The influence of regional feedbacks on circulation sensitivity

Weakening of the tropical overturning circulation in a warmer world is a robust feature in climate models. Here an idealized representation of ocean heat flux drives a Walker cell in an aquaplanet simulation. A goal of the study is to assess the influence of the Walker circulation on the magnitude and structure of climate feedbacks, as well as to global sensitivity. We compare two CO_2 perturbation experiments, one with and one without a Walker circulation, to isolate the differences attributable to tropical circulation and associated zonal asymmetries. For an imposed Walker circulation, the subtropical shortwave cloud feedback is reduced, which manifests as a weaker tropical-subtropical anomalous energy gradient and consequently a weaker slow down of the Hadley circulation, relative to the case without a Walker circulation. By focusing on the coupled feedback circulation system, these results offer insights into understanding changes in atmospheric circulation and hence the hydrological cycle under global warming

Tropical Intraseasonal Variability in Version 3 of the GFDL Atmosphere Model

Tropical intraseasonal variability is examined in version 3 of the Geophysical Fluid Dynamics Laboratory Atmosphere Model (AM3). In contrast to its predecessor AM2, AM3 uses a new treatment of deep and shallow cumulus convection and mesoscale clouds. The AM3 cumulus parameterization is a mass-flux-based scheme but also, unlike that in AM2, incorporates subgrid-scale vertical velocities; these play a key role in cumulus microphysical processes. The AM3 convection scheme allows multiphase water substance produced in deep cumuli to be transported directly into mesoscale clouds, which strongly influence large-scale moisture and radiation fields. The authors examine four AM3 simulations using a control model and three versions with different modifications to the deep convection scheme. In the control AM3, using a convective closure based on CAPE relaxation, both MJO and Kelvin waves are weak relative to those in observations. By modifying the convective closure and trigger assumptions to inhibit deep cumuli, AM3 produces reasonable intraseasonal variability but a degraded mean state. MJO-like disturbances in the modified AM3 propagate eastward at roughly the observed speed in the Indian Ocean but up to 2 times the observed speed in the west Pacific Ocean. Distinct differences in intraseasonal convective organization and propagation exist among the modified AM3 versions. Differences in vertical diabatic heating profiles associated with the MJO are also found. The two AM3 versions with the strongest intraseasonal signals have a more prominent “bottom heavy” heating profile leading the disturbance center and “top heavy” heating profile following the disturbance. The more realistic heating structures are associated with an improved depiction of moisture convergence and intraseasonal convective organization in AM3

Surface Fluxes and Tropical Intraseasonal Variability: a Reassessment

The authors argue that interactive feedbacks involving surface moist enthalpy fluxes, both turbulent and radiative, are important to the dynamics of tropical intraseasonal variability. Evidence in favor of this hypothesis includes the observed spatial distribution of intraseasonal variance in precipitation and outgoing longwave radiation, the observed relationship between intraseasonal latent heat flux and precipitation anomalies in regions where intraseasonal variability is strong, and sensitivity experiments performed with a small number of general circulation and idealized models. The authors argue that it would be useful to assess the importance of surface fluxes to intraseasonal variability in a larger number of comprehensive numerical models

Elucidating the role of Agl in bladder carcinogenesis by generation and characterization of genetically engineered mice

Amylo-\u3b1-1,6-glucosidase,4-\u3b1-glucanotransferase (AGL) is an enzyme primarily responsible for glycogen debranching. Germline mutations lead to glycogen storage disease type III (GSDIII). We recently found AGL to be a tumor suppressor in xenograft models of human bladder cancer (BC) and low levels of AGL expression in BC are associated with poor patient prognosis. However, the impact of low AGL expression on the susceptibility of normal bladder to carcinogenesis is unknown. We address this gap by developing a germline Agl knockout (Agl-/-) mouse that recapitulates biochemical and histological features of GSDIII. Agl-/- mice exposed to N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) had a higher BC incidence compared with wild-type mice (Agl+/+). To determine if the increased BC incidence observed was due to decreased Agl expression in the urothelium specifically, we developed a urothelium-specific conditional Agl knockout (Aglcko) mouse using a Uroplakin II-Cre allele. BBN-induced carcinogenesis experiments repeated in Aglcko mice revealed that Aglcko mice had a higher BC incidence than control (Aglfl/fl) mice. RNA sequencing revealed that tumors from Agl-/- mice had 19 differentially expressed genes compared with control mice. An 'Agl Loss' gene signature was developed and found to successfully stratify normal and tumor samples in two BC patient datasets. These results support the role of AGL loss in promoting carcinogenesis and provide a rationale for evaluating Agl expression levels, or Agl Loss gene signature scores, in normal urothelium of populations at risk of BC development such as older male smokers

Pulsar Wind Nebulae in Evolved Supernova Remnants

For pulsars similar to the one in the Crab Nebula, most of the energy input to the surrounding wind nebula occurs on a timescale of less than 1000 years; during this time, the nebula expands into freely expanding supernova ejecta. On a timescale 10,000 years, the interaction of the supernova with the surrounding medium drives a reverse shock front toward the center of the remnant, where it crushes the PWN (pulsar wind nebula). One- and two-dimensional, two-fluid simulations of the crushing and re-expansion phases of a PWN show that (1) these phases are subject to Rayleigh-Taylor instabilities that result in the mixing of thermal and nonthermal fluids, and (2) asymmetries in the surrounding interstellar medium give rise to asymmetries in the position of the PWN relative to the pulsar and explosion site. These effects are expected to be observable in the radio emission from evolved PWN because of the long lifetimes of radio emitting electrons. The scenario can explain the chaotic and asymmetric appearance of the Vela X PWN relative to the Vela pulsar without recourse to a directed flow from the vicinity of the pulsar. The displacement of the radio nebulae in G327.1--1.1, MSH15--56 (G326.3--1.8), G0.9+0.1, and W44 relative to the X-ray nebulae may be due to this mechanism. On timescales much greater than the nebular crushing time, the initial PWN may be mixed with thermal gas and become unobservable, so that even the radio emission is dominated by recently injected particles.Comment: 22 pages, 9 figures; submitted to Ap

