1 |
The frequency of tropopause-level thick and thin cirrus clouds as observed by CALIPSO and the relationship to relative humidity and outgoing longwave radiationCardona, Allison Leanne 10 October 2008 (has links)
Thin cirrus clouds play an important radiative role in the earth's atmosphere and
climate system, yet are one of the least understood components of the climate system.
With the use of data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observations (CALIPSO), thin cirrus and thick cloud distributions in the tropics are
analyzed at 121, 100, and 82 hPa. Observations obtained between December 2006 and
November 2007 show that thin cirrus between 30°N and 30°S occur in close proximity
to regions of intense convection and are positively correlated with low values of
outgoing longwave radiation (OLR).
In conjunction with the CALIPSO data, water vapor data from the Earth
Observing System (EOS) Microwave Limb Sounder (MLS), OLR data provided by the
NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at
http://www.cdc.noaa.gov/, and linearly interpolated NCEP reanalysis temperature data
were used. These data were used to examine how thick and thin cirrus cloud fractions at
121-hPa and 100-hPa are related to relative humidity with respect to ice (RHI), temperature, and OLR. Our observations show that both RHI and convection play
important roles in the development and maintenance of thick and thin cirrus clouds at the
pressure levels of interest. The highest fractions of clouds are almost always seen within
OLR values representative of convection and at relatively high values of RHI. However,
when peaks in cloud fraction are found above the convective threshold, higher RHI
values are needed than are needed when convection is responsible for the formation and
maintenance of these clouds.
|
2 |
Zjišťování dopadu disruptivních business modelů na české outgoingové cestovní kanceláře / Assessing the impact of disruptive business models on the Czech outbound travel agencyChreno, Petr January 2017 (has links)
The diploma thesis focuses on the identification of the impact of disruptive models in tourism at the Czech travel operators. The theoretical part describes the business model using the canvas method. Subsequently, various patterns of disruptive business models in tourism market are presented. In the practical part, a research was carried out to find out how Czech citizens use disruptive models for traveling abroad. Based on the results of research in the context of different areas, the impact of disruptive models on travel operators was assessed. This work did not confirm the direct negative impact of these models on the growth of Czech travel agencies, but points out the future threat that these disruptive models will introduce in the years to come
|
3 |
De vill bli förstådda : En kvalitativ studie om fritidshemslärarnas tolkning av utåtagerande elever i verksamheten / They want to be understood : A qualitative study of the leisure center teachers’ interpretation of outgoing students in the activityIbrahim Aden, Fatima, Kahsay, Meri January 2022 (has links)
The purpose of the study is to find out that the leisure time teachers’ interpretation of outgoing students and how they work to prevent it in the after-school program. In addition, it is observed the working methods of leisure time teachers’ and the influence of communication in the dealing of outgoing students. The study is based on three research questions that are relevant to find out the issue. To answer research questions, we have used a qualitative method where data was collected through interviews with four educated leisure time teachers in two schools. The study’s theoretical perspectives are based on the categorial, relational and micro-relations perspective. The result is analyzed based on the selected theoretical perspective in order to achieve a deeper understanding in the processing of the collected data from interviews. The result of the study shows that the interviewed leisure time teachers are aware of the afterschool centers mission and their role as the teachers in the after-school programs is to create a meaningful leisure time for all students. In addition, the result shows that outgoing students end up in categories, consciously or unconsciously, because the student’s actions explain based on the expected normality. The leisure time teachers agree that there is a lack of competent stuff, time, and resources to meet the outgoing students in the after-school programs.
