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Ocean dynamics at the submesoscale play a key role in mediating upper‐ocean energy dissipation and dispersion of tracers. Observations of ocean currents from synoptic mesoscale surveys at submesoscale resolution (250 m–100 km) from a novel airborne instrument (MASS DoppVis) reveal that the kinetic energy spectrum in the California Current System is nearly continuous from 100 km to sub‐kilometer scales, with a k−2 spectral slope. Although there is not a transition in the kinetic energy spectral slope, there is a transition in the dynamics to non‐linear ageostrophic interactions at scales of O $\mathcal{O}$(1 km). Kinetic energy transfer across spatial scales is enabled by interactions between the rotational and divergent components of the flow field at the submesoscale. Kinetic energy flux is patchy and localized at submesoscale fronts. Kinetic energy is transferred both downscale and upscale from 1 km in the observations of a cold filament. Plain Language Summary: Ocean dynamics at scales of 100 m–10 km, called the submesoscale, are important because they are associated with large velocity gradients and non‐linear interactions. Large gradients lead to vertical velocity, which facilitates ocean‐atmosphere interactions and ocean biological processes. Velocity gradients and non‐linear processes combine to transfer kinetic energy from the large‐scale flow to small‐scale perturbations. This can lead to instabilities that dissipate energy in the ocean surface layer (rather than the seafloor). Here we analyze novel observations that provide insight into ocean dynamics through the distributions of velocity gradients and energy transfer at 1 km scale. Dynamics at these scales have previously been modeled, but have not been observed directly. We observe a transition where non‐linear dynamics become more important at scales of order 10 km. We also introduce new interpretations of spectral analysis (analysis of energy and correlations across scales). Moreover, we analyze covariance of velocity gradient quantities and flow energetics to demonstrate that energy flux is episodic and localized at fronts. Together, these observations demonstrate that fronts play an important role in boundary‐layer kinetic energy processes and highlight the evolution of upwelling filaments. Key Points: Remote sensing observations reveal a kinetic energy spectrum with a continuous slope from 100 to 1 km in an eastern boundary regionBetween 1 and 10 km, ageostrophic non‐linear interactions become dynamically importantCross‐scale kinetic energy transfers computed from 2D velocity observations are associated with shear strain in the observed front [ABSTRACT FROM AUTHOR]

In this work we present a unique set of coincident and collocated high‐resolution observations of surface currents and directional properties of surface waves collected from an airborne instrument, the Modular Aerial Sensing System, collected off the coast of Southern California. High‐resolution observations of near surface current profiles and shear are obtained using a new instrument, "DoppVis", capable of capturing horizontal spatial current variability down to 128 m resolution. This data set provides a unique opportunity to examine how currents at scales ranging from 1 to 100 km modulate bulk (e.g., significant wave height), directional and spectral properties of surface gravity waves. Such observations are a step toward developing better understanding of the underlying physics of submesoscale processes (e.g., frontogenesis and frontal arrest) and the nature of transitions between mesoscale and submesoscale dynamics. Plain Language Summary: In recent years, through improvement of computational resolution of global ocean models, scientists have begun to suspect that kilometer‐scale eddies, whirlpools and fronts, called "submesoscale" variability, make important contributions to horizontal and vertical exchange of climate and biological variables in the upper ocean. Such features are challenging to analyze, because of their size (and how quickly they evolve; within hours), they are too large to study from a research vessel but smaller than regions typically studied with satellite measurements. In this work, we use a research aircraft instrumented to characterize ocean currents, temperature, color (in turn chlorophyll concentration) and the properties of surface waves over an area large enough to capture submesoscale processes. This approach is a step forward in understanding and quantifying the underlying physics of submesoscale processes, and in turn develops parameterization that can help improve the fidelity of weather and climate models. Key Points: Unique coincident and collocated airborne observations of Sea Surface Temperature, surface currents and properties of surface waves across submesoscales featuresA new airborne instrument enables observations of surface currents, vertical and horizontal shear to capture quickly evolving ocean featuresSuch observations are crucial to develop better understanding of the physics of submesoscale processes and wave‐current interaction [ABSTRACT FROM AUTHOR]

