A Climatology of the Tropospheric Thermal Stratification Using Saturation Potential Vorticity

The condition of convective neutrality is assessed in the troposphere by calculating the saturation potential vorticity P* from reanalysis data. Regions of the atmosphere in which saturation entropy is constant along isosurfaces of absolute angular momentum, a state indicative of slantwise-convective neutrality, have values of P* equal to zero. In a global reanalysis dataset spanning the years 1970–2004, tropospheric regions are identified in which P* is near zero, implying that vertical convection or slantwise convection may be important in determining the local thermal stratification. Convectively neutral air masses are common not only in the Tropics but also in higher latitudes, for example, over midlatitude continents in summer and in storm tracks over oceans in winter. Large-scale eddies appear to stabilize parts of the lower troposphere, particularly in winter

Generation of Synthetic Antenna Apertures In Swarm Unmanned Aerial Systems Using Tight-Coupling

Relative to their various land and air-based counterparts, swarm unmanned aerial system (SUAS) platforms, being comprised of many separate airborne bodies, or elements, possess a number of unique and advantageous characteristics, whether in the context of radar, or communications. These advantages include reduced element complexity, minimal size, weight, and power (SWaP) requirements, and a high degree of redundancy, among others. Because individual bodies in an SUAS are generally smaller than single UAS systems, however, it is generally imperative that the overall electromagnetic performance of the entire swarm match or even exceed that of its single-bodied counterpart, compensating for any reduction in the capabilities of individual radiators within the SUAS. Consequently, even with reduced complexity in the individual elements, the design and control of such large arrays of radiating bodies often presents a very significant challenge. Previous work has demonstrated the efficacy of design techniques involving widely-spaced, sparse arrays, and deliberate use of aperiodicity in order to maximize array radiation performance, while minimizing any deleterious effects. Such design techniques, however, are quite limited in their use, often requiring very large numbers of electromagnetically large elements, whilst only achieving fairly narrowband solutions. Consequently, attempts to make use of these techniques require both a high degree of control complexity, and vast amounts of space, being unable to bring elements close together, lest detrimental phenomena like mutual impedance arise. To enable the design of more tightly-spaced SUAS with fewer, and potentially smaller, elements, a fairly new antenna array design technique will be utilized, being now applied to the more challenging domain of SUAS for the first time. In particular, the following will be the application of tight-coupling, which exploits rather than mitigates the presence of mutual impedance, to closely-spaced antenna arrays. Thus, the ability of tight-coupling techniques, when applied to SUAS, to generate useful antenna array apertures will subsequently investigated. This exploration will pay particular attention to arrays comprised of elements with poor individual radiative capabilities. The performance of these SUAS arrays will be assessed primarily in terms of spectral impedance, efficiency, and realized gain behavior

Extent of Hadley circulations in dry atmospheres

The subtropical terminus of the Hadley circulation is interpreted as the latitude poleward of which vertical wave activity fluxes (meridional eddy entropy fluxes) become sufficiently deep to reach the upper troposphere. This leads to a sign change of the upper-tropospheric divergence of meridional wave activity fluxes (convergence of meridional eddy angular momentum fluxes) and marks the transition from the tropical Hadley cell to the extratropical Ferrel cell. A quantitative formulation for determining the depth of vertical wave activity fluxes and thus the terminus of the Hadley circulation is proposed based on the supercriticality, a measure of the slope of isentropes. The supercriticality assumes an approximately constant value at the terminus of the Hadley circulation in a series of simulations with an idealized dry general circulation model. However, it is unclear how to generalize this supercriticality-based formulation to moist atmospheres

That’s Not Fair!! Human Rights Violations during the 1800s

Grade Level(s): 1-5Background information, research data, continuing to learn the history of Indiana, promotion of higher order thinking skills, skills development with mapping, time lines, and Venn diagrams.Hall Elementary Monrovia, I

