveals a pronounced daily cycle, with a peak occurring late night/early morning. Seasonally, the diurnal cycle of closed MCC is most intense during the summer months (December–February; DJF). Conversely, almost no diurnal cycle is evident for open MCC

Characteristics and Variability of Precipitation Across Different Sectors of an Extra-Tropical Cyclone: A Case Study Over the High-Latitudes of the Southern Ocean

Abstract Shipborne observations from the CAPRICORN‐2018 field campaign were used to investigate the characteristics and variability of precipitation across different sectors of an extra‐tropical cyclone on 16 February 2018, over the Southern Ocean (SO). Three distinct time periods—frontal, post‐frontal, and cyclone—were identified during the day. The frontal passage recorded a total accumulation of 1.9 mm, where the precipitation phases were primarily composed of rain (96%), while the cyclone period recorded the largest precipitation (4.0 mm), where the precipitation phases varied with snow (10%), mixed‐phase (40%), and rain (50%). The BASTA radar suggests the freezing level was shallow (∼500 m) with snow present above. The cloud top heights, observed by a C‐band radar, were shallower in the cyclone period, although deeper cloud depths of ∼6 km were sporadically recorded. Increased surface fluxes and a southerly wind direction indicate that cold air advection, was likely the main cause of high precipitation during the cyclone period. A non‐precipitating multi‐layer cloud structure with a geometrically thin (200 m) homogeneous layer of supercooled liquid water (SLW) overlaying shallow boundary layer convection was seen during the post‐frontal period. The ship‐borne observations were used to evaluate Weather Research & Forecasting (WRF) simulations with different microphysics settings. We found the frontal precipitation intensity is well reproduced, but it is underestimated during the cyclone period. This study represents a unique set of observations and highlights the need for understanding how ice processes and potentially horizontal advection contribute to the development of precipitation and convection over the SO