Energetic Constraints on the ITCZ Position in Idealized Simulations with a Seasonal Cycle

The atmospheric energy budget has recently been shown to provide powerful constraints on the position and shifts of the zonal and annual mean intertropical convergence zone (ITCZ), which lies close to the latitude of zero vertically integrated energy transport (energy flux equator, EFE). Relatively little work has however explored the applicability of the energetic framework to ITCZ shifts on shorter timescales. This study investigates to what extent the EFE tracks the ITCZ on subseasonal timescales in idealized aquaplanet simulations with different mixed layer depths. It is shown that the ITCZ always lags the EFE, even in the simulation with the shallowest mixed layer depth, making it possible for the EFE and the ITCZ to reside on opposite sides of the equator. At these times, which occur as the winter cross‐equatorial Hadley circulation retreats from the summer hemisphere, the required energy balance is achieved not through shifts of the Hadley cell's ascending branch and ITCZ to track the EFE but through changes in the cell's vertical structure into one of negative gross moist stability (GMS). For any given position of the ascending branch, the winter cell is much weaker as it retreats from than as it expands into the summer hemisphere and develops a shallow return flow at mid‐to‐lower tropospheric levels where the moist static energy reaches its minimum, hence favoring a negative GMS. It is argued that the asymmetry between the expanding and retreating phases of the winter Hadley cell is linked to the nonlinear seasonal evolution of near‐surface temperatures

On the Role of the African Topography in the South Asian Monsoon

The Somali jet, a strong low-level cross-equatorial flow concentrated in a narrow longitudinal band near the coast of Somalia, is a key feature of the South Asian monsoon (SAM) circulation. Previous work has emphasized the role of the East African highlands in strengthening and concentrating the jet. However, the fundamental dynamics of the jet remains debated, as does its relation to the SAM precipitation. In this study, numerical experiments with modified topography over Africa are conducted with the GFDL atmospheric model, version 2.1 (AM2.1), general circulation model (GCM) to examine the influence of topography on the Somali jet and the SAM precipitation. It is found that when the African topography is removed, the SAM precipitation moderately increases in spite of a weakening of the cross-equatorial Somali jet. The counterintuitive precipitation increase is related to lower-level cyclonic wind anomalies, and associated meridional moisture convergence, which develop over the Arabian Sea in the absence of the African topography. Potential vorticity (PV) budget analyses along particle trajectories show that this cyclonic anomaly primarily arises because, in the absence of the blocking effect by the African topography and with weaker cross-equatorial flow, air particles originate from higher latitudes with larger background planetary vorticity and thus larger PV

Energetic Constraints on the Intertropical Convergence Zone Position in the Observed Seasonal Cycle From Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

Idealized simulations show that the approximate colocation between the ITCZ and the energy flux equator (EFE), which holds on the annual and zonal average, breaks down on subseasonal timescales, as the Hadley cell develops a shallow return flow and negative gross moist stability (GMS). Here, we explore if similar mechanisms are seen in reanalysis data. In the zonal mean, a temporal offset exists between the ITCZ and the EFE as the ITCZ is retreating from the Northern to Southern Hemisphere and the Hadley cell transports energy northward across the equator despite a northward‐shifted ITCZ. At these times, the southern cell has a bottom‐heavy structure, with a distorted cell boundary and northward energy transport. In the Eastern Pacific, while bottom‐heavy structures exist throughout the year, the bottom heaviness is stronger in boreal fall, when GMS is negative, and SSTs are weak while their Laplacian is large and negative below the ITCZ

Energetic Constraints on the Intertropical Convergence Zone Position in the Observed Seasonal Cycle From Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

Idealized simulations show that the approximate colocation between the ITCZ and the energy flux equator (EFE), which holds on the annual and zonal average, breaks down on subseasonal timescales, as the Hadley cell develops a shallow return flow and negative gross moist stability (GMS). Here, we explore if similar mechanisms are seen in reanalysis data. In the zonal mean, a temporal offset exists between the ITCZ and the EFE as the ITCZ is retreating from the Northern to Southern Hemisphere and the Hadley cell transports energy northward across the equator despite a northward‐shifted ITCZ. At these times, the southern cell has a bottom‐heavy structure, with a distorted cell boundary and northward energy transport. In the Eastern Pacific, while bottom‐heavy structures exist throughout the year, the bottom heaviness is stronger in boreal fall, when GMS is negative, and SSTs are weak while their Laplacian is large and negative below the ITCZ

Design, fabrication and characterization of polypyrrole trilayer actuators

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (leaf 48).Conducting polymers are currently studied as artificial muscle materials. They are used instead of traditional actuators because they mimic the movements of animal muscles. They can generate larger active stresses than real muscles as well as generate small strains which can be amplified to cause larger motions. Traditionally, conductive polymers are immersed in liquid electrolytes. Utilizing a trilayer configuration by sandwiching the ions between two strips of polypyrrole films can be actuated in air. This thesis compares two methods of constructing polypyrrole trilayers: an electrolyte gel method and a gold coated PVDF membrane method. It will discuss the construction processes as well as properties of resulting trilayers by looking at force production, strain rate, etc.by Wei Hsuan (Jessie) Ho.S.B

