Open water in sea ice, such as leads and polynyas, plays a crucial role in determining the formation of deep- and bottom-water, as well as their long-term global properties and circulation. Ocean general circulation models (GCMs) designed for studies of the long-term thermohaline circulation have typically coarse resolution, making it inevitable to parameterize subgrid-scale features such as leads and convective plumes. In this study, a hierarchy of higher-resolution sea-ice models is developed to reduce uncertainties due to coarse resolution, while keeping the ocean component at coarse resolution to maintain the efficiency of the GCM to study the long-term deep-ocean properties and circulation. The higher-resolved sea-ice component is restricted to the Southern Ocean. Compared with the coarse sea-ice model, the intermediate, higher-resolution version yields more detailed coastal polynyas, a realistically sharp ice edge, and an overall enhanced lead fraction. The latter gives enhanced rates of Antarctic Bottom Water formation through enhanced near-boundary convection. Sensitivity experiments revealed coastal katabatic winds accounted for in the higher resolution version, are the main reason for producing such an effect. For a more realistic coastline, satellite passive-microwave data for fine-grid land/ice-shelf – seaice/ ocean boundary were used. With a further enhancement of the resolution of the Southern Ocean’s sea-ice component, a grid spacing of 22 km is reached. This is about the size of the pixel resolution of satellite-passive microwave data from which ice concentration is retrieved. This product is used in this study to validate the sea-ice component of the global ocean GCM. The overall performance of the high-resolution sea-ice component is encouraging, particularly the representation of the crucial coastal polynyas. Enhancing the resolution of the convection parameterization reduces spurious coarse-grid polynyas. Constraining the upper-ocean temperature and modifying the plume velocity removes unrealistic small-scale convection within the ice pack. The observed highfrequency variability along the ice edge is to some extent captured by exposing the ice pack to upper-ocean currents that mimic tidal variability. While these measures improve several characteristics of the Southern Ocean sea-ice pack, they deteriorate the global deepocean properties and circulation, calling for further refinements and tuning to arrive at presently observed conditions.

This thesis presents an analysis of the implementation feasibility of RAM authentication and encryption. Past research as used simulations to establish that it is possible to authenticate and encrypt the contents of RAM with reasonable performance penalties by using clever implementations of tree data structures over the contents of RAM. However, previous work has largely bypassed implementation issues such as power consumption and silicon area required to implement the proposed schemes, leaving implementation details unspecified. This thesis studies the implementation cost of AES-GCM hardware and software solutions for memory authentication and encryption and shows that software solutions are infeasible because they are too costly in terms of performance and power, whereas hardware solutions are more feasible. / text

