Meteorology & Physical Oceanography

ATM/MPO/OCE Seminars

FALL SEMESTER

All seminars are in the SLAB seminar room at 3:00, unless stated otherwise

09/21--- Dr. Mahsa Mirzargar (UM CS Department): "Exploring the Potential of Data Depth for Uncertainty Characterization and Visualization of Ensembles"

Abstract: When computational methods or predictive simulations are used to model complex phenomena such as dynamics of physical systems, researchers, analysts and decision makers are not only interested in understanding the data but also interested in understanding the uncertainty present in the data as well. In such situations, using ensembles is a common approach to account for the uncertainty or, in a broader sense, explore the possible outcomes of a model. Visualization as an integral component of data-analysis task can significantly facilitate the communication of the characteristics of an ensemble including uncertainty information. Designing visualization schemes suitable for exploration of ensembles is specifically challenging if the quantities of interest are derived feature-sets such as isocontours or streamlines rather than fields of data.

09/28--- Dr. Naresh Kumar (UM Miller School of Medicine): “Personal Real-time Exposure using Cellphone Integrated SEnsor (PRECISE)”

Naresh Kumar , Sung Jin Kim , Diego Palacios , Joshua Krstic and Allen D. Chu

Abstract: One-quarter of the disease/disability burden can be attributed to environmental conditions (WHO 2006). While we have made great strides in characterizing an individual’s genotypes and phenotypes, it has been difficult to characterize and quantify an individual’s personal exposure due to the lack of location- and time-specific environmental measurement. A long-term mission of the University of Miami PRECISE (Personal Real-time Environmental Exposure using Cellphone Integrated SEnsors) is to provide patients (researchers, decision-makers and healthcare providers) with the concentrations of multiple gaseous, particulate and organic air pollutants and their associated personalized (or individual specific) risks in real time. Testing and validation of a portable sensor and a hybrid approach that can quantity time- and location-resolved exposure to gaseous and particulate air pollution is first critical step. To address this gap, we have developed a portable sampler that records gaseous and particulate air pollution and stream these data to a secure server in real-time through cellphones or WiFi.
The manufacturing cost of the instrument is < $750/unit. This sampler can also be mounted inside home, on a car and can be carried by study participants.

We have also developed a hybrid approach to estimate location specific concentration of fine particulate on a given day anywhere in the global cities. This approach capitalizes on satellite remote sensing, local time-space Kriging (an optimal interpolation technique) and in-situ monitored data to develop region-specific empirical model to quantify ambient PM2.5 estimates at 2 km spatial resolution, and then employ local-time space Kriging to impute estimates at any given location and day. Our portable sensor and hybrid approach together offer an unprecedented opportunity to quantify personal exposure to air pollution in real time and also changes in exposure due to changing meteorological conditions. Not only does this formulate bases for identifying personal health risk (including asthma, COPD, and other cardiopulmonary diseases) associated with the short- and long-term exposure to the mixture of air pollutants, needed to engage individuals in avoidance behavior but also quantify the burden of disease associated with extreme-weather mediated changes in personal and regional air pollution exposure.

Reference: WHO, Preventing disease through healthy environments - towards an estimate of the environmental burden of disease, 2006, World Health Organization: Geneva, Switzerland.

Web: precise.ccs.miami.edu

10/05--- Dr. Pierre L'hegaret (RSMAS) "Mesoscale circulation in the Arabian Sea and its impact on the Persian Gulf outflow"

10/12--- Dr. Amy Clement “The AMO and the AMOC Part 2: Diagnosing the roles of the ocean and historical forcings”

10/19--- Dr. Igor Kamenkovich "Eddy-induced transport in the ocean: Anisotropy and interactions with the mean flow"

Mesoscale currents (“eddies”) play an important role in distribution of many dynamically and climatically important quantities. The corresponding eddy-induced lateral transport is spatially inhomogeneous (i.e. it depends on location) and anisotropic (i.e. it depends on direction), as evidenced by observation- and model-based estimates. These important and complex properties of the eddy transport cannot be explained by local velocity statistics alone. Mechanisms for the inhomogeneous and anisotropic transport are frequently nonlocal, and include action of elongated eddies and their interactions with the mean flow, as is demonstrated by our numerical simulations and analysis of altimetry data. We will further discuss implications of these transport properties for lateral distribution of tracers, for ventilation of the Southern Ocean, and for the fidelity of numerical simulations.

