Jan 19: NO SEMINAR
Jan 26: NO SEMINAR (OCE Faculty Retreat)
Feb 02 (2:00 pm): Dr. Jie He (Princeton University / Georgia Tech)
Quantifying Tropical Air-Sea Interactions
It is well accepted that tropical atmospheric variability is largely regulated by variations in sea surface temperature (SST). On the other hand, the atmosphere is able to generate variability internally, which in turn influences the SST. As a result, the coupled climate system reflects a complex combination of oceanic and atmospheric forcing. This makes it challenging to understand either process directly from coupled air-sea relationships. For example, observations show a very weak correlation between convection and SST variability at high background SSTs. While this led some early studies to counterintuitively suggest that the SST forcing of convection might be weak in warm pool regions, the weak correlation could also result from a large atmospheric intrinsic variability. In this study, I will show that the uncoupled atmosphere-only simulations are a perfect stepping stone to understanding coupled air-sea relationships due to their ability to isolate SST forcing. Using these atmosphere-only simulations, I will discuss precipitation and evaporation sensitivity to tropical SST variability and will attempt to clarify some previous misunderstandings on this subject. I will finally present a linear framework derived from atmosphere-only simulations as an effective tool for the quantitative understanding of tropical air-sea relationships.
Feb 09: NO SEMINAR (Recruitment Day)
Feb 16: NO SEMINAR (Ocean Sciences Meeting)
Feb 23: STUDENT SEMINARS
James Hlywiak (MPO)
Coupled 3d Numerical Simulations of the Effects of Ocean Salinity on TC Intensity
Warm surface ocean waters are a necessary ingredient for the maintenance and intensification of tropical cyclones (TCs). Ocean heat content (OHC) is a valuable tool for quantifying the amount of upper ocean energy that may be available to a passing TC, and is based on the upper ocean temperature profile. However, observations from the past couple decades have suggested that strong salinity gradients in the upper ocean may play a significant role in suppressing entrainment mixing at the base of the oceanic mixed layer. Freshwater input at the ocean surface leads to the formation of oceanic barrier layers (BLs) between the mixed layer and isothermal depths, which are common features of summertime tropical oceans in regions where TCs regularly generate over. Previous studies have indicated that TC-induced SST cooling is suppressed in the presence of BLs, thus limiting the negative feedback between ocean cooling and TC intensity. Here, idealized 3D ocean-atmosphere model simulations initialized with various vertical salinity profiles are carried out with the goal of finding a correlation between salinity stratification and TC intensity.
Jeremy Klavans (MPO)
Estimating the Magnitude of the Lagged SST Response to the North Atlantic Oscillation
In the presence of an active ocean, North Atlantic sea-surface temperatures (SST) exhibit a lagged response to atmospheric forcing, in both models and observations. However, variable ocean currents are not necessary to reproduce the pattern and statistics of the Atlantic Multidecadal Oscillation (AMO). We examine these seemingly contradictory claims by estimating the magnitude and contribution of this ocean dynamics mechanism to multidecadal North Atlantic SST variability, in observations, observational products, and climate models. When testing a null hypothesis that accounts for spurious signals introduced by low-pass filtering, we find that the ocean response to the NAO is limited to the sub-polar gyre. Further, the lagged SST response to the NAO is small in magnitude and offers a ¬limited contribution to the AMO pattern, statistics, or predictability. We conclude that it is not necessary to invoke the full overturning of the Atlantic Ocean to explain this ocean dynamical response to the NAO.
Bosong Zhang (MPO)
Quasi-Biennial Oscillation - Madden-Julian Oscillation Connection
Activities of the Madden-Julian Oscillation (MJO) in boreal winter has recently been found to be stronger in easterly phases of the stratospheric quasi-biennial oscillation (QBO) than its westerly phases. This QBO-MJO connection was investigated in this study using a method that identifies individual MJO events by tracking their eastward propagating signals in precipitation. Stronger MJO activities in QBO easterly phases are a consequence of more MJO days, not larger amplitudes of individual MJO events as previously thought. More MJO days come from more MJO events initiated over the Indian Ocean and their longer duration because of a weaker barrier effect of the Maritime Continent on MJO propagation. Zonal heterogeneity exists in the connection between QBO, MJO, and tropical total precipitation in general. This poses a challenge to our current understanding of the MJO dynamics, which has yet to fully include upper-tropospheric and stratospheric processes.
