Global upper-atmospheric heating on Jupiter by the polar aurorae.

Jupiter's upper atmosphere is considerably hotter than expected from the amount of sunlight that it receives1-3. Processes that couple the magnetosphere to the atmosphere give rise to intense auroral emissions and enormous deposition of energy in the magnetic polar regions, so it has been presumed that redistribution of this energy could heat the rest of the planet4-6. Instead, most thermospheric global circulation models demonstrate that auroral energy is trapped at high latitudes by the strong winds on this rapidly rotating planet3,5,7-10. Consequently, other possible heat sources have continued to be studied, such as heating by gravity waves and acoustic waves emanating from the lower atmosphere2,11-13. Each mechanism would imprint a unique signature on the global Jovian temperature gradients, thus revealing the dominant heat source, but a lack of planet-wide, high-resolution data has meant that these gradients have not been determined. Here we report infrared spectroscopy of Jupiter with a spatial resolution of 2 degrees in longitude and latitude, extending from pole to equator. We find that temperatures decrease steadily from the auroral polar regions to the equator. Furthermore, during a period of enhanced activity possibly driven by a solar wind compression, a high-temperature planetary-scale structure was observed that may be propagating from the aurora. These observations indicate that Jupiter's upper atmosphere is predominantly heated by the redistribution of auroral energy.

Atmospheric implications of the lack of H3+ detection at Neptune.

H3+ has been detected at all of the solar system giant planets aside from Neptune. Current observational upper limits imply that there is far less H3+ emission at Neptune than rudimentary modelling would suggest. Here, we explore via modelling a range of atmospheric conditions in order to find some that could be consistent with observational constraints. In particular, we consider that the upper atmosphere might be much cooler than it was during the 1989 Voyager 2 encounter, and we examine the impact of an enhanced influx of external material that could act to reduce H3+ density. Resulting ionosphere models that are consistent with existing H3+ observational constraints have an exospheric temperature of 450 K or less, 300 K lower than the Voyager 2 value. Alternatively, if a topside CO influx of 2 × 108 cm-2 s-1 is imposed, the upper atmospheric temperature can be higher, up to 550 K. The potential cooling of Neptune's atmosphere is relevant for poorly understood giant planet thermospheric energetics, and would also impact aerobreaking manoeuvers for any future spacecraft. Such a large CO influx, if present, could imply Triton is a very active moon with prominent atmospheric escape, and/or that Neptune's rings significantly modify its upper atmosphere, and the introduction of so much exogenic material would complicate interpretation of the origin of species observed in Neptune's lower atmosphere. This article is part a discussion meeting issue 'Future exploration of ice giant systems'.

Why is the H3+ hot spot above Jupiter's Great Red Spot so hot?

Recent observations of Jupiter's Great Red Spot indicate that the thermosphere above the storm is hotter than its surroundings by more than 700 K. Possible suggested sources for this heating have thus far included atmospheric gravity waves and lightning-driven acoustic waves. Here, we propose that Joule heating, driven by Great Red Spot vorticity penetrating up into the lower stratosphere and coupling to the thermosphere, may contribute to the large observed temperatures. The strength of Joule heating will depend on the local inclination angle of the magnetic field and thus the observed emissions and inferred temperatures should vary with planetary longitude as the Great Red Spot tracks across the planet. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

Modelling H3+ in planetary atmospheres: effects of vertical gradients on observed quantities.

Since its detection in the aurorae of Jupiter approximately 30 years ago, the H3+ ion has served as an invaluable probe of giant planet upper atmospheres. However, the vast majority of monitoring of planetary H3+ radiation has followed from observations that rely on deriving parameters from column-integrated paths through the emitting layer. Here, we investigate the effects of density and temperature gradients along such paths on the measured H3+ spectrum and its resulting interpretation. In a non-isothermal atmosphere, H3+ column densities retrieved from such observations are found to represent a lower limit, reduced by 20% or more from the true atmospheric value. Global simulations of Uranus' ionosphere reveal that measured H3+ temperature variations are often attributable to well-understood solar zenith angle effects rather than indications of real atmospheric variability. Finally, based on these insights, a preliminary method of deriving vertical temperature structure is demonstrated at Jupiter using model reproductions of electron density and H3+ measurements. The sheer diversity and uncertainty of conditions in planetary atmospheres prohibits this work from providing blanket quantitative correction factors; nonetheless, we illustrate a few simple ways in which the already formidable utility of H3+ observations in understanding planetary atmospheres can be enhanced. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

The H3+ ionosphere of Uranus: decades-long cooling and local-time morphology.

