Recently published work has underlined the importance of longwave radiative heating in the formation of tropical cyclones; however, its effect on midlatitude transients is less clear. Using the GFDL Atmospheric Model 4, we perform a mechanism-denial experiment in which the radiative cooling profile at each model time step is overwritten with the climatological mean, computed from a control simulation. This approach separates the mean and transient effects of radiative heating on the midlatitude circulation. Our preliminary results indicate that, when radiative cooling is fixed, the eddy-driven jet shifts equatorward; the surface pressure variance, eddy kinetic energy, and eddy momentum fluxes are enhanced; and the Brewer-Dobson circulation, the mean stratospheric circulation that is mediated by vertically propagating Rossby waves, is strengthened. Overall we find that, while radiative interactions promote the formation of tropical cyclones, they inhibit transient activity in the extratropics.

Takuya Takahashi (ATM)
Evaluation of Surface Winds in WRF Simulations of Typhoon Faxai (2019)
in Urban Areas

The accuracy of numerical forecasts of tropical cyclones (TCs) has improved significantly with increasing spatial resolution and improved representation of model physics. However, point-by-point forecasts of the strong winds of TCs after landfall based on numerical models have yet to be realized. One issue to be addressed for such point-by-point wind forecasts is the ground-based validation of numerical expressions for TCs making landfall with hurricane-force winds. In this seminar talk, we will show the result of a detailed comparative analysis between WRF simulations and observations of Typhoon Faxai (2019), which made landfall in the Kanto region of Japan with the most intense wind force in recorded history. We will present the results of a detailed point-to-point comparison of the surface winds, especially those brought to urban areas during the passage of Typhoon Faxai. We will also briefly discuss the impact of surface and planetary boundary layer (PBL) parameterizations on the simulated surface wind fields and the dynamical decay of the TC vortex based on WRF simulations and radar observations.

Lev Looney (MPO)
Lessons Learned: 2022 Saildrone Hurricane Mission

Improving hurricane intensity forecasts, especially rapid intensification, remains a top priority within NOAA and across the broader research and operational communities. In-situ data is critical to expanding our understanding of the dynamics that influence a storm’s intensity and thus prove crucial for predictions. Currently, we have satellites, aircraft, and the instruments they deploy to collect atmospheric data within a hurricane. In the ocean, we have gliders that "swim" beneath the hurricane collecting oceanic data. One of the only current instruments collecting measurements at the air-sea interface is buoys. These are limited as they are immobile. In 2021, NOAA partnered with Saildrone to deploy 5 uncrewed drones to observe hurricanes at the air-sea interface. After a very successful first year, 7 Saildrones were deployed in the Gulf of Mexico and the Atlantic Ocean in 2022. The goals for this mission were to study the ocean-atmosphere interface to understand energy and momentum fluxes, to integrate observations to paint a fuller ocean-to-atmosphere picture by pairing with gliders and atmospheric assets, to transmit the data in real-time to operational centers, and to use the observations to improve our understanding of the air-sea interaction to advance predictions. I was fortunate enough to be the mission manager for the most active month of the 2022 season, September. In this talk, I will discuss the lessons learned through this experience, both in our drawbacks and successes, as well as what the future may hold.

Feb 24: STUDENT SEMINARS

Yueyang Lu (MPO)
Modeling the Ocean Mesoscale Eddy Effects on Tracer Transport

Mesoscale eddies greatly impact the distribution of heat and biogeochemical tracers in the ocean. However, resolving these eddies in ocean general circulation models is a significant computational challenge, as it requires a fine grid spacing of less than 1/10°. Therefore, the effects of eddies on tracer transport must be parameterized. This involves three key components: a precise definition of the eddy effects, a physically justiﬁed mathematical formulation, and a closure of relevant parameters. We propose a novel method that combines traditional eddy-induced diffusion and generalized eddy-induced advection to parameterize the eddy effect. We also consider closures for the eddy-induced velocity in terms of the large-scale flow, use numerical simulations to estimate the relevant non-dimensional parameters, and evaluate the scheme performance in the simulations. In this work, we define the unresolved eddy effects by coarse-graining the high-resolution numerical simulations. The diagnosed "eddy forcing" exactly augments the coarse resolution model solution towards the reference tracer. Our analysis of the eddy forcing suggests that unresolved eddies tend to partially offset the large-scale advection in regions of strong mean-eddy interactions. Our work provides new insights into the role of eddies in shaping the evolution of large-scale tracers, as well as guidance for future eddy parameterizations.

