Resonance of internal waves in fjords: A finite-difference model

After the time periodicity is removed from the problem, the spatial distribution of internal waves in a stratified fluid is governed by a hyperbolic equation. With boundary conditions specified all along the perimeter of the domain, information is transmitted in both directions (forward and backward) along every characteristic, and, unlike the typical temporal hyperbolic equation, the internal-wave equation is not amenable to a simple forward integration. The problem is tackled here with a finite-difference, relaxation technique by constructing a time-dependent, dissipative problem, the final steady state of which yields the solution of the original problem. Attempts at solving the problem for arbitrary topography then reveal multiple resonances, each resonance being caused by a ray path closing onto itself after multiple reflections. The finite-difference formulation is found to be a convenient vehicle to discuss resonances and to conclude that their existence renders the problem not only singular but also extremely sensitive to the details of the topography. The problem is easily overcome by the introduction of friction. The finite-difference representation of the problem is instrumental in serving as a guide for the investigation of the resonance problem. Indeed, it keeps the essence of the continuous problem and yet simplifies the analysis enormously. Although straightforward, robust and successful at providing a numerical solution to a first few examples, the relaxation component of the integration technique suffers from lack of efficiency. This is due to the particular nature of the hyperbolic problem, but it remains that numerical analysts could improve or replace the present scheme with a faster algorithm

ENSO-PDO rainfall relationships in the MCBR

The Mediterranean California Border Region (MCBR) rainfall's relationship with El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) is reexamined for the period 1951–2014. When stratifying data by ENSO events we found that strong events of either sign yield the highest ENSO–rainfall correlation; but when the stratification was done by rainfall the wet seasons yield the highest ENSO–rainfall correlation. Most strong ENSO events have the same sign as PDO; but the ENSO–rainfall correlation for all ENSO–PDO same-sign events is almost undistinguishable from the full-record's correlation. Timewise stratification shows that 30-year climatological values (MCBR precipitation, PDO and ENSO) and ENSO–rainfall correlations have decreased in recent years

The recent rainfall climatology of the Mediterranean Californias

ABSTRACT In this work, recent rainfall data in a southwestern California station (San Diego) and a northwestern Baja California station (Ensenada) within a region called Mediterranean California, around 33ЊN, 117ЊW, are studied. Cumulative annual means are used as indicators of climatological variability; but the entire datasets are analyzed by modeling the histogram of each set as a Weibull distribution probability density function, f . The climatology of both stations, defined simply as the arithmetic average, is compared with their theoretical mean; that is, the first moment of f . It is assumed that this comparison would be indicative of the reliability of the available rainfall climatologies. If these assumptions hold, in particular if the data is indeed Weibull distributed, it can be concluded that the climatological annual mean precipitation in this region is slightly overestimated at this time

Assessment of RegCM4 simulated inter-annual variability and daily-scale statistics of temperature and precipitation over Mexico

The skill of a regional climate model (RegCM4) in capturing the mean patterns, interannual variability and extreme statistics of daily-scale temperature and precipitation events over Mexico is assessed through a comparison of observations and a 27-year long simulation driven by reanalyses of observations covering the Central America CORDEX domain. The analysis also includes the simulation of tropical cyclones. It is found that RegCM4 reproduces adequately the mean spatial patterns of seasonal precipitation and temperature, along with the associated interannual variability characteristics. The main model bias is an overestimation of precipitation in mountainous regions. The 5 and 95 percentiles of daily temperature, as well as the maximum dry spell length are realistically simulated. The simulated distribution of precipitation events as well as the 95 percentile of precipitation shows a wet bias in topographically complex regions. Based on a simple detection method, the model produces realistic tropical cyclone distributions even at its relatively coarse resolution (dx = 50 km), although the number of cyclone days is underestimated over the Pacific and somewhat overestimated over the Atlantic and Caribbean basins. Overall, it is assessed that the performance of RegCM4 over Mexico is of sufficient quality to study not only mean precipitation and temperature patterns, but also higher order climate statistics

The post-vaccine microevolution of invasive Streptococcus pneumoniae

The 7-valent pneumococcal conjugated vaccine (PCV7) has affected the genetic population of Streptococcus pneumoniae in pediatric carriage. Little is known however about pneumococcal population genomics in adult invasive pneumococcal disease (IPD) under vaccine pressure. We sequenced and serotyped 349 strains of S. pneumoniae isolated from IPD patients in Nijmegen between 2001 and 2011. Introduction of PCV7 in the Dutch National Immunization Program in 2006 preluded substantial alterations in the IPD population structure caused by serotype replacement. No evidence could be found for vaccine induced capsular switches. We observed that after a temporary bottleneck in gene diversity after the introduction of PCV7, the accessory gene pool re-expanded mainly by genes already circulating pre-PCV7. In the post-vaccine genomic population a number of genes changed frequency, certain genes became overrepresented in vaccine serotypes, while others shifted towards non-vaccine serotypes. Whether these dynamics in the invasive pneumococcal population have truly contributed to invasiveness and manifestations of disease remains to be further elucidated. We suggest the use of whole genome sequencing for surveillance of pneumococcal population dynamics that could give a prospect on the course of disease, facilitating effective prevention and management of IPD

Recent ENSO–PDO

The Mediterranean California Border Region (MCBR) rainfall's relationship with El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) is reexamined for the period 1951–2014. When stratifying data by ENSO events we found that strong events of either sign yield the highest ENSO–rainfall correlation; but when the stratification was done by rainfall the wet seasons yield the highest ENSO–rainfall correlation. Most strong ENSO events have the same sign as PDO; but the ENSO–rainfall correlation for all ENSO–PDO same-sign events is almost undistinguishable from the full-record's correlation. Timewise stratification shows that 30-year climatological values (MCBR precipitation, PDO and ENSO) and ENSO–rainfall correlations have decreased in recent years