Student Seminars

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Nov 03 --- Student Seminars, Room MSC 343:

Andrew Smith (MPO)

"Dissipative Heating and the TKE Budget: Field Measurements and Implications for Air-Sea Exchanges"

Heat and momentum exchange are key physical processes underlying the energy budget at the air-sea interface. Dissipation of shear-induced turbulence results in momentum transfer to surface waves and dissipative heating, which can contribute significantly to the dynamics in the boundary layer atmosphere and upper ocean at larger scales.  (e.g. tropical cyclones, mixing, contributions to internal ocean waves, etc.). Here we present an examination of oft-neglected dissipative heating in the context of the turbulent kinetic energy budget, and its implications for air-sea exchanges. Prior studies have largely focused on the magnitude of dissipative heating in the hurricane environment (Bister and Emanuel, 1998; Businger and Businger, 2001; Zhang et al. 2011), or its parameterization in numerical hurricane models (Zhang D. and Altschuler, 1999; Jin et al. 2007) rather than connecting the physical process directly to the budget or exchanges of energy at the air-sea interface. In this study, we using use high-frequency (20 Hz) ship and radar data from the LAgrangian Submesoscale ExpeRiment (LASER) conducted in the Gulf of Mexico from January-February 2016 to compute the dissipative heating., evaluate the balance of TKE production with dissipation, and determine air-sea transfer coefficients as functions of stability and wind-speed in the low-wind (< 20 ms-1) non-hurricane environment. Surface density fronts (order 100 – 1000 m) identified from these data additionally allow us to investigate whether dissipation is enhanced near the fronts (e.g. D’Asaro et al. 2011), and the impact of changes in seawater properties on air-sea exchanges. Preliminary results have shown the ratio between the dissipative heating and thermodynamic (sensible and latent heat) fluxes to be between 40-80 percent in near-neutral stability conditions, where TKE shear and buoyancy production terms nearly balance to promote the dissipation while working to maintain the ambient stratification necessary to prevent a fully-homogenized boundary layer. This work will be combined with a forthcoming high-wind study in SUSTAIN to quantify the TKE budget in those conditions and examine the balance of sea-spray evaporation and dissipative heating.

Breanna Zavadoff (MPO)

"Anticyclonic Rossby Wave Breaking over the North Atlantic During Boreal Summer: Climatology and Impacts"

Anticyclonic Rossby wave breaking (ARWB) events are characterized by the rapid and irreversible deformation of PV contours on isentropic surfaces, manifesting themselves as tongues of high-PV stratospheric air extending from the extratropics into the tropics. Previous studies have highlighted the connection between Rossby wave breaking and the modulation of localized atmospheric phenomena such as the NAO and tropical cyclogenesis. However, to the author’s knowledge, Nno study,  hashowever, has focused on the evolution of the synoptic scale environment throughout the lifecycle of ARWB events over the entirety of the North Atlantic as well as the basin-wide environmental changes that occur related to development and decay of these events.
This study uses 54 years (1960-2013) of NCEP-NCAR Reanalysis data to identify and develop a comprehensive spatio-temporal climatological analysis of ARWB on the 350 K isentropic surface over the North Atlantic. This data is further utilized to investigate the synoptic environments surrounding these events from both basin-wide and high-PV streamer centroid-relative perspectives. Preliminary findings suggest that the high-PV streamers associated with ARWB events introduce dry stable air from the extratropics into the tropical environment, subsequently inhibiting convection there. Results from this study may provide aid in short to medium range forecasting of North Atlantic tropical convection, which could have applications extending into the field of tropical cyclogenesis forecasting as well.

Shun-Nan Wu (MPO)

"Signatures of Tropical Cyclone Intensification: An Assessment of Frozen Water Content in Numerical Simulations"