Mar 02: STUDENT SEMINARS
Kaycie Lanpher (OCE)
Deciphering the Relationships Between Phosphorus, Metabolic Energy Potential, and Microbes
Across the South Pacific
Important factors for ocean productivity are the relative availability of nutrients and the generation and storage of metabolic energy to convert these nutrients into biomass. Adenosine triphosphate (ATP) is a primary energy trafficking molecule in cells and plays a key role in providing intracellular energy for metabolism. We are investigating ATP, as a measure for metabolic energy potential, relative to other biogeochemical parameters: biomass, community composition, and nutrient resources in two dissolved phosphorus pools. These comparisons will address the relationship between availability of nutrient resources, metabolic energy, and biomass. We will be testing the hypothesis that the allocation of energy compounds as a fraction of biomass will have an inverse relationship with nutrient concentrations. We collected data across the P06 transect in the Southern Pacific Ocean, crossing several different ocean regimes, with depth profiles of the upper 200 m 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. I will be presenting a preliminary dataset investigating the cross correlations of these data in different ocean regimes to explore the variation in microbial allocation to energy storage and the relationship between microbial abundance and the dissolved phosphorus pools.
Molly Martin (MAC)
Decadal Changes in Oxygen Parameters in the Subtropical South Pacific
The ocean provides about half of the oxygen that living beings breathe. Climate models suggest that warming associated with greenhouse gases will lead to increased stratification and decreased solubility of gases in the ocean. Both increased stratification and decreased solubility will negatively impact the global ocean oxygen reservoir. We use data from GEOTRACES (2013), and the WOCE (1990s), CLIVAR (2000s), and GO-SHIP (2010s) repeat hydrography programs along ~12°S ± 3°. Analyzed sections span the subtropical eastern South Pacific (P19C, P17S, P16C, and GEOTRACES EPZT). Practically at least 3 stations of data were averaged together to diminish the effects of bias from eddies (radius of deformation along 12°S is 1°) and fronts. A new tracer O2*b, which is based on the O2* semi-conservative tracer is used to identify changes in biological activity. In the OMZ between 1993 and 2013, there is a decrease in oxygen concentration of ~5 μmol/kg or 0.25 μmol/kg. Of this decrease, most of it is appears to be due to physical processes and not biological. The decrease is ~2 times greater than Stramma et al. (2008) found over 50 years for 5°S-5°N in the eastern Pacific. It is not surprising that our increase is greater, as we expect the effect of climate change to be more for recent years. There are no discernable changes in oxygen parameters in the gyre regions.
Mingming Shao (AMP)
Enhanced Heat Fluxes Observed Near Sub-Mesoscale Fronts
Sub-mesoscale fronts (SF) may affect local air-sea interaction but limited observations have been done at such scales. To address this gap an investigation of air-sea interaction at SF was conducted in the northern part of Gulf of Mexico, during the LAgrangian Sub-mesoscale Experiment (LASER). A pair of flux towers were mounted on the twins bows of the catamaran RV Walton Smith. The flux data was accompanied with marine X-band radar measurements, shipboard flow through sampling, a towed CTD and drifter observations. Surface wind acceleration (deceleration) in several cross-frontal transects was observed, which was considered as mesoscale atmosphere features across. Momentum and heat fluxes were calculated from eddy covariance and the bulk method. The comparison between them indicates that momentum flux was closely related with local SST and structure near the front. Both sensible heat fluxes and latent heat flux were generally 1.5-2 times larger than a commonly used bulk algorithm, which indicated SF may significantly accelerate the energy exchange between the ocean and atmosphere. In particular cases, positive and negative heat flux appeared in different side of SF. Secondary circulation may account for that. The phenomena could have significant implications for air-sea flux parameterization and the sub-mesoscale energy cascade. Future work about symmetry instability phenomena observed near SF will also be discussed.
Mar 02 (5:00 pm, Wetlab): POSTER SESSION
Mar 09: Dr. Claire Paris (RSMAS)
From Crude Oil to Live Oil: The Story of the Deepwater Horizon Blowout
The Deepwater Horizon spill was unlike any other oil spill. It was the first uncontrolled release of gas and oil in the deep ocean, at 1522 m from the sea surface of the Gulf of Mexico. The spill was also unique since it was the first time that chemical dispersantS were applied at a subsea wellhead to keep oil submerged. This novel response posed a unique challenge for reliable predictions of oil transport and fate. Not only was there no operational three dimensional model to track the oil, but gas-saturated oil spewing under very high hydrostatic pressure has characteristics remarkably distinct from oil released in shallow water – one of the most sought after parameters was, and still is, the droplet size distribution (DSD) that controls how much oil reaches the surface.
