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Please note: These are preprints and have not been peer reviewed. Data may be preliminary.
Saturation-ratio Fluctuations from Scalar Transport in Moist Rayleigh-Bénard Convecti...
Kamal Kant Chandrakar
Will Cantrell

Kamal Kant Chandrakar

and 4 more

January 07, 2019
A careful characterization of moisture fluxes and saturation-ratio statistics in atmospheric convection is significant for cloud microphysical processes and dynamics. The saturation-ratio of water vapor is defined as the ratio of actual water vapor pressure and its equilibrium value at a given air temperature. Therefore, it is a function of two scalars (water vapor and temperature) and is coupled through the nonlinear Clausius-Clapeyron equation. Participation of both scalar fields in the convection process and the nonlinear coupling of both scalars in saturation-ratio make this problem more complex, as compared to its dry-convection counterpart. We have explored heat and water vapor fluxes and saturation-ratio statistic in the moist Rayleigh-Bénard convection case, using the one-dimensional-turbulence (ODT) model developed by Wunsch et al. JFM 2005. This idealized small-scale simulation is a step toward understanding the full atmospheric convection problem at a more fundamental level. We have obtained the thermal and moisture fluxes as a function of the non-dimensional buoyancy parameter, also known as moist Rayleigh number, and compared it with the scaling relations. Moreover, we have examined the mean and variance profiles of saturation-ratio, and analyzed the different contributing terms for saturation-ratio fluctuations. Based on the scaling analysis, a simplified relation between saturation-ratio variance and moist Rayleigh number has been derived and compared with the simulation results. Additionally, we found that different values of water vapor and thermal diffusivities make the saturation-ratio pdf broader than the case when they are considered equal.
Tools and Resources for Educators: Teaching Quantitative Thinking in Geoscience with...
Lisa Kempler
Cathryn Manduca

Lisa Kempler

and 2 more

January 30, 2019
Computational geoscience courses often combine domain science, math, programming, and hardware instrumentation. Ensuring students master all those skills can be daunting for professors, as well as for students who tackle these hybrid classes. Through a series of 3-day in-person workshops, faculty across the geoscience disciplines and allied science fields have collaborated to produce on-line teaching resources and a community of peers to support these multi-faceted but essential Geoscience courses. These resources support Geoscience and Science educators seeking to update their curriculum and even create whole new courses. Topics addressed include approaches to teaching, best practices for working group design, empowering students to self-advocate, building computational skills optimally, and coordinating curriculum across a department and even cross-departments. This e-lightning talk will show the resources available to educators – teaching activities including MATLAB code, presentations on teaching approaches, and course curriculum, among others. It will also highlight relevant MathWorks tools for learning and teaching, from online videos, to free, interactive MATLAB tutorials (MATLAB Onramp and more), to autograding software for MATLAB code (MATLAB Grader), with associated publicly available homework problem sets. Attendees will learn where and how to access these online resources, share their teaching challenges, and participate in future workshops.
4D-Var inversion of European NH3 emissions using CrIS NH3 measurements and GEOS-Chem...
Hansen Cao
Daven K. Henze

Hansen Cao

and 28 more

September 10, 2021
We conduct the first 4D-Var inversion of NH3 accounting for NH3 bidirectional flux, using CrIS satellite NH3 observations over Europe in 2016. We find posterior NH3 emissions peak more in springtime than prior emissions at continental to national scales, and annually they are generally smaller than the prior emissions over central Europe, but larger over most of the rest of Europe. Annual posterior anthropogenic NH3 emissions for 25 European Union members (EU25) are 25% higher than the prior emissions and very close(<2% difference) to other inventories. Our posterior annual anthropogenic emissions for EU25, the UK, the Netherlands, and Switzerland are generally 10-20% smaller than when treating NH3 fluxes as uni-directional emissions, while the monthly regional difference can be up to 34% (Switzerland in July). Compared to monthly mean in-situ observations, our posterior NH3 emissions from both schemes generally improve the magnitude and seasonality of simulated surface NH3 and bulk NHx wet deposition throughout most of Europe, whereas evaluation against hourly measurements at a background site shows the bi-directional scheme better captures observed diurnal variability of surface NH3. This contrast highlights the need for accurately simulating diurnal variability of NH3 in assimilation of sun-synchronous observations and also the potential value of future geostationary satellite observations. Overall, our top-down ammonia emissions can help to examine the effectiveness of air pollution control policies to facilitate future air pollution management, as well as helping us understand the uncertainty in top-downNH3emission estimates associated with treatment of NH3surface exchange.
Subglacial channels, climate warming, and increasing frequency of Alpine glacier snou...
Pascal Emanuel Egli
Bruno Belotti