The upper atmosphere of Uranus has been observed to be slowly cooling between 1993 and 2011. New analysis of near-infrared observations of emission from H3+ obtained between 2012 and 2018 reveals that this cooling trend has continued, showing that the upper atmosphere has cooled for 27 years, longer than the length of a nominal season of 21 years. The new observations have offered greater spatial resolution and higher sensitivity than previous ones, enabling the characterization of the H3+ intensity as a function of local time. These profiles peak between 13 and 15 h local time, later than models suggest. The NASA Infrared Telescope Facility iSHELL instrument also provides the detection of a bright H3+ signal on 16 October 2016, rotating into view from the dawn sector. This feature is consistent with an auroral signal, but is the only of its kind present in this comprehensive dataset. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

Heating of Jupiter's upper atmosphere above the Great Red Spot.

The temperatures of giant-planet upper atmospheres at mid- to low latitudes are measured to be hundreds of degrees warmer than simulations based on solar heating alone can explain. Modelling studies that focus on additional sources of heating have been unable to resolve this major discrepancy. Equatorward transport of energy from the hot auroral regions was expected to heat the low latitudes, but models have demonstrated that auroral energy is trapped at high latitudes, a consequence of the strong Coriolis forces on rapidly rotating planets. Wave heating, driven from below, represents another potential source of upper-atmospheric heating, though initial calculations have proven inconclusive for Jupiter, largely owing to a lack of observational constraints on wave parameters. Here we report that the upper atmosphere above Jupiter's Great Red Spot--the largest storm in the Solar System--is hundreds of degrees hotter than anywhere else on the planet. This hotspot, by process of elimination, must be heated from below, and this detection is therefore strong evidence for coupling between Jupiter's lower and upper atmospheres, probably the result of upwardly propagating acoustic or gravity waves.

Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope.

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.

The domination of Saturn's low-latitude ionosphere by ring 'rain'.

Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities.

Interactions between tidal turbine wakes: experimental study of a group of three-bladed rotors.

It is well known that a wake will develop downstream of a tidal stream turbine owing to extraction of axial momentum across the rotor plane. To select a suitable layout for an array of horizontal axis tidal stream turbines, it is important to understand the extent and structure of the wakes of each turbine. Studies of wind turbines and isolated tidal stream turbines have shown that the velocity reduction in the wake of a single device is a function of the rotor operating state (specifically thrust), and that the rate of recovery of wake velocity is dependent on mixing between the wake and the surrounding flow. For an unbounded flow, the velocity of the surrounding flow is similar to that of the incident flow. However, the velocity of the surrounding flow will be increased by the presence of bounding surfaces formed by the bed and free surface, and by the wake of adjacent devices. This paper presents the results of an experimental study investigating the influence of such bounding surfaces on the structure of the wake of tidal stream turbines.

Emergency department evaluation and treatment of knee and leg injuries.

The knee is one of the most commonly injured joints in the human body, and, largely because of athletic injuries, they are increasing in frequency in the United States. This article provides a brief overview of knee anatomy, examines radiographic imaging techniques and arthrocentesis of the knee, and discusses injuries specific to the knee. An overview of leg anatomy is also presented, along with discussions of specific fractures common to the leg.

The effects of acute and chronic dihydropyridine calcium antagonist therapy on baroreflex sensitivity: a re-analysis using the sequence method.

The objective of this study was to examine the effects of dihydropyridine calcium antagonist therapy on 24-h baroreflex sensitivity. Twenty-three patients with moderate essential hypertension were studied before and during acute (10 patients) and chronic (21 patients) treatment with a dihydropyridine calcium antagonist (nifedipine, nicardipine or felodipine) as monotherapy in a dose titrated to produce a fall in mean cuff pressure of at least 10%. Twenty-four hour unrestricted ambulatory intra-arterial blood pressure (IABP) and heart rate (R-R interval) were monitored. Baroreflex sensitivity (BRS) was assessed throughout the 24-h period by off-line computer analysis of spontaneous variations in IABP and R-R interval. During acute first dose treatment with a calcium antagonist there was a significant fall in blood pressure (BP), increase in heart rate and reduction in BRS. With chronic therapy (6-16 weeks) there was a continued reduction in mean BP of 11% (P < 0.001), but heart rate had returned to control levels and BRS was significantly increased over the 24 h by 14% (P < 0.01). The increase in BRS was evident during both the waking and sleeping periods, but the greatest increase was during sleep (awake 12% P = 0. 02, asleep 28% P = 0.003). In conclusion, although dihydropyridine calcium antagonists acutely cause a reflex tachycardia associated with a reduced BRS, there is no such effect with chronic therapy. BRS was significantly increased after chronic treatment, with exaggeration of the diurnal pattern. Journal of Human Hypertension (2000) 14, 189-194.

