Doctor of Philosophy

dissertationChanges in the stratospheric circulation have the potential to affect weather and climate in the troposphere, especially over the high latitudes. In order to better understand such influences, we analyze the relationships among stratospheric, tropospheric, and oceanic variability. We reach our goal with the aid of coupled chemistry-climate models and coupled atmosphere-ocean models. Over the past decades, ozone depletion in the Antarctic stratosphere has been accelerating the poleward side of the stratospheric polar vortex. We suspect that the change in the winds in turn affects the concentrations of ozone. This idea is investigated with coupled chemistry-climate models. We find a strong indication for the existence of a positive feedback between ozone depletion and change in the circulation: the chemical ozone loss feeds back into the stratospheric circulation, and changes in the circulation produce more ozone deficit. Climate models tend to systematically overestimate the persistence time scale of extratropical variability, in particular over the Southern Hemisphere. The systematic overestimation in climate models raises the concern that the models are overly sensitive to external forcings and that future projections based on those models are unreliable. We investigate issues concerning the persistence time scale of the annular mode using reanalysis and model data. We find that the 50-year record of historical observations is probably too short to derive a stable estimate of the annular mode time scale that may be used to evaluate climate models. We also find a robust relationship between the magnitude and the seasonal timing of the time scale in both stratosphere and troposphere, confirming and extending earlier results of a dynamical coupling between the stratosphere and the troposphere and of influences of stratospheric variability on the troposphere. Extreme events in the stratosphere are known to alter tropospheric weather and climate. However, it is still unclear whether the stratosphere also has the capacity to affect the ocean and its circulation. This possibility is suggested from observations which show low-frequency covariability between the stratosphere and the Atlantic thermohaline circulation. We use simulations from coupled atmosphere-ocean models to explore more systematically a possible stratospheric influence on the oceanic circulation over the North Atlantic Ocean on multidecadal time scales. Our analysis identifies the stratosphere as a previously unknown source for decadal climate variability in the troposphere and suggests that the stratosphere forms an important component of climate that should be well represented in models

A stratospheric connection to Atlantic climate variability

pre-printIt is well recognized that the stratosphere is connected to tropospheric weather and climate. In particular, extreme stratospheric circulation events and their dynamical feedback on the troposphere are known to play a major role1. However, what is not known to date is whether the state of the stratosphere also matters for the ocean and its circulation. Previous research suggests co-variability of decadal stratospheric flow variations and conditions in the North Atlantic Ocean, but such findings are based on short simulations with only one climate model2. Here we report that over the past 30 years the stratosphere and the Atlantic thermohaline circulation underwent low-frequency variations that were similar to each other

Synthetic aperture radar satellite imaging of Earth’s upper atmosphere and its potential application for upcoming Venus missions

Modern space-borne synthetic aperture radar satellite (SAR) can provide meter-scale resolution imaging of Earth’s ground surface. When SAR radio waves undergo propagation effects from the ionized atmosphere between the satellite and ground, the resulting SAR image contains information of the atmospheric plasma structures. Recent studies show that plasma density structures in Earth’s ionosphere can be captured in L-band SAR images. Different SAR processing techniques using interferometry and sub-band data have been developed to extract the two-dimensional variation of plasma density irregularities We present case studies of SAR imaging of Earth ionospheric density and discuss its potential application for recently selected SAR missions for Venus, whose ionosphere is not yet fully understood

Imaging ionospheric irregularities by earth observation radar satellite

The sensitivity of Synthetic Aperture Radar (SAR) satellite signal in the L-band to ionospheric plasma density is used to obtain two-dimensional imaging of ionospheric density irregularities. As an application for equatorial ionosphere, we have recently reported first simultaneous observation of equatorial plasma bubble by the ALOS-2/PALSAR-2 satellite and a ground 630-nm airglow imager in northern Brazil. In this case, SAR ionospheric scintillation are represented as stripe-like signature of radar image over the terrain along the local magnetic field lines near an airglow depletion region. This so-called SAR scintillation stripes are discussed to be the signature of existing small-scale plasma irregularities with the scale size of hundreds of meters associated with equatorial plasma bubbles. We present the observational setup and the interpretation of SAR signal parameters to characterize the two-dimensional ionospheric density structures, and discuss future studies

Design of an E-SCM System for an Auto-parts Companies

This paper deals with the design of e-SCM for a supply chain of a commercial vehicle company. Two first vendors and two second vendors of the company are included in the objects of developing e-SCM system. We analyzed the information flow and business process between 1st vendor and 2nd vendors. The database (DB) has to be designed for contents of easy access, correction and update, because DB is indispensable for developing the new system. A relational database concept was used to design tables which maintain data needed in the system. The paper uses data flow diagram to describe TO-BE model of the e-SCM system