10/26--- Dr. Pedro DiNezio (University of Texas Institute for Geophysics) "Challenges predicting La Niña"

In my talk I will discuss the two critical challenges concerning the prediction of La Niña.

The El Niño of 2015/16 has by now faded and given its record-breaking strength La Niña conditions were expected for the upcoming boreal winter. Observations and forecast models, however, do not consistently shown that that La Niña is underway raising questions on whether the onset of this year’s La Niña has stalled. I will show that: 1) climate anomalies this year are consistent with a developing La Niña and 2) long-term warming or multi-decadal trends in Pacific climate could be influencing our definition of the standard Nino indices, leading to an underestimating of the magnitude of the current anomalies. I propose that an index of the zonal SST gradient may become a more accurate index for monitoring El Niño and La Niña in a warming world.

Furthermore, historical observations and climate model simulations indicate that strong El Niño events are likely to be followed by La Niña conditions lasting 2 years or more. Our recent research shows that the Community Earth System Model Version 1 (CESM1), a model that realistically simulates multi-year La Niña events, is also capable of predicting their duration. Our forecasts are particularly more skillful and reliable when initialized on the wake of a strong EL Niño event, just like this year. I will use these idealized “perfect model” prediction experiments to explore whether the current ocean conditions could permit skillful predictions of the duration of upcoming La Niña.

11/02--- 15-min student seminars:

Shun-Nan Wu: he signal of future TC intensification in CloudSat measurements"

This study examines how the vertical structure of convective heating influences the evolution of tropical cyclone (TC) intensity using the CloudSat Tropical Cyclone (CSTC) dataset. Both theoretical and modeling studies demonstrate that the location of convective heating can play an important role in modulating changes in TC intensity. However, observations of vertical profiles of convective heating are limited. Fortunately, CloudSat measurements provide high-resolution observations of cloud ice and liquid water content that can serve as useful proxies for convective heating. To determine if there are observable signals of future TC intensity change, this study constructs composites of CloudSat profiles for strengthening and weakening TCs. While the difference in total rain rate between strengthening and weakening TCs is small, we find a significant difference in cloud water content between the two composites. In particular, strengthening TCs have higher ice water content than weakening TCs, especially between 6-10 km in vertical and within 2 radius of the maximum wind in horizontal.  This analysis provides observational evidence that even though the total convective heating rates are similar in both strengthening and weakening storms, different locations of convective heating alter the evolution of TC intensity.  Further investigation into the signal in different categories of TC intensity and the time scale of the relation between amount of ice water content and storm intensity will be presented.

Samantha Kramer: "Saharan Dust in Miami: How well is it represented by the MERRA2 Reanalysis"

Saharan dust has been studied at RSMAS since the mid-1970’s with great success. There remains large uncertainty in the radiative, climate, cloud, and human health impacts associated with Saharan dust due to individual and inter-model differences in size and vertical distributions. While detection and magnitude of dust events are generally captured across models, the largest error is in the size and vertical distributions, which are the most important for the study of these impacts. MERRA2 dust and aerosol properties are analyzed as they pertain to Saharan dust in Miami, using local observations across two years (2014, 2015). Two consecutive dust seasons with ground based lidar and daily surface measurements provide a comprehensive amount of evidence to determine the properties and aptitude of dust measurements in MERRA2. Daily, seasonal, and interannual analysis provide multiple temporal scales for comparison in the vertical distribution, size distribution, surface deposition, and background environment. This study is a precursor to further analysis of impacts based on the confidence in MERRA2 to capture realistic and reliable dust tendencies.

Yi Dai: "Secondary eyewall formation in tropical cyclones by outflow-jet-interaction"

 This study uses idealized numerical simulations to show that interaction between tropical cyclones and a mid-latitude jet can result in the secondary eyewall formation. It is argued that the eddy activity by the outflow-jet interaction can enhance the upper-level outflow, thereby creating an asymmetric stratiform region outside of the primary eyewall. Numerous long-lasting deep convective cells are able to form in the stratiform cloud, creating forcing necessary for the secondary eyewall. The low-level inflow and the TC’s primary circulation advect the deep convective cells inward and cyclonically. The secondary eyewall forms after the deep convection has surrounded the TC. Sensitivity experiments indicate that the result is robust to small perturbations of the initial conditions. Furthermore, the secondary eyewall formation is more sensitive to the jet-TC distance than the strength of the jet.