Sleep and blood pressure: spontaneous baroreflex sensitivity in dippers and non-dippers.

OBJECTIVE: Baroreflex sensitivity (BRS) increases during sleep, whereas arterial blood pressure falls. Some hypertensive patients do not have a nocturnal fall in blood pressure (non-dippers). The objective was to ascertain whether there is a difference between 24 h BRS values in dippers and non-dippers that might account for the difference in nocturnal blood pressure behaviour. DESIGN: In a group of consecutive untreated hypertensive patients undergoing 24 h ambulatory intra-arterial blood pressure (IABP) monitoring, 18 were non-dippers i.e., their mean IABP during sleep failed to drop by 10% of their waking IABP. Each non-dipper was matched for age and waking IABP with two dippers. The BRS had previously been assessed with the "Oxford' bolus phenylephrine technique; spontaneous BRS was assessed throughout the 24 h period by off-line computer analysis of spontaneous variations in IABP and R-R interval. RESULTS: In both groups there was a significant increase in spontaneous BRS during sleep (P < 0.0001 for dippers, P < 0.0001 for non-dippers). There was no significant difference between spontaneous BRS in dippers and non-dippers, when they were either awake or asleep. CONCLUSION: BRS did not differ significantly between dippers and non-dippers, when they were either awake or asleep. Changes in BRS during sleep are not likely to account for the abnormal dipping pattern in a minority of hypertensives and are not likely to contribute to the normally observed nocturnal fall in blood pressure.

Cardiac hypertrophy as a result of long-term thyroxine therapy and thyrotoxicosis.

OBJECTIVES: To define the effects of long-term thyroxine treatment upon heart rate, blood pressure, left ventricular systolic function, and left ventricular size, as well as indices of autonomic function, and to compare findings with those in patients with thyrotoxicosis before and during treatment. DESIGN: Cross sectional study of patients prescribed thyroxine long term (n = 11), patients with thyrotoxicosis studied at presentation (n = 23), compared with controls (n = 25); longitudinal study of patients with thyrotoxicosis studied at presentation and serially after beginning antithyroid drug treatment (n = 23). METHODS: 24 h ambulatory monitoring of pulse and blood pressure, echocardiography, forearm plethysmography, and autonomic function tests. RESULTS: Long-term thyroxine treatment in doses that reduced serum thyrotrophin to below normal had no effect on blood pressure, heart rate, left ventricular systolic function or stroke volume index, but was associated with an 18.4% increase in left ventricular mass index (mean (SEM) 101.9 (3.09) g/m2 v controls 86.1 (4.61), P < 0.01). Thryoxine treatment, like thyrotoxicosis, had no effect on tests of autonomic function. Untreated thyrotoxicosis resulted in pronounced changes in systolic and diastolic blood pressure and an increase in heart rate during waking and sleep. Patients with thyrotoxicosis at presentation had an increase in left ventricular systolic function (ejection fraction 70.5 (1.66)% v 65.4 (1.79), P < 0.01; fractional shortening 40.4 (1.54)% v 35.6 (1.46), P < 0.01), increased stroke volume index (45.9 (2.4) ml/m2 v 36.6 (1.7), P < 0.001), and an increase in forearm blood flow, and decrease in vascular resistance. They had a similar degree of left ventricular hypertrophy to that associated with thyroxine treatment (99.3 (4.03) g/m2); all changes were corrected within 2 months by antithyroid drugs. CONCLUSIONS: The development of left ventricular hypertrophy in patients receiving thyroxine in the absence of significant changes in heart rate, blood pressure, and left ventricular systolic function is consistent with a direct trophic effect of thyroid hormone on the myocardium. The presence of left ventricular hypertrophy determines that further studies are essential to assess cardiovascular risk in patients taking thyroxine long term.

Cardiovascular function and glucocorticoid replacement in patients with hypopituitarism.

