The annual cycle of Northern Hemisphere storm-tracks. Part 2: regional detail

In Part 1 of this study, the annual cycle of the Northern Hemisphere storm-tracks was investigated using feature tracking and Eulerian variance based diagnostics applied on both vorticity and meridional wind. Results were presented and discussed for the four seasons at both upper (250hPa) and lower (850hPa) tropospheric levels. Here, using the meridional wind diagnostics, the annual cycles of the North Pacific and North Atlantic storm-tracks are examined in detail. This is done using monthly and 20° longitudinal sector averages. Many sectors have been considered, but the focus is on sectors equally spaced in the two main oceanic storm-tracks situated at their western, central and eastern regions, the western ones being mainly over the upstream continents. The annual cycles of the upper and lower tropospheric storm-tracks in the central and eastern Pacific, and western and central Atlantic sectors all have rather similar structures. In amplitude, each sector at both levels has a summer minimum and a relatively uniform strength from October to April, despite the strong winter maxima in the westerly jets. However, high intensity storms occur over a much wider latitudinal band in winter. The storm-track in each sector moves poleward from May to August and returns equatorward from October to December, and there is a marked asymmetry between spring and autumn. There are many differences between the North Pacific and North Atlantic storm-tracks, and some of these seem to have their origin in the behaviour over the upstream East Asian and North American continents, suggesting the importance of seeding from these regions. The East Asian storm-track near 48°N has marked spring and autumn maxima and weak amplitude in winter and summer. The 33°N track is strong only in the first half of the year. In contrast, the eastern North American storm-track is well-organised all year, around the baroclinicity that moves latitudinally with the seasons. The signatures associated with these features are found to gradually decrease downstream in each case. In particular, there is very little latitudinal movement in the storm-track in the Eastern Atlantic

The annual cycle of Northern Hemisphere storm-tracks. Part 1: seasons

In this paper and Part 2 a comprehensive picture of the annual cycle of the Northern Hemisphere storm-tracks is presented and discussed for the first time. It is based on both feature tracking and Eulerian based diagnostics, applied to vorticity and meridional wind in the upper and lower troposphere. Here, the storm-tracks, as diagnosed using both variables and both diagnostic techniques, are presented for the four seasons for each of the two levels. The oceanic storm-tracks retain much of their winter mean intensity in spring with only a small change in their latitude. In the summer they are much weaker, particularly in the Pacific and are generally further poleward. In autumn the intensities are larger again, comparable with those in spring, but the latitude is still nearer to that of summer. However, in the lower troposphere in the eastern ocean basins the tracking metrics show northern and southern tracks that change little with latitude through the year. The Pacific mid-winter minimum is seen in upper troposphere standard deviation diagnostics, but a richer picture is obtained using tracking. In winter there are high intensities over a wide range of latitudes in the central and eastern Pacific, and the west Pacific has high track density but weak intensity. In the lower troposphere all the diagnostics show that the strength of the Pacific and Atlantic storm-tracks are generally quite uniform over the autumn-winter-spring period. There is a close relationship between the upper tropospheric storm-track, particularly that based on vorticity, and tropopause level winds and temperature gradients. In the lower troposphere, in winter the oceanic storm-tracks are in the region of the strong meridional SST gradients, but in summer they are located in regions of small or even reversed SST gradients. However, over North America the lower tropospheric baroclinicity and the upstream portion of the Atlantic storm-track stay together throughout the year

On the importance of testing gravity at distances less than 1cm

If the mechanism responsible for the smallness of the vacuum energy is consistent with local quantum field theory, general arguments suggest the existence of at least one unobserved scalar particle with Compton wavelength bounded from below by one tenth of a millimeter. We show that this bound is saturated if vacuum energy is a substantial component of the energy density of the universe. Therefore, the success of cosmological models with a significant vacuum energy component suggests the existence of new macroscopic forces with range in the sub-millimeter region. There are virtually no experimental constraints on the existence of quanta with this range of interaction.Comment: 9 pages TeX, 2 eps figures, uses mtexsis.tex and epsf.tex. Entry in 1996 Gravity Research Foundation essay competition. To be published in the Journal of General Relativity and Gravitatio

