An investigation of the impact of the subgrid-scale variability of cloud liquid water on the autoconversion process as parameterized in a general circulation model is presented in this paper. For this purpose, a prognostic statistical probability density distribution (PDF) of the subgrid scale variability of cloud water is incorporated in a continuous autoconversion parameterization. Thus, the revised autoconversion rate is calculated by an integral of the autoconversion equation over the PDF of total water mixing ratio from the saturation vapor mixing ratio to the maximum of total water mixing ratio. An evaluation of the new autoconversion parameterization is carried out by means of one year simulations with the ECHAM5 climate model. The results indicate that the new autoconversion scheme causes an increase of the frequency of occurrence of high autoconversion rates and a decrease of low ones compared to the original scheme. This expected result is due to the emphasis on areas of high cloud liquid water in the new approach, and the non-linearity of the autoconversion with respect to liquid water mixing ratio. A similar trend as in the autoconversion is observed in the accretion process resulting from the coupling of both processes. As a consequence of the altered autoconversion, large-scale surface precipitation also shows a shift of occurrence from lower to higher rates. The vertically integrated cloud liquid water estimated by the model shows slight improvements compared to satellite data. Most importantly, the artificial tuning factor for autoconversion in the continuous parameterization could be reduced by almost an order of magnitude using the revised parameterization.

Στην παρούσα εργασία ερευνώνται δύο σύνολα δεδομένων τεσσάρων μηνών, τρεχουσών μετρήσεων αέρα και ρεύματος, που λαμβάνονται από το σύστημα Poseidon, σε δύο θέσεις στο βόρειο αιγαίο πέλαγος. Οι μελετημένες χρονικές σειρές καλύπτουν τη θερινή εποχή που εκτείνεται την περίοδο από τον Ιούνιο μέχρι το τέλος Σεπτεμβρίου. Τα αποτελέσματα είναι συνεπή στα κύρια χαρακτηριστικά γνωρίσματα της επιφανειακής κυκλοφορίας στο βόρειο αιγαίο πέλαγος που δείχνει τις υψηλές τρέχουσες ταχύτητες μεταξύ Άθου και Λήμνου και την σχεδόν σταθερή βορειοδυτική ροή κοντά στη νοτιοδυτική ακτή του νησιού Λέσβος. Η παρατηρηθείς μεταβλητότητα ροής στην θαλάσσια περιοχή του Άθου συσχετίζεται με την αντικυκλωνική κυκλοφορία της λεκάνης του Άθου που περιγράφεται σε παλαιότερες μελέτες. Η ροή του νερού κοντά στο νησί Λέσβος είναι επίσης σύμφωνα με το σχέδιο κυκλοφορίας του ύδατος του βορείου αιγαίου πελάγους και θεωρείται ως επέκταση του δευτερεύοντος βορείου κατευθυνόμενου ρεύματος. Η έλλειψη συσχετισμού μεταξύ του ανέμου και του ρεύματος για τις δύο τοποθεσίες, δείχνει ότι ο άνεμος δεν ελέγχει το βαροκλινικό χαρακτήρα της επιφανειακής κυκλοφορίας του βορείου Αιγαίου. / Two 4-month, current and wind measurements datasets, obtained by Poseidon network at two locations in the North Aegean Sea are investigated. The studied time series cover the summer season spanning the period from June to the end of September. The results are consistent to the main surface circulation features of the North Aegean Sea indicating high current speeds between Athos and Limnos and an almost steady northwestwards flow near the southwestern coast of Lesvos Island. The observed flow variability in Athos sea area is related with the Athos basin anticyclonic circulation which is described in previous studies. The water flow near Lesvos island is also in accordance with the water circulation pattern of North Aegean Sea and is considered as a northward extension of the Asia Minor current. No correlation between wind and current at both sites verifies the bacoclinic character of the North Aegean surface circulation.

No description available.

This dissertation tracks the social circulation of media scripts and collaborative meaning-making in urban Moroccan and Lebanese families' domestic conversations as ways in which the social imaginary of a differentiated pan-Arab audience imaginary is performed. Media scripts refer to television input or information circulated through entextualization processes, embedded direct and indirect quotations framed by a particular discussion, in household dialogues. They include stories, statistics, historical dates, anecdotal observations, music tunes, quotes, iconic units of language varieties and their attendant identities that Moroccan and Lebanese families managed in interpretive discussions. Scripts are easily detached and mobile sound bites that serve on an affective level as possible identity performances. I argue that Fassi Moroccan and Beiruti families are interpretive communities created and who participate in creating a culture of circulation, which is not just about the objects moving through a culture, but the means, methods, and mechanisms of transmission and interpretation built around and negotiated by the members of that community (Lee and LiPuma 2002). Collaborative in this dissertation draws on the Bakhtinian concept that all interaction involves interlocutors, whether present or not, and a set of interpretive conditions affecting meaning (Bakhtin and Holquist 1982:424). Although the social imaginary of an Arab audience is perceived as unitary enough to merit regional satellite programming, the performances of Moroccan and Lebanese families illuminate the differentiated and fractured construction of a pan-Arab cultural project. Through domestic media ethnography of pan-Arab and national entertainment, talk shows, and news programming reception, I explore functional literacies tied to intervisual cues and the management of intergenerational authority; a pan-Arab language ideology that includes performances of multilingualism and shifting identity alignments linked to specific features of linguistic varieties encountered via television; and the link between language, gender, and confessionalism in morality evaluations of gendered media representations. I focus on the everyday domestic contexts, linguistic mechanisms, and discursive frameworks activated by Moroccan and Lebanese families in media engagements.

