Automated identification and tracking of polar-cap plasma patches at solar minimum

A method of automatically identifying and tracking polar-cap plasma patches, utilising data inversion and feature-tracking methods, is presented. A well-established and widely used 4-D ionospheric imaging algorithm, the Multi-Instrument Data Assimilation System (MIDAS), inverts slant total electron content (TEC) data from ground-based Global Navigation Satellite System (GNSS) receivers to produce images of the free electron distribution in the polar-cap ionosphere. These are integrated to form vertical TEC maps. A flexible feature-tracking algorithm, TRACK, previously used extensively in meteorological storm-tracking studies is used to identify and track maxima in the resulting 2-D data fields. Various criteria are used to discriminate between genuine patches and "false-positive" maxima such as the continuously moving day-side maximum, which results from the Earth's rotation rather than plasma motion. Results for a 12-month period at solar minimum, when extensive validation data are available, are presented. The method identifies 71 separate structures consistent with patch motion during this time. The limitations of solar minimum and the consequent small number of patches make climatological inferences difficult, but the feasibility of the method for patches larger than approximately 500 km in scale is demonstrated and a larger study incorporating other parts of the solar cycle is warranted. Possible further optimisation of discrimination criteria, particularly regarding the definition of a patch in terms of its plasma concentration enhancement over the surrounding background, may improve results.

Distinguishing the cold conveyor belt and sting jet air streams in an intense extratropical cyclone

Strong winds equatorwards and rearwards of a cyclone core have often been associated with two phenomena, the cold conveyor belt (CCB) jet and sting jets. Here, detailed observations of the mesoscale structure in this region of an intense cyclone are analysed. The {\it in-situ} and dropsonde observations were obtained during two research flights through the cyclone during the DIAMET (DIAbatic influences on Mesoscale structures in ExTratropical storms) field campaign. A numerical weather prediction model is used to link the strong wind regions with three types of ``air streams'', or coherent ensembles of trajectories: two types are identified with the CCB, hooking around the cyclone center, while the third is identified with a sting jet, descending from the cloud head to the west of the cyclone. Chemical tracer observations show for the first time that the CCB and sting jet air streams are distinct air masses even when the associated low-level wind maxima are not spatially distinct. In the model, the CCB experiences slow latent heating through weak resolved ascent and convection, while the sting jet experiences weak cooling associated with microphysics during its subsaturated descent. Diagnosis of mesoscale instabilities in the model shows that the CCB passes through largely stable regions, while the sting jet spends relatively long periods in locations characterized by conditional symmetric instability (CSI). The relation of CSI to the observed mesoscale structure of the bent-back front and its possible role in the cloud banding is discussed.

The effect of polyoxyethylene polymers on the transport of ranitidine in Caco-2 cell monolayers.

Previous in vivo studies using PEG 400 showed an enhancement in the bioavailability of ranitidine. This study investigated the effect of PEG 200, 300 and 400 on ranitidine transport across Caco-2 cells. The effect of PEG polymers (20%, v/v) on the bi-directional flux of (3)H-ranitidine across Caco-2 cell monolayers was measured. The concentration dependence of PEG 400 effects on ranitidine transport was also studied. A specific screen for P-glycoprotein (P-gp) activity was used to test for an interaction between PEG and P-gp. In the absence of PEG, ranitidine transport showed over 5-fold greater flux across Caco-2 monolayers in the secretory than the absorptive direction; efflux ratio 5.38. PEG 300 and 400 significantly reduced this efflux ratio (p<0.05), whereas PEG 200 had no effect (p>0.05). In concordance, PEG 300 and 400 showed an interaction with the P-gp transporter, whereas PEG 200 did not. Interestingly, with PEG 400 a non-linear concentration dependence was seen for the inhibition of the efflux ratio of ranitidine, with a maxima at 1%, v/v (p<0.05). The inhibition of ranitidine efflux by PEG 300 and 400 which interact with P-gp provides a mechanism that may account for the observations of ranitidine absorption enhancement by PEG 400 in vivo.