Η παρούσα διπλωματική προτείνει μια hardware υλοποίηση για κρυπτογράφηση μηνυμάτων βασισμένη στο πρότυπο ασφαλείας Galois/Counter Mode (GCM). O αλγόριθμος κρυπτογράφησης Galois/Counter Mode (GCM) εκδόθηκε από τον οργανισμό National Institute of Standards and Technology (NIST) τον Νοέμβριο του 2007. Σε συνεργασία με τον μηχανισμό πιστοποίησης μηνυμάτων, υλοποιείται το συνολικό πρότυπο GCM για online λειτουργία. Στο Κεφάλαιο 1, αρχικά γίνεται μια σύντομη ιστορική αναδρομή στον τομέα της κρυπτογραφίας. Στην συνέχεια παρουσιάζονται οι λόγοι που οδήγησαν στην δημιουργία αυτού του προτύπου ασφαλείας. Ακολουθεί μια σύντομη εισαγωγή στον GCM και στους τρόπους με τους οποίος αυτός δουλεύει. Στο τέλος του κεφαλαίου αναφέρονται οι πρακτικές εφαρμογές που έχει η χρήση του G. Στο Κεφάλαιο 2, αρχικά αναφέρονται οι συμβολισμοί και οι βασικές έννοιες που χρησιμοποιούνται στην διπλωματική. Στην συνέχεια, δίνονται συνοπτικές πληροφορίες για το μαθηματικό υπόβαθρο που είναι απαραίτητο για την κατανόηση των εσωτερικών μηχανισμών του GCM. Ακολουθεί η ανάλυση των μαθηματικών συνιστωσών του GCM. Επίσης, παρουσιάζεται το υπόβαθρο των τρόπων λειτουργίας (mode of operation) που υιοθετούνται στον GCM. Τέλος, δίνονται συνοπτικά βασικές πληροφορίες της FPGA πλατφόρμας, Στο Κεφάλαιο 3, γίνεται μια ολοκληρωμένη ανάλυση και μελέτη του Advanced Encryption Standard (AES) και πιο συγκεκριμένα της forward cipher function με υποστηριζόμενο κλειδί 128 bit, καθώς αυτή η διεργασία αποτελεί τον βασικό συμμετρικού κλειδιού block cipher που χρησιμοποιείται στον GCM. Στο Κεφάλαιο 4, πραγματοποιείται η ανάλυση του προτύπου GCM βασισμένη στο τέταρτο recommendation του NIST. Παρουσιάζονται όλοι οι επιμέρους αλγόριθμοι που χρησιμοποιούνται καθώς και ο τρόπος με τον οποίον αυτοί αλληλεπιδρούν και συνεργάζονται για την δημιουργία του GCM αλγορίθμου. Στο τέλος του κεφαλαίου, αναφέρονται οι απαιτήσεις για key και IV που πρέπει να ικανοποιούνται για να θεωρείται ο αλγόριθμος κρυπτογραφικά ισχυρός. Στο Κεφάλαιο 5, αρχικά γίνεται μια top down ανάλυση του GCM. Την ανάλυση αυτή συμπληρώνει η δεύτερη ενότητα στην οποία παρουσιάζεται και αναλύεται η προτεινόμενη αρχιτεκτονική για την hardware υλοποίηση. Στην συνέχεια, δίνεται ο σχεδιασμός των βασικών δομικών στοιχείων του GCM. Στην τελευταία ενότητα παρουσιάζεται η συνολική αρχιτεκτονική του GCM με σκοπό την υλοποίηση για high speed απαιτήσεις. Στο Κεφάλαιο 6, δίνεται μια συνοπτική περιγραφή στα γενικότερα θέματα μια γλώσσας περιγραφής υλικού, και των εργαλείων εξομοίωσης και σύνθεσης. Στο Κεφάλαιο 7, δίνονται τα αποτέλεσμα που προέκυψαν από την εξομοίωση του VHDL κώδικα. Ακολουθούν τα αποτελέσματα της σύνθεσης από δύο διαφορετικές FPGA τεχνολογίες. Στη συνέχεια γίνεται εισαγωγή στον τρόπο με τον οποίο ο μηχανισμός πιστοποίησης και κρυπτογράφησης μηνυμάτων συνεργάζονται για την υλοποίηση του GCM και δίνεται ο τρόπος λειτουργίας του GCM μηχανισμού που υλοποιήθηκε. Ακολουθούν τα αποτελέσματα της εξομοίωσης και σύνθεσης σε δύο διαφορετικές τεχνολογίες καθώς και μια σύγκριση μεταξύ των δύο τεχνολογιών που χρησιμοποιήθηκαν για την σύνθεση. Στο Παράρτημα Α παρουσιάζεται ο τρόπος χρήσης του Xilinx ISE που χρησιμοποιήθηκε για την σύνθεση του VHDL κώδικα για την τεχνολογία Virtex-V. / This thesis proposes a hardware implementation in high speed data rates for encrypting messages based on security standard Galois / Counter Mode (GCM). The encryption algorithm Galois / Counter Mode (GCM) was adopted by the National Institute of Standards and Technology (NIST) in November 2007. In cooperation with the authentication message mechanism, the standard for online GCM mode is fully implemented. The Galois/Counter Mode of Operation (GCM) simultaneously authenticates and encrypts data at speeds that were not previously possible for both software and hardware implementations. In GCM, data integrity is achieved by chaining Galois field multiplication operations while a symmetric key block cipher such as the Advanced Encryption Standard (AES), is used to meet goals of confidentiality.