Increasing wildfire and declining snowpacks in mountain regions threaten water availability. We combine satellite‐based fire detections with snow seasonality classifications to examine fire activity in California's seasonal and ephemeral snow zones. We find a nearly tenfold increase in fire activity during 2020–2021 versus 2001–2019. Accumulation season broadband snow albedo declined 25%–71% at two burned sites (2021 and 2022) according to in‐situ data relative to un‐burned conditions, with greater declines associated with increased burn severity. By enhancing snowpack susceptibility to melt, both decreased snow albedo and canopy drove midwinter melt during a multi‐week dry spell in 2022. Despite similar meteorological conditions in December–February 2013 and 2022–linked to persistent high pressure weather regimes–minimal melt occurred in 2013. Post‐fire snowpack differences are confirmed with satellite measurements. With growing geographical overlap between wildfire and snow, our findings suggest California's snowpack is increasingly vulnerable to the compounding effects of dry spells and wildfire. Plain Language Summary: Satellite fire detections indicate substantial increases in wildfire activity in California's snow‐covered landscapes during 2020 and 2021, suggesting wildfire is increasingly altering mountain hydrology. During 2022, a multi‐week mid‐winter drought, or dry spell, occurred. A meteorologically‐similar dry spell occurred in 2013, and the 2022 event provides a test case to examine how post‐fire changes (canopy loss and deposition of burned dark material on snowpack) alter snowmelt patterns. Using field observations, weather station data, and satellite remote sensing of snow, we find large reductions in snow albedo and canopy cover drove rapid melt during the 2022 dry spell in burned areas whereas during 2013, minimal melt occurred. The societal connection between mountains and humans will be strained as mountains face increasing climate‐related stressors. Midwinter drought, snow loss, and increasing wildfire are expectations of a warming world. Addressing these challenges requires innovative water and forest management paradigms. Our findings motivate additional research into assessing and planning for post‐fire hydrologic changes in snow‐dominated landscapes as both wildfire and dry spells will increase in frequency with climate warming. Key Points: A 9.8x increase in satellite fire detections in California's snow zones in 2020–2021 versus 2001–2019 implies growing overlap in fire and snowPost‐fire accumulation season broadband snow albedo declined 25%–71%, driving fewer snow‐covered days and lower snow‐cover fractionCompared with the meteorologically similar 2013 dry spell, albedo and canopy declines led to rapid midwinter melt in 2022 [ABSTRACT FROM AUTHOR]

Previous studies have found that Northern Hemisphere aerosol‐like cooling induces a La Niña‐like response in the tropical Indo‐Pacific. Here, we explore how a coupled ocean‐atmosphere feedback pathway communicates and sustains this response. We override ocean surface wind stress in a comprehensive climate model to decompose the total ocean‐atmosphere response to forced extratropical cooling into the response of surface buoyancy forcing alone and surface momentum forcing alone. In the subtropics, the buoyancy‐forced response dominates: the positive low cloud feedback amplifies sea surface temperature (SST) anomalies which wind‐driven evaporative cooling communicates to the tropics. In the equatorial Indo‐Pacific, buoyancy‐forced ocean dynamics cool the surface while the Bjerknes feedback creates zonally asymmetric SST patterns. Although subtropical cloud feedbacks are model‐dependent, our results suggest this feedback pathway is robust across a suite of models such that models with a stronger subtropical low cloud response exhibit a stronger La Niña response. Plain Language Summary: Anthropogenic aerosols are an important radiative forcing on the climate system contributing to observed climate variability. In prior modeling studies, idealized aerosol‐like forcing applied to Northern Hemisphere high latitude regions has resulted in a tropical La Niña‐like response in the Eastern Equatorial Pacific. In this study, we investigate the pathway by which high latitude aerosol‐like cooling is communicated to the tropics via a sequence of ocean‐atmosphere positive feedback processes. We explore this pathway further by parsing out the total climate response into surface forcing which alters the buoyancy of seawater via heat or freshwater and surface wind stress forcing which alters the momentum of seawater. We find that subtropical patterns, arising from low clouds and wind‐induced evaporative cooling, are primarily buoyancy‐forced, while tropical asymmetries arise from momentum forcing. The results show that this pathway is robust across seven climate models such that stronger subtropical cloud responses elicit stronger sea surface temperature responses in the equatorial Pacific. The results highlight the important link between extratropical aerosol‐like forcing and La Niña‐like patterns via these coupled ocean‐atmosphere feedbacks. The equatorial Pacific can drive major climate variability, suggesting global implications for these results. Key Points: A pathway of three coupled ocean‐atmosphere feedbacks communicates extratropical anomalous cooling and sustains a tropical responseBroadly, buoyancy‐forced adjustments dominate in the subtropics while momentum‐forced adjustments create zonal asymmetries in the tropicsThis mechanistic pathway seems to be robust across several global climate models [ABSTRACT FROM AUTHOR]

