COMPASS Friday - Archive

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Fridays at 11:00 am, RSMAS Auditorium



John Lodise (MPO)
Vertical Structure of Ocean Surface Currents Under High Winds
from Massive Arrays of Drifters
John Lodise, Tamay Özgökmen, Annalisa Griffa, and Maristella Berta

Very near surface ocean currents have large impacts on the transport of buoyant materials in the ocean, but have proved difficult to measure with modern instrumentation. Here, observations of ocean currents at two depths within the first meter of the surface are made utilizing trajectory data from both drogued and undrogued CARTHE drifters, which have draft depths of 60 cm and 5 cm, respectively. Trajectory data were collected during the LAgrangian Submesoscale ExpeRiment (LASER) that took place from January to March of 2016 in the Northern Gulf of Mexico. Examination of the drifter velocities reveal that the surface currents become strongly wind- and wave-driven during periods of high wind, with the pre-existing regional circulation contributing only a small fraction (~20-30%) to the total surface velocities. During these high wind events, we deconstruct the full surface current velocities captured by each drifter type into their wind- and wave-driven components after subtracting an estimate for the pre-existing circulation. The submesoscale to mesoscale circulation preceding each high wind event is estimated using a Lagrangian variational method to create hourly velocity fields using both drifter types, separately. Synoptic wind and wave output data from the Unified Wave INterface-Coupled Model (UWIN-CM), a fully coupled atmosphere, wave and ocean circulation model, are used for analysis. Results indicate there is significant vertical shear in the purely wind-driven component of the surface flow, which exhibits a rotation to the right with depth between the two surface layers measured, with both surface layers reaching higher deflection angles at higher wind speeds.

Bosong Zhang (ATM)
Constraining GCM Projections of Regional Precipitation Change

As communities prepare for the impacts of climate change, policy makers and stakeholders increasingly require locally resolved projections of future climate that often exceed the resolution of current models. Statistical downscaling (SD) uses low resolution outputs from global climate models and historical climate observations to both enhance the spatial resolution of the projections and correct for systematic model biases. Here we examine the efficacy of various SD methods to reduce the uncertainty in future rainfall projections over land. While bias corrections are effective in removing systematic biases in the representation of the current climate, they are ineffective in reducing the intermodel spread in future regional rainfall projections. However, the regional pattern of future rainfall change is shown to be strongly dependent upon the current climatological distribution of rainfall. We show that this dependence of future changes upon the current mean state provides an effective tool to constrain regional projections.

Feb 01: Yi Dai
Department of Atmospheric Sciences, RSMAS
(one-hour ATM student seminar)

The Effects of Outflow-Environmental-Flow Interaction on Tropical Cyclones

This research investigates the outflow of a tropical cyclone (TC) as an agent to relate the large-scale environmental flow to TC inner-core structural evolution. As the upper part of TC secondary circulation, the outflow often interacts with the upper-level environmental flow first, leading to the formation of an outflow channel. In an idealized simulation of a TC that interacts with an upper-level westerly jet, we find that the outflow-jet interaction induces a rainband outside the eyewall, creating conditions necessary for a secondary eyewall to form. Asymmetric convective cells outside the eyewall are advected radially inward and cyclonically by the low-level inflow and TC primary circulation. The secondary eyewall then forms after the deep convection has surrounded the TC. In contrast, simulations without the jet do not show secondary eyewall formation. Motivated by the limitations of bulk measures of vertical wind shear in representing the complete environmental flow, we find that the outflow channel and asymmetric rainband are directly connected under the presence of the environmental flow. Not only is the rainband an important source of the outflow, but they are also inherently connected through a descending inflow below the outflow, and both serve as the TC response to the environmental flow. Some of the main characteristics of the rainband-outflow relationship is also supported by a real-case simulation of Hurricane Bill (2009).

Feb 08: NO SEMINAR (Recruitment Weekend)

Feb 15: Dr. Georg Heygster
University of Bremen, Germany

Passive Microwave Remote Sensing of the Polar Ocean

Sea ice concentrations inferred from spaceborne microwave radiometers have been available since 1972 (ESMR) and belong to the longest and most reliable time series from satellite remote sensing. After a long period of relatively stable sensor configurations (SMMR, SSM/I, AMSR-E/2), sensor technology is now evolving towards lower frequencies and higher resolution by larger antenna reflectors (SMOS, SMAP, CIMR). The presentation will give an overview of today's capabilities and perspectives of observing sea ice and polar ocean parameters, such as ice type, thickness, snow depth on sea ice and sea ice drift, partly by including additional information from ocean and atmospheric models, and sensors like scatterometers.