OBJECTIVE: Retrospective analysis suggests an increased mortality from cardiovascular disease in hypopituitary adults; GH deficiency has been postulated to account for this. However, glucocorticoid replacement doses of 30 mg/day of hydrocortisone (HC) may be excessive, and could therefore be implicated in the increased cardiovascular mortality in this group of patients. The aims of this study were to establish whether patients with hypopituitarism have any abnormalities of the cardiovascular system compared to a control group and whether any of these parameters might be improved by reducing the replacement dose of glucocorticoid. PATIENTS AND MEASUREMENTS: A prospective analysis of cardiovascular function was carried out in 13 patients with hypopituitarism on routine replacement therapy and 20 normal controls who were matched for age and body mass index (BMI). Twenty-four-hour ambulatory blood pressure (BP), erect and supine BP, echocardiography, forearm plethysmography and cardiovascular reflexes in response to tilt, Valsalva and isometric hand grip were performed on controls and on patients taking 30 mg/day of HC and repeated following a reduction in HC dose to 15 mg/day for 3 months. Weight, plasma and urinary electrolytes, 24-hour urinary cortisol excretion, glucose, HbA1C and pituitary function were also assessed on HC 30 mg/day and 15 mg/day. RESULTS: Mean 24-hour ambulatory BP, in addition to day and night time BP, was lower in patients than in controls (achieving statistical significance in the male subgroup) and did not change significantly with a reduction in HC dose. Erect and supine BP was also lower in patients compared to controls and there was no evidence of postural hypotension following a reduction in HC dose to 15 mg/day. Systolic and diastolic left ventricular dimensions, interventricular septal thickness, ejection fraction and fractional shortening were similar in controls and patients and did not alter with a reduction in HC dose. Systolic and diastolic BP and heart rate responded appropriately to all tests of cardiovascular reflexes (tilt, Valsalva and isometric handgrip) in hypopituitary patients though again measurements of systolic BP were significantly lower in patients during these tests, independent of HC dose. Forearm plethysmography was similar in patients receiving 30 mg of HC and controls but forearm blood flow increased significantly when the HC dose was reduced to 15 mg/day. There was no change in weight, plasma and urinary electrolytes, glucose and HbA1C or pituitary function in the patient group throughout the study. CONCLUSIONS: In contrast to other studies we have failed to confirm cardiovascular dysfunction in GH deficient hypopituitary adults. Indeed, cardiovascular protection may be conferred on this group by the lower BP levels. Although a reduction in hydrocortisone dose was well tolerated in all patients, it appeared to confer no additional clinical benefit over the 3-month study period. In view of the conflicting data on cardiovascular function in hypopituitary patients, further prospective mortality studies are required in patients with adult GH deficiency.

Effect of unrestricted activity on accuracy of ambulatory blood pressure measurement.

A validation study of the Takeda TM-2420 ambulatory blood pressure recorder was performed on 10 subjects using the Oxford ambulatory intra-arterial recording apparatus during unrestricted activity. Electronic linkage of the two recorders ensured simultaneous blood pressure readings, taken from opposite arms. Although there was close approximation of intra-arterial and automated sphygmomanometric recordings over the range of blood pressure encountered in this study, there was a wide scatter of points and a tendency for the machine to underestimate systolic pressure by more than 15 mm Hg in the hypertensive range (systolic blood pressure more than 160 mm Hg) was detected. These findings suggest that automated recording of blood pressure during unrestricted activity may have a proportion of artifactual readings. Although simultaneous intra-arterial blood pressure recording may not be appropriate for widespread use in device validation, this study illustrated some potential disadvantages of the current validation recommendations, namely, the absence of assessment of device accuracy during unrestricted and ambulatory activity.

Effects of the angiotensin converting enzyme inhibitor, benazepril, on the sino-aortic baroreceptor heart rate reflex.

The effects of monotherapy with the angiotensin converting enzyme inhibitor benazepril (10 mg once daily) on cardiovascular baroreceptor reflexes were determined in 10 patients with essential hypertension using a randomized, double-blind, placebo-controlled, cross-over protocol. Early sino-aortic baroreceptor/heart rate reflex resetting was apparent with acute treatment; this effect persisted throughout the active treatment period. Changes in baroreflex sensitivity did not appear to mediate the hypotensive effect of benazepril.

Xamoterol in the treatment of orthostatic hypotension associated with multiple system atrophy (Shy-Drager syndrome).