This study diagnoses the drivers of intraseasonal variability of mixed layer chlorophyll‐a (Chl) concentration in the tropical Indian Ocean during boreal summer (June–September) using a well‐tested coupled ocean‐ecosystem model. Results show that wind forcing is the primary source for energetic intraseasonal Chl concentration variability in the eastern Arabian Sea and western Bay of Bengal (BoB) modulated by the Central Indian Ocean (CIO) mode. The atmospheric anomalous anticyclone associated with the positive phase of CIO mode drives southeastward currents in the Arabian Sea, which transport nutrient and Chl towards the east. Simultaneously, the wind‐induced offshore currents strengthen upwelling in the western boundary of BoB, resulting in enhanced Chl in the upper ocean. Conversely, because of the formation of a barrier layer, the nutrient supply is suppressed along the equator, which causes a negative correlation between the CIO mode and Chl. This study complements the Madden‐Julian Oscillation forcing on the intraseasonal Chl concentration anomaly in the tropical Indian Ocean. Plain Language Summary: A close examination in Chlorophyll‐a (Chl) is essential for monitoring in ocean biodiversity as well as fisheries resources. Previous studies have reported Chl concentration variability in the tropical Indian Ocean on intraseasonal timescale associated with Madden‐Julian Oscillation (MJO). Our study finds that the intraseasonal variability of mixed layer Chl concentration is modulated by the Central Indian Ocean (CIO) mode during boreal summer, which precedes monsoon intraseasonal oscillation. The CIO mode‐related winds induce anomalous currents in the upper ocean of tropical Indian Ocean, and thereby lead to nutrient supply, Chl blooms and advections. As a result, the Chl concentration is enhanced in the eastern Arabian Sea and western Bay of Bengal, but reduced in the tropical Indian Ocean during the positive phase of CIO mode. Our results elicit the role of the oceanic processes related to the CIO mode in the intraseasonal variability of Chl concentration, which is distinct from the MJO. Key Points: The Central Indian Ocean mode plays an important role in the intraseasonal variability of chlorophyll‐a (Chl) concentration in the mixed layer of tropical Indian OceanThe wind‐driven southeastward currents bring nutrient and Chl to the eastern Arabian Sea and enhance upwelling and nutrient supply in the western Bay of BengalThe barrier layer suppresses the nutrient supply in the tropical Indian Ocean and decreases the Chl concentration in the upper ocean [ABSTRACT FROM AUTHOR]

Airborne lidar altimetry can measure the sea surface height (SSH) over scales ranging from hundreds of kilometers to a few meters. Here, we analyze the spectrum of SSH observations collected during an airborne lidar campaign conducted off the California coast. We show that the variance in the surface wave band can be over 20 times larger than the variance at submesoscales and that the observed SSH variability is sensitive to the directionality of surface waves. Our results support the hypothesis that there is a spectral gap between meso‐to‐submesoscale motions and small‐scale surface waves and also indicate that aliasing of surface waves into lower wavenumbers may complicate the interpretation of SSH spectra. These results highlight the importance of better understanding the contributions of different physics to the SSH variability and considering the SSH spectrum as a continuum in the context of future satellite altimetry missions. Plain Language Summary: Using unique measurements of the sea surface height (SSH) taken from an instrument onboard an airplane off the California coast, we examine how the variance of the SSH is distributed across different spatial scales, ranging from hundreds of kilometers to a few meters. We show that surface waves can be 20 times more energetic than motions with larger scales (known as submesocales) and that the direction of surface waves impacts the SSH variability depending on different sampling and averaging strategies. These results highlight the importance of better understanding the contributions of different types of motions and physics to the SSH variability. In particular, we advocate measuring scales from meters to hundreds of kilometers as a continuum to better inform future satellite altimetry missions. Key Points: We present unique broadband airborne lidar observations of sea surface height spanning scales from hundreds of kilometers to a few metersThe sea surface height variance due to surface waves can be over an order of magnitude larger than the variance at submesoscalesThe observed sea surface height is sensitive to the direction of waves which may impact the interpretation of remote sensing measurements [ABSTRACT FROM AUTHOR]