Observations of urban boundary layer structure during a strong urban heat island event

It has long been known that the urban surface energy balance is different to that of a rural surface, and that heating of the urban surface after sunset gives rise to the Urban Heat Island (UHI). Less well known is how flow and turbulence structure above the urban surface are changed during different phases of the urban boundary layer (UBL). This paper presents new observations above both an urban and rural surface and investigates how much UBL structure deviates from classical behaviour. A 5-day, low wind, cloudless, high pressure period over London, UK, was chosen for analysis, during which there was a strong UHI. Boundary layer evolution for both sites was determined by the diurnal cycle in sensible heat flux, with an extended decay period of approximately 4 h for the convective UBL. This is referred to as the “Urban Convective Island” as the surrounding rural area was already stable at this time. Mixing height magnitude depended on the combination of regional temperature profiles and surface temperature. Given the daytime UHI intensity of 1.5∘C, combined with multiple inversions in the temperature profile, urban and rural mixing heights underwent opposite trends over the period, resulting in a factor of three height difference by the fifth day. Nocturnal jets undergoing inertial oscillations were observed aloft in the urban wind profile as soon as the rural boundary layer became stable: clear jet maxima over the urban surface only emerged once the UBL had become stable. This was due to mixing during the Urban Convective Island reducing shear. Analysis of turbulent moments (variance, skewness and kurtosis) showed “upside-down” boundary layer characteristics on some mornings during initial rapid growth of the convective UBL. During the “Urban Convective Island” phase, turbulence structure still resembled a classical convective boundary layer but with some influence from shear aloft, depending on jet strength. These results demonstrate that appropriate choice of Doppler lidar scan patterns can give detailed profiles of UBL flow. Insights drawn from the observations have implications for accuracy of boundary conditions when simulating urban flow and dispersion, as the UBL is clearly the result of processes driven not only by local surface conditions but also regional atmospheric structure.

Satiation attenuates BOLD activity in brain regions involved in reward and increases activity in dorsolateral prefrontal cortex: an fMRI study in healthy volunteers

BACKGROUND: Neural responses to rewarding food cues are significantly different in the fed vs. fasted (>8 h food-deprived) state. However, the effect of eating to satiety after a shorter (more natural) intermeal interval on neural responses to both rewarding and aversive cues has not been examined. OBJECTIVE: With the use of a novel functional magnetic resonance imaging (fMRI) task, we investigated the effect of satiation on neural responses to both rewarding and aversive food tastes and pictures. DESIGN: Sixteen healthy participants (8 men, 8 women) were scanned on 2 separate test days, before and after eating a meal to satiation or after not eating for 4 h (satiated vs. premeal). fMRI blood oxygen level-dependent (BOLD) signals to the sight and/or taste of the stimuli were recorded. RESULTS: A whole-brain cluster-corrected analysis (P < 0.05) showed that satiation attenuated the BOLD response to both stimulus types in the ventromedial prefrontal cortex (vmPFC), orbitofrontal cortex, nucleus accumbens, hypothalamus, and insula but increased BOLD activity in the dorsolateral prefrontal cortex (dlPFC; local maxima corrected to P ≤ 0.001). A psychophysiological interaction analysis showed that the vmPFC was more highly connected to the dlPFC when individuals were exposed to food stimuli when satiated than when not satiated. CONCLUSIONS: These results suggest that natural satiation attenuates activity in reward-related brain regions and increases activity in the dlPFC, which may reflect a "top down" cognitive influence on satiation. This trial was registered at clinicaltrials.gov as NCT02298049.

Sea level extremes at the coasts of China

Hourly sea level records from 1954 to 2012 at 20 tide gauges at and adjacent to the Chinese coasts are used to analyze extremes in sea level and in tidal residual. Tides and tropical cyclones determine the spatial distribution of sea level maxima. Tidal residual maxima are predominantly determined by tropical cyclones. The 50 year return level is found to be sensitive to the number of extreme events used in the estimation. This is caused by the small number of tropical cyclone events happening each year which lead to other local storm events included thus significantly affecting the estimates. Significant increase in sea level extremes is found with trends in the range between 2.0 and 14.1 mm yr−1. The trends are primarily driven by changes in median sea level but also linked with increases in tidal amplitudes at three stations. Tropical cyclones cause significant interannual variations in the extremes. The interannual variability in the sea level extremes is also influenced by the changes in median sea level at the north and by the 18.6 year nodal cycle at the South China Sea. Neither of PDO and ENSO is found to be an indicator of changes in the size of extremes, but ENSO appears to regulate the number of tropical cyclones that reach the Chinese coasts. Global mean atmospheric temperature appears to be a good descriptor of the interannual variability of tidal residual extremes induced by tropical cyclones but the trend in global temperature is inconsistent with the lack of trend in the residuals.