Pascal Emanuel Egli

and 4 more

September 10, 2021
Alpine glacier retreat has increased markedly since the late 1980s, and is commonly linked to the effects of rising temperature on surface melt. Less considered are processes associated with glacier surface collapse. A survey of 22 retreating Swiss glaciers suggests that snout marginal collapse events have increased in frequency since the late 1980s, driven by ice thinning and reductions in glacier-longitudinal ice flux. Detailed measurement of a collapse event at one glacier showed vertical deformation of the surface above the main subglacial channel. But with low rates of longitudinal flux and vertical creep closure, this was insufficient to close the channel in the snout marginal zone. We hypothesise that this maintains contact between subglacial ice and the atmosphere, allowing greater incursion of warm air up-glacier, thus enhancing melt from below. The associated enlargening of subglacial channels at glacier snouts leads to surface collapse and removal of ice via fluvial processes.
Expanding the GLOBE International STEM Network (GISN) to Include “Early Career STEM P...
Amy Barfield

Amy Barfield

January 30, 2019
The Global Learning and Observations to Benefit the Environment (GLOBE) Program is an international science and education program that connects a network of communities around the world and gives them the opportunity to participate in data collection and the scientific process, and contribute meaningfully to our understanding of the Earth system and global environment. GLOBE hosts the GLOBE International STEM Network (GISN), which is an international network of STEM professionals that work with GLOBE students, teachers, and other STEM professionals around the world. Members of the GISN may mentor students and teachers, collaborate on scientific research, use GLOBE data in their research, judge student research projects, and write blogs for the GLOBE website, among other things. In January 2018, the GISN, which was previously only open to graduate students and seasoned STEM professionals, was expanded to include “Early Career STEM Professionals” which includes upper-level undergraduates or master’s students pursuing a degree in a STEM field or recent graduates working in STEM fields but have less than five years’ experience. Goals for expanding the the GISN include granting early career professionals a chance to establish ties with the next generation of STEM professionals, connecting early career professionals and students with potential mentors and collaborators, and allowing early career professionals and students to explore what a career in a STEM field can look like. All GISN members will benefit from an increase in the number of members as well as an increase in the numbers of members who have more flexibility in terms of time and finances. As well, it is another opportunity for GLOBE to engage with alumni of the program who have continued a career in STEM. Unlike other ECS networks, the GISN does not separate the ECS’ out from the other members so all members have equal access to resources and each other. Since opening up the GISN in January, 17 Early Career STEM Professionals representing 5 of our 6 regions (Africa, Asia and the Pacific, Europe and Eurasia, Latin America and the Caribbean, and North America, but not Near East and North Africa) have joined the network bringing total membership to 421 members.
Mars Methane Sources in Northwestern Gale Crater Inferred from Back-Trajectory Modeli...
Yangcheng Luo
Michael A Mischna

Yangcheng Luo

and 5 more

July 15, 2021
During its five years of operation as of 2017, the Sample Analysis at Mars (SAM) Tunable Laser Spectrometer (TLS) on board the Curiosity rover has detected six methane spikes above a low background abundance in Gale crater. The methane spikes are likely sourced by nearby emission from the surface. Here we use inverse Lagrangian modeling techniques to identify upstream emission regions on the Martian surface for these methane spikes at unprecedented spatial resolutions. Inside Gale crater, the northwestern crater floor casts the strongest influence on the detections. Outside Gale crater, the upstream regions extend towards the north. The contrasting results from two consecutive TLS methane measurements point to an active emission site to the west and the southwest of the Curiosity rover on the northwestern crater floor. The observed spike magnitude and frequency also favor emission sites on the northwestern crater floor, unless there are fast methane removal mechanisms at work, or either the TLS methane spikes or the Trace Gas Orbiter (TGO) non-detections can not be trusted.
Observational Constraints on Southern Ocean Cloud-phase Feedback
Casey Wall
Trude Storelvmo