Chelsi Lopez (OCE)
Seasonal Dynamics of Organic Carbon in the Deep Eastern North Pacific

Organic carbon is a vital product of ocean primary productivity, but most consideration of production has been in the euphotic zone. Here we consider the variability of total organic carbon (TOC) in the deep water column as a consequence of sinking particulate organic carbon (POC) and its ability to transport dissolved organic carbon (DOC) to depth. Samples throughout the water column were collected tri-annually in 2017 and 2018 on Line P cruises in the Eastern North Pacific, a productive area, to characterize seasonal variability in TOC in the bathypelagic. Variance in concentration (i.e. high heterogeneity) suggest that particles may be delivering dissolved carbon to depth. To further understand the observed heterogeneity, samples typically analyzed unfiltered due to low particulate matter, were filtered to determine whether the signal originates from solubilized carbon or the particles themselves. Our findings suggest that the signal captures events of particle export at off-shore stations, with some particle dissolution occurring, in turn adding a few micromolar DOC at depth. It is this carbon that will support the deep microbial heterotroph community and thus aid in sequestration of anthropogenic CO2.

Mingming Shao (AMP)
Observed High Frequency Internal Wave
Accompanied by Unstable Submesoscale Fronts
Mingming Shao, Brian Haus, and Björn Lund

A marine X-band Doppler radar observed a series of organized  bands, with an interval ~150 m, near a submesoscle front in the northern Gulf of Mexico. The conditions under which these bands were observed exclude the possibility that they were signatures of Langmuir circulation cells, nor could they have been the footprint of atmospheric surface rolls. The vertical profile of potential vorticity indicated that the dynamic conditions near the front were conducive to symmetric instabilities. However, the bands were observed, via continuous 1-minute radar images, to propagate away from the front at 0.3 m/s. This celerity and interval of bands is considered to be the surface expression of  high-frequency internal waves. These waves have been shown to be generated by symmetrically unstable submesoscale fronts. These are the first observations that capture high-frequency internal waves accompanied by a symmetrically unstable ocean front, a process which represents a new energy cascade in the upper ocean and merits further exploration.


James Hlywiak (MPO)
Wind Field Decay of Idealized Landfalling Hurricanes
Traversing Simplified Land and Urban Boundaries

Idealized simulations using the Weather and Research Forecasting model (WRF) of tropical cyclones making landfall contrast the spatial and temporal decay of the wind field over two types of simplified land boundaries: one resembling a sparsely populated wooded region and another resembling a high density urban area. Accurately predicting cyclone size and intensity in the hours before, during, and after landfall remains a challenging problem. Slight deviations in track or intensity forecasts of a landfalling storm can be the difference between minimal and significant damages to life and property. Additionally, inland cyclonic winds and rainfall can still pose major threats days after landfall. The high resolution numerical results presented here indicate that differences in even simplified land representations result in clear differences in the cyclone wind field decay. These preliminary results provide a starting point for further investigations of the interactions between landfalling storms and the surrounding evironment.

Kelsey Malloy (ATM)
Predictability of Mid-Summer Great Plains Low-Level Jet
and Its Associated Precipitation

Warm-season precipitation in the Great Plains and Midwest has significant socioeconomic implications, ranging from agricultural production to human and property loss from associated flooding. Unfortunately, current seasonal and subseasonal forecasts for summer precipitation have relatively low skill. There has been an increasing effort to understand Great Plains hydroclimate variability, particularly through its primary transporter of moisture: the Great Plains low-level jet (GPLLJ). This study uses the Community Climate System Model, version 4 (CCSM4) July forecasts, made as part of the North American Multi-Model Ensemble (NMME), to assess skill in reproducing the monthly GPLLJ and associated precipitation. Generally, the CCSM4 forecasts can simulate the climatological jet, but has issues rooted in its limit in representing variability past ~2 weeks. In addition, there are large-scale variability drivers identified through linear regression analysis and shifts in kernel density estimators. The Caribbean low-level jet, Pacific-North American teleconnection, El Nino-Southern Oscillation, and the Atlantic Multidecadal Oscillation have a relatively strong and consistent relationship with the GPLLJ.

Sara Purdue (ATM)
Analysis of the Semi-Direct Effect on Stratocumulus Clouds in the SE Atlantic
Using In-Situ and Remote Sensing Measurements from the 2017 and 2018
ORACLES Campaigns

Marine stratocumulus clouds (MSc) are an important part of the earth's climate, producing a net cooling effect in the global radiation budget. Biomass burning aerosols, when found in the same locations as the semi-permanent decks of MSc, alter the impact of these clouds. Solar absorption by biomass burning aerosol located above the cloud deck heats the atmosphere, which can further stabilize the lower troposphere and thereby strengthen the cloud deck, known as the semi-direct effect. This effect is thought to impact the SE Atlantic, but has limited evidence outside of modeling and satellite analyses. The influence of local meteorology and accompanying changes in the boundary layer thermodynamic and microphysical structure also raise questions as to which factors hold most importance when considering changes in the stratocumulus structure. The NASA ORACLES aircraft campaign in the southeast Atlantic provides multiple sources of in-situ and remotely-sensed measurements of cloud properties, such as liquid water path, cloud droplet number concentration, above-cloud aerosol optical depth, and in-situ derived thermodynamic profiles. These measurements are coordinated with remotely-sensed sea surface temperatures as a first step towards investigating the presence of the semi-direct effect over the southeast Atlantic during the ORACLES campaign, and are compared against prior satellite studies of the semi-direct effect in the SE Atlantic.


