Presented by

Dr. Yu Du
Associate Professor
School of Atmospheric Sciences
Sun Yat-sen University

Date:                Wednesday, February 3, 2021

To view the recording, please follow this link:

http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Yu Du 20210203.mp4

Abstract:

Convection initiation (CI) and the subsequent upscale convective growth (UCG) at the coast of South China in a warm-sector heavy rainfall event are shown to be closely linked to a varying low-level jet over the northern South China Sea (NSCS). The nocturnal LLJ peaks at 950 hPa and significantly intensifies with turning from southwesterly to nearly southerly by inertial oscillation. The strengthened LLJ promotes mesoscale ascent on its northwestern edge and terminus where enhanced convergence zones occur. Located directly downstream of the LLJ, the coastal CI and UCG are dynamically supported by mesoscale ascent. From a thermodynamic perspective, a warm moist tongue over the NSCS is strengthened by the LLJ-driven mesoscale ascent as well as by a high sea surface temperature. The warm moist tongue farther extends northeastward by horizontal transport and arrives at the coast where CI and UCG occur.

Through conducting dynamic and thermodynamic diagnoses as well as a series of numerical sensitivity simulations, we further investigated the effects of the terrain, coastline, and cold pools on CI and UCG. CI occurred at the vertex of the coastal concave mountain geometry as a combined result of coastal convergence, orographic lifting, and mesoscale ascent driven by the terminus of a LLJ. In numerical simulations with the coastline or terrain of South China removed, the coastal CI does not occur or becomes weaker as the LLJ extends farther north. In addition, local small-scale terrain can modulate the detailed location and timing of CI and UCG. From a thermodynamic perspective, the coastal concave terrain plays the role of a local moisture ‘‘catcher’’, which promotes low-level moistening by blocking water vapor coming from an upstream moist tongue over the ocean. Furthermore, new convection is continuously generated by the lifting of low-level moist southerlies at the leading edges of cold pools that tend to move southeastward because of the blocking coastal mountains.

Presented by

Professor Yu-Chieng Liou
Department of Atmospheric SciencesCollege of Earth Sciences
National Central University

Date:                Wednesday, January 27, 2021

To view the recording, please follow this link:

http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Yu-Chieng Liou 2021012.mp4

Abstract:

In this seminar two variational-based retrieval algorithms are introduced. The first algorithm, called WISSDOM (WInd Synthesis System using Doppler Measurements), is a multiple-Doppler radar three-dimensional wind synthesis method. Compared to the traditional techniques, WISSDOM is able to recover three-dimensional wind field along the radar baseline and over complex terrain. Data from any number of radars, surface station, wind profiler, sounding, and meso-scale numerical model outputs can all be utilized by WISSDOM at the same time. The second algorithm, called TPTRS (Terrain-Permitting Thermodynamic Retrieval Scheme), can directly use the wind fields from WISSDOM to retrieve the three-dimensional pressure, temperature, and moisture fields. By using idealized data and real cases observations, the accuracy of WISSDOM and TPTRS is examined. By combing WISSDOM and TPTRS, one can obtain a complete set of high resolution meteorological variables. The applications of this high quality data set in weather diagnosis and improving short-term quantitative precipitation forecast (QPF), especially in mountainous areas, are also discussed.

Presented by

Professor Ming-Jen Yang
Department of Atmospheric SciencesCollege of Science
National Taiwan University

Wednesday, January 20, 2021

To view the recording, please follow this link:

http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Ming-Jen Yang 20210120.mp4

Abstract:

On 14 June 2015, severe afternoon thunderstorms developed in the Taipei basin, producing intense rainfall (with the rainrate of 131 mm/h) and urban-scale flooding. High-resolution simulations using the Weather Research and Forecasting (WRF) model with the finest grid size of 0.5 km were performed to capture reasonably well the onset of sea breeze, the development and evolution of this afternoon thunderstorm system.

Convection was initiated both by sea breeze at foothill and by upslope wind at mountain peak. Convective available potential energy (CAPE) was increased from 800 to 3200 J/kg with abundant moisture transport by the sea breeze from 08 to 12 LST, fueling large thermodynamic instability for the development of afternoon thunderstorm. Strong convergence between sea breeze and cold-air outflow triggered further development of intense convection, resulting in heavy rainfall. Microphysics experiments show that evaporative cooling played a major role in the propagation of cold-air outflow and the production of heavy rainfall, while melting cooling played a minor role. The local topography of Mount Datun at coastal region produced the channel effect through Danshui River Valley, intensifying sea-breeze circulation and transporting more moisture.