Tropical Cyclone Genesis Factors in Simulations of the Last Glacial Maximum

Large-scale environmental factors that favor tropical cyclogenesis are calculated and examined in simulations of the Last Glacial Maximum (LGM) from the Paleoclimate Modelling Intercomparison Project Phase 2 (PMIP2). Despite universally colder conditions at the LGM, values of tropical cyclone potential intensity, which both serves as an upper bound on thermodynamically achievable intensity and indicates regions supportive of the deep convection required, are broadly similar in magnitude to those in preindustrial era control simulation. Some regions, including large areas of the central and western North Pacific, feature higher potential intensities at the LGM than they do in the control runs, while other regions including much of the Atlantic and Indian Oceans are lower. Changes in potential intensity are strongly correlated with the degree of surface cooling during the LGM. Additionally, two thermodynamic parameters—one that measures midtropospheric entropy deficits relevant for tropical cyclogenesis and another related to the time required for genesis—are broadly more favorable in the LGM simulation than in the preindustrial era control. A genesis potential index yields higher values for the LGM in much of the western Pacific, a feature common to nearly all of the individual models examined

Variations in Tropical Cyclone Genesis Factors in Simulations of the Holocene Epoch

The thermodynamic factors related to tropical cyclone genesis are examined in several simulations of the middle part of the Holocene epoch when the precession of Earth’s orbit altered the seasonal distribution of solar radiation and in one transient simulation of the millennium preceding the industrial era. The thermodynamic properties most crucial for genesis display a broad stability across both periods, although both orbital variations during the mid-Holocene (MH) 6000 years ago (6ka) and volcanic eruptions in the transient simulation have detectable effects. It is shown that the distribution of top-of-the-atmosphere radiation 6ka altered the Northern Hemisphere seasonal cycle of the potential intensity of tropical cyclones in addition to slightly increasing the difference between middle tropospheric and boundary layer entropy, a parameter that has been related to the incubation period required for genesis. The Southern Hemisphere, which receives more solar radiation during its storm season today than it did 6ka, displays slightly more favorable thermodynamic properties during the MH than in the preindustrial era control. Surface temperatures over the ocean in both hemispheres respond to radiation anomalies more slowly than those in upper levels, altering the thermal stability. Volcanism produces a sharp but transient temperature response in the last-millennium simulation that strongly reduces potential intensity during the seasons immediately following a major eruption. Here, too, the differential vertical temperature response is key: temperatures in the lower and middle troposphere cool, while those near the tropopause rise. Aside from these deviations, there is no substantial variation in thermodynamic properties over the 1000-yr simulation

On the maintenance of weak meridional temperature gradients during warm climates

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.Includes bibliographical references (p. 238-248).This thesis examines the dynamics of equable climates. The underlying physics of two mechanisms by which weak meridional temperature gradients might be maintained are studied. First, I examine the evolution of stratospheric dynamics and winter temperatures when the surface temperature gradient and tropospheric eddy energy decrease in order to assess whether large-scale conditions are more favorable for polar stratospheric cloud formation. Second, I examine whether the combination of high carbon dioxide and interactive, tropical cyclone dependent ocean mixing is sufficient to maintain a weak temperature gradient. I examine planetary wave generation, the energetics of the general circulation, and vertical wave propagation in a general circulation model with a resolved stratosphere forced with a weak surface temperature gradient. Compared to the present climate, transient eddy energy decreases, but stationary eddy energy does not. The polar tropopause rises, which supports a weaker temperature gradient in the lower stratosphere, a weaker stratospheric jet, and an increase in the wave activity vertically propagating into the stratosphere.(cont.) As a result, the residual mean circulation strengthens and temperatures in the polar stratosphere change little even when the surface temperature gradient is quite weak. Temperatures in the Arctic polar vortex remain much warmer than radiative equilibrium, inhibiting large-scale polar stratospheric cloud formation. The height of the extratropical tropopause rises and the tropospheric lapse rate follows a moist adiabat when surface temperatures are warm, suggesting convection plays a significant role in setting extratropical tropospheric stratification during warm climates. The second part of the thesis addresses the role of tropical cyclone induced mixing in the oceans' general circulation. I examine the sensitivity of the oceans' meridional overturning circulation and heat flux to the locations at which mixing occurs. When confined to the tropical Atlantic, a robust single-basin circulation can be maintained, but the Indian and Pacific become quiescent, cut off from the dynamics occurring in the Atlantic. Mixing isolated in the tropical Pacific, however, can support a global circulation by mechanically lifting deep fluid parcels formed in the Atlantic, raising their potential energy.(cont.) The oceans' total heat flux is found to be sensitive to mixing in the tropics, in both the Atlantic and the Pacific, and in the upper 400 meters of the ocean. Coupling mixing with a measure of tropical cyclone intensity and frequency creates a positive feedback between climate and the poleward energy flux. When combined with a parameterization of the background mixing that evolves with stratification, a warmer, less stratified ocean can support a stronger diapycnal mixing during warm climates with high loads of carbon dioxide. In these simulations, tropical cyclones are stronger and more frequent, providing an increased energy source for more vigorous mixing in the tropical oceans. Combined with a stratification-dependent mixing scheme, such mixing provides a sufficiently strong heat flux that is able to maintain weak sea surface temperature gradients.by Robert Lindsay Korty.Ph.D