|
4 |
Hållbarhet i leveranskedjan : Miljöpåverkan av transporter inom klädbranschen / Sustainable Supply chain : The environmental impact of transport in the clothing industryLi, Zhihao, Sezkir, David January 2019 (has links)
Miljön har blivit en allt mer vital fråga. För att öka vår bekvämhet har det lett att vi har orsakat mycket negativa effekter på miljön. En stor del orsakas av våra dagliga oaktsamma aktiviteter. Många diskussioner har tagits upp kring detta problem. En punk som har stor vikt inom dessa diskussioner handlar om negativa påverkan av miljoner transporter som sker dagligen. Klädbranschen är en av de branscherna som bidrar till en stor del av alla transporter. En grund av denna ökade transport är en ökad efterfrågan på onlinehandel av fast fashion och en mogen global marknad. Därför syftar studie att undersöka hur olika klädföretag rapporterar transporter av deras in- och utleveranser och hur detta påverkar miljön. Ytterligare kommer studien att analysera vilken information de utvalda företagen redovisar i sina publicerade rapporter. Den valda forskningsstrategin är en kvalitativ forskning. Studien består av en innehållsanalys av tretton utvalda företags årsrapporter och/eller hållbarhetsrapporter. Datan som samlats in från rapporterna är olika leveranssätt samt utsläpp, leveransoptimering och framtida strategier/mål. Sekundära data har använts som primära data i studien för att sedan med hjälp av grundad teori har analyserats och lett till slutsatsen. Genom analys av rapporterna har vi upptäckt att exempelvis flera av de utvalda företagen lyft fram deras mål med stora siffror, men den information som inte var lika positiv skrevs med en finare stil. Därför har vi dragit en slutsats att de mer eller mindre har grönmålat deras verksamhet inom hållbarhetsområdet. Vi har kommit fram till att många företag har förmågan att påverka sina leverantörer och transportörer, men sällan har de gjort eller rapporterat det. En annan slutsats vi har dragit är att många företag inte har rapporterat miljöpåverkan som orsakas av transporter tillräckligt och vissa inte heller har framtida lösningar. Vidare forskning skulle en jämförelse mellan e-handelsföretag och fysiska företag göras genom att undersöka hur stor andel av hållbarhetsrapporten företagen väljer att skriva om miljöpåverkan. Ett annat förslag kan vara att jämföra ett företags rapporter över tid för att kunna se om de har förändrat det sättet att rapportera när det gäller miljöpåverkan som orsakas av transporter över åren. / The environment has become an increasingly vital issue. In order to increase our comfort, it has led to very negative effects on the environment. A large part is caused by our daily negligent activities. Many discussions have been raised on this issue. One thing that has great importance in these discussions is about the negative impact of millions of transports that take place daily. The clothing industry is one of the industries that contributes to a large part of all transports. One reason for this increased transport is the increased demand for online shopping of fast fashion and a mature global market. Therefore, the study aims to investigate how different clothing companies report their in and out deliveries and how this affects the environment. Furthermore, the study will analyze what information the selected companies report in their published reports. The chosen research strategy is a qualitative research. The study consists of a content analysis of thirteen selected companies' annual reports and / or sustainability reports. The data collected from the reports are different delivery methods, emissions, delivery optimization and future strategies / goals. Secondary data has been used as primary data in the study and with the use of grounded theory it has been analyzed and led to the conclusion. Through analysis of the reports, we have discovered that, for example, several of the selected companies highlight their goals with large numbers, but the information that was not as positive was written indistinct. Therefore, we have concluded that they have more or less greenwashed their published report, we have come to the conclusion that many companies have the ability to influence their suppliers and transporters, but rarely have they made or reported it. Another conclusion we have drawn is that many companies have not reported the environmental impact caused by transport enough and some do not have future solutions either. Further research would make a comparison between e-commerce companies and physical companies by examining how large a proportion of the sustainability report companies choose to write about the environmental impact. Another proposal may be to compare a company's reports over time to see if they have changed the way of reporting when it comes to the environmental impact caused by transport over the years.
|
5 |
Holistický přístup k pozůstalým při náhlém úmrtí z pohledu všeobecné sestry, členky výjezdového týmu záchranné služby / A holistic approach to the bereaved in case of a sudden death from a nurse´s point of view a member of the medical emergency servicesGUTOVÁ, Alena January 2013 (has links)
The dissertation deals with holistic approach of nursing staff of the Rescue Service by providing pszchosicial support and crisis communication to the survivors or direct sudden death participants from nurse´s }member of the Rescue Service team]perspective. The goal of the dissertation has been 1. To detect problems which nursing staff members of the Rescue Service are prepared for communication with the survivors.
|
6 |
Padrões de anomalias da temperatura da superfície dos Oceanos Pacífico e Atlântico associados à Radiação de Onda Longa na América do Sul e à precipitação no Brasil.Reinke, Guilherme Lauxe, Reinke, Guilherme Lauxe 13 March 2009 (has links)
Made available in DSpace on 2014-08-20T14:25:47Z (GMT). No. of bitstreams: 1
dissertacao_guilherme_reinke.pdf: 5244899 bytes, checksum: 883a2f12008ef21f2da3eb9001e720b6 (MD5)
Previous issue date: 2009-03-13 / The main objective of the study was to obtain the relation between Pacific and
Atlantic Sea Surface Temperature (SST) anomalies and Outgoing Longwave
Radiation (OLR) anomalies in South America (SA) and, moreover, evaluate the
relationship of rainfall in Brazil to SST. Data from reanalysis of SST and OLR of the
NCEP/NCAR were used, between the months of October and March of the period
from 1982 to 2007, which was applied the statistical technique of Principal
Components (PC), allowing the study of the correlation between the two variables.