11/09--- 15 min student seminars:

Eleanor Middlemas: "Implementing cloud locking in CAM5"

The goal of this study is to pinpoint how the NCAR model (CESM) responds to various changes in cloud-radiative feedbacks.  Clouds’ impact on climate variability remains uncertain partially due to the large model spread in cloud radiative feedback.  Models may not agree because of various parameterizations of nonlinear and unresolvable cloudradiative processes.   A previous experiment “locked” clouds, or separated clouds from circulation and radiation, in the Max Planck Institute Earth System Model (MPI-ESM) to find significantly reduced El Nino and decadal variability (Radel et al. 2015).  These authors performed “cloud locking” by prescribing cloud parameters in the radiation module in a random sequence in time to disable cloud feedback in the model while maintaining radiation balance. To test the model-dependency of their results, we are reproducing this methodology in the NCAR atmospheric model CAM5.  This seminar will review other modeling attempts at understanding cloud radiative feedback’s impact on climate as well as cover our recent progress at implementing cloud-locking in the NCAR model.

Ryan Kramer: "Evaluating surface feedbacks and forcings using the radiative kernel technique"

Feedbacks and forcings at the surface have important effects on surface temperature, the hydrological cycle and large-scale circulation, yet have not been thoroughly studied.  Using a combined radiative kernel-regression approach, we evaluate surface feedbacks, rapid adjustments and direct forcing under an abrupt increase in CO2 in a suite of CMIP5 global climate models.  We find that rapid adjustments in clouds are a large contributor to inter-model spread in the total surface radiative response, and we find notable inter-model spread in direct surface forcing.  We also compare surface radiative kernels generated from multiple models, to investigate the extent that differences in radiative transfer modeling contributes to inter-model spread in surface energy changes. We note that the majority of surface radiative kernels analyzed in this study contain an unexpected change in downwelling longwave radiation when the surface is warmed in isolation.

11/16--- 15-min student seminars:

Kayleen McMonigal: "Resolving temperature transport of the Agulhas Current using moored instruments"

The Agulhas System Climate Array (ASCA) is a currently ongoing project to measure the temporally varying temperature transport of the Agulhas Current (AC) at 34 S. The ten currently deployed moorings consist of acoustic Doppler current profilers (ADCPs), Nortek and Aandara current meters, and microCATs which will produce full depth temperature, salinity, and velocity data for the AC. Further offshore, current and pressure-sensing inverted echo sounders (CPIES) extend the array to span the full current, including during meander times. CTD and lowered ADCP data from 2013 can be utilized to determine the best method to interpolate the lower density mooring data onto a regular grid and to yield error bars for interpolated temperature, salinity, and velocity. Upon turnaround of the moorings in November 2017, these methods can be used to determine the temperature and freshwater transport of the AC over a 1.5 year period. Optimal interpolation using estimated field statistics on two scales (Roemmich 1983) is found to be a robust method for data interpolation. Root mean square errors of the interpolated data as compared to CTD data are .5 degrees C, .03 psu, and 5 cm/s for potential temperature, salinity, current velocity respectively. There is little bias except in the upper 100 m of the ocean, where an SST product may be beneficial to constrain upper ocean temperature. Velocity data is also biased low in the upper 100 m and an alternative method may be necessary to extrapolate above the top instrument. Estimated field statistics can be improved using the data that will be collected in 2017. This may reduce the bias and root mean square errors.

Joaquin Blanco "An objective analysis of tropical Cloud Cluster motion associated with Super Cloud Clusters"

The nature and characteristics of Super Cloud Clusters (SCCs), also known as Convectively Coupled Kelvin Waves, have been studied extensively. A systematic result has been the westward propagation of short-lived cloud clusters (CCs) within the eastward-moving SCC. A careful visualization of sequences of precipitation and OLR fields in the tropical region of aquaplanet-like simulations yield several recognizable patterns of propagation that cannot be restricted to the generally accepted idea of westward-moving CCs within eastward-moving SCCs. These features are better discernible in longitude-time diagrams, with clear “S-shaped” signals in OLR and precipitation: the westward-moving CCs are driven by easterlies ahead of the SCC axis, but they are stationary when they develop nearly collocated with it, while behind the SCC axis the CC motion is typically eastward due to the associated westerly wind bursts.

