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.

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.

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'.

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'.

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'.

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'.

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.

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.

Blood flow in pulmonary veins: I. Studies in dog and man.

The pattern of blood flow in the large extra parenchymal pulmonary veins is pulsatile in both dog and man. This pulsatility is dominated by the changes in left atrial pressure taking place throughout the cardiac cycle. No pulsatile component of low in the large pulmonary veins could be attributed to forward transmission of a flow pulse conducted from the lung capillaries. The findings suggest that there must be a region of considerable compliance in the pulmonary venous system which can absorb pulsations from the lung capillaries and eliminate their transmission to the left atrium.

Blood flow in pulmonary veins: II. The influence of events transmitted from the right and left sides of the heart.

The wave form of blood flow in the large extra parenchymal pulmonary veins has an inverse relationship to the pressure wave form in the left atrium during each cardiac cycle. However, when vein flow from the lungs is separated from the left atrium by diverting it into a constant pressure reservoir, its wave form then resembles a lung capillary flow pulse, though delayed from it in time and reduced in ampliture. The pulsatility of flow in pulmonary veins separated from the left atrium is further reduced when transcapillary pressure is elevated by lung inflation. However, in the intact state, the relation between the pattern of pulmonary vein flow and left atrial pressure remains unaffected by lung inflation. It is postulated that the thin walled extraperenchymal pulmonary veins together behave as a collapsible reservoir which enables outflow from them to be determined by changes in left atrial pressure, in spite of variations of pulsatile flow into them from the lungs.

Blood flow in pulmonary veins: III. Simultaneous measurements of their dimensions, intravascular pressure and flow.

Vein flow in the large extraparenchymal pulmonary veins is pulsatile and its wave form has an inverse relationship to left atrial pressure. Extraparenchymal pulmonary veins are thin walled and collapsible. This enables them to behave as highly compliant structures. Dimensional measurements of their cross sectional area in living open chested dogs showed them to be non circular at low left atrial pressures. They rapidly assumed a circular cross section as left atrial pressure rose. Only at pressures above 1.5 kPa (11 mmHg) were the pulmonary veins circular in cross section. The aggregate volume of the large extraparenchymal pulmonary veins, when fully distended, was found to be equal to or greater than one stroke volume of the heart. The extraparenchymal pulmonary veins act as a reservoir to the left atrium so that left ventricular stroke volume can be maintained relatively unaffected by beat by beat changes in right ventricular stroke output. Their behaviour at normal mean left atrial pressures also enables them to isolate the lung capillaries from retrograde transmission of positive pressure transients from the left atrium, which could otherwise impede venous outflow of blood from the lung capillary bed.

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.

Estimation of sinoaortic baroreceptor heart rate reflex sensitivity and latency in man: a new microcomputer assisted method of analysis.

A new method for analysing baroreflex sensitivity has been developed. It obviates the mathematical bias inherent in earlier methods and in addition provides a direct measurement of reflex latency. Sensitivity results obtained using this method in 25 patients with a wide range of ages and resting blood pressures were similar to, but consistently lower than, those achieved with the Oxford method. Baroreflex latency results ranged from 650 to 2900 ms (mean(SD) 1084(427) ms) and were reproducible within individuals. Sensitivity results were inversely related to age and resting systolic blood pressure. Reflex latency was not related to these variables or to resting heart rate or reflex sensitivity. This method was able to identify inadequate starting data and greatly reduced the analysis time.

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.

Factors determining direct arterial pressure and its variability in hypertensive man.

Intra-arterial pressure was recorded continuously in 26 patients with uncomplicated essential hypertension under standardized conditions. Recordings were analyzed beat by beat to obtain mean pressures and variability, expressed as the standard deviation of the frequency histogram. The major factors influencing variability were the level of pressure and the intensity of physical activity; systolic variability increased with progressive impairment of sino-aortic baroreflexes. Diastolic pressure increased with the level of sympathetic activity as reflected by plasma norepinephrine levels. After allowance for the decrease of plasma renin activity (PRA) with age, direct relationships were observed between PRA (log values) and the level of pressure and systolic variability; plasma angiotensin II values did not correlate. Systolic variability increased with the systolic response to cold but was unrelated to the response to dynamic or isometric exercise. Variability also tended to increase with obesity and was unrelated to age, sex, or race.

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.

Cardiovascular response in black and white hypertensives.

Sixteen untreated black patients with mild-to-moderate hypertension and no evidence of target organ damage were matched for age, sex, casual blood pressure (BP), and socioeconomic status with 16 white hypertensives. All patients were studied under standardized conditions in the hospital where they underwent continuous intraarterial ambulatory monitoring of BP and assessment of BP control mechanisms. BP characteristics over prolonged periods of recording were similar for both groups, as were sinoaortic baroreflex activity and pressor response to isometric and dynamic exercise and to cold. Fasting cholesterol and triglyceride levels in both groups were similar. Resting plasma renin activity (PRA) was significantly lower in blacks, but no difference was observed in resting plasma norepinephrine levels. Urinary excretion of NA+ and K+ was also similar in both groups. Thus, results showed that casual BPs matched for black and whites, and recorded over a prolonged period, were similar in pattern, variability, and response to pressor stimuli. It appears that, if BP contributes to the different patterns of morbidity in blacks and whites, it is more likely to be the actual level of BP rather than differences in BP characteristics.

Continuous ambulatory monitoring of blood pressure and assessment of cardiovascular reflexes in the elderly hypertensive.

Thirteen elderly hypertensives underwent continuous ambulatory blood pressure (BP) monitoring and measurement of cardiovascular reflexes. The results were compared with elderly normotensives and young hypertensives studied using the same protocol. There was a greater disparity between casual systolic BP (SBP) and ambulatory awake SBP in the elderly hypertensives than either the elderly normotensives or young hypertensives. Variability of SBP was greater in the elderly than the young, whilst baroreflex activity was reduced in the elderly, and more markedly so in the elderly hypertensives. Response to tilt and pressor tests was similar for the elderly. The elderly hypertensives showed a greater fall of SBP in response to tilt and a greater rise of SBP during dynamic exercise than the young hypertensives. Stimulation of plasma renin activity (PRA) in response to upright tilt was less in the elderly hypertensives than the young hypertensives. Resting plasma noradrenaline (PNA) increased with age.

Variation in cuff blood pressure in untreated outpatients with mild hypertension--implications for initiating antihypertensive treatment.

Thirty-two patients with mildly elevated blood pressure (BP), but without target organ damage, attended a BP measuring clinic where duplicate BP measurements were made on 12 visits. During visits 1-3, BP showed a systematic decrease which varied from patient to patient. During visits 4-12, no further systematic changes in BP were observed. During the latter period, between-visit variation in BP was substantial, the standard deviation of the difference in BP from one visit to another being 10.4 mmHg for systolic, 6.8 mmHg for diastolic (phase IV) and 7.0 mmHg for diastolic (phase V). These values were used to determine the chance that the BP estimated after a number of visits differed from the average stable BP. After visit 4, the chance of a difference of 5 mmHg or more was 0.50 systolic blood pressure (SBP) and 0.32 diastolic blood pressure (DBP; phase V). Increasing the number of visits to six or more reduced the chance of error. Before initiating lifelong treatment in mild hypertensives free of target organ damage, BP should be recorded in duplicate on a minimum of six visits.

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.