Data of precipitation of 691 stations in Brazil, obtained from the Instituto Nacional de
Meteorologia (INMET), Agência Nacional de Águas (ANA) and Fundação Estadual
de Pesquisa Agropecuária (FEPAGRO), were correlated with the scores of the SST
and were used to prepare the rainfall climatology in the country, which enabled the
understanding of the rainfall regime in spring and summer. Finally, a model was
developed to forecast of the rainfall in Brazil with two months for advance, between
December and March, using as predictors the first five scores of the SST. The
correlations between the PC1 of the SST and the PC1 of the OLR shown to be
significants at 1%, where the PC1 of SST is related with the ENSO pattern, showing
in October: desintensification or intensification of convection in central and southern
of Argentina; November: opposite pattern of OLR anomalies between south of Brazil
and the area of activity of the South Atlantic Convergence Zone (SACZ); January:
reduction or increase of convection in the northwestern of SA; December, February
and March: intensification or desintensification of convection associated with the
Bolivian High, and also in north of the North and Northeast Regions of Brazil.
Moreover, in all months of the study, the PC2 of the SST showed the indication of a
dipole pattern between the Central and Equatorial Atlantic adjacent to the
northeastern coast of Brazil, and South Atlantic, in middle latitudes. In October,
November and March, OLR anomalies areas associated with a pattern of more
oceanic SACZ seem to be directly related to a strong gradient of SST anomalies, with
positive anomalies in the northeast coast of Brazil and negative anomalies on the
south-southeast coast of the country. When it was of the SST with the rainfall in
Brazil, it was found in the months of November, December and January, similar
patterns seen in the correlations between the SST and OLR. In the four months in
which the model was applied to predict the rainfall, it was noted that South and
Northeast regions of Brazil have the best potential for forecasting. / O principal objetivo do estudo foi obter a relação entre anomalias de Temperatura da
Superfície do Mar (TSM) dos Oceanos Pacífico e Atlântico e anomalias de Radiação
de Onda Longa (ROL) na América do Sul (AS) e, além disso, avaliar a relação da
TSM com a precipitação no Brasil. Foram utilizados dados de reanálises de TSM e
ROL do NCEP/NCAR, entre os meses de outubro a março do período de 1982 até
2007, aos quais foi aplicada a técnica estatística de Componentes Principais (CP),
possibilitando o estudo da correlação entre as duas variáveis. Dados de precipitação
de 691 estações no Brasil, obtidos junto ao Instituto Nacional de Meteorologia
(INMET), Agência Nacional de Águas (ANA) e Fundação Estadual de Pesquisa
Agropecuária (FEPAGRO), foram correlacionados com os escores da TSM e usados
na elaboração da climatologia da precipitação no país, que permitiu um
entendimento do regime de chuvas nos períodos de primavera e verão. Por fim, foi
desenvolvido um modelo de previsão da precipitação no Brasil com dois meses de
antecedência, entre dezembro e março, usando como preditores os cinco primeiros
escores da TSM. As correlações entre a CP1 da TSM e a CP1 da ROL mostraram
ser significativas a 1%, em que a CP1 da TSM está relacionada com o padrão
ENOS, apresentando em outubro: intensificação ou desintensificação da convecção
no centro e sul da Argentina; novembro: padrão oposto de anomalias de ROL entre
o Sul do Brasil e a área de atuação da Zona de Convergência do Atlântico Sul
(ZCAS); janeiro: redução ou aumento da convecção no noroeste da AS; dezembro,
fevereiro e março: intensificação ou desintensificação da convecção associada à Alta
da Bolívia e, também, no norte das Regiões Norte e Nordeste do Brasil. Além disso,
em todos os meses do estudo, a CP2 da TSM mostrou no Oceano Atlântico a
indicação de um padrão de dipolo entre o Atlântico Equatorial e Central adjacente à
costa Nordeste do Brasil, e o Atlântico Sul, em latitudes médias. Em outubro,
novembro e março, áreas de anomalias de ROL associadas com um padrão de
ZCAS mais oceânica parecem estar diretamente relacionadas com um forte
gradiente de anomalias de TSM, com anomalias positivas na costa nordeste do
Brasil e negativas na costa Sul-Sudeste do país. Ao relacionar a TSM com a
precipitação no Brasil foram encontrados nos meses de novembro, dezembro e
janeiro, padrões semelhantes aos vistos nas correlações entre a TSM e ROL. Nos
quatro meses em que foi aplicado o modelo de previsão da precipitação, pôde-se
notar que as Regiões Sul e Nordeste do Brasil apresentam os melhores potenciais
para a previsão.