Casey James Wall

and 3 more

September 10, 2021
Shortwave radiative feedbacks from Southern Ocean clouds are a major source of uncertainty in climate projections. Much of this uncertainty arises from changes in cloud scattering properties and lifetimes that are caused by changes in cloud thermodynamic phase. Here we use satellite observations to infer the scattering component of the cloud-phase feedback mechanism and determine its relative importance by comparing it with an estimate of the overall temperature-driven cloud feedback. The overall feedback is dominated by an optical thinning of low-level clouds. In contrast, the scattering component of cloud-phase feedback is an order of magnitude smaller and is primarily confined to free-tropospheric clouds. The small magnitude of this feedback component is a consequence of counteracting changes in albedo from cloud optical thickening and shifts in the scattering direction of cloud particles. These results indicate that shortwave cloud feedback is likely positive over the Southern Ocean and that changes in cloud scattering properties arising from phase changes make a small contribution to the overall feedback. The feedback constraints shift the projected 66% confidence range for the global equilibrium temperature response to doubling atmospheric CO2 by about +0.1 K relative to a recent consensus estimate of cloud feedback.
Sea surface temperature control on the aerosol-induced brightness of marine clouds ov...
Xiaoli Zhou
Jianhao Zhang

Xiaoli Zhou

and 2 more

September 09, 2021
Marine low clouds are one of the greatest sources of uncertainty for climate projection. We present an observed climatology of cloud albedo susceptibility to cloud droplet number concentration perturbations (S0) with changing sea surface temperature (SST) and estimated inversion strength for single-layer warm clouds over the North Atlantic Ocean, using eight years of satellite and reanalysis data. The key findings are that SST has a dominant control on S0 in the presence of co-varying synoptic conditions and aerosol perturbations. Regions conducive to aerosol-induced darkening (brightening) clouds occur with high (low) local SST. Higher SST significantly hastens cloud-top evaporation with increasing aerosol loading, by accelerating entrainment and facilitating entrainment drying. In a global-warming-like scenario, cloud darkening is expected, mainly as a result of increased entrainment drying via Clausius-Clapeyron scaling. Our results imply a more (less) positive low-cloud liquid water path feedback in a warmer climate with increasing (decreasing) aerosol loading.
Virtual sounding of solar-wind effects on the AU and AL indices based on an echo stat...
Shin'ya Nakano
Ryuho Kataoka

Shin'ya Nakano

and 1 more

September 09, 2021
The properties of the auroral electrojets are studied by modeling the relationships between the solar-wind parameters and the AU and AL indices with a trained echo state network (ESN), a kind of recurrent neural network. To identify the properties of auroral electrojets, we obtain various synthetic AU and AL data by using various artificial inputs with the trained ESN. The synthetic data show that the AU and AL indices are significantly affected by the solar-wind speed in addition to Bz of the interplanetary magnetic field (IMF). A contributions from IMF By is are also suggested. In addition, the synthetic data indicate nonlinear effects from the solar-wind density, which is strong when the solar-wind speed is high and when IMF Bz is near zero.
Upward bipolar lightning flashes originated from interaction with intracloud lightnin...
Ivan Toucedo Cruz
Marcelo Magalhães Fares Saba

Ivan Toucedo Cruz

and 3 more

September 02, 2022
The present work shows high-speed videos of two upward flashes that started with positive upward leaders and, instead of being followed by negative subsequent return strokes, they were followed by positive subsequent return strokes. In both cases, after the positive leaders developed, recoil leaders appeared in their decayed branches as would be usual in negative upward lightning flashes. However, in these flashes the negative end of a recoil leader connected to a positive leader of an intracloud flash nearby. The connection initiated a downward positive leader that re-ionized the decayed channel of the upward flash all the way to the tower giving origin to a positive subsequent return stroke. This work shows that recoil leaders do play an important role in the occurrence of bipolar upward flashes and their interaction with intracloud flashes can provide explanations for all types of bipolar upward flashes initiated by upward positive leaders.
Colder eastern equatorial Pacific and stronger Walker cell in the early 21st century:...
Ulla Klint Heede
alexey