Studies over the last two decades have shown that submicron particulates (SMPs) can be transferred from the seawater into sea spray aerosol (SSA), potentially impacting SSA cloud seeding ability. This work reports the first concurrent bulk and sea surface microlayer (SSML) SMP (0.4–1.0 μm) measurements, made during two mesocosm phytoplankton blooms in a region devoid of active wave breaking and bubble formation, providing insight into how biological and physicochemical processes influence seawater SMP distributions. Modal analyses of the SMP size distributions revealed contributions from multiple, biologically related particulate populations that were controlled by the microbial loop. With negligible bubble scavenging occurring, SSML enrichment of SMPs remained low throughout both experiments, suggesting scavenging is vital for SMP enrichment in the SSML. Our findings are discussed in the context of SMP transfer into SSA and its potential importance for SSA cloud seeding ability. Plain Language Summary: Research has shown that particulates can be transferred from the ocean into sea spray aerosol (SSA) when bubbles burst at the ocean surface. This transfer is important because incorporation of seawater particulates into SSA can impact its ability to seed water and ice clouds. During the Sea Spray Chemistry and Particulate Evolution (SeaSCAPE) study, submicron particulates (SMPs, 0.4–1.0 μm) were measured daily in the sea surface microlayer (SSML), the topmost 1–1,000 μm of the ocean surface, and the underlying bulk seawater over the course of two phytoplankton growth experiments. The objective of this study was to assess the influence of biological activity on SMP concentrations and distributions in the seawater. Our results indicate that biological growth led to increased SMP production, and the size distribution of SMPs produced was dependent on the phase of the bloom growth. Additionally, almost no SSML enrichment of SMPs occurred without active wave breaking and bubble formation, highlighting the significance of biological activity and bubble scavenging/bursting for particulate transfer into SSA. These findings are discussed in the context of potential SMP impacts on SSA cloud forming ability. Key Points: The concentration of 0.4–1.0 μm seawater particulates is higher during a phytoplankton bloomThe biologically induced increase in seawater submicron particulates is size dependent and influenced by the phase of the bloomParticulate enrichment in the sea surface microlayer is low in the absence of wave breaking and bubble scavenging [ABSTRACT FROM AUTHOR]

The origin of electrical activity accompanying volcanic ash plumes is an area of heightened interest in volcanology. However, it is unclear how intense an eruption needs to be to produce lightning flashes as opposed to "vent discharges," which represent the smallest scale of electrical activity. This study targets 97 carefully monitored plumes <3 km high from Sakurajima volcano in Japan, from June 1 to 7, 2015. We use multiparametric measurements from sensors including a nine-station lightning mapping array and an infrared camera to characterize plume ascent. Findings demonstrate that the impulsive, high velocity plumes (>55 m/s) were most likely to create vent discharges, whereas lightning flashes occurred in plumes with high volume flux. We identified conditions where volcanic lightning occurred without detectable vent discharges, highlighting their independent source mechanisms. Our results imply that plume dynamics govern the charging for volcanic lightning, while the characteristics of the source explosion control vent discharges. Plain Language Summary There are different types of electrical activity that occur within volcanic ash plumes. One well-known type is volcanic lightning, which creates the familiar flashes of visible light. Another, lesser-known type is called "vent discharges," which are tiny and invisible but create a peculiar signal known as continual radio frequency. Vent discharges are important because they sometimes occur very early in an eruption and may provide a way to give early warning of volcanic hazards. For this study, we used a specialized instrument called a lightning mapping array to measure the electrical activity during small eruptions at Sakurajima volcano. We explored when lightning flashes and vent discharges occurred during 97 different explosions. First, we found that the two types did not always happen in the same explosion, showing they are caused by different processes. Second, we found that vent discharges were more likely to occur when the explosive plume rose quickly, possibly because rock breakup and particles rubbing together create a static charge close to the vent. In contrast, lightning flashes occurred when the plume had high volume flux. These findings give clues about how to link electrical signals to eruptive processes for volcano monitoring. [ABSTRACT FROM AUTHOR]