Selection Determinants In Education Major Graduates Occupations

Taiwan’s teacher training system currently faces a serious disorder. The excessive number of teacher education programs being set up in universities by the Ministry of Education has dramatically increased the number of teachers. The situation, coupled with the country of low birth rate and high retirement age, brings about fewer teaching vacancies than the number of available teachers. The over-expansion of universities has resulted in a situation that almost every secondary school graduate can access higher education institutions, which subsequently produce a great number of graduates, far exceeding the vacancies in the workplace. This plus with the recent economic recession intensifies competition among individuals hunting for jobs. Thus, it is imperative to identify the ideal jobs for graduates, and the first step is figuring out the main determinants for selecting jobs and the relative importance of these determinants. A self-developed questionnaire was administered to 200 education major graduates in Taiwan. The result indicated that high job stability was perceived to be the most important factor among participants. Also, the education students considered school teacher or administrator to be the ideal jobs

Dynamics of Seasonally-Varying Tropical Convergence Zones

In the tropics, rain tends to be organized along concentrated rain bands, with the Intertropical Convergence Zone (ITCZ) over the ocean and monsoonal convergence zones over tropical land masses being particularly prominent features affecting hundreds of millions of people. What fundamentally controls the spatial and temporal distribution of these tropical rainbands remains an outstanding question in the literature. This thesis aims to enhance our understanding of the dynamics of seasonally migrating convergence zones over the ocean and in the South Asian monsoon region. First, we explore to what extent energetic arguments that have provided insight into the position and shifts of the annual and zonal mean ITCZ can also be applied on shorter timescales. Idealized aquaplanet simulations show that the energy flux equator (EFE) always leads the ITCZ, leading to a breakdown of the commonly assumed anti-correlation between the ITCZ position and the cross-equatorial energy transport. At times during which the EFE and the ITCZ reside on opposite sides of the equator, the required energy transport is in fact achieved by the Hadley cell, in which the ITCZ is embedded, changing its vertical structure into one of negative gross moist stability. One way in which this is accomplished is through the development of a shallow return flow at levels near minimum moist static energy. While the relationship between the EFE and the ITCZ in the observed seasonal cycle is more complex than what is seen in the idealized simulations, the development of bottom-heavy circulations is a common feature both in the zonal mean and in individual longitudinal sectors at times when the EFE and the ITCZ are in opposite hemispheres. In the last chapter of this thesis, we explore changes in the South Asian monsoon as topography over Africa is removed in the full-physics GFDL AM2.1 GCM. Against expectations, the removal of the African topography is accompanied by a strengthening of the precipitation over India despite a weakening of the Somali jet. This counter-intuitive precipitation increase is associated with the development of a lower-level cyclonic wind anomaly, and associated meridional moisture flux convergence, over the Indian peninsula. Potential vorticity (PV) budget analyses following air parcel trajectories show that this cyclonic anomaly arises because, in the absence of the blocking effect of the African topography, air particles that reach the Arabian Sea originate at higher latitude and hence have a higher background planetary vorticity.</p

Enhancing The Quality Of University Career Services In Taiwan: Perceptions Of University Alumni

An adequate supply of a high quality labor force is crucial for national economic and social well-being; consequently, nations worldwide have placed significant emphasis on university graduate employability. Nonetheless, in Taiwan, a mismatch between knowledge acquired in universities and competences required by the job market has dramatically encumbered the supply of a high quality labor force. Thus, this research endeavored to determine the major career services that should be offered in higher educational institutions to alleviate the aforementioned human resource problems.The analytic hierarchy process was adopted as the major instrument for calculating the relative importance of each career service task, and 169 university alumni working&nbsp;in four major career fields participated in this&nbsp;research. The results indicated that participants from&nbsp;different career fields and who graduated from different colleges at different times have very different opinions of job service requests; therefore, universities should seriously consider the differences among students and provide the necessary services for each student in line with his/her particular requests. Moreover, although almost all participants agreed that sharpening students’ job-search and interview skills was crucial in assisting students to find their first jobs, this service was extremely insufficient in universities, and universities thus have to place particular emphasis on this task in the future

Energetic Constraints on the ITCZ Position in Idealized Simulations with a Seasonal Cycle

The atmospheric energy budget has recently been shown to provide powerful constraints on the position and shifts of the zonal and annual mean intertropical convergence zone (ITCZ), which lies close to the latitude of zero vertically integrated energy transport (energy flux equator, EFE). Relatively little work has however explored the applicability of the energetic framework to ITCZ shifts on shorter timescales. This study investigates to what extent the EFE tracks the ITCZ on subseasonal timescales in idealized aquaplanet simulations with different mixed layer depths. It is shown that the ITCZ always lags the EFE, even in the simulation with the shallowest mixed layer depth, making it possible for the EFE and the ITCZ to reside on opposite sides of the equator. At these times, which occur as the winter cross‐equatorial Hadley circulation retreats from the summer hemisphere, the required energy balance is achieved not through shifts of the Hadley cell's ascending branch and ITCZ to track the EFE but through changes in the cell's vertical structure into one of negative gross moist stability (GMS). For any given position of the ascending branch, the winter cell is much weaker as it retreats from than as it expands into the summer hemisphere and develops a shallow return flow at mid‐to‐lower tropospheric levels where the moist static energy reaches its minimum, hence favoring a negative GMS. It is argued that the asymmetry between the expanding and retreating phases of the winter Hadley cell is linked to the nonlinear seasonal evolution of near‐surface temperatures