Bingkun Luo (MPO)
Improving Satellite Retrieved Night-Time Infrared Sea Surface Temperatures
in Aerosol Contaminated Regions

Satellite retrievals of sea surface temperature (SST) have become necessary for many applications. Satellite infrared imaging radiometers passively measure the radiance emitted and reflected by the surface of the Earth and atmosphere. Tropospheric aerosols increase the signal attenuation at the satellite height, degrading the accuracy of SST retrievals. In this study to assess the infrared radiative effects of aerosols on satellite-derived skin SSTs (SSTskin), MODIS (MODerate-resolution Imaging Spectroradiometer) SSTskin retrievals are compared with quality-controlled, collocated SSTskin measurements from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) deployed on research cruises during the Aerosols and Ocean Science Expeditions (AEROSE), and sub-surface temperatures measured by thermistors on drifting buoys. In this region, SSTskin retrievals from the MODIS on the Aqua satellite are generally much cooler than the in-situ measurements. In the Saharan outflow area between 90° W to 90° E and 20° S to 35° N where aerosol optical depths may be greater than 0.5, satellite SSTskin are often more than 1 K cooler than the in-situ data. The goal of this research is to determine the characteristics of aerosol effects on satellite retrieved infrared SST, and to derive formulae for improving accuracies of infrared-derived SSTs in aerosol-contaminated regions. A new method to derive a night-time Dust-induced SST Difference Index (DSDI) algorithm based on simulated brightness temperatures and Principal Component (PC) analysis (PCA) at infrared wavelengths of 3.8, 8.9, 10.8 and 12.0 μm, was developed using radiative transfer simulations. The satellite SSTskin biases and standard deviations, derive by comparisons with coincident and collocated surface and in situ measurements, are reduced by 0.263 K and 0.166 K after the DSDI correction. This method can also improve the fraction of useful data available compared to the usual approach of discarding measurements identified as being contaminated by the effects of aerosols.

Xingchen Yang (MPO)
Evolution of Loop Current Frontal Eddies Potential Vorticity
During Loop Current Eddy Shedding

An analysis of the Potential Vorticity (PV) evolution in the Loop Current region is presented for a 49-member HYCOM ensemble. The first two leading Empirical Orthogonal Functions (EOF) modes obtained from a multivariate EOF analysis of two weeks of daily outputs of HYCOM simulation are used to perturb the initial conditions. The modal amplitudes are assumed as uniformly distributed uncertain random variables. The ensemble members differ in their initial conditions of the circulation in the LC region and primarily over the strength of a WFCE. As the depth of the WFCE extends to ~120 m, so the PV analysis is performed in a two-layer structure. The EOF modes perturb the strength and paths of WFCE, and consequently the timing of LCE detachment. Ensembles with positive EOF amplitude perturbations yield higher PV in the WFCE and further intrusion than those with negative perturbations. The differences in PV among ensemble members occur later over the Campeche Bank, whereas these differences appear earlier in the WFCE. In the ensemble members with positive perturbation, the high PV aggregation region is larger and CBCE detaches from the Campeche Bank sooner than those in ensemble members with negative perturbation. PV standard deviation is calculated based on Polynomial Chaos (PC) methods, which are used to model response to changes in the uncertain inputs. The standard deviation presents the major variance existing in WFCE and CBCE, agreeing with the differences shown among ensemble members.

Simge Bilgen (MPO)
The Role of Ocean Eddies in the Southern Ocean Response
to Observed Greenhouse Gas Forcing

Here, a fully coupled model run at multiple resolutions from coarse to eddy resolving, driven by observed atmospheric and fixed CO2 concentration is used to investigate the role of ocean eddies in modulating the Southern Ocean response to greenhouse gas forcing (GHG). We examine the 1941–2014 Southern Ocean (SO) sea surface temperature (SST) trends simulated in coupled general circulation models and evaluate possible causes of the models’ consistency and ability to reproduce the observed SO cooling by using NCAR’s Community Climate System Model version 4 (CCSM4) and the ensemble of comprehensive GCMs participating in the Climate Modeling Intercomparison Project phase 5 (CMIP5). Instead of delayed warming for near Antarctic as revealed previous studies, a notable multidecadal cooling trend was captured for the first time with the numerical simulations. By comparing coarse – with fine – resolution models we have demonstrated the impact of explicitly resolved eddies. At all resolutions the models successfully reproduce the observed warming response for the northern flank of the ACC. This response is evident that eddies do not play an important role in this region. However, in the coarse-resolution implementation of the model (CMIP5), the SO response to SST is inconsistent with the eddy resolving model (CCSM4) for the south of the Antarctic Circumpolar Current. This region is likely to have a high degree of SST variability because it coincides with an area of high mesoscale eddy activity. Therefore it is unable to directly resolve the effects of eddies in coarse resolution simulations. This study elucidates, the observed SO cooling which has not been fully tested in multi-decadal global coupled eddy-resolving simulations until now, and this response shows that eddies may play an important role especially for near Antarctic.