Ulla Klint Heede

and 1 more

September 02, 2022
Since the early 1990s the Pacific Walker circulation shows a multi-decadal strengthening, contradicting future model projections. Whether this trend, evident in a range of indices especially before the 2015 El Niño, reflects the coupled ocean-atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature (SST) trends during 1980-2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere/Indo-West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat-like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central-eastern Pacific but warming in the western Pacific and tropical Indian ocean. This pattern contributes to the Walker circulation strengthening along with the PDO. Historical simulations appear to underestimate this pattern, contributing to the models’ inability to replicate the Walker cell strengthening.
Increasing intensity of extreme global heatwaves: the crucial role of metrics
Emmanuele Russo
Daniela I.V. Domeisen

Emmanuele Russo

and 1 more

September 02, 2022
Many indices have been defined to estimate the intensity of a heatwave. However, these indices are often used indiscriminately, without sufficient consideration of their possible different results and of the challenges that this poses to a proper characterization and comparison of events. This study, by comparing four different indices applied to reanalyses data, shows that the choice of heatwave intensity metrics has important effects on the detection of the most intense events for the period 1950-2021, with indices based on cumulative values of a target variable that must be preferred over the ones relying on temporal averages. Under these considerations, one of the given indices is additionally selected for the study of heatwaves of the period 1950-2021, showing that heatwaves that were unlikely before 1986 have become up to ten times more usual and up to three times more intense during recent times.
Comparing the importance of iodine and isoprene on tropospheric photochemistry
Ryan J Pound
Mathew J. Evans

Ryan J Pound

and 2 more

September 02, 2022
Naturally emitted reactive trace gases are thought to impact tropospheric composition, predominantly through the emission and chemistry of isoprene (C5H8). Other species are thought to play a less important role. Here the GEOS-Chem model is used to compare the impacts of isoprene and iodine emissions on present-day tropospheric composition. Removing isoprene emissions leads to a 4.4% decrease in tropospheric O3 burden, a smaller absolute change than the 5.7% increase from removing iodine emissions. Iodine has a negligible impact on global mean OH concentrations and methane lifetime (-0.2% and +0.1%). Isoprene has a substantial impact on both (-7% and +6.5%). Isoprene emissions and chemistry are seen as essential for tropospheric chemistry models, but iodine is often not. We suggest iodine should receive greater attention in model development and experimental research to allow improved predictions of past, present and future tropospheric O3.
Influence of the Solar Cycle on the North Atlantic Oscillation
Yuhji Kuroda
Kunihiko Kodera

Yuhji Kuroda

and 4 more

July 15, 2021
We examine the influence of the solar cycle on the North Atlantic Oscillation (NAO) on its pathway from the upper stratosphere to the surface by applying lagged regression analyses to recent observations, historical observations covering 194 years, and an Earth system model simulation covering 165 years. The propagation of the solar signal can well be explained by a top-down mechanism, but one that was strongly affected by ocean dynamics. The solar signal first appears in the subtropical upper stratosphere as a temperature signal. The associated zonal wind signal then propagates downward to the surface in response to stratospheric variability known as the Polar-night Jet Oscillation. The NAO signal tends to appear in February during years of peak solar activity. The solar signal is further modulated such that positive NAO signals tend to appear earlier in winter with increasing years after peak solar activity, which we think to be an oceanic effect. The fluctuations and amplitude modulation of the solar–NAO relationship on a 50-year time scale also suggest that there will be nonlinear interactions between solar forcing and ocean dynamics.
The state of the atmosphere throughout the seasons: how well can atmospheric models e...
Karl Koch
Christoph Pilger

Karl Koch

and 1 more

July 15, 2021
Over the past two decades the German Aerospace Center facility near Heilbronn, Germany, has conducted a considerable number of tests of the ARIANE-5 main rocket engine. From the 159 studied tests a large portion (~45%) was detected at IMS infrasound station IS26 in the Bavarian forest, located at a distance of about 320 km in an eastward direction (99° clockwise from North). Observations were mostly made during the winter season between October and April with a detection rate of more than 70%, as stratospheric winds then favour atmospheric infrasound propagation within a stratospheric duct. For the summer season the reversal of middle atmospheric wind patterns generally inhibits signal detections, as is found by comparisons of numerical weather prediction models. A significant portion of non-detection cases during winter, however, also exhibit a sound speed profile that should enable infrasound signal observations due to the presence of a stratospheric duct. Using European Centre for Medium-Range Weather Forecast (ECMWF) atmospheric model analysis and infrasound propagation modelling it was found that about two-thirds can be explained by the existence of a shadow zone near the station. For one third of the cases, however, such a shadow zone does not exist and it must be concluded that the applied atmospheric model is more often than expected unable to correctly explain infrasound propagation to regional distances, as has been found in previous studies.
Climate impact comparison of electric and gas-powered end-user appliances
Florian Dietrich
Jia Chen