Rapid changes in the redox conditions of the western Tethys Ocean during the early Aptian oceanic anoxic event

The early Aptian (125 to 121 Ma) records an episode of severe environmental change including a major perturbation of the carbon cycle, an oceanic anoxic event (OAE 1a, 122.5 Ma), a platform drowning episode and a biocalcification crisis. We propose to trace changes in the oxygenation state of the ocean during the early Aptian anoxic event using the redox-sensitive trace-element (RSTE) distribution, phosphorus accumulation rates (PARs) and organic-matter characterization in three different basins of the western Tethys. The following sections have been investigated: Gorgo a Cerbara (central Italy) in the Umbria Marche basin, Glaise (SE France) in the Vocontian basin and Cassis/La Bédoule (SE France) located in the Provencal basin. In the Gorgo a Cerbara section, RSTE distributions show a low background level along the main part of the section, contrasted by different maxima in concentrations within the Selli level. In the Glaise section, the Goguel level displays a weak increase in RSTE contents coeval with moderate TOC values. At Cassis/La Bédoule, no significant RSTE enrichments have been observed in sediments equivalent to the Selli level. These differences in the records of the geochemical proxies of the Selli level or its equivalent indicate the deposition under different redox conditions, probably related to the paleogeography. Our data indicate the development of anoxic–euxinic conditions in the deeper part of the Tethys during OAE 1a, whereas in the shallower environments, conditions were less reducing. Moreover, at Gorgo a Cerbara, the Selli level is characterized by rapid changes in the intensity of reducing conditions in the water column. Ocean eutrophication seems to be a major factor in the development and the persistence of anoxia as suggested by the PAR evolution. Higher PAR values at the onset of OAE 1a suggest an increase in nutrient input, whereas the return to lower values through the first part of the OAE 1a interval may be related to the weakened capacity to retain P in the sedimentary reservoir due to bottom-water oxygen depletion. This general pattern is contrasted by the data of Gorgo a Cerbara, where the sediments deposited during the OAE 1a interval show P-enrichments (mainly authigenic P). This is associated with maxima in TOC values and Corg:Ptot ratios, suggesting that a part of the remobilized P was trapped in the sediments and as such prevented from returning to the water column.

Diagnosing links between atmospheric moisture and extreme daily precipitation over the UK

Atmospheric moisture characteristics associated with the heaviest 1% of daily rainfall events affecting regions of the British Isles are analysed over the period 1997–2008. A blended satellite/rain-gauge data set (GPCP-1DD) and regionally averaged daily rain-gauge observations (HadUKP) are combined with the ERA Interim reanalysis. These are compared with simulations from the HadGEM2-A climate model which applied observed sea surface temperature and realistic radiative forcings. Median extreme daily rainfall across the identified events and locations is larger for GPCP (32 mm day−1) than HadUKP and the simulations (∼25 mm day−1). The heaviest observed and simulated daily rainfall events are associated with increased specific humidity and horizontal transport of moisture (median 850 hPa specific humidity of ∼6 g kg−1 and vapour transport of ∼150 g kg−1 m s−1 for both observed and simulated events). Extreme daily rainfall events are less common during spring and summer across much of the British Isles, but in the south east region, they contribute up to 60% of the total number of distinct extreme daily rainfall events during these months. Compared to winter events, the summer events over south east Britain are associated with a greater magnitude and more southerly location of moisture maxima and less spatially extensive regions of enhanced moisture transport. This contrasting dependence of extreme daily rainfall on moisture characteristics implies a range of driving mechanisms that depend upon location and season. Higher spatial and temporal resolution data are required to explore these processes further, which is vital in assessing future projected changes in rainfall and associated flooding.

Effect of simulated rainfall during wheat seed development and maturation on subsequent seed longevity is reversible

Poor wheat seed quality in temperate regions is often ascribed to wet production environments. We investigated the possible effect of simulated rain during seed development and maturation on seed longevity in wheat (Triticum aestivum L.) cv. Tybalt grown in the field (2008, 2009) or a polythene tunnel house (2010). To mimic rain, the seed crops were wetted from above with the equivalent of 30mm (2008, 2009) or 25mm rainfall (2010) at different stages of seed development and maturation (17 to 58 DAA, days after 50% anthesis), samples harvested serially, and subsequent air-dry seed longevity estimated. No pre-harvest sprouting occurred. Seed longevity (p50, 50% survival period in experimental hermetic storage at 40°C with c. 15% moisture content) in field-grown controls increased during seed development and maturation attaining maxima at 37 (2008) or 44 DAA (2009); it declined thereafter. Immediate effects of simulated rain at 17-58 DAA in field studies (2008, 2009) on subsequent seed longevity were negative but small, e.g. a 1-4 d delay in seed quality improvement for treatments early in development but with no damage detected at final harvests. In rainfall-protected conditions (2010), simulated rain close to harvest maturity (55-56 DAA) reduced longevity immediately and substantially, with greater damage from two sequential days of wetting than one; again, later harvests provided evidence of recovery in subsequent longevity. In the absence of pre-harvest sprouting, the potentially deleterious effects of rainfall to wheat seed crops on subsequent seed longevity may be reversible in full or in part.