To address these challenges, we have taken a two-prong approach, developing (1) a DSD model based on turbulent dissipation rate TDR validated with laboratory high-pressure and field experiments, and (2) a Lagrangian-inertial blowout modeling tool, whose algorithm and configuration has improved over the years with findings of fundamental processes. A key finding is the behavior of live oil versus crude oil and how it regulates the blowout characteristics. The blowout model resolves the complex thermodynamic processes occurring in the near field, meters above the wellhead, and the hydrodynamic processes in the far field, up to kilometers away – including he decay rate of hydrocarbons untreated and treated with dispersants. We demonstrate that the model provides accurate predictions of oil concentration at the sea surface and of its mass partition in the water column. Additional discoveries of live oil processes, such as degasing in the oil droplet, are being incorporated in the model. We briefly discuss the use of the model in advancing ongoing impact studies of the DWH disaster and for improved first response in the future.
Mar 16: NO SEMINAR (Spring Recess)
Mar 23: STUDENT SEMINARS
John Lodise (MPO)
Vertical Structure of Wind Driven Currents at the Very Near Surface
Observations of wind and wave driven currents at two depths within the first meter of the surface are made utilizing trajectory data from both drogued and undrogued drifters during the LAgrangian Submesoscale ExpeRiment (LASER) that took place from January to March of 2016 in the Northern Gulf of Mexico. Examination of dense, collocated populations of drifters during periods of high wind speeds (greater than 12 m/s) reveal that the surface currents captured by both drogued and undrogued drifters are dominantly wind and wave driven. A Lagrangian variational method is used in order to create hourly Eulerian velocity fields from trajectory data of both drifter types, separately. To quantify the direct effect of the wind on the surface flow, we use wind and Stokes drift output data from the Unified Wave INterface-Coupled Model (UWIN-CM), that were stored during the experiment for later analysis. We calculate the purely wind-driven surface current by subtracting the Stokes drift velocity fields from the full velocity fields constructed from the drifter data, thus removing the wave component from the flow. We then calculate the deflection angle and velocity magnitude of the calculated wind driven surface currents with respect to the wind.
Joshua Wadler (MPO)
Downdrafts and the Evolution of Boundary Layer Thermodynamics in Hurricane Earl (2010)
Before and During Rapid Intensification
Using a combination of NOAA P-3 aircraft Doppler radar, NOAA and NASA dropsondes, and buoy and drifter based sea surface temperature data, different types of downdrafts and their influence on boundary layer (BL) thermodynamics are examined in Hurricane Earl (2010) during periods right prior to rapid intensification (RI; a 30 knot increase in intensity over 24 hours) and during RI. Before RI, the BL was generally warm and moist. Convectively driven downdrafts inside the radius of maximum winds (RMW) and upshear-right quadrant, and vortex-tilt induced downdrafts outside the RMW in the upshear-left quadrant were the largest hindrances for intensification. Possible mechanisms for overcoming the low entropy (θe) air induced by these downdrafts are BL recovery through air-sea enthalpy fluxes and turbulent mixing by atmospheric eddies.
During RI, convective downdrafts of varying strengths in the upshear-left quadrant had differing effects on the low-level entropy and surface heat fluxes. Interestingly, the stronger downdrafts corresponded with maximums in 10-m θe. It is hypothesized that the large amount of evaporation in a strong (>2 ms–1) downdraft underneath a precipitation core can lead to high amounts of near-surface specific humidity. By contrast, weaker downdrafts corresponded with minimums in 10-m θe, likely because they contained lower evaporation rates. Since weak and dry downdrafts require more surface fluxes to recover the low entropy air than strong and moist downdrafts, they are greater hindrances to storm intensity. This study emphasizes different types of downdrafts and their role in air-sea interaction which is linked to hurricane intensity change.