Florian Dietrich

and 9 more

January 03, 2022
Natural gas is considered a bridging technology in the energy transition because it produces fewer carbon emissions than coal, for example. However, when leaks exist, methane is released into the atmosphere, leading to a dramatic increase in the carbon footprint of natural gas, as methane is a much stronger greenhouse gas than carbon dioxide. Therefore, we conducted a detailed study of methane emissions from gas-powered end-use appliances and then compared their climate impacts with those of electricity-powered appliances. We used the Munich Oktoberfest as a case study and then extended the study to 25 major natural gas consuming countries. This showed that electricity has been the more climate-friendly energy source at Oktoberfest since 2005, due to the extensive use of renewable electricity at the festival and the presence of methane emissions, particularly caused by incomplete combustion of natural gas appliances. Further, our global study shows that using electric appliances for cooking and heating would be more climate-friendly not only at Oktoberfest but also in several countries around the world, depending on the energy mix used and the leakage rate of natural gas. With this study, we demonstrate one way in which countries with a high renewable share in power generation, in particular, can reduce a significant amount of carbon emissions in the future.
Microclimates in fumarole ice caves on volcanic edifices-Mount Rainier, Washington, U...
Lee John Florea
Andreas Pflitsch

Lee John Florea

and 3 more

August 05, 2020
The fumarole ice caves of Mount Rainier in the Cascade Volcanic Arc in Washington, USA, provide unique insight into the dynamic equilibrium between thermal flux on volcanic edifices and snow accumulation on summit glaciers. More than 3.5 km of surveyed cave passage nearly circumnavigate the East Crater, reaching within 19 m of the 4392-m summit and extending to 144-m-deep along the glacier-crater boundary. The large circum-crater passage connects entrances on the crater rim to steep transverse passages, and cave morphology is maintained by fumarole gas convection and advection. A melt- and condensate-formed lake, Lake Adélie, occupies a portion of the circum-crater passage. Hourly data were collected between August 2016 and August 2017 and included the measured temperatures at three fumarole, the cave air temperature and pressure, the lake water temperature and depth, and the outside temperature and snow depth at Paradise Visitors Center. Time-series analyses of these data reveal complex associations between synoptic to seasonal weather, fumarole activity, and lake level. On seasonal and longer scales, fumarole temperatures follow independent pathways connected to spatial and temporal changes in volcanic heat flux and the circulation of glacial melt. For synoptic-scale meteorology, major snowfall seals the cave entrances, increasing cave air temperature and pressure from fumarole output and causing rising lake levels from increased melt until entrances reopen. Repeating freeze-thaw cycles observed in the cave monitoring data are a primary cause of crater mass wasting. Despite these variations, the scale and morphology of the caves is preserved over decadal or longer scales.
Electron-Only Tail Current Sheets and Their Temporal Evolution
Mark Alexander Hubbert
Yi Qi

Mark Alexander Hubbert

and 5 more

August 28, 2020
The Earth’s magnetotail contains a current sheet separating the anti-Sunward field of the southern lobe from the sunward-pointing northern lobe. Herein, we report tail current sheets that are supported by only electron currents. We examine one electron-only current sheet in detail, and briefly discuss ten others. Three current sheets are interpreted in terms of the time-evolution of reconnection onset. These current sheets show evidence of parallel electron heating, perpendicular ion heating, and current sheet expansion. These features are consistent with electron and ion behavior during traditional “electron-ion” reconnection. Ground-based and in-situ data show that electron-ion reconnection occurs shortly after each “pre-ion reconnection” electron-only reconnection event. This suggests that electron-only reconnection can act as a precursor to electron-ion reconnection. We note that five events occur shortly after a period of electron-ion reconnection, which suggests that electron-only reconnection is more than merely a precursor to ion reconnection.
Simultaneous creation of a large vapor plume and pumice raft by a shallow submarine e...
Kristen Fauria
Martin Jutzeler