|
7 |
När inkludering blir exkludering : En essä om hur man tar sig an rollen som elevassistent till ett barn med NPFBlomhage Engdahl, Matilda January 2020 (has links)
Syftet med denna essä är att undersöka hur elever med NPF (neuropsykiska funktionsnedsättningar) kan bli inkluderade i skolan och på fritidshemmet, samt öka kunskapen kring hur lärare ska bemöta elever med NPF. Denna uppsats är skriven i essäform. I essän delar jag med mig av händelser där dilemman uppstått från min yrkeserfarenhet gällande en elev med NPF. I början av essän försöker jag, genom att berätta om några konkreta händelser från mitt arbete som assistent till en pojke med NPF, få läsaren att se vad mitt arbete innebär. Essän har fyra frågeställningar som uppsatsen utgår från: Hur ska jag inkludera elever i behov av stöd på bästa sätt på fritidshemmet men även i klassrummet? Vilka kunskaper hade jag behövt för att möta Noel på bästa sätt? Vem ansvarar för Noels skolgång och tillvaro? Vad hade behövts för skapa en hållbar arbetssituation för mig? Essän avslutas med en reflektion kring resultatet som framkommit i essän. Jag har genom denna essä kommit till slutsatsen om att teoretisk kunskap är en viktigt del i arbete med elever med NPF. / The purpose of this essay is to investigate how students with NPF (neuropsychiatric disabilities) can be included in school and at the after-school center, as well as increase knowledge about how teachers should treat students with NPF. This article is written in essay form. In the essay, I share events where dilemmas have arisen from my own professional experience regarding a student with NPF. At the beginning of the essay, by telling a story about my own work with a boy with NPF, I try to involve a readers a wittnes of my work etails. The essay deals with four questions on which the essay is based: How should I include students in need of support in the best way in the after-school center but also in the classroom? What knowledge would I have needed to meet Noel in the best way? Who is responsible for Noel's schooling and existence? What would have been needed to create a sustainable work situation for me? The essay ends with a reflection on the results that have emerged in the essay. Through this essay, I have come to the conclusion that theoretical knowledge is an important part of working with students with NPF.
|
8 |
Suggested actions to improve the warehouse layout at Nordic E-commerce groupEricsson, Sandra, Frid, Marielle January 2013 (has links)
Background: Nordic E-commerce group (NECG) consists of affiliated companies NordicInk, NordicFeel and PetsOnline. Three different types of companies in one warehouse area contribute to a wide range of products held in inventory. NECG’s problem derives in the fact that the company’s warehouse layout needs to handle a larger volume of sales, but is not capable of doing this in a structured way today. This matter of fact has led to new thoughts concerning improvements of the layout. The warehouse layout referred to in this thesis includes input and output doors, receiving and outgoing areas, material handling equipment and the placement of articles in inventory. Although article placement is per definition a part of warehouse layout, it will be given extra emphasis in this thesis as it is one of NECG’s most critical issues. Purpose: The purpose of this thesis is to identify NECG’s current warehouse layout and article placement and the problems associated with it, as well as to provide suggested actions for improvements. This is to be done so NECG can better utilize the warehouse space, and thus prepare the warehouse to handle a larger volume of sales. Methodology: Qualitative and quantitative data was collected through semi-structured interviews and observations at NECG, as well as through excel files containing transactional data for NordicInk’s products. Through a non-probability, snowball selection the respondents were chosen. There have not been any requirements from NECG regarding confidentiality in terms of the warehouse layout. Findings: There are a number of suggested actions that NECG may apply to improve the warehouse layout; two separate doors for incoming and outgoing deliveries, one designated receiving and one outgoing area, and a flow shop layout combined with a U-form layout would be the most beneficial for NECG’s warehouse. Furthermore, NECG needs a more consistent article placement and it is recommended for the company to apply a floating location system to its high-picked products and a fixed location system for its low-picked