Mar 15:  Dr. Yoshiaki Miyamoto
Keio University, Fujisawa, Japan

A Linear Thermal Stability Analysis of Discretized Fluid Equations
Paper Available at SpringerLink

The effects of discretization on the equations, and their solutions, describing Rayleigh–Benard convection are studied through linear stability analysis and numerical integration of the discretized equations. Linear stability analyses of the discretized equations were conducted in the usual manner except that the assumed solution contained discretized components (e.g., spatial grid interval in the x direction, Δx). As the resolution became infinitely high (Δx → 0), the solutions approached those obtained from the continuous equations. The wavenumber of the maximum growth rate increased with increasing Δx until the wavenumber reached a minimum resolvable resolution, πΔx−1. Therefore, the discretization of equations tends to reproduce higher-wavenumber structures than those predicted by the continuous equations. This behavior is counter intuitive and opposed to the expectation of Δx leading to blurred simulated convection structures. However, when the analysis is conducted for discretized equations that are not combined into a single equation, as is the case for practically solved numerical models, the maximum growing wavenumber rather tends to decrease with increasing Δx as intuitively expected. The degree of the decrease depends on the discretization accuracy of the first-order differentials.When the accuracy of the discretization scheme is of low order, the wavenumber monotonically decreases with increasing Δx. On the other hand, when higher-order schemes are used for the discretization, the wavenumber does increase with increasing Δx, a similar trend to that in the case of the single-discretized equation for smaller Δx.


Houraa Daher (OCE)
A New Improved Estimation of Agulhas Leakage
Using Observations and Simulations of Lagrangian Floats and Drifters

A new improved estimate of Agulhas Leakage (AL) transport is calculated using Lagrangian floats and drifters. Observations of floats and drifters passing through the Agulhas Current have quadrupled since a leakage transport of 15 Sv was calculated by Richardson in 2007, calling for an updated transport estimate. We analyze these observations, and simulate the isobaric and profiling behavior of the floats and drifters to provide a complete Agulhas Leakage transport approximation. These simulations quantify, for the first time, the sampling biases associated with the observed floats and drifters. The simulations are run using an off-line Lagrangian particle-tracking tool and velocity outputs from a coupled climate model, CCSM and an ocean only model, INALT. We find that drifters tend to leak northward into the Benguela system at the surface, while floats follow the northwestward Agulhas leakage corridor identified through satellite altimetry. The isobaric behavior of floats leads to less leakage, while their profiling behavior leads to more. We find that the isobaric behavior of drifters tends to have a minimal effect on leakage. Using the observed transport of the Agulhas Current at 34°S, combined with the corrected Lagrangian observations, we estimate a new leakage transport of 22 Sv.

Shannon Doherty (OCE)
Deciphering Organic Matter Sources and Interactions in a Near-Shore Water Column
Using Compound-Specific Isotope Analysis

Sinking particulate organic matter (POM) is the major component in the transfer of carbon from the surface to the ocean interior and feeds the midwater food web. Understanding POM dynamics is therefore important for determining controls on the biological pump and food availability for midwater organisms. Here I investigate fine-scale variation in a 10-depth water column profile of POM from Monterey Bay by sampling three particle size classes: small (0.7-20 µm), intermediate (20-100 µm), and large (>100 µm). Bulk carbon isotope ratios suggest varying sources and/or organic compositions of POC with depth and size class, while bulk nitrogen isotope ratios suggest increasing degradation with depth and distinct food web interactions between size classes. Compound-specific carbon isotope ratios of amino acids help to untangle ambiguity in bulk isotope measurements in a subset of sampled depths. The patterns in carbon isotope ratios of essential amino acids demonstrate changing terrigenous, phytoplankton, and bacterial carbon sources with depth and between size classes. A comparison of the bulk carbon isotope ratio and the carbon isotope ratio of total hydrolysable amino acids also demonstrates changes in the organic composition of particles. Future work will include nitrogen isotope analysis of individual amino acids to address particle-food web interactions and degradation, as well as lipid biomarker analysis to determine the relative influence of zooplankton between particle size classes and depths.

Kaycie Lanpher (OCE)
Trends in Environmental Metabolic Energy Potential
Across the South Pacific Ocean

Ocean productivity is defined as the production of biomass, primarily by microbes (phytoplankton and bacteria). This production depends on the availability of nutrients, and it also requires metabolic energy to fuel the microbial processes that both build biomass and maintain life.  We investigated the quantitative relationship between the levels of metabolic energy, nutrient availability, and biomass production across an ocean transect. We investigated particulate adenosine triphosphate (ATP) as a measure for metabolic energy potential, since ATP is a primary energy trafficking molecule in cells and plays a key role in providing the intracellular energy for metabolism. Our hypothesis was that changes in metabolic energy potential will be driven by nutrient availability. We collected data across the P06 transect in the Southern Pacific Ocean with depth profiles of the upper 200 m of the water column for concentrations of dissolved organic phosphorus (DOP), dissolved inorganic phosphorus (DIP), particulate phosphorus (PP), particulate ATP (p-ATP), dissolved ATP (d-ATP), and cell counts of phytoplankton and heterotrophic bacteria as well as hydrographic properties. To investigate trends across the transect we looked at metabolic energy potential relative to biomass, measured as p-ATP normalized to particulate phosphorus (p-ATP/PP). Examining the statistical relationships of these data in depth profiles across a latitudinal transect allowed us to investigate the factors associated with the variation in microbial allocation to energy storage. Data were grouped into four environmental regimes characterized by variations in nutrients and microbial community composition. We found there to be a significant increase in metabolic energy potential below the deep chlorophyll maximum, where inorganic nutrients were significantly greater, in support of the hypothesis. However, comparing across other regimes there were changes in nutrients that were not accompanied by shifts in metabolic energy potential – across these regimes there were also significant changes in microbial community composition. This points towards a dynamic relationship where microbial metabolic energy potential is influenced by both nutrient resource availability and the microbial community composition.