Jianhao Zhang (MPO)
Boundary Layer Characteristics Above Ascension During Biomass Burning Seasons
Inferred from LASIC Field Campaign Observations
The areal extent of the absorbing aerosol above low clouds in the Southeast Atlantic is large enough for the coupled cloud-aerosol-ocean system to have a regional climate impact, but the cloud adjustments to the presence of the aerosol are still poorly understood. Cloud responses to the aerosol presence can be both radiative and microphysical, depending on the relative location of the aerosol to the cloud. This study focuses on observations collected by DOE ARM Mobile Facility during the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign from June 2016 to October 2017, at Ascension Island (8°S, 14°W), located ~2,000 km offshore of continental Africa in the trade-wind regime. Micropulse-lidar-derived extinction profiles suggest that aerosol is almost always present in the atmospheric column during July-October, if in varying amounts and within multiple layers. A two-layer cloud structure is representative of a boundary layer that is usually decoupled. The July-August observations reveal that, when absorbing aerosol is present in the cloudy boundary layer, the diurnal cycle of the potential temperature vertical profile is more prominent, the boundary layer is deeper and more well-mixed, the cloud top inversion is weaker, and the atmosphere is less stable, despite the presence of absorbing aerosol aloft. The weaker inversion under smoky conditions co-occurs with higher cloud bases at both levels. The near-surface cloud condensation nuclei concentration increase, correlating well with black carbon mass concentration. Drizzle suppression and reduced drop sizes near the cloud base are also apparent in the radar reflectivity composites under smoky conditions.
Mar 30: STUDENT SEMINARS
Luna Hiron (MPO)
Loop Current Intensification by Frontal Eddy Cyclones in the Gulf of Mexico
Loop Current Frontal Eddies (LCFE) are known to have an important role in the Loop Current Eddy (LCE) shedding, but their influence is still not fully understood. The interaction between the Loop Current (LC) and a LCFE prior to the detachment of Eddy Franklin (2010) was analyzed using observational data from tall moorings. Application of an objective analysis provided a 4-dimensional high resolution map of temperature, and zonal and meridional velocities. The mooring array showed that the interaction between LC and LCFE can start up to 2 to 3 weeks before the shedding. As the LCFE propagates southward on the eastern side of the LC, we observe an increase of 35% in kinetic energy and 130% in meridional strain for all the layers of the LC between 600m and the surface. The horizontal gradient of density also appears to peak, increasing by 30%, concomitant to a 30m deepening of the base of the LC. However, the total volume of the LC appears to be constant. These results indicate that the mechanism behind the LC intensifi
cation prior the shedding is lead by vortex stretching. The deformation caused by the LCFE leads to deepening of the base of the LC, tilting of the isopycnals, increase in the density gradient and, consequently, increase in kinetic energy. The correlation coefficient between total (vertically integrated) kinetic energy and horizontal density gradient is 0.99 (p < 0.01) and the correlation coefficient between meridional strain and horizontal density gradient is 0.71 (p < 0.01), which supports our hypothesis.
Rachel Sodowsky (MPO)
The Impact of Ocean Coupling on a High-Resolution MJO Simulation
The Madden-Julian Oscillation (MJO) is the largest source of intraseasonal variability in the tropics and it is an important link between weather and climate. Successful simulations of the MJO are highly model dependent. Ocean-atmosphere coupling is shown to have conflicting results on MJO simulations. Many studies suggest ocean coupling organizes and intensifies intraseasonal variability in the tropics and is important to MJO development in models. However, other studies indicate ocean coupling has a negligible or negative impact on MJO simulations. In this study, two experiments are preformed to simulate the same MJO event. The first experiment uses only the atmospheric component of a regional model. The second experiment couples the ocean to the atmosphere. The objective is to determine the effect of a dynamic ocean on the initiation and early development of an MJO event. Results show that the coupled experiment produces features more like the observed MJO event than the uncoupled experiment. The coupled-model experiment produces an organized precipitation pattern that propagates eastward, whereas the rain event produced in the uncoupled-model experiment is mostly unorganized.
Apr 06: STUDENT SEMINARS
Marybeth Arcodia (ATM)
MJO Teleconnection in the North American Region
This study will aim to answer how the Madden-Julian Oscillation (MJO) affects North American rainfall via a Rossby wave teleconnection. The question will be addressed by looking at daily OLR, rainfall, and zonal wind vectors at 850mb and 200mb obtained from the NCAR-NCEP Reanalysis data set. Using combined EOF analysis and following the Wheeler and Hendon (2004) methodology and MJO Index, criteria for a strong and "active" MJO are obtained. A teleconnection associated with the tropical rainfall of the MJO will be determined by a signal in the subtropics. This indicates that the tropical-mid-latitude coupling has an influence in the North American region via Rossby wave forcing. Composite analyses show a rainfall perturbation in the United States associated with the MJO. The timeline and mechanisms of the potential MJO teleconnection are currently being investigated.