products. This will make NECG take better use of the available space and a more structured warehouse will be achieved. / Bakgrund: Nordic E-commerce Group (NECG) består utav dotterbolagen NordicInk, NordicFeel och PetsOnline. Då lagret består utav tre olika företag finns ett brett utbud av produkter. NECG:s problem härrör i att företagets lagerlayout inte har följt med i företagets utveckling. För att kunna hantera en större försäljningsvolym, behöver lagerområdet kunna hantera nuvarande och framtida lagervolymer, men är inte kapabel till att göra detta på ett strukturerat sätt i dag. Detta har lett till nya tankar om förbättringsförslag kring lagerlayout. I detta examensarbete avser lagerlayout ingående och utgående portar, inkommande och utgående lagringsområden, materialhanteringsutrustning och artikelplacering i lager. Även om artikeln placering är per definition en del av lagerlayout, kommer det att ges extra fokus i detta examensarbete eftersom det är en av NECG mest kritiska frågor. Syfte: Syftet med detta examensarbete är att identifiera NECG nuvarande lagerlayout och artikel placering samt vilka eventuella problem som finns, för att kunna ge förslag på förbättringar. Detta ska göras så att NECG kan utnyttja sitt lagerutrymme bättre och förbereda sig inför ökade försäljningsvolymer. Metod: Kvalitativ och kvantitativ data samlades in genom semistrukturerade intervjuer och observationer på NECG, samt genom excel filer innehållande transaktionsdata kring NordicInk’s produkter. Genom ett icke-sannolikt, snöbollsurval valdes respondenterna ut. NECG har inte uttryckt några krav om att sekretessbelägga arbetet kring lagerlayout. Resultat: Det finns ett antal förslag på åtgärder som NECG kan tillämpa för att förbättra lagerlayouten: två separata dörrar för inkommande och utgående leveranser, ett designerat område för inkommande och ett för utgående leveranser samt en flow shop layout kombinerat med en U-form layout skulle vara mest fördelaktigt för NECG:s lager. Vidare behöver NECG en mer konsekvent artikelplacering och det rekommenderas för företaget att tillämpa ett flytande system för dess högfrekvent plockade produkter och ett fast system för dess lågfrekvent plockade produkter. Detta kommer att göra så att NECG bättre utnyttjar det tillgängliga lagerutrymmet och ett mer strukturerat system kommer att uppnås. Bakgrund: Nordic E-commerce Group (NECG) består utav dotterbolagen NordicInk, NordicFeel och PetsOnline. Då lagret består utav tre olika företag finns ett brett utbud av produkter. NECG:s problem härrör i att företagets lagerlayout inte har följt med i företagets utveckling. För att kunna hantera en större försäljningsvolym, behöver lagerområdet kunna hantera nuvarande och framtida lagervolymer, men är inte kapabel till att göra detta på ett strukturerat sätt i dag. Detta har lett till nya tankar om förbättringsförslag kring lagerlayout. I detta examensarbete avser lagerlayout ingående och utgående portar, inkommande och utgående lagringsområden, materialhanteringsutrustning och artikelplacering i lager. Även om artikeln placering är per definition en del av lagerlayout, kommer det att ges extra fokus i detta examensarbete eftersom det är en av NECG mest kritiska frågor. Syfte: Syftet med detta examensarbete är att identifiera NECG nuvarande lagerlayout och artikel placering samt vilka eventuella problem som finns, för att kunna ge förslag på förbättringar. Detta ska göras så att NECG kan utnyttja sitt lagerutrymme bättre och förbereda sig inför ökade försäljningsvolymer. Metod: Kvalitativ och kvantitativ data samlades in genom semistrukturerade intervjuer och observationer på NECG, samt genom excel filer innehållande transaktionsdata kring NordicInk’s produkter. Genom ett icke-sannolikt, snöbollsurval valdes respondenterna ut. NECG har inte uttryckt några krav om att sekretessbelägga arbetet kring lagerlayout. Resultat: Det finns ett antal förslag på åtgärder som NECG kan tillämpa för att förbättra lagerlayouten: två separata dörrar för inkommande och utgående leveranser, ett designerat område för inkommande och ett för utgående leveranser samt en flow shop layout kombinerat med en U-form layout skulle vara mest fördelaktigt för NECG:s lager. Vidare behöver NECG en mer konsekvent artikelplacering och det rekommenderas för företaget att tillämpa ett flytande system för dess högfrekvent plockade produkter och ett fast system för dess lågfrekvent plockade produkter. Detta kommer att göra så att NECG bättre utnyttjar det tillgängliga lagerutrymmet och ett mer strukturerat system kommer att uppnås.