Chong Jia (MPO)
High Latitude Sea Surface Skin Temperatures
Derived from Saildrone Infrared Measurements

Infrared (IR) radiometers mounted on ships or other platforms to measure the ocean sea surface skin temperature (SST_skin) have been recognized as providing appropriate, accurate surface measurements for the validation of IR satellite remote sensing. From May 15 to October 11, 2019, six Saildrone uncrewed surface vehicles (USVs) were deployed for 150-day cruises collecting a suite of atmospheric and oceanographic measurements from Dutch Harbor, Alaska, transiting the Bering Strait into the Chukchi Sea and the Arctic Ocean. Two Saildrones funded by the National Aeronautics and Space Administration (NASA), SD-1036 and SD-1037, were equipped with IR radiation pyrometers in a "unicorn" structure on the deck for the determination of the SST_skin. We present an algorithm to derive SST_skin from the downward- and upward-looking radiometers and estimate the main contributions to the inaccuracy of SST_skin. After stringent quality control of data and eliminating measurements influenced by sea ice and precipitation, and restricting the acceptable tilt angles of the USV based on radiative transfer simulations, SST_skin can be derived to an accuracy of approximately 0.12 K. The error budget of the derived SST_skin is developed, and the largest component comes from the instrumental uncertainties, assuming that the viewing geometry is adequately determined. Thus, Saildrones equipped with these sensors could provide sufficiently accurate SST_skin retrievals for studying the physics of the thermal skin effect, in conjunction with accurate subsurface thermometer measurements, and for validating satellite-derived SST_skin fields at high latitudes.

Leah Chomiak (MPO)
The Interior Spreading Story of Labrador Sea Water

The convectively-driven formation processes in the Labrador Sea generate water masses that are imprinted with unique density, temperature, and salinity anomalies. These anomalies can be used as advective tracers when assessing the equatorward spreading pathways and advective timescales of the major component of upper North Atlantic Deep Water, Labrador Sea Water (LSW). LSW is formed in the Labrador Sea and exported predominantly via the Deep Western Boundary Current (DWBC). The DWBC is an essential component of Atlantic Meridional Overturning Circulation advecting deep waters southward, flowing at depth along the continental slope of the western Atlantic. In this study, the spreading pathways of two LSW classes formed between 1987-1994 and 2000-2003 are inferred by following convective salinity anomalies along constant density planes from sustained hydrographic observations, spanning the Labrador Sea to the Subtropical North Atlantic along both the western boundary and the entire North Atlantic domain. Both LSW classes are observed to advect on timescales that validate a previously hypothesized alternative-interior advective pathway branching from the DWBC. The arrival of LSW is observed simultaneously outside of the DWBC within the Atlantic interior and along the western boundary at 26.5°N, both 10-15 years after leaving the source region. Further investigation of this interior pathway suggests it is likely the main advective pathway that exports LSW from the western boundary to the interior, leading us to stress the importance of interior advective pathways on overturning circulation.

Mar 03: NO SEMINAR

Mar 10: STUDENT SEMINARS

Alexis Wilson (ATM)
An Investigation of Caribbean Easterly Wave Amplification
in the Pre-Genesis Environment of Hurricane Ida

Even though many Caribbean tropical cyclones (TCs) impact land, the formation and amplification of easterly waves in the Caribbean basin and the resulting influence on Caribbean TC genesis is a relatively understudied phenomenon. In 2021, the NASA CPEX-AW field experiment observed the environment in and around a weak easterly wave in the central Caribbean. In less than two days, the wave intensified and underwent genesis in the Northwest Caribbean much sooner and further northward than previously anticipated. An evaluation of the pre-genesis environment of this wave, which eventually intensified into Hurricane Ida, was performed using standard wind anomalies and relative vorticity from ERA5 Reanalysis data coupled with GridSat IR brightness temperatures and in-situ aircraft data from NASA CPEX-AW. Two main genesis factors were observed: the northward propagation of a topographically induced mesoscale convective system (MCS) and associated relative vorticity from just offshore of South America, and a breakdown of the Caribbean Low-Level Jet (CLLJ) from anomalously strong to weak occurring concurrently with the amplification of the easterly wave. Through this study, we demonstrate that the generation and amplification of easterly waves in the Caribbean basin is a complex and potentially important factor in Caribbean TC genesis that warrants further investigation.