The prediction of Northern Hemisphere tropical cyclone extended life cycles by the ECMWF Ensemble and Deterministic Prediction Systems. Part I: tropical cyclone stage

This study has explored the prediction errors of tropical cyclones (TCs) in the European Centre for Medium-Range Weather Forecasts (ECMWF) Ensemble Prediction System (EPS) for the Northern Hemisphere summer period for five recent years. Results for the EPS are contrasted with those for the higher-resolution deterministic forecasts. Various metrics of location and intensity errors are considered and contrasted for verification based on IBTrACS and the numerical weather prediction (NWP) analysis (NWPa). Motivated by the aim of exploring extended TC life cycles, location and intensity measures are introduced based on lower-tropospheric vorticity, which is contrasted with traditional verification metrics. Results show that location errors are almost identical when verified against IBTrACS or the NWPa. However, intensity in the form of the mean sea level pressure (MSLP) minima and 10-m wind speed maxima is significantly underpredicted relative to IBTrACS. Using the NWPa for verification results in much better consistency between the different intensity error metrics and indicates that the lower-tropospheric vorticity provides a good indication of vortex strength, with error results showing similar relationships to those based on MSLP and 10-m wind speeds for the different forecast types. The interannual variation in forecast errors are discussed in relation to changes in the forecast and NWPa system and variations in forecast errors between different ocean basins are discussed in terms of the propagation characteristics of the TCs.

The impact of oceanic heat transport on the atmospheric circulation

A general circulation model of intermediate complexity with an idealized Earth-like aquaplanet setup is used to study the impact of changes in the oceanic heat transport on the global atmospheric circulation. Focus is on the atmospheric mean meridional circulation and global thermodynamic properties. The atmosphere counterbalances to a large extent the imposed changes in the oceanic heat transport, but, nonetheless, significant modifications to the atmospheric general circulation are found. Increasing the strength of the oceanic heat transport up to 2.5 PW leads to an increase in the global mean near-surface temperature and to a decrease in its equator-to-pole gradient. For stronger transports, the gradient is reduced further, but the global mean remains approximately constant. This is linked to a cooling and a reversal of the temperature gradient in the tropics. Additionally, a stronger oceanic heat transport leads to a decline in the intensity and a poleward shift of the maxima of both the Hadley and Ferrel cells. Changes in zonal mean diabatic heating and friction impact the properties of the Hadley cell, while the behavior of the Ferrel cell is mostly controlled by friction. The efficiency of the climate machine, the intensity of the Lorenz energy cycle and the material entropy production of the system decline with increased oceanic heat transport. This suggests that the climate system becomes less efficient and turns into a state of reduced entropy production as the enhanced oceanic transport performs a stronger large-scale mixing between geophysical fluids with different temperatures, thus reducing the available energy in the climate system and bringing it closer to a state of thermal equilibrium.

Climatology and variability of trace gases in extratropical double-tropopause regions from MLS, HIRDLS, and ACE-FTS measurements

Upper tropospheric and lower stratospheric measurements from the Aura Microwave Limb Sounder (MLS), the Aura High Resolution Dynamics Limb Sounder (HIRDLS), and the Atmospheric Chemistry Experiment-Fourier transform spectrometer (ACE-FTS) are used to present the first global climatological comparison of extratropical, nonpolar trace gas distributions in double-tropopause (DT) and single-tropopause (ST) regions. Stratospheric tracers, O3, HNO3, and HCl, have lower mixing ratios ∼2–8 km above the primary (lowermost) tropopause in DT than in ST regions in all seasons, with maximum Northern Hemisphere (NH) differences near 50% in winter and 30% in summer. Southern Hemisphere winter differences are somewhat smaller, but summer differences are similar in the two hemispheres. H2O in DT regions of both hemispheres shows strong negative anomalies in November through February and positive anomalies in July through October, reflecting the strong seasonal cycle in H2O near the tropical tropopause. CO and other tropospheric tracers examined have higher DT than ST values 2–7 km above the primary tropopause, with the largest differences in winter. Large DT-ST differences extend to high NH latitudes in fall and winter, with longitudinal maxima in regions associated with enhanced wave activity and subtropical jet variations. Results for O3 and HNO3 agree closely between MLS and HIRDLS, and differences from ACE-FTS are consistent with its sparse and irregular midlatitude sampling. Consistent signatures in climatological trace gas fields provide strong evidence that transport from the tropical upper troposphere into the layer between double tropopauses is an important pathway for stratosphere-troposphere exchange.