Kristen Fauria

and 8 more

February 05, 2022
The August 12, 2021 eruption of Fukutoku-Okanoba, a shallow submarine volcano in the Izu-Bonin arc of Japan, is one of few documented submarine eruptions to make a large aerial plume and floating pumice raft. Relative to past eruptions, this event was well-covered by multiple high resolution satellite remote sensors. Here we use satellite remote sensing to assess the eruption style, rates, and products. We find that the 16 km plume was water-rich. Furthermore, we conclude that the 0.1 km^3 raft and 16 km plume were co-genetic and suggest that pumice clasts were delivered to the raft by tephra jets rather than plume fallout. Finally, this eruption highlights a discrepancy between small erupted volumes and high plume heights that may be common for shallow explosive subaqueous eruptions.
Precipitating Solar Wind Hydrogen at Mars: Improved Calculations of the Backscatter a...
Zachary Girazian
Jasper, S. Halekas

Zachary Girazian

and 1 more

August 28, 2020
Outside the Martian bow shock, charge exchange between solar wind protons and exospheric hydrogen produces energetic neutral atoms (ENAs) that travel towards Mars at the solar wind velocity. The penetrating ENAs deposit most of their energy near 150 km, but a fraction of them undergo enough collisions to be scattered back to space, resulting in a hydrogen albedo. Some of the penetrating ENAs are converted into protons upon reaching the collisional upper atmosphere. These protons can be measured by the Mars Atmosphere and Volatile EvolutioN’s Solar Wind Ion Analzyer (SWIA) during periapsis passes, providing information about the penetrating and backscatter populations. In this work, we perform the first detailed analysis of the backscatter and albedo using SWIA observations. We find that our calculated backscatter energy spectra are consistent with model predictions and that, as expected, the penetrating and backscatter particle fluxes increase with solar wind speed and decrease with solar zenith angle (SZA). We also find that the albedo, which has an average value of 0.20±0.16, decreases with solar wind speed and increases at high SZAs near the terminator.
Progress in Understanding the Low Marine Cloud-Aerosol Interactions during CSET using...
Ehsan Erfani

Ehsan Erfani

January 04, 2022
Low marine clouds are a major source of uncertainty in cloud simulations across models from LES to global scale. To address this issue, we conducted Lagrangian LES experiments that explore the aerosol-cloud interactions for case studies covering a spectrum of observed ambient conditions, and evaluated the model against observations. Our LES benefits from a prognostic aerosol model that simulates aerosol budget tendencies such as coalescence and interstitial scavenging, surface sources, and entrainment from free troposphere. To initialize, force, and evaluate the LES, we used a combination of reanalysis, satellite, and aircraft data from the Cloud System Evolution in the Trades (CSET) field campaign in summer 2015 over the Northeast Pacific. The LES follows two Lagrangian trajectories from subtropical stratocumulus (Sc) deck region offshore of California to tropical shallow cumulus (Cu) region near Hawaii. The first trajectory is characterized by a clean, well-mixed Sc-topped marine boundary layer (MBL) on the first day, and continuous MBL deepening and precipitation onset after the first day followed by a clear Sc-to-Cu transition (SCT) and a consistent reduction of aerosols that ultimately leads to an ultra-clean layer at the top of MBL. Overall, the LES simulates general MBL features seen in observations. The runs with enhanced aerosols show distinct changes in microphysics and macrophysics such as delayed precipitation onset and SCT. The second trajectory is characterized by an initially polluted and decoupled MBL, weak or no precipitation, and no clear sign of SCT throughout the simulations. It is challenging for LES to simulate observed features, and the LES underestimates (overestimates) low cloud fraction in the first (last) day. Although enhancing aerosols among cases leads to distinct changes in microphysics (e.g., enhancement of cloud optical depth and reduction of effective radius), it does not affect cloud macrophysical properties significantly. Finally, a theoretical analysis was conducted to decompose contributions to albedo of the Twomey effect and cloud adjustments. The cloud radiative forcing due to the Twomey effect shows an enhancement with an increase in aerosol, however, the cloud radiative forcing due to cloud adjustments is strongly dependent on ambient meteorological conditions.
Multi-campaign analysis of smoke properties and cloud interactions in the Southeast A...
Calvin Howes
Pablo Saide