An algorithm is especially designed for the identification and tracking of CCs, also called “time-clusters” in time-longitude coordinates. In successive steps, the OLR or precipitation thresholds are changed to accurately assess CC motion in both regions of enhanced and relatively suppressed convection. Then, all detected CCs as well as their tracks are combined for a systematic analysis, in which results are categorized according to variables such as: location and width of tropical band, CC position relative to the SCC axis, stage of the SCC life cycle, vertical profile of zonal wind, CC size, CC lifespan, travelled distance, etc. This work will help elucidate aspects of the SCC-CC interaction over the tropical ocean.

Tiago Bilo: “Deep Western Boundary Current in the North Atlantic: Recirculation Dynamics and Patterns”

The Deep Western Boundary Current (DWBC) is the primary component of the cold or lower (depths > 1000 m) branch of the Atlantic Meridional Overturning Circulation (AMOC). As the DWBC flows southward along the Americas continental slope it carries North Atlantic deep waters in a highly variable and dynamically complex path. One remarkable characteristic of the DWBC flow is the presence of recirculation cells. Although we are aware of such features, their dynamics and interactions with the mean DWBC path, and consequently with the AMOC, are still not completely understood. The state of knowledge on the DWBC recirculation patterns in the subtropical region will be reviewed, and the main knowledge gaps discussed.  I will outline a plan of study for my PhD to further the understanding of the forcing and dynamics of these recirculation cells, and their impact on NADW pathways and mixing with deep interior waters in the subtropical North Atlantic.

11/23--- THANKSGIVING BREAK

11/30--- 15min student seminars:

Rafael Goncalves "Reconstruction of the velocity field from Lagrangian observations using Gaussian process regression"

The extensive drifter deployment during the Lagrangian Submesoscale Experiment (LASER) provided observations of submesoscale activity with high resolution in space and time. Estimating the Eulerian velocity field on a regular grid from this drifter data would be valuable to characterize the submesocales, as it provides means to compute strain rate, relative vorticity and divergence. We present a technique to infer the velocity field from sparse observations using Gaussian process regression (GPR). The novelty of our approach is in mining the LASER data to optimize, via a Bayesian procedure, the hyper-parameters specifying the space-time scales of the covariance function and the data noise level. The GPR also provides an estimate of the error of the regression, which can be verified with observations that are not used in the velocity reconstruction procedure. Here, the reconstruction of the velocity field is presented, along with estimates of relative vorticity, divergence and strain rate. The regression was carried out in a 20 x 20 km grid with 500 meters resolution, during a 24 hours window. A subset of about 150 drifters were used in the regression, while another 150 drifters were used for error verification. The optimization procedure resulted in spatial decorrelation scales of 1-4 km, with decorrelation time of 2-4 hours.

Jianhao Zhang: "Tropical humidity vertical structure inferred from a microwave radiometer during DYNAMO"

In the Tropics, convection is sensitive to small variations in humidity, especially within the free troposphere. Radiosondes, although they provide high vertical resolution profiles, do not resolve variations in humidity fields at high temporal and spatial resolution well. Such variations are valuable for understanding the relationship of convection to tropical humidity at small time and space scales, such as at convectively-induced cold pools and as part of the shallow-to-deep cloud transition. Microwave radiometers (MWR), are able to profile and horizontally-scan autonomously and output measurements frequently (~ 1 Hz). To date, few assessments of microwave humidity profiling in the Tropics have been undertaken. This study evaluates the ability of a MWR to observe the tropical humidity structure using four months of data from the equatorial Indian Ocean, at Gan Island, collected from University of Miami's 22-30 GHz radiometer during the Dynamics of Madden-Julian Oscillation (DYNAMO) field campaign. Column-integrated liquid water paths and water vapor paths, and water vapor mixing ratio profiles, are physically retrieved using an iterative Gauss-Newton optimal-estimation approach. After careful calibration of the instrument, the MWR-retrieved water vapor paths agree well with those from radiosondes. This study shows that the integrated profiling technique (IPT) provides about 2 degrees of freedom in the vertical and possesses a bias of about 1 g/kg when compared to radiosondes, particularly under moist condition. Moisture structure analysis based on these retrievals show a MWR is able to capture the vertically resolved advective tendency of humidity and small-scale variability in water vapor close to the onset of deep convections and cold pools in the Tropics.