The influence of sea ice dynamics on the climate sensitivity and memory to increased Antarctic sea ice

The study analyzes the sensitivity and memory of the Southern Hemisphere coupled climate system to increased Antarctic sea ice (ASI), taking into account the persistence of the sea ice maxima in the current climate. The mechanisms involved in restoring the climate balance under two sets of experiments, which differ in regard to their sea ice models, are discussed. The experiments are perturbed with extremes of ASI and integrated for 10 yr in a large 30-member ensemble. The results show that an ASI maximum is able to persist for ; 4 yr in the current climate, followed by a negative sea ice phase. The sea ice insulating effect during the positive phase reduces heat fluxes south of 60 8 S, while at the same time these are intensified at the sea ice edge. The increased air stability over the sea ice field strengthens the polar cell while the baroclinicity increases at midlatitudes. The mean sea level pressure is reduced (increased) over high latitudes (midlatitudes), typical of the southern annular mode (SAM) positive phase. The Southern Ocean (SO) becomes colder and fresher as the sea ice melts mainly through sea ice lateral melting, the consequence of which is an increase in the ocean stability by buoyancy and mixing changes. The climate sensitivity is triggered by the sea ice insulating process and the resulting freshwater pulse (fast response), while the climate equilibrium is restored by the heat stored in the SO subsurface layers (long response). It is concluded that the time needed for the ASI anomaly to be dissipated and/or melted is shortened by the sea ice dynamical processes.

In situ observations in cyclones over Fram Strait

During the international FRAMZY expedition in March 2002 in-situ observations of Fram Strait cyclones were made by aircraft, ship and automatic buoys in order to study the interaction between cyclones and sea ice. The atmospheric characteristics of the observed cyclones are presented in this paper. The cyclones were generated in the baroclinic zone at the ice edge and moved NNE-ward along the ice edge. This was supported by warm air advection from WSW by an upper-level wave. The cyclones were rather small (diameter 200– 700 km) and shallow (1–1.5 km e-folding height for the horizontal pressure and temperature difference) with life times between 12 and 36 hours. In spite of the small space and time scales, remarkable extremes were observed within the cyclones. Winds reached maxima above 20 ms−1 lasting for only a few hours. The transition from the cold to the advancing warm air over sea ice occurred within narrow (5–30 km) frontal zones in which vorticity and convergence reached maxima on the order of 10−3 s−1. It is discussed whether the sea ice in spite of its inertia is able to react on these strong sub cyclone-scale processes and, thus, these processes have to be taken into account in models in order to simulate the cyclone-sea ice interaction properly.

The longitudinal variation of equatorial waves due to propagation on a varying zonal flow

The general 1-D theory of waves propagating on a zonally varying flow is developed from basic wave theory, and equations are derived for the variation of wavenumber and energy along ray paths. Different categories of behaviour are found, depending on the sign of the group velocity (cg) and a wave property, B. For B positive the wave energy and the wave number vary in the same sense, with maxima in relative easterlies or westerlies, depending on the sign of cg. Also the wave accumulation of Webster and Chang (1988) occurs where cg goes to zero. However for B negative they behave in opposite senses and wave accumulation does not occur. The zonal propagation of the gravest equatorial waves is analysed in detail using the theory. For non-dispersive Kelvin waves, B reduces to 2, and analytic solution is possible. B is positive for all the waves considered, except for the westward moving mixed Rossby-gravity (WMRG) wave which can have negative as well as positive B. Comparison is made between the observed climatologies of the individual equatorial waves and the result of pure propagation on the climatological upper tropospheric flow. The Kelvin wave distribution is in remarkable agreement, considering the approximations made. Some aspects of the WMRG and Rossby wave distributions are also in qualitative agreement. However the observed maxima in these waves in the winter westerlies in the eastern Pacific and Atlantic are not consistent with the theory. This is consistent with the importance of the sources of equatorial waves in these westerly duct regions due to higher latitude wave activity.