Nd Isotopic Structure of the Pacific Ocean 70-30 and Numerical Evidence for Vigorous Ocean Circulation and Ocean Heat Transport in a Greenhouse World

The oceanic meridional overturning circulation (MOC) is a crucial component of the climate system, impacting heat and nutrient transport, and global carbon cycling. Past greenhouse climate intervals present a paradox because their weak equator-to-pole temperature gradients imply a weaker MOC, yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients. To investigate the mode of MOC that operated during the early Cenozoic, we compare new Nd isotope data with Nd tracer-enabled numerical ocean circulation and coupled climate model simulations. Assimilation of new Nd isotope data from South Pacific Deep Sea Drilling Project and Ocean Drilling Program Sites 323, 463, 596, 865, and 869 with previously published data confirm the hypothesized MOC characterized by vigorous sinking in the South and North Pacific ~70 to 30 Ma. Compilation of all Pacific Nd isotope data indicates vigorous, distinct, and separate overturning circulations in each basin until ~40 Ma. Simulations consistently reproduce South Pacific and North Pacific deep convection over a broad range of conditions, but cases using strong deep ocean vertical mixing produced the best data-model match. Strong mixing, potentially resulting from enhanced abyssal tidal dissipation, greater interaction of wind-driven internal wave activity with submarine plateaus, or higher than modern values of the geothermal heat flux enable models to achieve enhanced MOC circulation rates with resulting Nd isotope distributions consistent with the proxy data. The consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients

Increased hurricane frequency near Florida during Younger Dryas Atlantic Meridional Overturning Circulation slowdown

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geology 45 (2017): 1047-1050, doi:10.1130/G39270.1.The risk posed by intensification of North Atlantic hurricane activity remains controversial, in part due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Here we present a record of storm-triggered turbidite deposition offshore the Dry Tortugas, south Florida, USA, that spans abrupt transitions in North Atlantic sea-surface temperature and Atlantic Meridional Overturning Circulation (AMOC) during the Younger Dryas (12.9–11.7 k.y. B.P.). Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at this time, our record and numerical experiments suggest that strong hurricanes may have regularly impacted Florida. Less severe surface cooling at mid-latitudes (~20–40°N) than across much of the tropical North Atlantic (~10–20°N) in response to AMOC reduction may best explain strong hurricane activity during the Younger Dryas near the Dry Tortugas and, potentially, along the entire southeastern coast of the United States.This work was supported by the U. S. Geological Survey Climate and Land Use Change Research and Development Program (Toomey), the Woods Hole Oceanographic Institution Ocean and Climate Change Institute (Toomey) and National Science Foundation grants (OCE-1356708 to Donnelly; 1356509 to van Hengstum)

Balancing risk with virtual private networking during a pandemic

When the pandemic struck and teaching went online worldwide, universities had to make pressing decisions that balanced cybersecurity against other factors, including health and safety, usability, and cost. One such challenge Indiana University (IU) faced was how to accommodate the secure telecommunications needs of 130,000 faculty, staff, and students who would now be teaching, learning, doing research, and working from home. Some universities reflexively promoted virtual private network (VPN) use for all activities. Such an approach would have been unsustainable at IU, however, owing both to the licenses and resources needed for the sheer number of users and to the high-throughput applications on which they rely. Perhaps even worse, it would have increased the chances that the VPN would be unavailable during a critical incident or other situation in which secure communications must be guaranteed. Instead, IU launched an awareness campaign demonstrating exactly when VPN use is and isn’t needed. In addition, network staff employed a VPN feature called split tunneling to reduce the load. This article discusses the advantages and disadvantages of this approach and how IU made the decision to balance both sides of the risk equation to ensure the continued advancement of its mission throughout the pandemic