The original intention of this thesis was to investigate Climate Change (CC), in particular the meteorological impacts of CC on New Zealand (NZ). Succinctly, “to understand what NZ’s future weather may entail”. However, as the research progressed it has led to the larger circulation and has highlighted the teleconnections that are present and the importance of the wider circulation and to NZ . It is apparent that the larger scale circulation needs to be considered in conjunction with, if not before, the synoptic scale. Thus, in order to understand NZ’s future weather first we must understand the Southern Hemisphere and the circulation within it. CC is often described in a broad global scale and it is difficult to translate and relate these mechanisms into day to day weather terms, which have the advantage of being commonly understood. Synoptic Climatology (SC) can bridge this gap by simplifying the wide variety of weather into a small grouping of types, and thus can provide an understandable alternative. To undertake this research an existing SC scheme known as the Kidson Types (KTs) was extended with the use of General Circulation Model (GCM) output. The KTs have been widely used in NZ, thus work detailing their future would be advantageous. The GCMs were able to reproduce the observed frequencies of occurrence of the KTs during the late 20th century. Future projections for the late 21st century surprisingly showed little change in annual type frequencies. To investigate this further a sensitivity study was undertaken, which revealed that the methodology was insensitive to annual type frequency change. The range of response from the GCM projections also inhibited determining significant changes in KT frequencies. Additionally, trend analysis using four realisations from one GCM noted both positive and negative trends in some of the types. This also highlights the difficulty in using GCM output, as a larger ensemble can diffuse results and in a small ensemble individual GCMs can unduly bias the results. Further scrutiny of the KT was then undertaken. An investigation of the KTs to ascertain their influence in the wider circulation using the ERA Interim (ERA-I) reanalysis and trends within the KT using a long term reanalysis data set, the Twentieth Century Reanalysis (20CR). Due to the high year to year variability in the KTs, significant trends were only determined in the 20CR with a reduction in the Zonal Regime representing the occurrence of strong westerly flows over NZ. A composite analysis was also undertaken to evaluate the KTs within the Southern Hemisphere (SH). A positive pressure anomaly was detected far from the Kidson domain, which is defined over NZ, during the SW type. This motivated another study on SH Blocking. Blocking is a large scale phenomena that can influence the paths of synoptic systems and thus potentially cause or exacerbate adverse weather events. Blocking is an area of climate research that requires further work, as there is a deficit of GCM studies in the SH. This study utilised a Persistent Positive Anomaly (PPA) methodology which is advantageous as the spatial pattern, latitude and longitude, of the Blocking Events (BEs) is determined. To our knowledge, this is the first study to use GCM output using the PPA methodology in the SH and this is also the first blocking study using Coupled Model Inter-comparison Project (CMIP)5 GCM output in the SH. A reduction of BEs was observed over the South Pacific Ocean (SPO) region during summer and spring, in the GCM projections between 2041-2070 and 2071- 2100. The Southern Annular Mode (SAM) has been suggested as an influence on blocking frequency in previous work and this relationship was studied. A high negative correlation between SAM + and BEs was observed in summer with the reanalysis and GCM historical output. This correlation was reduced in 21st century. However, further work is needed in this study in order to gain an understanding of the mechanisms and linkages between SAM and the BEs.

To date more than 1500 exoplanets have been discovered. A large number of these are hot Jupiters, Jupiter-sized planets orbiting < 0.1 au from their parent stars, due to limitations in observational techniques making them easier to detect than smaller planets in wider orbits. This is also, for the same reasons, the class of exoplanets with the most observational constraints. Due to the very large interaction between these planets and their parent stars they are believed to be tidally locked, causing a large temperature contrast between the permanently hot day side and colder night side. There are still many open questions about these planets. Many are observed to have inflated radii, i.e. the observed radius is larger for a given mass than evolutionary models predict. A mechanism that can transport some of the stellar heating into the interior of the planet may be able to explain this. The presence of hazes or clouds has been inferred on some planets, but their composition and distribution remain unknown. According to chemical equilibrium models TiO and VO should be present on the day side of the hottest of these planets, but these molecules have not yet been detected. Cold traps, where these molecules condense out on the night side, have been suggested to explain this. The efficiency of the heat redistribution from the day side to the night side has been found to vary significantly between different planets; the mechanism behind this is still unknown. To begin to answer many of these questions we need models capturing the three-dimensional nature of the atmospheres of these planets. General circulation models (GCMs) do this by solving the equations of fluid dynamics for the atmosphere coupled to a radiative transfer scheme. GCMs have previously been applied to several