With oceans covering 71% of the Earth's surface, sea spray aerosol (SSA) particles play an important role in the global radiative budget by acting as cloud condensation nuclei and ice nucleating particles (INPs). By acting as INPs, SSA particles affect the structure and properties of mixed‐phase clouds by inducing freezing at warmer temperatures than the homogeneous freezing temperature. Climate models that incorporate marine INPs use the emission of submicron SSA in INP parameterizations because these particles contain a higher fraction of organic mass. Here we show supermicron SSA particles, produced using a natural breaking wave analogue, are the major source of INPs throughout the lifecycle of a phytoplankton bloom. Additionally, supermicron SSA particles are shown to be more efficient INPs than submicron SSA particles, because they carry a greater number of ice active components. Thus, supermicron SSA needs to be incorporated in INP parameterizations for future climate models. Plain Language Summary: Clouds over high latitude oceans are a major source of uncertainty in global climate models. Sea spray aerosol (SSA) particles are the dominant source of cloud seeds over remote marine locations. Ice nucleating particles (INPs) initiate cloud freezing. Previous climate models approximated INPs released from oceans using the number of submicron SSA. However, field studies show supermicron particles are effective INPs over marine locations. This study was designed to understand the role of particle size for marine INPs in an isolated ocean/atmosphere laboratory setting. Two phytoplankton blooms were induced in seawater and a breaking wave proxy generated SSA. The ice nucleating activities of SSA particles in two size‐segregated populations were measured. Throughout both blooms, supermicron SSA particles were the most ice active population. The efficiency of supermicron particles was still apparent after normalizing to particle surface area. Following normalization to aerosol volume, submicron and total particle populations were comparable, suggesting ice active components in SSA scale with particle volume in the observed temperature range (−26°C to −8°C). These results suggest that climate models use size‐dependent INP activities for SSA. Proper representation of marine INPs will increase model accuracy of ice content in clouds and radiative forcing over high latitude oceans. Key Points: Supermicron sea spray aerosols have higher ice nucleating particle (INP) concentrations at warm temperatures than submicron sea spray aerosolsThe higher concentrations of INPs in supermicron sea spray aerosols occur independent of phytoplankton bloom stateThe ice nucleating ability of a sea spray aerosol (SSA) is roughly proportional to the dry particle volume [ABSTRACT FROM AUTHOR]

Observations of surface waves and ice drift along a compact sea ice edge demonstrate the importance of waves in a marginal ice zone. An analytic model is presented for the along‐ice drift forced by the radiation stress gradient of oblique waves. A momentum balance using quadratic drag to oppose the wave forcing is sufficient to explain the observations. Lateral shear stresses in the ice are also evaluated, though this balance does not match the observations as well. Additional forcing by local winds is included and is small relative to the wave forcing. However, the wave forcing is isolated to a narrow region around 500‐m wide, whereas the wind forcing has effects on larger scales. The simplistic drag is assessed using observations of shear and turbulent dissipation rates. The results have implications for the shape and evolution of the ice edge, because the lateral shear may be a source of instabilities. Plain Language Summary: Ocean surface waves rapidly get smaller when traveling from open water into sea ice. Although waves in sea ice do not break, there are some similarities to waves traveling through the surf zone, which lose most of their energy and momentum before reaching the shore. Here, the wave momentum is transferred to the sea ice and can cause strong ice drift. In the case of waves arriving at an oblique angle to the ice edge, the ice drift is directed along the ice edge, similar to alongshore currents in the surf zone. Continuing the surf‐zone analogy, the wave energy is transferred into turbulence below the water (ice) surface. Finally, there are fluctuations in the ice edge shape that may be related to this wave forcing. Key Points: Obliquely propagating surface waves drive flow (ice drift) along a marginal ice zoneGradients in the waves provide the momentum for the ice drift, which is opposed by ice‐ocean stress in a simple modelInstabilities in the strongly sheared ice drift may cause fluctuations in the ice edge shape [ABSTRACT FROM AUTHOR]

