Topographic preconditioning of open ocean deep convection

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1995Evidence of enhanced oceanic convection over Maud Rise in the Weddell Sea indicates that bottom topography may play a role in selecting the location and scale of deep convecting oceanic chimneys below large scale atmospheric negative buoyancy forcing. Topographic preconditioning of open ocean deep convection is studied using an idealized, three-dimensional, primitive-equation model. A barotropic mean flow impinges on an isolated Gaussian-shaped seamount in a stratified domain with uniform negative surface buoyancy forcing. A region of topographically trapped flow forms over the topography. When this "Taylor cap" is tall enough to interact with the surface mixed-layer, the local isolation from mean horizontal advection forms a conduit into the deep water. The convective penetration depth within this local region is significantly enhanced relative to ambient levels away from the seamount and to similar runs performed without bottom topography. The parameter dependencies for these preconditioning processes are investigated. With uniform background stratification, the doming of isopycnals does not play a major role in the preconditioning process. However, when a surface intensified stratification is included, domed isopycnals associated with the Taylor cap circulation can also play a preconditioning role. In this case, the pycnocline is first ventilated over the seamount, leading to rapid convective deepening into the weakly stratified deep water. An analytical formula for one-dimensional, non-penetrative convection into an exponential stratification profile is derived and compares well with results from the numerical model. Previous modeling studies have often parameterized the mehanism by which the horizontal scale of oceanographic chimneys is set through the use of disk-shaped surface forcing functions. Unlike in such experiments, topographically preconditioned chimneys are not prone to breakup by the growth of baroclinic instabilities. Instead, convection is generally shut down by horizontal fluxes of heat due to the mean flow across the temperature gradients of the chimney walls. The presence of the mean flow, which is neccessary in order for the topographic preconditioning to work, causes instabilities to be advected downstream faster than they can grow locally. These results suggest that the role of baroclinic eddies in shutting down oceanographic convection is probably misrepresented in studies which parameterize the preconditioning mechanism, particularly if the preconditioning mechanism being parameterized is a topographic one.Financial support for the thesis research was provided by NOAA grant number NA16RC0073 and NSF grant number OCE90-04864. Additional financial support was provided by the Office of Naval Research, Physical Oceanography Division under grant number N00014- 86-K-0751 as well as an AASERT fellowship, grant number N00014-89-J-1106

The scope of science for the International Polar Year, 2007-2008

The International Polar Year 2007““2008 will be the largest internationally coordinated research programme in 50 years. It will be an intensive period of interdisciplinary science focused on the Arctic and the Antarctic. IPY 2007““2008 research activities were assembled from the ideas of researchers in more than 60 countries. A total of 228 projects have been endorsed by the ICSU/WMO Joint Committee for IPY 2007““2008. These projects have a strong interdisciplinary emphasis and address the six themes as well as education and outreach objectives. IPY projects will exploit new technological and logistical capabilities and strengthen international coordination of research. They aim to attract, engage and develop a new generation of researchers and raise the awareness, interest and understanding of polar residents, educators, students, the general public and decision makers worldwide. IPY projects will collect a broad-ranging set of samples, data and information which will be made available to an unprecedented degree. IPY 2007““2008 aims to leave a legacy of enhanced observational systems, facilities and infrastructure. The observational networks to be established during IPY include integrated ocean observing systems in both the Arctic and Southern Oceans, coordinated acquisition of satellite data products from multiple space agencies and observational systems for astronomy, sun““earth physics, atmospheric chemistry, meteorology, ecosystems, permafrost, glaciers and geophysics. Many observing systems within IPY will be developed within the framework of existing international global observing systems

International Geosphere-Biosphere Programme (IGBP) Science No. 3

The PAGES research community works toward improving our understanding of the Earth's changing environment. By placing current and future global changes in a long term perspective, they can be assessed relative to natural variability. Since the industrial revolution, the Earth System has become increasingly affected by human activities. Natural and human processes are woven into a complex tapestry of forcings, responses, feedbacks and consequences. Deciphering this complexity is essential as we plan for the future. Paleoenvironmental research is the only way to investigate Earth System processes that operate on timescales longer than the period of instrumental records