The effect of xamoterol on the orthostatic hypotension associated with Shy-Drager syndrome was investigated in three patients. Intra-arterial blood pressure was measured during a control period and during treatment with xamoterol, both in a cardiovascular investigation laboratory and for 24 h of unrestricted activity using portable apparatus. Xamoterol lessened the total number of symptomatic episodes of orthostatic hypotension by 67 per cent. Average untreated 24-h intra-arterial blood pressure was 132/78 mmHg; during treatment with xamoterol it rose to 138/90 mmHg. However episodes of severe hypertension (defined as a systolic intra-arterial blood pressure above 200 mmHg) were more frequent with xamoterol. Although xamoterol attenuated orthostatic hypotension, careful monitoring of ambulatory blood pressure may be necessary, particularly at the start of treatment, because of the development of severe supine hypertension. Intravenous test doses of xamoterol did not predict either the attenuation of orthostatic hypotension or the development of supine hypertension in all patients.

Effects of perindopril on ambulatory intra-arterial blood pressure, cardiovascular reflexes and forearm blood flow in essential hypertension.

The effects of monotherapy with the angiotensin converting enzyme (ACE) inhibitor perindopril (8 mg once daily) on 24-h ambulatory intra-arterial blood pressure, forearm blood flow, left ventricular mass, vasoactive hormones and cardiovascular reflexes were determined in eight hypertensive patients using a randomized, double blind, placebo-controlled, cross-over protocol. Six weeks of perindopril treatment was associated with a significant reduction of ambulatory blood pressure and a significant increase in forearm blood flow. Whilst the haemodynamic responses to Valsalva's manoeuvre, tilt, isometric forearm exercise and cold pressor testing were unaffected by perindopril, significant augmentation of the bradycardia during facial immersion was seen after chronic therapy. Sino-aortic baroreceptor-heart rate reflex resetting was apparent within 2 h of the first dose; this effect persisted throughout the active treatment period. Withdrawal of treatment was associated with a persisting hypotensive effect and an increase in heart rate which was not accompanied by an increase in plasma catecholamines. We conclude that perindopril, in a dose of 8 mg once daily, was an effective antihypertensive agent. We postulate that chronic therapy was associated with a sustained increase in parasympathetic tone.

Forearm haemodynamics and blood pressure variability in hypertensive patients.

Ambulatory blood pressure variability and forearm haemodynamics were measured in 23 untreated hypertensive patients with a mean casual blood pressure of 162/102(11/9) mmHg (without target organ damage). There was a good inverse correlation between blood pressure variability and the ability of the forearm resistance vessels to dilate after a period of venous occlusion. Previous work has shown that this vasodilatory component of the response to forearm venous occlusion is significantly reduced in hypertensive patients compared with normotensive controls and is probably an indicator of the compliance properties of these vessels. The present results suggest that blood pressure variability is greater when resistance vessels are stiffer and emphasise the need to account for this vascular factor in studies of blood pressure behaviour.

Can sinoaortic baroreceptor heart rate reflex sensitivity be determined from phase IV of the Valsalva manoeuvre?

A new time related method of analysing the sinoaortic baroreceptor heart rate reflex, which determines reflex latency as well as sensitivity, was used to compare the results obtained with a phenylephrine ramp method (P) with those obtained using the whole of phase IV of Valsalva (V1) and using the phase IV systolic blood pressure overshoot alone (V2). Twenty five subjects with large ranges of age and resting blood pressures were studied. Each performed two standardised Valsalva manoeuvres and received three bolus injections of phenylephrine sufficient to cause transient pressor responses of 20-30 mmHg. Mean sensitivity values with P (6.2(3.5) ms.mmHg-1) were greater than those with V1 (4.6(2.3) ms.mmHg-1, p less than 0.001) and less than V2 (7.8(4.0) ms.mmHg-1, p less than 0.001). However, linear regression analysis showed a correlation of P with V1 (r = 0.76, p less than 0.0001) and with V2 (r = 0.80, p less than 0.0001). Reflex latency with P (1084(427) ms) was less than V1 (2416(423) ms, p less than 0.0001) and V2 (1504(441) ms, p less than 0.0005). Reflex sensitivity results obtained using phase IV of Valsalva's manoeuvre are proportionately related to phenylephrine results, but large errors were introduced into the absolute values obtained when relatively small changes were made to the method of analysis.