Mar 29: NO SEMINAR (Ultra Music Festival)


Kayla Besong (ATM)
Does Increasing Horizontal Resolution Improve the Forecast of
Winter Atmospheric Blocking?

Atmospheric blocking is a sub-seasonal phenomenon that causes a large-scale obstruction of westerly flow leading to a split jet stream and storm track displacement. As a consequence there are periods of weather extremes such as droughts and prolonged cold spells. While the societal implications are large, predictability of blocking has notoriously been poor across a wide array of climate models, primarily with strong underestimations of blocking frequencies. One possibility to decrease model biases in blocking frequency is by increasing horizontal resolution. Therefore both 1.0°×1.0° and 0.5°×0.5° outputs of the Community Climate System Model, version 4 (CCSM4) have been evaluated in their ability to capture January-February blocking frequency. Results show poor skill from both resolutions with a large negative bias over the North Atlantic. Differences between the higher and lower resolutions are minimal, revealing that increased resolution does not improve CCSM4 blocking performance. This finding suggests potential biases in the model's mean state and sets precedence for further evaluation of CCSM4 and its dynamical outputs related to atmospheric blocking.

Matthew Grossi (MPO)
Predicting Particle Trajectories in Simulated Oceanic Flow
Using Artificial Neural Networks
Matthew D. Grossi1, Miroslav Kubat2, and Tamay M. Özgökmen1
University of Miami Rosenstiel School of Marine and Atmospheric Science, Miami, FL, USA
University of Miami College of Electrical and Computer Science, Miami, FL, USA

Predicting the transport of spilled oil in a turbulent ocean is no easy task. Artificial neural networks (ANN), machine learning paradigms that use interconnected "neurons" to mimic how the human brain learns through experience, have demonstrated remarkable success at handling many challenging prediction problems. This provokes the question: Can ANNs predict the dispersion of spilled oil? Preliminary experimental results suggest that the answer may indeed be a hopeful "Yes". We systematically investigate the potential and limitations of a simple single-layer ANN at predicting particle trajectories in a hierarchy of simulated oceanic flow regimes ranging from uniform steady flow to more complex cases involving turbulent coherent structures. ANNs are trained to predict a particle's velocity at time tm using its previous velocity at time tm–1. We show that trajectories computed from ANN-predicted velocities often agree qualitatively well with real trajectories and provide striking improvement over persistence predictions, defined as the best prediction that can be made if only a single instantaneous velocity measurement is known. Not surprisingly, prediction within complex flows of turbulent coherent structures is notably more challenging. Nevertheless, the results are sufficiently promising to test these techniques on realistic flows generated by theory-driven general ocean circulation models. Our preliminary results suggest that ANNs may provide a new data-driven approach to modeling and forecasting the transport of spilled oil in the ocean.

Chong Jia (MPO)
Satellite Infrared Retrievals of Sea-Surface Temperature at High Latitudes
Chong Jia and Peter Minnett

Climate change is amplified in the Arctic region relative to elsewhere. This Arctic amplification has also been found in past changes in warm and glacial climates, as well as in historical simulations. The phenomenon is often explained by retreating snow and ice leading to more solar surface warming (surface albedo feedback). However, by analyzing climate model simulations Pithan and Mauritsen (2014) found that the largest contribution to Arctic amplification comes from temperature feedbacks, due to the smaller increase in heat loss by longwave emission per unit of warming at colder temperatures compared to tropical conditions. Satellite remote sensing offers the best way of deriving surface temperatures in the Arctic, but given that the surface temperature retrieval algorithms in the infrared are designed to compensate for the effects of the atmosphere, mainly water vapor, satellite-derived surface temperature have larger uncertainties at high latitudes because the atmosphere is very dry and cold. When the water vapor concentrations are low, the correction algorithms tend to over-compensate leading to warm biases. So, the motivation of the study is to improve the algorithms to obtain more accurate surface temperatures which can be used to research the feedback mechanisms. To undertake the study, we use collocated, simultaneous satellite measurements of brightness temperature at the top of atmosphere and in situ measurements of surface temperature. We have analyzed the matchup databases for MODIS on Aqua and Terra to characterize the differences between satellite retrieved temperatures and in-situ measurements, and to identify the main causes of the discrepancies. This leads to regional optimization of the surface temperature retrievals. We will report on the progress towards improving the satellite-derived surface temperatures with the expectation that the near two-decadal time series of MODIS surface temperature fields will contribute to studying climate change in the Arctic.

Pithan, F., and T. Mauritsen, Arctic amplification dominated by temperature feedbacks in contemporary climate models, Nature Geoscience 7, 181, 10.1038/ngeo2071, 2014.