|
9 |
Intraseasonal Variations In Sea Level Pressure And Association With Tropical ConvectionKiranmayi, L 01 July 2008 (has links)
This thesis deals with tropical intraseasonal variation (TISV) having time scales in 20-80 day range. Variations on this time scale have been observed to have profound influence on the weather and climate of the entire globe, and hence its study forms an important area of current research. A large number of studies have been carried out on this topic since the pioneering work of Madden and Julian in 1971. However, the observational studies are biased towards using the outgoing longwave radiation (OLR) as the variable of interest, and other variables, pressure in particular, have received less attention. The present thesis explores features of intraseasonal variations in sea level pressure (SLP) with the following main objectives.
1. Compare and contrast wavenumber – frequency spectra of OLR, zonal winds and SLP.
2. Quantify temporal and spatial variations of different tropical modes observed in the above variables.
3. Investigate intraseasonal variations in sea level pressure in the tropics and its meridional connections.
4. Document the movement of cloud bands during the periods of high and low TISV activity during different seasons.
5. Explore the relations between intraseasonal variations in SLP and monsoon rainfall over India.
The study considered global data for a time period of 25 years from 1979 to 2003. Spectral analysis and correlations are the main tools of analysis. A combined FFT-wavelet spectral method, which uses FFT in longitude and wavelet transform in time, was developed for this purpose. This method provided an effective way of obtaining wavenumber - frequency spectra as well as in quantifying temporal variations of different modes. The transform gives spectral intensity as a function of wavenumber, frequency and time. The analysis is applied to OLR, zonal wind and SLP to understand spectral characteristics of different modes and their temporal variations.
The thesis shows that the nature of spectra for OLR, SLP and wind is different although these variables are physically connected. OLR spectrum shows many of the equatorial modes observed from the previous studies for an equivalent depth of 40 m. Spectra of zonal winds at three vertical levels (850 mb, 500 mb and 200 mb) shows peaks corresponding to MJO, Kelvin modes at an equivalent depth of 75 m and Rossby Haurwitz modes. SLP spectrum is different from others. It has peaks at wavenumber zero and at MJO and Rossby Haurwitz modes. Another important new result of the thesis is the spatial and temporal behavior of SLP on intraseasonal time scales. It is shown that the the global atmosphere exhibits quasi-periodic oscillations in SLP with variations in the tropics and high latitudes strongly correlated but in opposite phases. Importantly, the strength of TISV is correlated with sea surface temperature (SST) anomalies in the equatorial Pacific Ocean. This may have some predictive value for predicting the active and weak TISV activity.
|
10 |
Structure and Dynamics of the Inter-tropical Convergence zonesDixit, Vijay Vishal January 2015 (has links) (PDF)
The east-west oriented cloud bands in the tropics are called the Inter-tropical Con-vergence Zones (ITCZ). Till recently, the ITCZ has been assumed to have a simple vertical structure with convergence near the surface boundary layer and divergence near the tropopause. Recent work has shown that the ITCZ can have a complex ver-tical structure with multi-level ows. This complex structure has a profound impact on the mass, momentum and energy budget in the ITCZ. This thesis addresses the factors that govern the shallow meridional circulation that occurs in the ITCZ and the mechanisms that govern the abrupt poleward transition and the gradual poleward migration .
The shallow meridional circulation forms when the boundary layer ow that con-verges in the ITCZ, rises above the boundary layer and diverges in the lower tropo-sphere. The ow above the boundary layer is in the direction opposite to the direction of the ow within the boundary layer. Some authors have argued that this is caused by the reversal of pressure gradients just above the boundary layer in response to strong sea surface temperature gradients. This hypothesis neglects the eect of plan-etary rotation on the ow and was found to be insucient to explain the formation of shallow meridional circulation.