Luo Bingkun "The impact of Saharan Outflow on Satellite Retrieved Sea Surface Temperature"

The accuracy of the Sea Surface Temperature (SST) derived from satellite measurements and models is important for climate research and prediction. But high tropospheric aerosol concentrations in the atmosphere significantly increase infrared signal attenuation and prevent the retrieval of accurate satellite SSTs. We compare model and satellite-derived skin SSTs with measurements from the ship-based Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) on the Aerosols and Ocean Science Expeditions (AEROSE) tracks. As expected, the results indicate that SSTs retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) aboard the Terra and Aqua satellites (data quality flag ≤1) and Meteosat Spinning Enhanced Visible and Infrared Imager (SEVIRI) (data quality level ≥4) have negative (cool) biases compared to shipboard radiometric measurements. Using Aerosol Optical Depths (AOD) data and radiosonde atmosphere profiles, we find that aerosols and an atmospheric dry layer from Sahara reduce the accuracy of the SST derived from satellite. Errors larger than the current stated accuracy of 1 K for SSTs are possible at AOD>0.5, especially in the Atlantic tropical region where large-scale Saharan dust outbreaks occur. The Saharan Aerosol Layer causes a negative SST bias and satellite retrieved SST errors depend on the height and density of aerosol layers. So the AEROSE scientific investigations provide very important information on the research of Saharan Aerosol Layer. Current SST algorithms are very sensitive to aerosol contamination and there is a need to develop an algorithm for correcting the aerosol effects on SST retrievals.

12/01 (MSC 343, 3:00) --- Dr. Pavel Berloff (Imperial College London): "Dynamically consistent parameterization of mesoscale eddies"

This work aims at developing new approach for parameterizing mesoscale eddy effects for use in non-eddy-resolving ocean circulation models. The idea is to approximate transient eddy flux divergence in a simple way, to find its actual dynamical footprints, and to relate these footprints to large-scale flow properties.

12/07--- Dr. Arunchandra Chandra (RSMAS)

12/08 (SLAB, 2:00) --- Dr. Sergey Kravtsov (University of Wisconsin): "On semi-empirical decomposition of multidecadal climate variability into forced and internally generated components"

This study combines CMIP5 historical simulations and observations of surface temperature to investigate relative contributions of forced and internal climate variability to long-term climate trends. A suite of estimated forced signals based on surrogate multi-model ensembles mimicking the statistical characteristics of individual models is used to show that, in contrast to earlier claims, scaled versions of the multi-model ensemble mean cannot adequately characterize the full spectrum of CMIP5 forced responses, due to misrepresenting the model uncertainty. The same suite of multiple forced signals is also used to derive unbiased estimates of the model simulated internal variability in historical simulations and, after appropriate scaling to match the observed climate sensitivity, to estimate the internally generated component of climate variability in the observed temperatures. On average, climate models simulate the non-uniform warming of Northern Hemisphere mean surface temperature well, but are overly sensitive to forcing in the North Atlantic and North Pacific, where the simulations have to be scaled back to match observed trends. In contrast, the simulated internal variability is much weaker than observed. There is no evidence of coupling between the model simulated forced signals and internal variability, suggesting that their underlying dominant physical mechanisms are different. Analysis of regional contributions to the recent global warming hiatus points to the presence of a hemispheric mode of internal climate variability, rather than to internal processes local to the Pacific Ocean. Large discrepancies between present estimates of the simulated and observed internal climate variability suggest that our ability to attribute and predict climate change using current generation of climate models is limited.

12/14--- Pete Finocchio (one-hour student seminar)

SPRING SEMESTER

02/01--- Dr. Pierre Sochala (TBA)

02/08--- Dr. Yoshiaki Miyamoto (TBA)

03/01(2:00p.m.) --- Dr. Phil Klotzbach (Colorado State University)

03/22--- Dr. Peter Hamilton (TBA)

04/19--- Johna Rudzin (1-hour student seminar)

04/26--- Dr. Eileen Hofmann (Old Dominion University)