A mid-level dry layer with layer-mean relative humidity of 50% occurred at 500–700 hPa for the Banchiao (near Taipei) sounding at 00 UTC (08 LST). Four sensitivity experiments with the increase or decrease of mid-level relative humidity of 10% and 20% were conducted. Experiments with a drier middle layer would result in stronger cold pool, more organized and deeper convection, stronger updrafts and more latent heating above the melting level, and a much larger area of intense-rainrate region (>80 mm/h). Statistics from 200 backward trajectories indicated that 37% of air parcels within the cold pool came from the middle levels (3–6 km). Domain-accumulated rainfall was not positively correlated to the rainfall rate. Finally, numerical experiments found a nonlinear response of simulated convection intensity to the mid-level moisture content in the environment.

Presented by

Dr. David Noone Buckley-Glavish Professor of Climate Physics
Department of Physics
University of Auckland

Wednesday, November 25, 2020

To view the recording, please follow this link:

http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by David Noone 20201125.mp4

Presented by

Dr. Rosimar Rios-Berrios
Scientist I
Mesoscale and Microscale Laboratory
National Center for Atmospheric Research (NCAR)

Wednesday, October 28, 2020

To view the recording, please follow this link: http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Rosimar Rios-Berrios 20201028.mp4

Abstract:

Four decades ago, scientists noticed that tropical cyclones form in clusters followed by several weeks of inactivity. This finding was long overlooked until the recent growing interest in subseasonal-to-seasonal prediction of high-impact weather. Research in this area has uncovered that convectively coupled equatorial waves (CCEWs) can partly explain week-to-week tropical cyclone activity through modulations of environmental conditions. However, the physical processes behind that relationship remain unexplored because previous studies have relied on reanalysis datasets, which cannot capture the mesoscale and convective-scale processes that are ultimately necessary for tropical cyclogenesis. That limitation motivates this study, which aims at developing a modeling framework that can capture both planetary-scale waves and tropical cyclones, while using that framework to explore if and how CCEWs modulate tropical cyclogenesis. In the first part of this talk, I will describe the modeling framework—aquaplanet experiments using the Model for Prediction Across Scales-Atmosphere (MPAS-A). I will demonstrate that the MPAS-A aquaplanet experiments produce a climate and weather systems that are consistent with other models and with the real world. In the second part, I will demonstrate that a relationship exists between CCEWs and TC activity in the aquaplanet experiments, but the relationship is different from that identified using reanalysis datasets and it depends on the horizontal grid spacing of the simulations.

Presented by

Dr. Ángel F. Adames-Corraliza
Assistant Professor
Department of Atmospheric and Oceanic Sciences
University of Wisconsin-Madison

Wednesday, October 21, 2020

To view the recording, please follow this link:  http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Angel Adames-Corraliza 20201021.mp4

Abstract:

A linear two-layer model is used to elucidate the role of prognostic moisture on quasi-geostrophic (QG) motions in the presence of a mean thermal wind. Solutions to the basic equations reveal two instabilities.  The well-documented baroclinic instability is characterized by growth at the synoptic scale (horizontal scale of∼1000 km) and systems that grow from this instability tilt against the shear.  Moisture-vortex instability— an instability that occurs when moisture and lower-tropospheric vorticity exhibit an in-phase component— exists only when moisture is prognostic.  The instability is also strongest at the synoptic scale, but systems that grow from it exhibit a vertically-stacked structure.  When moisture is prognostic, baroclinic instability exhibits a pronounced weakening when the thermal wind is easterly. On the other hand, moisture-vortex instability is strongest in this mean state. Based on these results, it is hypothesized that moisture-vortex instability is the dominant instability in humid regions of easterly thermal wind such as the South Asian and African monsoons.

Presented by

Dr. Kathy Quardokus Fisher
Assistant Professor
Department of Earth and Environment
STEM Transformation Institute
Florida International University

Wednesday, October 14, 2020

To view the recording, please follow this link:  http://www.soest.hawaii.edu/met/seminar_recordings/ATMO 765 Seminar presented by Kathy Quardokus Fisher 20201014.mp4

Abstract:

Diverse and inclusive universities and workplaces lead to improvements in science through increased innovation and complex problem solving. The discipline of atmospheric science in the United States has faced challenges in attracting and retaining scientists who are women, people of color, Black, Indigenous, from the LBGTQ community, and people with disabilities. Many of these scientists leave because of exclusive cultures. As concerned members of the atmospheric science community, this may lead one to ask: how can I be an agent of change? Years of research on diversity training have found that simply having the desire to be inclusive does not result in inclusivity. Instead, change needs to happen at the organizational and system level. As individuals, we are part of social systems (e.g., departments, professional societies, institutions) that can be challenging to navigate and change. This seminar will explore how individuals in a community can conceptualize an organization and their potential for enacting change by analyzing their social connections, knowledge and skills, and formal responsibilities. This discussion will be guided by specific examples of creating change in the geosciences from research on a professional development program – Hearts of GOLD (Geo Opportunities for Leadership in Diversity).