Jimmy Yunge (MPO)
Observations and Simulations of Eyewall Misovortices in Tropical Cyclones

The tropical cyclone (TC) boundary layer is widely acknowledged to have a crucial role in the storm-scale circulation and evolution, and its importance is further emphasized by the direct surface impacts from TCs on society and the environment. Observations of turbulence in the TC boundary layer have revealed coherent features that may contribute significantly to eddy transport. Here we examine one such phenomenon, which appears as filamentary, cellular, or lobed structures in radar reflectivity in the eyewalls of some TCs, with azimuthal wavelengths of only a few km. These "misovortices" are associated with intense localized vorticity and horizontal and vertical wind perturbations, and have been attributed to incidents of extreme turbulence during aircraft missions and enhanced surface damage. Visible satellite imagery of several strong TCs shows wavelike structures that rarely appear in the low-level, inner eyewall edge. We also present a survey of ground-based radar observations of U.S. landfalling TCs of varying sizes and intensities across different synoptic environments. Commonalities between cases indicate that these features may be related to vortex-scale structural change or large-scale forcing. Preliminary comparisons of simulated winds, radar reflectivity, and cloud top temperature from high-resolution numerical simulations of Hurricane Laura (2020) suggest that the radar- and satellite-observed structures are connected. Future evaluation of the realism of model data using observed radar velocities is outlined. We discuss a hypothesis that these features are related to three-dimensional dynamical instabilities of the TC boundary layer jet and consider a linear stability analysis framework. Broader implications are briefly mentioned.

Mar 17: NO SEMINAR (Spring Recess)

Mar 24: STUDENT SEMINARS

Samantha Nebylitsa (ATM)
Evaluating the Wind and Moisture Around Idealized Tropical Cyclones

The study of Tropical Cyclones (TCs) relies heavily on accurate modeling to help scientists understand both small- and large-scale factors that may influence TC intensification. The mechanisms behind TC rapid intensification (RI), defined as an increase in maximum winds of at least 30 knots in 24 hours, have gained traction in recent years as the number of storms that experience RI have increased. Before TC RI may be studied more in-depth, it is important to see how accurately the larger scale wind and moisture are represented in models. Average shear, calculated as the difference between the 200 and 850 hPa winds, identified from a 42-year climatology for three different intensification rates, are used to define the zonal shear. The Weather Research and Forecasting model is initialized with this wind along with commonly used tropical temperature and moisture profiles. The evolution of the wind and moisture in various areas around the TC are analyzed and compared to the climatology. Preliminary results indicate similar patterns for wind and moisture in the simulations as the climatology. This provides confidence in the use of the model to study more complicated interactions between the TC and its environment in relation to intensification.

Tyler Tatro (ATM)
A Dynamical Characterization of Smoke Transport Over the Southeast Atlantic

The southeast Atlantic is home to one of the world's largest subtropical stratocumulus decks, with the lower free troposphere often polluted by biomass-burning aerosol (smoke) emanating from continental Africa. The vertical and horizontal distribution of biomass-burning aerosol impacts the cloud properties both radiatively and microphysically, altering the region's radiation fields and atmospheric circulations. Here we examine the processes that govern smoke variability on both the weekly and multi-year time scales during June-November, using primarily a 40-year ERA5 data record and 17-year carbon monoxide time series from an ECMWF aerosol reanalysis. Observations of smoke from Ascension Island serve as the reference. Leading questions are understanding how smoke enters the cloudy boundary layer, and if smoke transport may be changing over time. Using empirical orthogonal functions, we find the modulation and displacement of the south Atlantic high can promote smokier conditions at Ascension Island. We also find free-tropospheric easterly winds over the southeast Atlantic have significantly increased over time, contributing to farther smoke transport over the ocean. The strengthening of the winds is attributed to either a warmer southern Africa or a westward shift in the Asian monsoon.

Will Downs (ATM)
The Effects of Multi-Disturbance Interactions on the Early Stages of Tropical Cyclones

African Easterly Waves (AEWs) are common precursors to tropical cyclogenesis in the North Atlantic, but not all genesis events can be attributed to single discrete AEWs. AEWs can become entangled with one another or with other synoptic-scale low pressure systems such as monsoon depressions and frontal surface troughs. These multi-disturbance interactions are sometimes followed by tropical cyclogenesis that is poorly predicted by numerical modeling and / or human forecasters, as was the case for Gonzalo and Zeta in 2020. Here we investigate how interactions between AEWs and other disturbances impact the cyclogenesis process and early organization of tropical cyclones (TCs). We present a newly machine-usable dataset of AEW locations that we have parsed from the National Hurricane Center's Tropical Weather Discussions. We diagnose entanglement between AEWs and other synoptic-scale disturbances by tracking local maxima in curvature vorticity fields from ERA5 reanalysis data. Multi-disturbance interactions events that are followed by cyclogenesis often feature a jump in vorticity at the time of interaction that persists through genesis, suggesting that some multi-disturbance interactions help develop a coherent TC vortex. TCs that form following these interactions may be broader and of lower intensity early in their existence. The possible impacts of these interaction events on the early stages of TCs warrant further investigation of the dynamics governing these interactions.