DroneBased Parcel Delivery Using the Rooftops of City Buildings: Model and Solution

In general, the demand for delivery cannot be fulfilled efficiently due to the excessive traffic in dense urban areas. Therefore, many innovative concepts for intelligent transportation of freight have recently been developed. One of these concepts relies on drone-based parcel delivery using rooftops of city buildings. To apply drone logistics system in cities, the operation design should be adequately prepared. In this regard, a mixed integer programming model for drone operation planning and a heuristic based on block stacking are newly proposed to provide solutions. Additionally, numerical experiments with three different problem sizes are conducted to check the feasibility of the proposed model and to assess the performance of the proposed heuristic. The experimental results show that the proposed model seems to be viable and that the developed heuristic provides very good operation plans in terms of the optimality gap and the computation time. Document type: Articl

Regional characteristics of fine aerosol mass increase elucidated from long-term observations and KORUS-AQ campaign at a Northeast Asian background site

Funding Information: This research was supported by the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (MSIT) (NRF2020M3G1A111499813). S. Lim was supported by the National Research Foundation of Korea (NRF) from the Ministry of Science and ICT (2018R1D1A1B07050849 and 2021R1C1C2011543). M. Lee thanks to the support by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF2020R1A2C301459213). S.-W. Kim was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2017R1D1A1B06032548). Funding to K.-S. Kang was provided by the National Institute of Environmental Research (NIER-RP2017-166). Funding Information: This research was supported by the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (MSIT) (NRF2020M3G1A111499813). S. Lim was supported by the National Research Foundation of Korea (NRF) from the Ministry of Science and ICT (2018R1D1A1B07050849 and 2021R1C1C2011543). M. Lee thanks to the support by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF2020R1A2C301459213). S.-W. Kim was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2017R1D1A1B06032548). Funding to K.-S. Kang was provided by the National Institute of Environmental Research (NIER-RP2017-166). Publisher Copyright: © 2022 The Author(s)Northeast Asia has suffered from severe PM2.5 pollution and the exact mechanisms have yet to be fully understood. Here, we investigated the transformation processes of submicron aerosols using a 4-year data set obtained at Jeju, a Northeast Asian background site. The diurnal-cycle constrained empirical orthogonal function analysis of nanoparticle size-number distribution distinguished 2 modes: burst of nucleation-Aitken particles and increase in accumulation mode particles, representing “new particle formation and growth” and “PM2.5 mass increase,” respectively. In these events, aerosol and meteorological characteristics changed progressively over several days, revealing that the PM2.5 mass increase is an episodic event occurring on a regional scale. The increase in PM2.5 mass was accompanied by an increase in aerosol liquid water content, which correlated well with SO4-2 and NO3, and a decrease in incoming solar radiation (-14.1 Wm-2 day-1) constituting a positive feedback. The “transport/haze” episode of KOREA-U.S. Air Quality campaign corresponds to “PM2.5 mass increase,” during which the vertical evolution of particles demonstrates that nanoparticles ≥3.5 nm were entrained into the shallow boundary layer upon vertical mixing and converted to accumulation-mode particles ≥0.3 mm at relative humidity (RH) exceeding the deliquescence RH of secondary inorganic aerosol (SIA). Coincidently, at ground, the coating thickness of refractory black carbon (rBC) (48 ± 39 nm) and SIA concentration increased. Furthermore, the diameter of rBC (180-220 nm)-containing particle in core-shell configuration linearly increased with PM2.5 mass, reaching 300-400 nm at PM2.5 ≥ 40 mg m-3.This observational evidence suggests that the thick coating of rBCs resulted from the active conversion of condensable gases into the particulate phase on the rBC surface, thereby increasing the mass of the accumulation-mode aerosol. Consequently, this result complies with the strategy to reduce primary emissions of gaseous precursors for SIA and particulates such as rBC as a way to effectively mitigate haze pollution as well as climate change in Northeast Asia.Peer reviewe

Tuning-free controller to accurately regulate flow rates in a microfluidic network

We describe a control algorithm that can improve accuracy and stability of flow regulation in a microfluidic network that uses a conventional pressure pump system. The algorithm enables simultaneous and independent control of fluid flows in multiple micro-channels of a microfluidic network, but does not require any model parameters or tuning process. We investigate robustness and optimality of the proposed control algorithm and those are verified by simulations and experiments. In addition, the control algorithm is compared with a conventional PID controller to show that the proposed control algorithm resolves critical problems induced by the PID control. The capability of the control algorithm can be used not only in high-precision flow regulation in the presence of disturbance, but in some useful functions for lab-on-a-chip devices such as regulation of volumetric flow rate, interface position control of two laminar flows, valveless flow switching, droplet generation and particle manipulation. We demonstrate those functions and also suggest further potential biological applications which can be accomplished by the proposed control framework.open1142sciescopu