In the east Pacic ocean, the shallow circulation forms only to the south of the ITCZ when the ITCZ forms away from the equator, while it is absent when the ITCZ forms close to the equator. The aqua-planet simulations of the equatorial and the o-equatorial ITCZ were conducted using Community Atmosphere Model (CAM 3.0). The model used the Eulerian dynamical core with T42 horizontal resolution and 26 levels in vertical. Each simulation was run for 3 years and analysis of last six months was presented. The simulations reproduced the contrast in the vertical structure of the equatorial and o-equatorial ITCZ. The shallow circulation was simulated with-out the reversal of pressure gradients and the SST gradients were weakest when the shallow circulation was simulated. We have proposed a new mechanism for the exis-tence of shallow meridional circulation in the ITCZ. We have argued that, in Earth's atmosphere, the mean horizontal ow generally occurs in the direction perpendicular to the direction of applied pressure gradient due to the action of Coriolis force. If the local rotational eects of the ow (relative vorticity) cancels the action of the Coriolis force, then a ow along the pressure gradient is possible. We demonstrated that this condition was satised only to the south of the ITCZ when it forms away from the equator.
The ITCZ is characterized by the maximum mass convergence in the boundary layer. The mass convergence is mainly caused by the deceleration of poleward ow in the boundary layer. When the ITCZ forms close to the equator, the ow in the boundary layer is a resultant of vector addition of three forces, a pressure gradient force in the north-south direction (i.e., the ow towards low pressure), a Coriolis force which acts in the east-west direction( perpendicular to the direction of the ow), and surface friction which opposes the resultant ow. When the ITCZ forms away from the equator a three way balance does not capture the dynamics of ow. As the poleward ow is accelerated towards low pressure, it has to advect a considerable amount of zonal momentum with it which acts to retard the poleward ow. This eect of advection of zonal momentum has to be included in the force balance to obtain an accurate estimate of the ow and associated convergence.
The ITCZ acts like a heat engine. The energy is gained near the surface, some energy is transported towards pole while some is utilized in driving the meridional circulation. The rest is rejected near the tropopause. The transport within the troposphere occurs through the vertical or horizontal advection of the energy due to vertical and horizontal motions respectively. Our analysis of the ITCZ suggests that; a large amount of transport occurs through horizontal motions that was neglected in the previous studies. The detailed analysis suggests that the latent energy in the form of mass of water vapor is exported out of the ITCZ at dierent levels in association with the multilevel ows. The equatorial and the o-equatorial ITCZ are dierent because, evaporation is larger in the o-equatorial ITCZ when compared to the equatorial ITCZ.
The ITCZ shows a strong sub-seasonal variability in its location in the Indian Ocean and the west Pacic Ocean during boreal summer. There are two favorable locations, one near the equator and another away from the equator, for formation of the ITCZ. The equatorial ITCZ either propagates abruptly or gradually to the o-equatorial location. A detailed analysis of moisture and momentum budget of the simulated abrupt and gradual propagations enabled us to separate the role of thermo-dynamic and dynamic processes. We found that, if the equatorial ITCZ would propa-gate abruptly or gradually to the o-equatorial location is decided by the availability of the water vapor in the boundary layer between the two locations of the ITCZ, i.e., by the thermodynamic processes. But, such a transition to the o-equatorial location is allowed only when the constraints imposed by the re-adjustment in the circulation are satised. In simple terms, these constraints emerge due to two processes.
1. The Earth (lower boundary of the atmosphere) spins at maximum eective radius near the equator. As a result, the atmosphere gains maximum angular momentum near the equator (`zonal momentum' in Cartesian co-ordinates) .
The ITCZ is one of the primary avenues to transport the zonal momentum from the lower troposphere to the upper troposphere.
When the favorable location of ITCZ is near the equator, the location of ITCZ and the location where atmosphere gains maximum zonal momentum are coincident. The ITCZ and associated meridional circulation transports the zonal momentum upwards which is then transported polewards. As the favorable location of ITCZ moves away from the equator, the two locations are die rent. As a result, the atmospheric ow has to re-adjust so that the zonal momentum is transported from the equator to the favorable location of the ITCZ which then transports it upwards and polewards.
In summary, this thesis proposes a new mechanism for the generation of shallow meridional circulation, the abrupt transition and the gradual propagations of the ITCZ.
|
Page generated in 0.07 seconds