Madeleine Dawson (OCE)
Synthetic Aperture Radar Retrievals of Arctic Sea Ice

Significant Arctic warming in the past decades has led to dramatic changes in polar sea ice such as the extent, thickness, and properties. Thus, there is heightened interest in utilizing satellite remote sensing acquisitions to gather high resolution sea ice concentration (SIC). Synthetic Aperture Radar (SAR) is the exemplary remote sensing satellite for this task region due to its inherent benefits of operating without sun illumination requirements and through cloud cover. Due to the high complexity of SAR, deep learning is an optimal technique for processing these images. Existing literature has explored the development of such models, yet the nuances of SAR datasets parameter integration require further exploration for model deployment. Therefore, we propose a deep learning model pipeline to automate sea ice extraction to fully utilize the characteristics of SAR datasets. The University of Miami's Center for Southeastern Tropical Advanced Remote Sensing (CSTARS) provided the SAR Images used for this research investigation. The images were obtained through the Stratified Ocean Dynamics of the Arctic (SODA) program funded through the Office of Naval Research that was conducted from 2016 to 2021. This work applies a state-of-the-art computer vision encoder / decoder architecture on SAR images to investigate the capability of sea ice retrievals.

Mar 31: Dr. David Lawrence
Invited Speaker of the Department of Atmospheric Sciences
Climate and Global Dynamics Laboratory, NCAR, Boulder, CO

Towards Improved Capacity of the Community Land Model for Actionable Science
Click to Attend via Zoom

The Community Land Model (CLM) is the land component of the Community Earth System Model (CESM). As the science of climate change evolves from questions about how much global climate change there will be to questions of what we are going to do to mitigate and adapt to this climate, the requirements for Earth System models (ESMs) are changing. Here, I will review how land models in ESMs are evolving to answer an ever-growing range of questions related to food and water security, effectiveness of nature-based carbon dioxide removal methods, ecosystem vulnerability, and changes in extremes. I will focus on advances related to land management, agriculture, hydrology, and parameter estimation, and will provide examples of how CLM is being used to support actionable science objectives.

Apr 07: Dr. Angeline Pendergrass
Invited Speaker of the students of Atmospheric Sciences
College of Agriculture and Life Sciences and
Cornell Atkinson Center for Sustainability, Cornell University, Ithaca, NY

Implications of Time Varying Climate Feedbacks for Precipitation
Click to Attend via Zoom

Climate sensitivity varies on multiple timescales with different magnitudes as climate feedbacks evolve over time. This timescale dependence of climate feedbacks can be understood through the radiative fluxes at the top of the atmosphere. If TOA fluxes respond on multiple timescales, then surface fluxes may as well, which would lead to timescale dependence of global mean precipitation. We investigate whether it does in millennial-length simulations of the response to abrupt increase in carbon dioxide from LongRunMIP. In order to compare the slope of precipitation versus temperature (also known as "hydrologic sensitivity") among timescales, we must first calculate this slope. Ordinary least squares, the most common regression technique often used by default for calculating a slope, provides (on average) the correct slope of a trend over time. But, when regressing against an independent variable with internal variability, such as temperature, it systematically underestimates the slope (called "regression dilution"). This is well known to statisticians, and at least beginning to be appreciated in climate science. And still further problems can arise of the variability between variables is correlated. We introduce a new approach to quantify these biases specific to the climate context. We apply them to investigating the time-dependence of climate sensitivity and hydrologic sensitivity.

Apr 14: STUDENT SEMINARS

Elizabeth Yanuskiewicz (OCE)

Samantha Medina (OCE)

Hope Elliott (OCE)

Apr 21: Dr. Adeyemi Adebiyi
Invited Speaker of the COMPASS Student Committee
Life and Environmental Sciences, School of Natural Sciences, University of California Merced

Apr 28: STUDENT SEMINARS

Paul Wojtal (OCE)

Lillian Henderson (OCE)

Marian Alicea (OCE)

COMPASS Friday

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