Calvin Howes

and 22 more

January 03, 2022
The southeast Atlantic Ocean provides an excellent natural laboratory to study smoke-cloud interactions, a large driver of uncertainty in climate projections. The value of studying this in particular region is largely attributable to two factors---the expansive, bright, semi-permanent stratocumulus cloud deck and the fact that southern Africa is the largest source of biomass-burning aerosols in the world. We study this region using the WRF-Chem model with CAM5 aerosols and in situ observations from the ORACLES, LASIC, and CLARIFY field campaigns, all of which overlapped in August 2017. Across these campaigns, we compare aerosol, cloud, and thermodynamic variables to quantify model performance and expand upon observational findings of aerosol-cloud effects. Specifically, our approach is to analyze aerosol and cloud properties along flight tracks, picking out uniform legs within tropospheric smoke plumes and in the boundary layer. This unique approach allows us to sample the high spatiotemporal variability that can get lost to large-scale averaging. It also allows process-level comparison of local cloud responses to aerosol conditions, and measure model performance in those same processes. Along with better quantifying model predictive power, we find and justify updates to model parameters and processes to better emulate observations, notably aerosol size parameters. Preliminary results suggest that WRF-CAM5 is activating a smaller percentage of aerosols into cloud droplets than shown in observations, which could lead to biased modeling of aerosol indirect radiative effects on a larger scale. We explore this effect further with CCN activation tendency, updraft, particle sizing, and composition analysis, as well as broader dynamics like entrainment and removal rates. Comparing the model with similar instrument suites across multiple colocated campaigns also allows us to quantify instrument uncertainty in ways that a focus on a single campaign cannot and gives further context to the model performance.
Drivers of Low-Frequency Sahel Precipitation Variability: Comparing CMIP5 and CMIP6 w...
Rebecca Herman
Michela Biasutti

Rebecca Herman

and 2 more

January 03, 2022
We examine and contrast the simulation of Sahel rainfall in phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6). On average, both ensembles grossly underestimate the magnitude of low-frequency variability in Sahel rainfall. But while CMIP5 partially matches the timing and pattern of observed multi-decadal rainfall swings in its historical simulations, CMIP6 does not. To classify model deficiency, we use the previously-established link between changes in Sahelian precipitation and the North Atlantic Relative Index (NARI) for sea surface temperature (SST) to partition all influences on Sahelian precipitation into five components: (1) teleconnections to SST variations; the effects of (2) atmospheric and (3) SST variability internal to the climate system; (4) the SST response to external radiative forcing; and (5) the “fast” response to forcing, which is not mediated by SST. CMIP6 atmosphere-only simulations indicate that the fast response to forcing plays only a small role relative to the predominant effect of observed SST variability on low-frequency Sahel precipitation variability, and that the strength of the NARI teleconnection is consistent with observations. Applying the lessons of atmosphere-only models to coupled settings, we imply that the failure of coupled models in simulating 20th century Sahel rainfall derives from their failure to simulate the observed combination of forced and internal variability in SST. Yet differences between CMIP5 and CMIP6 Sahel precipitation do not mainly derive from differences in NARI, but from either their fast response to forcing or the role of other SST patterns.
A Test of Energetic Particle Precipitation Models Using Simultaneous Incoherent Scatt...
Ennio Sanchez
Qianli Ma

Ennio Sanchez

and 7 more

January 03, 2022
Quantification of energetic electron precipitation caused by wave-particle interactions is fundamentally important to understand the cycle of particle energization and loss of the radiation belts. One important way to determine how well the wave-particle interaction models predict losses through pitch-angle scattering into the atmospheric loss cone is the direct comparison between the ionization altitude profiles expected in the atmosphere due to the precipitating fluxes and the ionization profiles actually measured with incoherent scatter radars. This paper reports such a comparison using a forward propagation of loss-cone electron fluxes, calculated with the electron pitch angle diffusion model applied to Van Allen Probes measurements, coupled with the Boulder Electron Radiation to Ionization (BERI) model, which propagates the fluxes into the atmosphere. The density profiles measured with the Poker Flat Incoherent Scatter Radar operating in modes especially designed to optimize measurements in the D-region, show multiple instances of quantitative agreement with predicted density profiles from precipitation of electrons caused by wave-particle interactions in the inner magnetosphere. There are two several-minute long intervals of close prediction-observation approximation in the 65-93 km altitude range. These results indicate that the whistler wave-electron interactions models are realistic and produce precipitation fluxes of electrons with energies between 10 keV to >100 keV that are consistent with observations.
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