exoplanets, but many solve simplified fluid equations (shallow water or primitive equations) or highly parametrised radiation schemes (temperature-forcing, gray or band-averaged opacities). We here present an adaptation of the Met Office Unified Model (UM), a GCM used for weather predictions and climate studies for the Earth, to hot Jupiters. The UM solves the full 3D Euler equations for the fluid, and the radiation scheme uses the two-stream approximation and correlated-k method, which are state of the art for both Earth and exoplanet GCMs. This makes it ideally suited for the study of hot Jupiters. An important part of this work is devoted to the adaptation of the radiation scheme of the UM to hot Jupiters. This includes calculation of opacities for the main absorbers in these atmospheres from state-of-the-art high temperature line lists, the calculation of k-coefficients from these opacities, and making sure all aspects of the scheme perform satisfactorily at high temperatures and pressures. We have tested approximations made in previous works such as the two-stream approximation, use of band-averaged opacities and different treatments of gaseous overlap. Uncertainties in current models, such as the lack of high temperature line broadening parameters for these atmospheres, are discussed. We couple the adapted radiation scheme to the UM dynamical core, which has been tested independently. Our first application is devoted to one of the most well-observed hot Jupiters, HD 209458b. Differences between previous modelling works and our model are discussed, and we compare results from the full coupled model with results obtained using a temperature-forcing scheme. We have also developed a tool to calculate synthetic phase curves, and emission and transmission spectra from the output of our 3D model. This enables us to directly compare our model results to observations and test the effect of various parameters and model choices on observable quantities.

The forth recommendation of symmetric block cipher mode of operation SP800-38D, <em>Galois/Counter Mode of Operation</em> (GCM) was developed by David A McGrew and John Viega. GCM uses an approved symmetric key block cipher with a block size of 128 bits and a universal hashing over a binary Galois field to provide confidentiality and authentication. It is built specifically to support very high data rates as it can take advantage of pipelining and parallel processing techniques. <br /><br /> Before GCM, SP800-38A only provided confidentiality and SP800-38B provided authentication. SP800-38C provided confidentiality using the counter mode and authentication. However the authentication technique in SP800-38C was not parallelizable and slowed down the throughput of the cipher. Hence, none of these three recommendations were suitable for high speed network and computer system applications. <br /><br /> With the advent of GCM, authenticated encryption at data rates of several Gbps is now practical, permitting high grade encryption and authentication on systems which previously could not be fully protected. However there have not yet been any published results on actual architectures for this standard based on FPGA technology. <br /><br /> This thesis presents a fully pipelined and parallelized hardware architecture for AES-GCM which is GCM running under symmetric block cipher AES on a FPGA multi-core platform corresponding to the IPsec ESP data flow. <br /><br /> The results from this thesis show that the round transformations of confidentiality and hash operations of authentication in AES-GCM can cooperate very efficiently within this pipelined architecture. Furthermore, this AES-GCM hardware architecture never unnecessarily stalls data pipelines. For the first time this thesis provides a complete FPGA-based high speed architecture for the AES-GCM standard, suitable for high speed embedded applications.

The forth recommendation of symmetric block cipher mode of operation SP800-38D, <em>Galois/Counter Mode of Operation</em> (GCM) was developed by David A McGrew and John Viega. GCM uses an approved symmetric key block cipher with a block size of 128 bits and a universal hashing over a binary Galois field to provide confidentiality and authentication. It is built specifically to support very high data rates as it can take advantage of pipelining and parallel processing techniques. <br /><br /> Before GCM, SP800-38A only provided confidentiality and SP800-38B provided authentication. SP800-38C provided confidentiality using the counter mode and authentication. However the authentication technique in SP800-38C was not parallelizable and slowed down the throughput of the cipher. Hence, none of these three recommendations were suitable for high speed network and computer system applications. <br /><br /> With the advent of GCM, authenticated encryption at data rates of several Gbps is now practical, permitting high grade encryption and authentication on systems which previously could not be fully protected. However there have not yet been any published results on actual architectures for this standard based on FPGA technology. <br /><br /> This thesis presents a fully pipelined and parallelized hardware architecture for AES-GCM which is GCM running under symmetric block cipher AES on a FPGA multi-core platform corresponding to the IPsec ESP data flow. <br /><br /> The results from this thesis show that the round transformations of confidentiality and hash operations of authentication in AES-GCM can cooperate very efficiently within this pipelined architecture. Furthermore, this AES-GCM hardware architecture never unnecessarily stalls data pipelines. For the first time this thesis provides a complete FPGA-based high speed architecture for the AES-GCM standard, suitable for high speed embedded applications.