Wei Zhang (MPO)
Estimates of Decadal Climate Predictability from an Interactive Ensemble Model

Decadal climate predictability has received considerable scientific interest in recent years; yet, the limits and mechanisms for decadal predictability are currently not well known. It is widely accepted that noise due to internal atmospheric dynamics at the air-sea interface influences predictability. The purpose of this paper is to use the interactive ensemble (IE) coupling strategy to quantify how internal atmospheric noise at the air-sea interface impacts decadal predictability. The IE technique can significantly reduce internal atmospheric noise and has proven useful in assessing seasonal-to-interannual variability and predictability. Here we focus on decadal timescales and apply the Nonlinear Local Lyapunov Exponent (NLLE) method to the Community Climate System Model comparing control simulations with IE simulations. This is the first time the NLLE has been applied to the state-of-the-art coupled models. The global patterns of decadal predictability are discussed from the perspective of internal atmospheric noise and ocean dynamics.


Romain Chaput (OCE)
Environmental Conditions and Parental Cares Determine the
Hatching Strategies of Coral Reef Fish Larvae

In all fishes, hatching from the eggs takes a negligibly short time compared to the remainder of their lives. However, it is a crucial event, and when, and under what conditions it occurs influence considerably the survival, development and success of the fish larvae. Furthermore, for coral reef fish, hatching not only marks the beginning of life, but also of the dispersal phase. The timing of hatching dictates the conditions that the larvae will encounter, potentially influencing their survival and dispersal. Despite this importance, very few studies looked at hatching in the natural environment because of important technical constrains. Yet, it is necessary to study the characteristics of the hatching events and the surrounding environmental conditions to better understand the larval phase. Observing the hatching events in situ is particularly challenging because this process occurs mostly at night and underwater. Furthermore, the minute size of the eggs and larvae complicates direct observations. In order to overcome these constrains, we developed infra-red underwater video cameras and remotely monitored the clutches of fish eggs for the entire night. Our approach allows for long observation times, without being limited by safety or resources, and the use of infra-red lights avoids disturbances to the fish. Using this method, we successfully documented for the first time the hatching events of three coral reef fish species, all benthic brooders (Abudefduf saxatilis, Elacatinus lori, and Stegastes partitus). Using the observations, we show that the timing, rate and duration of the hatching events are different for the three species, but consistent within each species, highlighting different hatching strategies. The analysis of the fish behaviors shows that the males display parental cares beyond the incubation period of the eggs and play an active role in the hatching events. With this study, we can finally relate the hatching events to the environmental context. This gives us a better understanding of the factors influencing the beginning of the larval phase. It also opens to speculation about the consequences of different hatching strategies for the survival and dispersal of fish larvae.

Alessandro Cresci (OCE)
Glass Eels Imprint the Magnetic Direction of Tidal Currents
at the Estuaries Where They Recruit

The European eel hatches in the Sargasso Sea, migrates across the Atlantic, and spends many years in European and North African freshwater habitats. At the glass eel stage, eels recruit to estuaries along the continental coast, where they metamorphose and eventually migrate upstream. Glass eels use a tidal phase-dependent magnetic compass for orientation, but whether the magnetic direction followed by the eels is innate or imprinted during migration is still unknown. We tested the hypothesis that glass eels imprint their tidal phase-dependent magnetic compass direction at the estuaries where they recruit. To accomplish this, we collected 222 glass eels from estuaries flowing in different cardinal directions in Austevoll, Norway. We observed the orientation of the glass eels in a magnetic laboratory where we manipulated the magnetic field while depriving the eels of additional external cues. Tests occurred throughout the tidal cycle. Glass eels in the laboratory oriented towards the magnetic direction of the prevailing tidal current occurring at their recruitment estuary. These results demonstrate that glass eels use their magnetic compass to imprint the magnetic direction of tidal flows. This mechanism could help glass eels to maintain their position in an estuary and to migrate upstream. 


Greg Koman (MPO)
Transport, Seasonality and Evolution of the East Reykjanes Ridge Current

The first continuous estimates of the East Reykjanes Ridge Current (ERRC) – a fundamental component of the North Atlantic Subpolar Gyre circulation – reveal a highly variable, mostly barotropic southwestward flow with a mean transport of nearly 12 Sv. The ERRC effectively acts as a western boundary current on the eastern flank of the Reykjanes Ridge that recirculates a portion of the North Atlantic Current as well as Labrador Sea water within the Iceland Basin. Previous estimates of the ERRC have been made from a limited number of hydrographic and ADCP sections, but continuous estimates of its transport have not been available until the advent of the Overturning in the Subpolar North Atlantic Project (OSNAP). Through OSNAP, continuous measurements of the ERRC have been maintained through ADCPs, current meters and dynamic height moorings at six mooring sites near 58°N. Together with satellite altimetry and Argo data, the mean transport, synoptic variability, seasonality and upstream evolution of the ERRC are evaluated for the period from July 2014 to July 2018. Estimates of the ERRC will assist in monitoring unprecedented changes in the North Atlantic Subpolar Gyre and the Atlantic Meridional Overturning Circulation.

