SCALING METHODOLOGY FOR BUCKLING OF COMPOSITE CONICAL SHELLS IN AXIAL COMPRESSIONConical shells are commonly used as structural components for launch vehicles. The axial compression experienced during launch is one of the sizing load cases, because it can lead to loss of structural stability. Because experimentally testing these full-scale structures is cumbersome and expensive, it is expedient to understand how reduced-scale shells can be designed such that their buckling behavior is representative of the full-scale shell behavior. An analytical, sequential scaling methodology is developed based on the nondimensional governing equations for composite conical shells with a symmetric, balanced layup and negligible flexural anisotropy. Linear and nonlinear finite element analyses characterizing the buckling behavior of the different size shells yielded comparable results in terms of buckling load, meridional displacement, and buckling mode. The inclusion of geometric imperfections affects the prediction accuracy, but not to the extent that the methodology is no longer valid.

Conical shells are commonly used as structural components for launch vehicles. The axial compression experienced during launch is one of the sizing load cases, because it can lead to loss of structural stability. Because experimentally testing these full-scale structures is cumbersome and expensive, it is expedient to understand how reduced-scale shells can be designed such that their buckling behavior is representative of the full-scale shell behavior. An analytical, sequential scaling methodology is developed based on the nondimensional governing equations for composite conical shells with a symmetric, balanced layup and negligible flexural anisotropy. Linear and nonlinear finite element analyses characterizing the buckling behavior of the different size shells yielded comparable results in terms of buckling load, meridional displacement, and buckling mode. The inclusion of geometric imperfections affects the prediction accuracy, but not to the extent that the methodology is no longer valid.

Tropical expansion driven by poleward advancing subtropical front

<p>Abundance of evidence shows that the tropics are expanding in the past four decades. Despite many attempts to decipher its cause, the underlying dynamical mechanism driving tropical expansion is still not clear. Here, based on observations and multi-model simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5), the variations and trends of tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the meridional displacement of oceanic subtropical front. Under global warming, the subtropical ocean experiences more surface warming due to convergence of surface water. Such enhanced warming, superimposing onto the variation of Pacific Decadal Oscillation, leads to poleward advancing of subtropical front and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that the observed expanding tropics may largely attributed to the anthropogenic global warming rather than the natural climate variability.</p>

Effect of Siberian high and remote forcings on winter precipitation in the Kingdom of Saudi Arabia

In the current literature, little is known about the role of Siberian High (SbH) on precipitation variability over the Kingdom of Saudi Arabia. The technique of centers of action (COA) has been employed here to study the possible impact of SbH on interannual variations in winter precipitation over the kingdom because the COA methodology helps us to find changes in interannual variations of pressure intensity, latitudinal and longitudinal positions of the pressure system using sea-level pressure data. The results show that there are two regions of the kingdom whose precipitation is significantly affected by SbH, the southeast region and the region from northeast to central Saudi Arabia. The precipitation over the southeastern region is significantly influenced by the intensity of SbH as well as its meridional displacement whereas the precipitation variability from northeast to the central kingdom is significantly influenced by the meridional displacement of SbH. The effect of remote forcings of North Atlantic Oscillation and El Niño–Southern Oscillation on precipitation of the kingdom has also been discussed in the paper. The empirical results can be understood by the mechanism of changes and circulations in the atmosphere.