Student mobility is a common phenomenon in longitudinal data in educational research. The characteristics of education longitudinal data create a problem for the conventional multilevel model. Grady and Beretvas (2010) introduced a cross-classified multiple membership growth curve (CCMM-GCM) model to handle Student mobility over time by capturing complex higher level clustering structure in the data. There are some limitations in the CCMM-GCM model. By creating dummy coded indicators for each measurement occasion, the new model can improve the accuracy and provides an easier and more flexible structure at the higher level. This study provides some support that the new model better fits a dataset than the CCMM-GCM model / text

Η παρούσα διπλωματική προτείνει μια hardware υλοποίηση του μηχανισμού πιστοποίησης μηνυμάτων βασισμένη στο πρότυπο Galois/Counter Mode (GCM) . O αλγόριθμος κρυπτογράφησης Galois/Counter Mode (GCM) εκδόθηκε από τον οργανισμό National Institute of Standards and Technology (NIST) τον Νοέμβριο του 2007. Σε συνεργασία με τον μηχανισμός κρυπτογράφησης μηνυμάτων, υλοποιείται το πρότυπο GCM για online λειτουργία. Στο Κεφάλαιο 1, αρχικά γίνεται μια σύντομη ιστορική αναδρομή στον τομέα της κρυπτογραφίας. Στην συνέχεια παρουσιάζονται οι λόγοι που οδήγησαν στην δημιουργία αυτού του αλγορίθμου. Ακολουθεί μια σύντομη εισαγωγή στον GCM και στους τρόπους με τους οποίος αυτός δουλεύει. Στο τέλος του κεφαλαίου αναφέρονται οι πρακτικές εφαρμογές που έχει η χρήση του GCM. Στο Κεφάλαιο 2, αρχικά αναφέρονται οι συμβολισμοί που χρησιμοποιούνται στην διπλωματική καθώς και οι βασικές έννοιες που χρησιμοποιούνται. Στην συνέχεια, αναλύεται το μαθηματικό υπόβαθρο που είναι απαραίτητο για την κατανόηση των εσωτερικών μηχανισμών του GCM. Η ανάλυση που γίνεται σε αυτή την ενότητα αποτελεί και την βασική αρχή στην οποία στηρίχτηκε η δημιουργία του αλγορίθμου. Ακολουθεί η ανάλυση των μαθηματικών συνιστωσών του GCM. Η ενότητα αυτή κατατάσσεται τόσο σε μαθηματική ανάλυση όσο και σε hardware προσέγγιση των επιμέρους συνιστωσών . Ιδιαίτερο ενδιαφέρον παρουσιάζει η τελευταία υποενότητα του κεφαλαίου που παρουσιάζει τον τρόπο με τον οποίο από τον σειριακό πολλαπλασιαστή στο GF(2128) οδηγούμαστε στον παράλληλο πολλαπλασιαστή. Στο Κεφάλαιο 3, αρχικά παρουσιάζεται ο Advanced Encryption Standard (AES) και πιο συγκεκριμένα η forward function αυτού με υποστηριζόμενο κλειδί 128 bit. Στην συνέχεια του κεφαλαίου, παρουσιάζονται τα πλεονεκτήματα για την υλοποίηση με χρήση FPGAs, επίσης γίνεται μια σύντομη περιγραφή των βασικών διαφορών που παρουσιάζονται στις δύο οικογένειες FPGAs που χρησιμοποιήθηκαν. Στο Κεφάλαιο 4 , πραγματοποιείται η ανάλυση του αλγορίθμου GCM βασισμένη στο recommendation του NIST. Παρουσιάζονται όλοι οι επιμέρους αλγόριθμοι που χρησιμοποιούνται καθώς και ο τρόπος με τον οποίον αυτοί αλληλεπιδρούν και συνεργάζονται για την δημιουργία του GCM αλγορίθμου. Στο τέλος του κεφαλαίου, αναφέρονται οι απαιτήσεις για key και IV που πρέπει να ικανοποιούνται για να θεωρείται ο αλγόριθμος κρυπτογραφικά ισχυρός. Στο Κεφάλαιο 5, αρχικά γίνεται μια top down ανάλυση του GCM. Η ανάλυση αυτή χρησιμοποιείται στην δεύτερη ενότητα όπου προτείνεται και αναλύεται η αρχιτεκτονική που χρησιμοποιήθηκε για την hardware υλοποίηση. Στην συνέχεια, αναλύονται τα βασικά δομικά στοιχεία του GCM. Στην τελευταία ενότητα αναφέρεται η δομή που χρησιμοποιήθηκε με σκοπό την υλοποίηση για high speed απαιτήσεις. Στο Κεφάλαιο 6, αρχικά γίνεται εισαγωγή στον μηχανισμό πιστοποίησης