A Lagrangian analysis of ice-supersaturated air over the North Atlantic

Understanding the nature of air parcels that exhibit ice-supersaturation is important because they are the regions of potential formation of both cirrus and aircraft contrails, which affect the radiation balance. Ice-supersaturated air parcels in the upper troposphere and lower stratosphere over the North Atlantic are investigated using Lagrangian trajectories. The trajectory calculations use ERA-Interim data for three winter and three summer seasons, resulting in approximately 200,000 trajectories with ice-supersaturation for each season. For both summer and winter, the median duration of ice-supersaturation along a trajectory is less than 6 hours. 5% of air which becomes ice-supersaturated in the troposphere, and 23% of air which becomes ice-supersaturated in the stratosphere will remain ice-supersaturated for at least 24 hours. Weighting the ice-supersaturation duration with the observed frequency indicates the likely overall importance of the longer duration ice-supersaturated trajectories. Ice-supersaturated air parcels typically experience a decrease in moisture content while ice-supersaturated, suggesting that cirrus clouds eventually form in the majority of such air. A comparison is made between short-lived (less than 24 h) and long-lived (greater than 24 h) ice-supersaturated air flows. For both air flows, ice-supersaturation occurs around the northernmost part of the trajectory. Short-lived ice-supersaturated air flows show no significant differences in speed or direction of movement to subsaturated air parcels. However, long-lived ice-supersaturated air occurs in slower moving air flows, which implies that they are not associated with the fastest moving air through a jet stream

Diagnosing topographic forcing in an atmospheric dataset: the case of the North American Cordillera

It is well known from modelling studies that surface topography influences the large-scale atmospheric circulation and that several model biases are associated with incorrect representation of topography. The textbook explanation of topographic effects on large-scale circulation appeals to the theoretical relationship between surface forcing and vortex stretching along trajectories in single-layer models. The goal of this study is to design and use a simple diagnostic of the large-scale forcing on the atmosphere when air is passing over topography, directly from atmospheric fields, based on this theoretical relationship. The study examines the interaction of the atmosphere with the North American Cordillera and samples the flow by means of trajectories during Northern Hemisphere winter. We detect a signal of topographic forcing in the atmospheric dataset, which, although much less distinct than in the theoretical relationship, nevertheless exhibits a number of expected properties. Namely, the signal increases with latitude, is usually stronger upslope than downslope, and is enhanced if the flow is more orthogonal to the mountain ridge, for example during periods of positive PNA. Furthermore, a connection is found between an enhanced signal of topographic forcing downslope of the North American Cordillera and periods of more frequent downstream European blocking

A Search for Scalar Chameleons with ADMX

Scalar fields with a "chameleon" property, in which the effective particle mass is a function of its local environment, are common to many theories beyond the standard model and could be responsible for dark energy. If these fields couple weakly to the photon, they could be detectable through the "afterglow" effect of photon-chameleon-photon transitions. The ADMX experiment was used in the first chameleon search with a microwave cavity to set a new limit on scalar chameleon-photon coupling excluding values between 2*10^9 and 5*10^14 for effective chameleon masses between 1.9510 and 1.9525 micro-eV.Comment: 4 pages, 3 figure

A SQUID-based microwave cavity search for dark-matter axions

Axions in the micro eV mass range are a plausible cold dark matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. The first result from such an axion search using a superconducting first-stage amplifier (SQUID) is reported. The SQUID amplifier, replacing a conventional GaAs field-effect transistor amplifier, successfully reached axion-photon coupling sensitivity in the band set by present axion models and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.Comment: 4 pages, 5 figures, submitted to PR

Move of a large but delicate apparatus on a trailer with air-ride suspension

When valuable delicate goods are shipped by truck, attention must be paid to vibrations that may cause damage. We present a case study of moving an extremely delicate 6230-kg superconducting magnet, immersed in liquid nitrogen, from Livermore, CA to Seattle, WA showing the steps of fatigue analysis of the load, a test move, and acceleration monitoring of the final move to ensure a successful damage-free transport

Impact of Gulf Stream SST biases on the global atmospheric circulation

The UK Met Office Unified Model in the Global Coupled 2 (GC2) configuration has a warm bias of up to almost 7K in the Gulf Stream SSTs in the winter season, which is associated with surface heat flux biases and potentially related to biases in the atmospheric circulation. The role of this SST bias is examined with a focus on the tropospheric response by performing three sensitivity experiments. The SST biases are imposed on the atmosphere-only configuration of the model over a small and medium section of the Gulf Stream, and also the wider North Atlantic. Here we show that the dynamical response to this anomalous Gulf Stream heating (and associated shifting and changing SST gradients) is to enhance vertical motion in the transient eddies over the Gulf Stream, rather than balance the heating with a linear dynamical meridional wind or meridional eddy heat transport. Together with the imposed Gulf Stream heating bias, the response affects the troposphere not only locally but also in remote regions of the Northern Hemisphere via a planetary Rossby wave response. The sensitivity experiments partially reproduce some of the differences in the coupled configuration of the model relative to the atmosphere-only configuration and to the ERA-Interim reanalysis. These biases may have implications for the ability of the model to respond correctly to variability or changes in the Gulf Stream. Better global prediction therefore requires particular focus on reducing any large western boundary current SST biases in these regions of high ocean-atmosphere interaction