Precipitation in California is highly variable and not well forecasted on subseasonal‐to‐seasonal (S2S) timescales. Understanding relationships between synoptic‐scale atmospheric circulation and hydrometeorological extremes could improve predictability. This work demonstrates the importance of four North Pacific circulation regimes (called the NP4 modes) in modulating precipitation, flooding, and water resources in California. Here we demonstrate how, on daily timescales, interactions between the NP4 modes drive coastal flow that can result in dry conditions from atmospheric ridging or wet conditions associated with enhanced onshore flow and atmospheric river (AR) landfalls. Seasonally, the prevalence of certain NP4 phase relationships can tip the scale toward wet or dry conditions. Relationships between El Niño Southern Oscillation (ENSO) and the NP4 are explored, and we provide insight into the poorly forecasted Western US seasonal precipitation during the "Godzilla" El Niño winter of 2016 by examining climate‐weather linkages in a historical context. Plain Language Summary: The amount of precipitation that falls over California in a given water year is highly variable, which presents challenges for water resource management. Skill of both dynamical and statistical models in forecasting precipitation is low at lead times beyond 2 weeks. Recent research has explored relationships between atmospheric circulation patterns and precipitation extremes in the western United States, with the goal of improving predictability. This work demonstrates the importance of four North Pacific circulation regimes in modulating coastal flow patterns that ultimately determines the amount and spatial distribution of precipitation over California on daily and seasonal timescales. We show how the interaction between these modes on daily timescales drives wet and dry episodes within a season. Seasonally, we show how the daily variability occurs within certain constraints established by the larger, more slowly varying climate system, including (but not limited to) El Niño‐Southern Oscillation. This work improves understanding of climate‐weather relationships, which has implications for predictability of hydrometeorological extremes over California and the western United States. Key Points: Coastal vapor transport and California precipitation are modulated by four North Pacific circulation regimes on daily to seasonal timescalesThe most damaging California floods have occurred when these modes were jointly aligned to reinforce onshore flowSeasonally, these modes are influenced by ENSO but much variability occurs within the constraints set by the larger‐scale climate system [ABSTRACT FROM AUTHOR]

We present flow‐through experiments to delineate the processes involved in permeability changes driven by effective stress variations and mineral cement dissolution in porous rocks. CO2‐enriched brine is injected continuously into a tight sandstone under in situ reservoir conditions for 455 hrs. Due to the dolomite cement dissolution, the bulk permeability of the sandstone specimen significantly increases, and two dissolution passages are identified near the fluid inlet by X‐ray CT imaging. Prereaction and postreaction examinations of the effective stress law for permeability suggest that after reaction, the bulk permeability is more sensitive to pore pressure changes and less sensitive to effective stress changes. These observations are corroborated by Scanning Electron Microscopy and X‐ray CT observations. This study deepens our understanding of the effect of mineral dissolution on the effective stress law for permeability, with implications for characterizing subsurface mass and energy transport, particularly during fluid injection/production into/from geologic reservoirs. Plain Language Summary: The effective stress law for permeability describes the pore pressure‐effective stress‐permeability relationships and constitutes an essential law in poroelasticity theory. These relationships may change due to chemical fluid‐mineral reactions that modify the geometry of the fluid flow paths. In this work, we conduct laboratory experiments to investigate the evolution of the effective stress law for permeability in a tight sandstone specimen after acid stimulation. Two dissolution passages, formed due to carbonate mineral dissolution, are identified near the injection inlet by X‐ray CT imaging. These passages significantly increase the postreaction specimen permeability and lower the permeability sensitivity to effective stresses. The dissolution of carbonate minerals further exposes previously covered clay minerals to the pore fluid, resulting in a higher sensitivity of pore fluid pressure changes to the bulk permeability. These results are particularly important for geological operations involving fluid injection or production, such as Carbon Capture (Utilization) and Storage (CC(U)S), fluid production, and injection in geothermal systems, oil/gas production, and gas storage. Key Points: During dolomite dissolution, the specimen's bulk permeability is enhanced, due to the formation of two dissolution passagesPermeability is more sensitive to the pore pressure after dolomite dissolution, likely due to the increasing exposure of clay mineralsPermeability is less sensitive to the effective stress after reaction, due to high resistance to pore closure in the dissolution passages [ABSTRACT FROM AUTHOR]