μηνυμάτων έτσι όπως αυτό υλοποιήθηκε. Στην συνέχεια , παραθέτονται τα αποτέλεσμα που προέκυψαν από την εξομοίωση του VHDL κώδικα. Ακολουθούν τα αποτελέσματα της σύνθεσης και σύγκριση μεταξύ διαφορετικών τρόπων υλοποίησης. Στο τέλος του κεφαλαίου γίνεται σύγκριση μεταξύ των δύο τεχνολογιών που χρησιμοποιήθηκαν για την σύνθεση. Στο κεφάλαιο 7, αρχικά γίνεται εισαγωγή στον τρόπο με τον οποίο ο μηχανισμός πιστοποίησης και κρυπτογράφησης μηνυμάτων συνεργάζονται. Στην δεύτερη ενότητα παραθέτεται ο τρόπος λειτουργίας του GCM μηχανισμού που υλοποιήθηκε. Ακολουθούν τα αποτελέσματα της εξομοίωσης. Στην τελευταία ενότητα παραθέτονται τα αποτέλεσμα σύνθεσης σε δύο διαφορετικές τεχνολογίες. Στο Παράρτημα Α παρουσιάζεται ο τρόπος χρήσης του Xilinx ISE που χρησιμοποιήθηκε για την σύνθεση του VHDL κώδικα για την τεχνολογία Virtex 5. Τέλος στο Παράρτημα Β παρουσιάζονται κάποια βασικά κομμάτια του κώδικα C. / The Galois/Counter Mode of Operation (GCM), recently standardized by NIST, simultaneously authenticates and encrypts data at speeds not previously possible for both software and hardware implementations. In GCM, data integrity is achieved by chaining Galois field multiplication operations while a symmetric key block cipher such as the Advanced Encryption Standard (AES), is used to meet goals of confidentiality.

The SST bias in the tropical Atlantic exists in the early to latest generation of coupled general circulation models. The maximum bias is not on the equator but at 16°S, the cause of which has not been thoroughly studied. Newly released CMIP5 models provide a useful tool to investigate the contributions of different physical processes to the SST bias in this area in the coupled system. We tested three existing mechanisms and found that: 1) there is no significant relationship between the SST bias and surface heat flux bias; 2) deficient coastal upwelling is a contributing but not the sole source of the bias; and 3) the SST bias is correlated with temperature biases in the upstream equatorial region. The Angola-Benguela front is displaced southward by more than 10° in latitude in many CIMP5 models. Due to the huge temperature contrasts on two sides of the front, such a frontal displacement generates a very strong SST bias. The correlation between the SST bias and frontal location error in this region is significant at the 99% level, demonstrating that the SST bias in coupled GCMs is attributable to the models’ inability to reproduce a realistic position of the front and the consequent erroneous advection by the southward Angola current. This is due to both errors in the simulated surface wind field and systematic errors in ocean models. Ocean reanalysis datasets and a high-resolution regional model simulation suffer a similar pattern of SST biases. Although they produce a more realistic ocean circulation than coarser resolution simulations and alleviate some of the severe SST bias near the front, a warm bias overlies on a northward current to the south of the front, which actually comes from the north of the front through a subsurface passage. We identify a strong subsurface temperature bias caused by a too-deep and diffused simulated thermocline along the coast of Angola, originating from the equatorial thermocline, advected by the Angola Current and an undercurrent beneath the Benguela current, and then brought to the surface by the coastal upwelling along the Benguela coast, contributing to the warm SST bias south of the front.