On the Relation between the Boreal Spring Position of the Atlantic Intertropical Convergence Zone and Atlantic Zonal Mode

Previous studies have talked about the existence of a relation between the Atlantic meridional mode (AMM) and Atlantic zonal mode (AZM) via the meridional displacement of the intertropical convergence zone (ITCZ) in the Atlantic during boreal spring and the resulting cross-equatorial zonal winds. However, why the strong relation between the ITCZ (or AMM) and zonal winds does not translate into a strong relation between the ITCZ and AZM has not been explained. This question is addressed here, and it is found that there is a skewness in the relation between ITCZ and AZM: while a northward migration of ITCZ during spring in general leads to a cold AZM event in the ensuing summer, the southward migration of the ITCZ is less likely to lead to a warm event. This is contrary to what the previous studies imply. The skewness is attributed to the Atlantic seasonal cycle and to the strong seasonality of the AZM. All those cold AZM events preceded by a northward ITCZ movement during spring are found to strictly adhere to typical timings and evolution of the different Bjerknes feedback components involved. It is also observed that the causative mechanisms of warm events are more diverse than those of the cold events. These results can be expected to enhance our understanding of the AZM as well as that of chronic model biases and contribute to the predictability of the Indian summer monsoon through the links between the two as shown in our earlier studies.

Gulf Stream Excursions and Sectional Detachments Generate the Decadal Pulses in the Atlantic Multidecadal Oscillation

Decadal pulses within the lower-frequency Atlantic multidecadal oscillation (AMO) are a prominent but underappreciated AMO feature, representing decadal variability of the subpolar gyre (e.g., the Great Salinity Anomaly of the 1970s) and wielding notable influence on the hydroclimate of the African and American continents. Here clues are sought into their origin in the spatiotemporal development of the Gulf Stream’s (GS) meridional excursions and sectional detachments apparent in the 1954–2012 record of ocean surface and subsurface salinity and temperature observations. The GS excursions are tracked via meridional displacement of the 15°C isotherm at 200-m depth—the GS index—whereas the AMO’s decadal pulses are targeted through the AMO tendency, which implicitly highlights the shorter time scales of the AMO index. The GS’s northward shift is shown to be preceded by the positive phase of the low-frequency North Atlantic Oscillation (LF-NAO) and followed by a positive AMO tendency by 1.25 and 2.5 years, respectively. The temporal phasing is such that the GS’s northward shift is nearly concurrent with the AMO’s cold decadal phase (cold, fresh subpolar gyre). Ocean–atmosphere processes that can initiate phase reversal of the gyre state are discussed, starting with the reversal of the LF-NAO, leading to a mechanistic hypothesis for decadal fluctuations of the subpolar gyre. According to the hypothesis, the fluctuation time scale is set by the self-feedback of the LF-NAO from its influence on SSTs in the seas around Greenland, and by the cross-basin transit of the GS’s detached eastern section; the latter is produced by the southward intrusion of subpolar water through the Newfoundland basin, just prior to the GS’s northward shift in the western basin.

The Large-Scale Dynamical Response of Clouds to Aerosol Forcing

Radiative kernels are used to quantify the instantaneous radiative forcing of aerosols and the aerosol-mediated cloud response in coupled ocean–atmosphere model simulations under both historical and future emission scenarios. The method is evaluated using matching pairs of historical climate change experiments with and without aerosol forcing and accurately captures the spatial pattern and global-mean effects of aerosol forcing. It is shown that aerosol-driven changes in the atmospheric circulation induce additional cloud changes. Thus, the total aerosol-mediated cloud response consists of both local microphysical changes and nonlocal dynamical changes that are driven by hemispheric asymmetries in aerosol forcing. By comparing coupled and fixed sea surface temperature (SST) simulations with identical aerosol forcing, the relative contributions of these two components are isolated, exploiting the ability of prescribed SSTs to also suppress changes in the atmospheric circulation. The radiative impact of the dynamical cloud changes is found to be comparable in magnitude to that of the microphysical cloud changes and acts to further amplify the interhemispheric asymmetry of the aerosol radiative forcing. The dynamical cloud response is closely linked to the meridional displacement of the Hadley cell, which, in turn, is driven by changes in the cross-equatorial energy transport. In this way, the dynamical cloud changes act as a positive feedback on the meridional displacement of the Hadley cell, roughly doubling the projected changes in cross-equatorial energy transport compared to that from the microphysical changes alone.