Szandra Peter (MPO)
Characteristics of Summer Heat Waves Across Europe

Heat waves are a serious threat to ecosystems, society and the economy of Europe. According to the WMO, extreme temperatures were the cause of 94% of the total lives lost due to natural disasters in Europe during the 1970-2012 period. Accurate prediction of the frequency of heat waves is necessary to better prepare for impacts. Our first step is to analyze the characteristics of maximum 2m temperatures by utilizing daily NCEP/NCAR reanalysis data (Kalnay et al. 1996). We also use retrospective forecasts with 12-month hindcasts from the NMME to evaluate heat wave frequency in the boreal summer from 1982 to 2016. For each June initialization, an ensemble of 10-12 hindcasts is used.

Mampi Sarkar (ATM)
Observations Pertaining to the Role of Precipitation to the
Northeast Pacifc Stratocumulus-to-Cumulus Transition

The stratocumulus-to-cumulus transitions (SCT) sampled during three flight pairs of the Cloud System Evolution over the Trades (CSET) campaign are documented, with a focus on the precipitation characteristics. The transition clearly emanated from stratocumulus clouds for three flight pairs, encompassing a useful diversity in initial conditions, all suitable for further investigation with dedicated modeling studies. The 17 July stratocumulus layer was lower-lying, with cloud droplet number concentrations Nd of ~20 cm3, and precipitation capable of reaching the surface, unusual for stratocumulus. Five trajectories emanating from two similar 17 July stratocumulus boundary layer modules diverged into a cumulus region spanning over 2000 km, with a westward increase in boundary layer depth that is mirrored in the accompanying precipitation frequency and rainrates. The 27 July stratocumulus layer was polluted by biomass-burning aerosol (Nd ~225 cm3), limiting its precipitation. The 7 August stratocumulus Nd was similar to that on 17 July, but with less precipitation reaching the surface, and it did not transition into the ultra-clean conditions notable for 19 July. The rain dropsize distributions shift towards larger drop sizes in all cases. GOES-derived cloud fraction shows a strong link in the pace of cloud transition and an increase in precipitation. The transition timing, while linked to the daytime portion of the diurnal cycle, could begin either in the morning or late afternoon, suggesting that nighttime pre-conditiong of boundary layer decoupling is important for setting the overall time scale. The co-association between boundary layer depth and precipitation does not allow for definitive conclusions on the isolated effect of precipitation.

Wei-Ming Tsai (ATM)
Can "Convective Aggregation" be Observed in the Real World?

The clustering of tropical clouds strongly modulates radiative forcing, the hydrological cycle, moisture fields, and large-scale circulations. Advances in understanding convection's organization process could refine model parameterizations, a long-ignored effect in global climate prediction. Cloud model simulations have demonstrated a slow “self-aggregation” process among deep cumulus, where convective clouds and vapor merge into a huge cluster, and speculated that this could impact long-term climate sensitivity. But can such simulated clusters be observed in data from the real world? Water vapor plays an important role in delineating where deep convection is thermodynamically feasible, a necessary condition for it to become 'organized'. This study aims to (1) understand the relationship between tropical convection and water vapor and to (2) seek examples of the aggregation process by identifying isolated water vapor objects, patches with ~1000 km scale, of air with high column-integrated water vapor (CWV). Using multiple observations and reanalysis data from 2017 to 2018, the results confirm that deep convection is confined in meandering areas of CWV above ~48 mm. Isolated water vapor clumps are therefore spatially beneficial for convection clumps. After examining budget terms, I hypothesize that surface flux may be essential for sustenance of aggregated precipitating convection in a drier environment. Features like those in the idealized modeling can be observed to some extent, but how directly they relate to the speculated mechanism, rather than external forcing, requires further investigations.


Valeria Donets (ATM)
Transport of Trace Species in the Vicinity of Tropical Cyclone (TC) Systems in the
Tropical Pacific – What are the Implications for Reactive Tracer Distributions in the
Pacific Upper Tropopshere (UT) and Tropical Tropopause Layer (TTL)?

Convective activity associated with tropical cyclones (TCs) is considered to play an important role in the exchange of chemical constituents between the troposphere and the stratosphere. TC systems have been shown to contribute disproportionate amount of the tropical deep convection that penetrates the Tropical Tropopause Layer (TTL). Accounting only for ~7% of the deep convection in the tropics, TCs contribute 15% of convection that reaches the Lower Stratosphere (LS). The resultant redistribution of the chemical tracers in both the troposphere and the LS has a substantial impact on natural photochemical cycles in both atmospheric layers as well as Earth's planetary radiative budget. Gauging the regional and global impact of TCs on the Upper Troposphere / LS chemical composition as well as two-way exchanges between the UT and the LS from observations has been limited due to the scarcity of in-situ data with necessary vertical resolution and dense spatial sampling. Most researchers are therefore limited to satellite observations, which are only available for a limited number of chemical species (ozone, carbon monoxide, etc.). In this seminar I will present the results of measurements of various trace gases of natural and anthropogenic origin in the vicinity of TC systems in the tropical Pacific Ocean collected during CONvective Transport of Active Species in the Tropics / Airborne Tropical TRopopause EXperiment (ATTREX-2014), Volcano-plume Investigation Readiness and Gas-phase and Aerosol Sulfur (VIRGAS-2015) and Pacific Oxidants Sulfur Ice and Dehydratin and cONvection (POSIDON-2016) research campaigns.

