The seasonal cycle of energetics from the GLAS/UMD climate GCM

The annual cycle of atmospheric energetics from a 2-year integration of the GLAS/UMD Climate GCM is computed and compared to results from the European Centre analyses of the GWE year, and to previously published results on a global basis. All calculations are done in the mixed space-time domain. The main conclusions are: (1) the seasonal cycle of today's eddy kinetic energy (in both hemispheres), and of the transient eddy available potential energy and the potential-to-kinetic energy conversions (mean and eddy) in the Northern Hemisphere are well simulated by the GCM; (2) the GCM's tendency to have anomalously large mean u-winds at upper levels in high latitudes leads to excessive wintertime values of mean kinetic and available potential energies, and causes distortions in the GCM latitude-height distribution of kinetic energy and of many of the conversions; (3) the eddy conversion of available potential-to-kinetic energy obtained from the ageostrophic wind in these analyses; and (4) the conversions in the Southern Hemisphere are not well simulated by the GCM, although the observations are somewhat questionable

An intercomparison of intraseasonal variability in general circulation models and observations

Low frequency oscillations appearing in three GCM seasonal cycle integrations are compared with the analyses of the European Center for Medium Range Weather Forecasting (ECMWF). All three models have the same resolution: 4 deg latitude by 5 deg longitude, with 9 levels. The dominant phase speeds and the differential vertical structure of the heating profiles in the GCMs are in general agreement with current theory involving the positive feedback between latent heating and moist static stability. All three GCMs fail to capture the detailed evolution in the different stages of the development and decay of the oscillation. The results suggest that an improvement in the boundary layer moisture processes may be crucial for a better simulation of the oscillation

Circulation Regimes: Chaotic Variability versus SST-Forced Predictability

Abstract The circulation regimes in the Pacific–North American region are studied using the NCEP–NCAR reanalyses for the 18-winter period (1981/82–1998/99; NCEP18) and for the 54-winter period (1948/49–2001/02; NCEP54). The sampling properties of the regimes are estimated using very large ensembles (of size 55) of winter simulations made for the NCEP18 period with the atmospheric general circulation model of the Center for Ocean–Land–Atmosphere Studies, forced by observed SST and sea ice. The regimes are identified using a modified version of the k-means method. From the NCEP54 dataset a set of four clusters was found [i.e., the Alaskan ridge (AR), Arctic low (AL), Pacific trough (PT), and the Arctic high (AH)], which are significant (vis-à-vis a multinormal background), and more reproducible (within randomly chosen half-length samples) than would be expected from a multinormal process. The frequency of occurrence of the PT (AH) has increased (decreased) significantly during the past two decades. The PT cluster obtained from NCEP18 dataset more closely resembles the El Niño–forced seasonal mean pattern of recent decades than it does the traditional PNA. The GCM simulates the AR, AL, and PT clusters (but not the AH). The simulated AR and PT patterns have errors (cf. the NCEP18 results), which are outside the range of internal variability. The simulated frequency of occurrence agrees with the NCEP18 results within sampling variability. The differences in cluster properties of the PT and AR regimes between the NCEP18 and NCEP54 datasets are due to changes in SST forcing, not sampling error. Year-to-year changes in the frequency of occurrence of the PT, AL, and AR clusters in the simulations and the NCEP18 dataset are generally consistent with each other

HIV-1 Directly Kills CD4+ T Cells by a Fas-independent Mechanism

The mechanism by which HIV-1 induces CD4+ T cell death is not known. A fundamental issue is whether HIV-1 primarily induces direct killing of infected cells or indirectly causes death of uninfected bystander cells. This question was studied using a reporter virus system in which infected cells are marked with the cell surface protein placental alkaline phosphatase (PLAP). Infection by HIV-PLAP of peripheral blood mononuclear cells (PBMCs) and T cell lines leads to rapid depletion of CD4+ T cells and induction of apoptosis. The great majority of HIV-induced T cell death in vitro involves direct loss of infected cells rather than indirect effects on uninfected bystander cells. Because of its proposed role in HIV-induced cell death, we also examined the Fas (CD95/Apo1) pathway in killing of T cells by HIV-1. Infected PBMCs or CEM cells display no increase in surface Fas relative to uninfected cells. In addition, HIV-1 kills CEM and Jurkat T cells in the presence of a caspase inhibitor that completely blocks Fas-mediated apoptosis. HIV-1 also depletes CD4+ T cells in PBMCs from patients who have a genetically defective Fas pathway. These results suggest that HIV-1 induces direct apoptosis of infected cells and kills T cells by a Fas-independent mechanism

How can we improve the interpretation of systematic reviews?

A study conducted by Lai and colleagues, published this week in BMC Medicine, suggests that more guidance might be required for interpreting systematic review (SR) results. In the study by Lai and colleagues, positive (or favorable) results were influential in changing participants' prior beliefs about the interventions presented in the systematic review. Other studies have examined the relationship between favorable systematic review results and the publication of systematic reviews. An international registry may decrease the number of unpublished systematic reviews and will hopefully decrease redundancy, increase transparency, and increase collaboration within the SR community. In addition, using guidance from the Preferred Items for Systematic Reviews and Meta-analyses (PRISMA: http://www.prisma-statement.org/) Statement and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE: http://www.gradeworkinggroup.org/) approach can also be used to improve the interpretation of systematic reviews. In this commentary, we highlight important methodological issues related to the conduct and reporting of systematic reviews and also present our own guidance on interpreting systematic reviews

Carotid-ophthalmic aneurysms – protective features making them a rare cause of subarachnoid hemorrhage

Objective: To review the rate of carotid-ophthalmic aneurysm (COA) rupture and to identify protective features that may contribute to their low rupture rate.Methods: We reviewed the records of 790 patients with 773 aneurysms greater than 2 mm treated by endovascular routes between 2002 and 2012 at our institution. Seventy five carotid-ophthalmic aneurysms were identified in 72 patients. Three injected human cadaver heads were studied to evaluate the perianeurysmal environment of the carotid-ophthalmic region.Results: Only 2 (2.8%) of these 72 patients presented with acute SAH due to a ruptured carotid-ophthalmic aneurysm. The average size of ruptured COA was 11.3 mm versus 7 mm for unruptured aneurysms. Most of the aneurysms were discovered in patients who were asymptomatic. The most common presenting symptom was headache. In this study, we also provide cadaveric anatomic illustrations of the perianeurysmal environment in order to investigate the low rate of COA rupture. Additionally, we highlight the existence of a double arachnoid layer consisting of the arachnoid on the inferior aspect of the optic nerve and surrounding the internal carotid artery (ICA), which could further contribute to the low rupture rate of these aneurysms.Conclusions: Carotid-ophthalmic aneurysms are uncommon sources of subarachnoid hemorrhage. The perianeurysmal environment surrounding these aneurysms may provide protection, lending these aneurysms to a relatively benign natural history