In this thesis we will investigate the role of diapycnal mixing on the ocean general circulation. This thesis is divided into three main parts. In the first part we show that there exists an almost infinite number of pathways to turbulence in oceanic energetic shear zones at high Reynolds number. Such a large number of accessible routes to truly chaotic motion is not typical of most of the existing body of laboratory and numerical experiments of shear-induced diapycnal mixing, but is shown to be of relevance to diapycnal mixing in geophysical flows. A key finding is that the use of generally accepted empirical relations based on laboratory experiments for the quantification of diapycnal mixing leads to large inaccuracies. In the second part we perform high resolution numerical experiments of diapycnal mixing in the oceanographically relevant high Reynolds number parameter range. Through detailed analysis of the flow energetics and mixing properties of these flows, we show that the net buoyancy flux facilitated by turbulence, the efficiency of diapycnal mixing, and the resultant effective diffusivity, all depend in non-trivial ways on the specific route to turbulence for each individual mixing event. This has important implications for practical methods of estimating an effective diapycnal mixing diffusivity from observations as well as for parametrization of mixing in ocean general circulation models. We show quantitatively that such methods can be inaccurate to the extent that they will need to be completely revised or replaced. In the third and final part of the thesis we investigate the sensitivity of the meridional overturning circulation of the abyssal ocean to the intensity and spatial variations of diapycnal mixing. We show that changes in intensity of mixing by factors well within the errors associated with practical estimates (as discussed above) lead to significant changes in ocean circulation. We show that enhanced abyssal mixing, surface winds, and meso-scale eddies play leading roles in driving the abyssal ocean circulation and in setting the stratification. As an example of the application of our analysis we show that proper parametrization of enhanced abyssal mixing leads to realization of the important role of the (often neglected) geothermal heat flux in driving the Antarctic Bottom Water circulation.

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No description available.

No description available.

Circulation and associated variability in the Intra-Americas Sea (IAS) are examined using observations and numerical models. Vertically integrated transport variations through the Yucatan Channel in the model are found to be related to the intrusion of the Loop Current into the Gulf of Mexico. We argue that the transport variations are part of a “compensation effect” by which transport variations through the Yucatan Channel are at least partly compensated by flow around Cuba. Numerical experiments show that the transport variations result from the interaction between the density anomalies associated with the Loop Current intrusion and the variable bottom topography. The compensation effect is found to be associated with baroclinic (2-layer) flow through the Yucatan Channel at timescales longer than a month, while at shorter timescales (less than a month) the vertical structure of the flow is barotropic. An index, that can be computed from satellite data, is proposed for measuring the impact of the Loop Current intrusion on the transport variability through the Yucatan Channel. This index is shown to be significantly correlated at low frequencies (cutoff 120 days) with the cable estimates of transport between Florida and the Bahamas. We argue that it is the geometric connectivity between the Yucatan Channel and the Straits of Florida between Florida and the Bahamas that accounts for the relationship. A three-dimensional, data-assimilative, ocean circulation model is developed in order to simulate circulation, hydrography and associated variability in the IAS from 1999 to 2002. The model performance is assessed by comparing model results with various observations made in the IAS during this period. Model results are used to study the role played by Caribbean eddies in the dynamics of monthly to seasonal (with timescales of 30-120 days) circulation variability in the IAS. It is shown that the variations in vertically integrated transport between Nicaragua and Jamaica are linked to the interaction of Caribbean eddies with the Nicaraguan Rise. The mechanism can be explained in terms of the form drag effect acting across the Nicaraguan Rise.

In this thesis we will investigate the role of diapycnal mixing on the ocean general circulation. This thesis is divided into three main parts. In the first part we show that there exists an almost infinite number of pathways to turbulence in oceanic energetic shear zones at high Reynolds number. Such a large number of accessible routes to truly chaotic motion is not typical of most of the existing body of laboratory and numerical experiments of shear-induced diapycnal mixing, but is shown to be of relevance to diapycnal mixing in geophysical flows. A key finding is that the use of generally accepted empirical relations based on laboratory experiments for the quantification of diapycnal mixing leads to large inaccuracies. In the second part we perform high resolution numerical experiments of diapycnal mixing in the oceanographically relevant high Reynolds number parameter range. Through detailed analysis of the flow energetics and mixing properties of these flows, we show that the net buoyancy flux facilitated by turbulence, the efficiency of diapycnal mixing, and the resultant effective diffusivity, all depend in non-trivial ways on the specific route to turbulence for each individual mixing event. This has important implications for practical methods of estimating an effective diapycnal mixing diffusivity from observations as well as for parametrization of mixing in ocean general circulation models. We show quantitatively that such methods can be inaccurate to the extent that they will need to be completely revised or replaced. In the third and final part of the thesis we investigate the sensitivity of the meridional overturning circulation of the abyssal ocean to the intensity and spatial variations of diapycnal mixing. We show that changes in intensity of mixing by factors well within the errors associated with practical estimates (as discussed above) lead to significant changes in ocean circulation. We show that enhanced abyssal mixing, surface winds, and meso-scale eddies play leading roles in driving the abyssal ocean circulation and in setting the stratification. As an example of the application of our analysis we show that proper parametrization of enhanced abyssal mixing leads to realization of the important role of the (often neglected) geothermal heat flux in driving the Antarctic Bottom Water circulation.