Yu Gao (MPO)
The Role of Mesoscale Currents in Ocean Mixed Layer Heat Balance

Ocean mixed layer (OML) depth modulates the air-sea heat exchange by changing the effective heat capacity of the surface water. The negative relationship between the mixed layer depth and SST anomalies holds true in most of the ocean, since cooler SSTs lead to weaker stratification and deeper mixed layer, and vice versa. However, this relationship is broken in parts of the Antarctic Circumpolar Current, where the mean currents and eddy activity are both strong, and heat advection plays a big role in the mixed-layer heat balance. This property is observed in both comprehensive climate-model simulations and high-resolution idealized simulations of a sector of the Southern Ocean. In order to quantify the role of ocean currents, the idealized simulations were analyzed to break down the mixed layer heat balance and explore the role of mesoscale currents. The results show that heat budget in OML is dominated by both horizontal and vertical ocean advection by the time-mean flow and mesoscale currents. On average, the heat advection by the time-mean flow is balanced by the advection by mesoscale currents. SST variability shows weak correlation with OML-integrated advection by the time-mean flow, but strong correlation with the heat advection by mesoscale flow. Therefore, neglecting mesoscale currents in low-resolution climate models may lead to errors in SST variability and air-sea heat exchange. The origins of SST and OML variability are being further explored in a fully-coupled regional model.

Luna Hiron (MPO)
Evidence of Loop Current Frontal Eddy Intensification
Through Interactions with the Loop Current

During the Deepwater Horizon oil spill in 2010, an underestimated part of the oil was trapped in an intensified Loop Current Frontal Eddy (LCFE); cold-core eddies formed in the vicinity of the Loop Current (LC). These eddies, which are also known to play an important role in the Loop Current Eddy (LCE) shedding, are difficult to predict, and the dynamics involving their intensification is still not fully understood. The LC and its stronger LCFEs were continuously tracked during the 2009-2011 period using sea surface height (SSH) data from AVISO. A mooring array provided complementary information about the internal structure of the LC-LCFE interaction. The intensification of the LCFEs tracked showed similar characteristics independent of their location around the LC: a steep increase in kinetic energy, a corresponding decrease in SSH, and an increase in the area of the cyclone. Some cyclones experienced an increase of up to ten times their kinetic energy. As the LCFE grows, the flow at the interface with the LC becomes stronger and deeper, and the horizontal temperature gradient between the features increases. Evidence shows that LCFEs could be extracting energy and mass from the background field to the zone of contact between the LC and the LCFE, strengthening the front, and allowing the LCFEs to grow during the periods of intensification. Understanding the physics driving the LCFE intensification is the first step to improving LC forecast models, and better predicting LCE shedding events and oil transport around the LC.

Breanna Zavadoff (MPO)
Quantifying the Relationship Between the Pacific Decadal Oscillation and the
Intra-Basin Frequency of North Atlantic Anticyclonic Rossby Wave Breaking
Understanding the Influence of Large Scale Extratropical Dynamics on
Landfalling Atmospheric Rivers over Europe and the Central-Eastern United States

Part 1: In a recent study by Zavadoff and Kirtman (2019), a 58 year (1960-2017) climatology of summertime North Atlantic anticyclonic Rossby wave breaking (RWB) was developed in which a multidecadal pattern of intra-basin RWB frequency was observed. Results suggested a connection between atmospheric responses to Pacific decadal oscillation (PDO) sea surface temperature (SST) anomalies and the intra-basin frequency of anticyclonic RWB exists, such that East (West) basin anticyclonic RWB events are favored during PDO+(–). To test this hypothesized relationship, an idealized modeling study is performed using the NCAR Community Earth System Model. Eleven simulations are run using unique sets of prescribed SSTs corresponding to different PDO configurations regressed onto climatological SSTs. Preliminary results are consistent with the findings in Zavadoff and Kirtman (2019). Further analysis will be performed to determine how each configuration of the PDO+/- signals alter the large scale circulation and the intra-basin frequencies of North Atlantic anticyclonic RWB.

Part 2: Atmospheric rivers (ARs) are long, narrow filaments of high water vapor content that account for over 90% of poleward water vapor transport. Recent studies suggest the large scale dynamics surrounding landfalling US west coast ARs are connected to RWB. While European and central-eastern US (CEUS) ARs have not explicitly been shown to have this connection, case studies indicate potential vorticity (PV) patterns reminiscent of RWB can drive AR-like  moisture transport in these regions. To test if landfalling ARs over Europe and the CEUS are connected to RWB, 38 years (1980-2017) of the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reanalysis dataset is utilized to calculate integrated vapor transport (IVT) thresholds for landfalling AR identification. Preliminary analysis indicates European ARs are dynamically linked to the north-western flank of anticyclonic RWB, while CEUS ARs are not. Next steps include determining if any large scale patterns drive CEUS ARs and if the landfalling European AR - anticyclonic RWB relationship provides a foundation for AR predictability.