The relationship between the structure and amount of frozen water particles and tropical cyclone (TC) intensity change is examined using numerical simulations based on an idealized 3-D full physics model with different initial TC structures. Previous observational studies have demonstrated a large-scale enhancement of ice water content (IWC) for intensifying TCs, with the largest increases occurring near the eyewall.  The increased IWC near the eyewall is consistent with theoretical studies that have emphasized the importance of latent heat release in this region to TC intensification. However, the cause and consequences of increased IWC outside the eyewall remain unclear due, in part, to the lack of observations with sufficient coverage to characterize the spatial structure of IWC. To investigate this issue, we use an idealized WRF model with high temporal and spatial resolutions to examine the mechanisms responsible for greater IWC in intensifying TCs. In the WRF simulations, we find that strengthening storms have ~20% more frozen water content than weakening storms, especially in the mid-troposphere near the eyewall region. The signature of TC intensification found in the WRF simulations is shown to be consistent with IWC observations from CloudSat, both in amplitude and spatial extent. Such consistency encourages the use of numerically based simulations to further investigate the mechanism for such precursors of TC intensity change.  Moreover, the major source of the extensive increases in IWC, either from the local production associated with convections or advection by TC outflow, can be examined.

Nov 10 --- Student Seminars, Room MSC 343:

Gedun Chen (MAC)

"Processes Responsible for the Linear Shape of the Cu Concentration Profiles"

Hanjing Dai (AMP)

"Physical Processes Influencing Surface Roughness Variability at Submesoscale Fronts"

Oceanic fronts are often highly visible in active remote sensing images due to changes in the surface roughness. Quantifying these roughness changes in different wind, wave, and current for a range of density gradients can help to improve the interpretation of these images. During the Lagrangian Submesoscale Experiment (LASER) in the Gulf of Mexico, our research cruise crossed frontal interfaces up to 23 times. Fronts were located based on temperature, salinity, and X-band radar backscatter intensity and current maps. Direct measurements of winds, waves and currents were collected across these frontal interfaces. The detailed manifestations of the frontal interfaces on the surface roughness were sampled using a Polarimetric Slope Sensing (PSS) optical system. Polarimetric images of the short wave slopes crossing three frontal interfaces were obtained and one has analyzed in terms of the directional wave slope spectra, omnidirectional slope spectra, and the surface mean square slope (mss). The slope spectra dependence on winds, currents and sea-state at frontal interfaces, and the effect of fronts on short scale surface roughness will be discussed first. Moreover, the preliminary results of corresponding time-series of mean square slope before, during and after crossing the frontal interface show that the surface roughness changes dramatically to respond to the existence of a convergent or divergent front. The changes in mean square slope of short gravity waves and capillary gravity ones crossing the frontal interface also highlight the short time-scales of the frontal processes shaping the roughness of sea surface.

Nov 17 --- Student Seminars, Room MSC 343:

Nektaria Ntaganou (MPO)

Tiago Bilo (MPO)

Gregory Koman (MPO)

Alexis Denton (AMP)

"Tracking Arctic Sea Ice Buoys with Radar Reflectors"

In the Arctic Ocean, data collocations between satellite imagery and in-situ, sea ice-tethered measurements are usually done via interpolation between the two datasets, leading to unavoidable uncertainty in the position of an instrument within a satellite footprint. Even in very high resolution imagery, where pixel lengths range from 1 to 20 meters, instruments are not resolvable; beyond that, in the submeter resolution, the chance of imaging drifting instruments is small as the narrow swath widths require target acquisition to be precise. To reduce this location uncertainty, radar reflectors were deployed at various ice-stations in the Chukchi Sea within arrays of in-situ instruments as part of a joint effort with the Korean Polar Institute (KOPRI) and the EU’s ICE-ARC Program. Included in the arrays were high precision (within cm) GPS systems called SATICE. Synthetic Aperture Radar (SAR) imagery was acquired by the Center for Southeastern Tropical Advanced Remote Sensing (CSTARS) at the University of Miami to track the arrays and reflectors. The presence of the reflectors allows for the locations of the arrays to be directly discernable within the imagery, thus enabling more precise coordination of the ground and satellite data sets. A more detailed picture of ice dynamics may be formed by this simultaneous monitoring and matching between remote sensing and in-situ data. In addition, the SATICE systems allow for evaluation and comparison of SAR georeferenced locations of the reflectors across three types of SAR products offering varying degrees of spatial accuracy.

Nov 24 --- THANKSGIVING BREAK

Dec 01 --- Student Seminars, Room MSC 343:

Anne Barkley (ATM)

Lisa Bucci (ATM)

Kurt Hansen (ATM)

Szandra Peters (MPO)

Dec 08 --- Eleanor Middlemas (MPO, 1-Hour Student Seminar)