Measurement of the Average Lifetime of b-Hadrons in Z Decays

We present a measurement of the average b-hadron lifetime ${\rm \tau_b}$ at the $\mathrm{e^+e^-} \,$ collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of ${\rm \tau_b}$ using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} ${\rm \tau_b= [ 1549 \pm 9 \, (stat) \, \pm 15 \, (syst) ] \; fs \,}$ . \end{center} In addition, we measure the average charged b-decay multiplicity ${\rm \langle n_{\rm b}} \rangle$ and the normalized average b-energy ${\rm \langle x_E \rangle_{\rm b}}$ at LEP to be \begin{center} ${\rm \langle n_{\rm b} \rangle = 4.90 \pm 0.04 \ (stat) \pm 0.11 \, (syst)}$ , \end{center} \begin{center} ${\rm \langle x_E \rangle_{\rm b} = 0.709 \pm 0.004 \, (stat + syst).}$ \end{center

Υ\Upsilon production in Z Decays

We have searched for evidence of Upsilon production in 3.5 million hadronic Z decays collected by the L3 detector at LEP in 1991-1995. No signals are observed for the decay chain Z -> Upsilon X; Upsilon -> l+l- (l= e, mu), therefore upper limits at the 95% confidence level are set on the following Z branching fractions: BR (Z -> Upsilon(1S) X) Upsilon(2S) X) Upsilon(3S) X) < 9.4 x 10**-5

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Severe early onset preeclampsia: short and long term clinical, psychosocial and biochemical aspects

Preeclampsia is a pregnancy specific disorder commonly defined as de novo hypertension and proteinuria after 20 weeks gestational age. It occurs in approximately 3-5% of pregnancies and it is still a major cause of both foetal and maternal morbidity and mortality worldwide1. As extensive research has not yet elucidated the aetiology of preeclampsia, there are no rational preventive or therapeutic interventions available. The only rational treatment is delivery, which benefits the mother but is not in the interest of the foetus, if remote from term. Early onset preeclampsia (<32 weeks’ gestational age) occurs in less than 1% of pregnancies. It is, however often associated with maternal morbidity as the risk of progression to severe maternal disease is inversely related with gestational age at onset2. Resulting prematurity is therefore the main cause of neonatal mortality and morbidity in patients with severe preeclampsia3. Although the discussion is ongoing, perinatal survival is suggested to be increased in patients with preterm preeclampsia by expectant, non-interventional management. This temporising treatment option to lengthen pregnancy includes the use of antihypertensive medication to control hypertension, magnesium sulphate to prevent eclampsia and corticosteroids to enhance foetal lung maturity4. With optimal maternal haemodynamic status and reassuring foetal condition this results on average in an extension of 2 weeks. Prolongation of these pregnancies is a great challenge for clinicians to balance between potential maternal risks on one the eve hand and possible foetal benefits on the other. Clinical controversies regarding prolongation of preterm preeclamptic pregnancies still exist – also taking into account that preeclampsia is the leading cause of maternal mortality in the Netherlands5 - a debate which is even more pronounced in very preterm pregnancies with questionable foetal viability6-9. Do maternal risks of prolongation of these very early pregnancies outweigh the chances of neonatal survival? Counselling of women with very early onset preeclampsia not only comprises of knowledge of the outcome of those particular pregnancies, but also knowledge of outcomes of future pregnancies of these women is of major clinical importance. This thesis opens with a review of the literature on identifiable risk factors of preeclampsia

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Measurements of the pp → ZZ production cross section and the Z → 4ℓ branching fraction, and constraints on anomalous triple gauge couplings at √s = 13 TeV

Four-lepton production in proton-proton collisions, pp -> (Z/gamma*)(Z/gamma*) -> 4l, where l = e or mu, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb(-1). The ZZ production cross section, sigma(pp -> ZZ) = 17.2 +/- 0.5 (stat) +/- 0.7 (syst) +/- 0.4 (theo) +/- 0.4 (lumi) pb, measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 4l) = 4.83(-0.22)(+0.23) (stat)(-0.29)(+0.32) (syst) +/- 0.08 (theo) +/- 0.12(lumi) x 10(-6) for events with a four-lepton invariant mass in the range 80 4GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ. couplings at 95% confidence level: -0.0012 < f(4)(Z) < 0.0010, -0.0010 < f(5)(Z) < 0.0013, -0.0012 < f(4)(gamma) < 0.0013, -0.0012 < f(5)(gamma) < 0.0013