Xingchen Yang (MPO)
Analysis of Potential Vorticity Evolution in a Polynomial Chaos Based Ensemble
and its Role in the Shedding of the Loop Current Eddy Franklin
Loop Current (LC) and its eddy field are the dominant dynamic features in the Gulf of Mexico (GoM). The LC extension and the eddy shedding events are highly variable, in both spatial and temporal domains. The shedding events are controlled by the interactions between the LC and its frontal eddies (LCFEs) on the northern edge of extended LC. The smooth northern gulf shelf is prone to the formation of a positive potential vorticity (PV) anomalies, which leads to the intensification of the frontal eddies, and consequently affects the LC eddy shedding.
Polynomial Chaos (PC) techniques is a method of uncertainty quantification (UQ) to estimate the impact of the uncertain input data on the model's outputs. The PC method constructs a model surrogate, which is then used to explore the space of uncertain inputs using a large number of samples, so that reliable estimates of the model's output statistics can be calculated.
A recent UQ study found that perturbation of the initial conditions reflects realistic uncertainties and showed that the PC approach has produced reasonable forecasts for the future location of the LC. We plan to investigate how these initial condition perturbations impacted the initial PV of the system and how they impact the timing of the LC separation.
Wei Zhang (MPO)
Estimates of Decadal Climate Predictability in the Interactive Ensemble NCAR Climate Model
Great progress has been made in seasonal climate prediction over the past several decades, which is mainly driven by better understanding of the limits and mechanisms of seasonal predictability. However, decadal prediction remains a challenge in climate research. The purpose of this study is to use the newly developed interactive ensemble (IE) coupling strategy to quantify how internal atmospheric dynamics noise at the air-sea interface limits decadal predictability. The IE approach couples multiple realizations of the atmospheric model to a single realization of the ocean model. The IE technique has proven useful in quantifying how internal atmospheric dynamics noise limits interannual predictability. Here we focus on decadal timescales and apply the Nonlinear Local Lyapunov Exponent (NLLE) method to the NCAR Community Climate System Model comparing control simulations with IE simulations. This is the first time NLLE method is applied to the state-of-the-art coupled climate models. Both IE and control simulations show relatively longer predictability in the North Pacific and North Atlantic Ocean, while low predictability limit is detected over the tropical central-eastern Pacific. We find an even longer decadal predictability with IE compared with control simulation in the North Atlantic, which could be due to the spatial coherence of the weather noise and unstable coupling. Both model simulations overestimate the predictability limit in the North Atlantic region compared with observations.
Steven Simon (MPO)
Spatiotemporal Midtropospheric Humidity Variability
and its Modulation of Convective Precipitation Intensity in the Global Tropics
as Remotely Sensed from Satellite-Based Microwave Retrievals
As Earth's primary greenhouse gas, water vapor strongly influences cloud distributions and atmospheric column and surface radiative budgets. Further, phase changes in tropical tropospheric water, driven and supported by strong moist convective events, provide sources of heating and cooling that in turn drive the horizontal and vertical transport of heat and moisture which underlie the global general circulation. At short timescales, the majority of tropical precipitation manifests as intense events with rainfall rates exceeding the climatological mean by at least one order of magnitude. Past observational and modeling studies alike have found moist tropical convection and its associated precipitation to be sensitive to vertical variations in water vapor on large space and timescales. Notably, the transition to strong convection and intense tropical precipitation were found to occur at a critical value of tropospheric column integrated water vapor, such that precipitation intensity would "pick up" exponentially following a power law relationship common to critical phenomena and their continuous phase transitions. While tropical precipitation is sensitive to variations in column integrated water vapor, there are uncertainties with respect to the relative roles played by lower and middle tropospheric layer averaged moisture in influencing the transition to strong convection in the Tropics. Using daily high resolution microwave-sensed satellite retrievals of tropospheric water vapor and tropical precipitation from 1999-2016, we argue that the pickup in tropical precipitation is constrained by a critical value in midtropospheric relative humidity and that this critical value underlies the sensitivity of precipitation intensity to water vapor integrated throughout the entire tropospheric column. This implies that this pickup in tropical precipitation intensity requires a preconditioned moistening of the middle troposphere that will insulate convective plumes from the deleterious effects of dry air entrainment and ensure a persistent moist neutral environment that can sustain these strong quasi-convective-radiative equilibrium precipitation events.
Apr 13: STUDENT SEMINARS
Simge Bilgen
Yi Dai
Yu Gao
Matthew Grossi
Apr 20: STUDENT SEMINARS
Alessandro Cresci (OCE)
Houraa Daher (OCE)
Shannon Doherty (OCE)
Apr 27: STUDENT SEMINARS
Romain Chaput (OCE)
Valeria Donets (ATM)
Mampi Sarkar