Synthesis of Alkaline Earth Diazenides MAEN2 (MAE = Ca, Sr, Ba) by Controlled Thermal Decomposition of Azides under High Pressure

The alkaline earth diazenides MAEN2 with MAE = Ca, Sr and Ba were synthesized by a novel synthetic approach, namely, a controlled decomposition of the corresponding azides in a multianvil press at highpressure/ high-temperature conditions. The crystal structure of hitherto unknown calcium diazenide (space group I4/mmm (no. 139), a = 3.5747(6) Å, c = 5.9844(9) Å, Z = 2, wRp = 0.078) was solved and refined on the basis of powder X-ray diffraction data as well as that of SrN2 and BaN2. Accordingly, CaN2 is isotypic with SrN2 (space group I4/mmm (no. 139), a = 3.8054(2) Å, c = 6.8961(4) Å, Z = 2, wRp = 0.057) and the corresponding alkaline earth acetylenides (MAEC2) crystallizing in a tetragonally distorted NaCl structure type. In accordance with literature data, BaN2 adopts a more distorted structure in space group C2/c (no. 15) with a = 7.1608(4) Å, b = 4.3776(3) Å, c = 7.2188(4) Å, β = 104.9679(33)°, Z = 4 and wRp = 0.049). The N−N bond lengths of 1.202(4) Å in CaN2 (SrN2 1.239(4) Å, BaN2 1.23(2) Å) correspond well with a double-bonded dinitrogen unit confirming a diazenide ion [N2]2−. Temperature-dependent in situ powder X-ray diffractometry of the three alkaline earth diazenides resulted in formation of the corresponding subnitrides MAE2N (MAE = Ca, Sr, Ba) at higher temperatures. FTIR spectroscopy revealed a band at about 1380 cm−1 assigned to the N−N stretching vibration of the diazenide unit. Electronic structure calculations support the metallic character of alkaline earth diazenides

Recent Advances Concerning Certain Class of Geophysical Flows

This paper is devoted to reviewing several recent developments concerning certain class of geophysical models, including the primitive equations (PEs) of atmospheric and oceanic dynamics and a tropical atmosphere model. The PEs for large-scale oceanic and atmospheric dynamics are derived from the Navier-Stokes equations coupled to the heat convection by adopting the Boussinesq and hydrostatic approximations, while the tropical atmosphere model considered here is a nonlinear interaction system between the barotropic mode and the first baroclinic mode of the tropical atmosphere with moisture. We are mainly concerned with the global well-posedness of strong solutions to these systems, with full or partial viscosity, as well as certain singular perturbation small parameter limits related to these systems, including the small aspect ratio limit from the Navier-Stokes equations to the PEs, and a small relaxation-parameter in the tropical atmosphere model. These limits provide a rigorous justification to the hydrostatic balance in the PEs, and to the relaxation limit of the tropical atmosphere model, respectively. Some conditional uniqueness of weak solutions, and the global well-posedness of weak solutions with certain class of discontinuous initial data, to the PEs are also presented.Comment: arXiv admin note: text overlap with arXiv:1507.0523

Extratropical forcing and tropical rainfall distribution: energetics framework and ocean Ekman advection

Intense tropical rainfall occurs in a narrow belt near the equator, called the inter-tropical convergence zone (ITCZ). In the past decade, the atmospheric energy budget has been used to explain changes in the zonal-mean ITCZ position. The energetics framework provides a mechanism for extratropics-to-tropics teleconnections, which have been postulated from paleoclimate records. In atmosphere models coupled with a motionless slab ocean, the ITCZ shifts toward the warmed hemisphere in order for the Hadley circulation to transport energy toward the colder hemisphere. However, recent studies using fully coupled models show that tropical rainfall can be rather insensitive to extratropical forcing when ocean dynamics is included. Here, we explore the effect of meridional Ekman heat advection while neglecting the upwelling effect on the ITCZ response to prescribed extratropical thermal forcing. The tropical component of Ekman advection is a negative feedback that partially compensates the prescribed forcing, whereas the extratropical component is a positive feedback that amplifies the prescribed forcing. Overall, the tropical negative feedback dominates over the extratropical positive feedback. Thus, including Ekman advection reduces the need for atmospheric energy transport, dampening the ITCZ response. We propose to build a hierarchy of ocean models to systematically explore the full dynamical response of the coupled climate system

Challenges and opportunities for improved understanding of regional climate dynamics

Dynamical processes in the atmosphere and ocean are central to determining the large-scale drivers of regional climate change, yet their predictive understanding is poor. Here, we identify three frontline challenges in climate dynamics where significant progress can be made to inform adaptation: response of storms, blocks and jet streams to external forcing; basin-to-basin and tropical–extratropical teleconnections; and the development of non-linear predictive theory. We highlight opportunities and techniques for making immediate progress in these areas, which critically involve the development of high-resolution coupled model simulations, partial coupling or pacemaker experiments, as well as the development and use of dynamical metrics and exploitation of hierarchies of models