Colorado State University

Remote Sensing

Development of High Impact Weather Research Tools and Technology

Remote sensing observation tools such as radar, lidar, and satellite provide important data to better understand and forecast various aspects of high impact weather. This project will assist in developing new technology and tools such as APAR and LROSE to address community needs, as well as utilize machine learning in tandem with satellite multi-spectral infrared and passive microwave brightness temperatures to address scientific hypotheses and develop new forecasting tools. More details about LROSE can be found HERE.

Acknowledgement: NSF SI2-LROSE OAC-1661663, NOAA APAR NA19OAR4590245, NASA Earth and Space Science Fellowship, United States Air Force -- Air Force Institute of Technology


Are the asymmetric dynamics of Hurricane Michael (2018) polygonal eyewall consistent with vortex Rossby wave (VRW) theory?

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Group Members: Ting-Yu Cha , Michael M. Bell , Alex DesRosiers

While polygonal eyewall shapes have been seen in previous hurricanes, the corresponding evolution of wind asymmetries has never been quantitatively deduced due to limitations from previous observations. Here we show the first observational evidence of the evolving wind field of a polygonal eyewall during RI to Category 5 intensity by deducing the winds at 5-minute intervals from single-Doppler Next Generation Weather Radar (NEXRAD) observations. The single Doppler radar analysis shows that the propagation speeds of different VRWs are consistent with linear wave theory.


A Comparison of the Polarimetric Radar Characteristics of Heavy Rainfall From Hurricanes Harvey (2017) and Florence (2018)

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Group Members: Jennifer C. DeHart , Michael M. Bell

Polarimetric coastal radar data are used to compare the rainfall characteristics of Hurricanes Harvey (2017) and Florence (2018). Intense rainfall was an infrequent yet important contributor to the total rainfall in Harvey, but its relative contribution varied spatially. The total rainfall over land maximized near the coast over Beaumont, TX due to intense convection resulting from prolonged onshore flow downshear from the circulation center. Overall, polarimetric radar observations in Harvey show a dominance of high concentrations of small-to-medium drops, consistent with prior tropical cyclone studies. The microphysical characteristics were spatially and temporally inhomogeneous however, with larger drops more frequent on 27 August and higher number concentrations more frequent on 28 and 30 August. The polarimetric variables and raindrop characteristics observed during Florence share broad similarities to Harvey, but had reduced variability, fewer observations of stronger reflectivity and differential reflectivity, and a lower frequency of high number concentrations and medium-sized drops. The radar data indicate Florence had reduced coverage of stronger convection compared to Harvey. We hypothesize that differences in storm motion, intensity decay rates, and vertical wind shear produce the distinct precipitation structures and microphysical differences seen in Harvey and Florence.


Tropical Cyclone Precipitation, Infrared, Microwave, and Environmental Dataset (TC PRIMED)

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Group Members: Naufal Razin , Michael M. Bell

TC PRIMED is a comprehensive dataset of global tropical cyclone (TC) satellite passive microwave observations. The central components of this dataset are TC-centered 1) multi-channel microwave brightness temperatures inter-calibrated across all available imagers using NASA's Global Precipitation Measurement (GPM) mission's microwave imager and 2) rainfall retrieval from NASA's Goddard Profiling Algorithm (GPROF). Auxiliary data include nearly coincident geostationary satellite infrared imagery around the satellite overpass time, TC best-track information, ECMWF ERA5 reanalysis fields and derived environmental diagnostics at each synoptic time, and TRMM/GPM precipitation radar variables. This dataset includes 157,400 overpasses of 1996 storms from 1998 to 2018, and will be updated annually.


How do the asymmetric processes impact Hurricane Matthew's (2016) Eyewall replacement cycle?

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Group Members: Ting-Yu Cha , Michael M. Bell , Alex DesRosiers

Hurricane Matthew was observed by the NEXRAD KAMX, KMLB, and KJAX polarimetric radars and NOAA P-3 airborne radar when it approached the southeastern United States during an ERC event. The radar observations indicate that Matthew's primary eyewall was replaced with a weaker outer eyewall, but unlike a classic ERC, Matthew did not reintensify after the inner eyewall disappeared. The single-Doppler analyses indicate that the inner eyewall decayed a few hours after the P-3 flight, while the outer eyewall contracted but did not reintensify and the asymmetries increased episodically. The analysis suggests that the resilient outer eyewall was influenced by both environmental vertical wind shear and an internal vortex Rossby wave damping mechanism during the ERC evolution.


What are the pros and cons of using single Doppler radar technique (GVTD) and pseudo-dual Doppler airborne retrievals for studying advantages and disadvantages of each technique for studying tropical cyclone structure?

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Group Members: Ting-Yu Cha , Michael M. Bell

In this study, a comparison between the two techniques shows that the axisymmetric tangential winds are generally comparable between the two techniques after the improvements to Generalized Velocity Track Display (GVTD) retrievals. Fourier decomposition of asymmetric kinematic and convective structure shows more discrepancies due to spatial and temporal aliasing in the retrievals. Complementary information can be retrieved from both single and multiple Doppler retrievals.