Day-night Temperature Difference Research Articles

Influence of climate, soil and vegetation diversity on the leaf area index as measured by canopy hemispherical photography in tropical rainforests across a wide elevational gradient

Tropical rainforests (TRFs) play an important role in regulating the global climate and conserving biodiversity. Leaf area index (LAI) determines the capacity of TRFs for radiation interception and carbon sequestration via photosynthesis while also influencing the water loss from TRF canopies via transpiration. Elevational gradients in tropical environments provide an approach to investigate the influence of environmental variations on key vegetation properties such as the LAI. In this work we determined the concurrent, interactive influences of the elevational gradients of the environment (i.e. selected climatic and soil properties) and vegetation (tree diversity and structure) in determining the variation of LAI of one-hectare permanent sampling plots (PSPs) within TRFs across a wide elevational gradient (from 117 m to 2132 m above sea level). Eight rounds of canopy hemispherical photography were carried out at three-month intervals over a 24-month period from 2019 to 2022. Canopy LAI was estimated using HemiView image processing software. Long-term mean climatic data from 1990 to 2021 were extracted for the PSPs from monthly global weather database of CRU-TS-4.06-bias corrected with WorldClim-2.1. Key soil properties were measured at 0–15 cm and 15–30 cm depths via soil sampling. Tree diversity was determined by a complete census of all trees with equal or greater than 10 cm in diameter at breast height. Total tree biomass was estimated using allometric equations. Linear mixed model analysis of LAI showed significant (p < 0.05) variance for the random effects of elevation and elevation × time interaction. In a majority of measurement rounds, variance of LAI due to elevation was significant while at a majority of elevations, the fixed effect of measurement round on LAI was significant. Leaf area index showed significant linear reductions with elevation in all rounds, at rates ranging from 0.175 to 0.357 per 1000 m. Linear and multiple regression analyses identified increasing maximum cumulative soil water deficit, CSWDMax (an index of water deficit computed as the difference between evapotranspiration and precipitation), as the major climatic factor responsible for the reduction of LAI with elevation. Decreasing solar irradiance (SR) and increasing day-night temperature difference (DTR) with elevation also contributed to the observed LAI trend. Multiple regression analysis showed soil exchangeable potassium (KEx) and available phosphorus (PAv) influencing LAI positively while electrical conductivity (EC) and total nitrogen (NTot) influencing LAI negatively. Variation of Shannon-Wiener tree diversity index (H) and total tree biomass per hectare (TBM) contributed positively to the observed elevational variation of LAI. Factor analysis extracted two underlying factor constructs which accounted for 86 % of the combined variation in climate, soil and vegetation across the elevational gradient. Plot-wise scores of Factor 1, which had CSWDMax, SR, DTR, soil EC, NTot and H loading strongly and accounting for 70 % of the variation, showed a significant linear relationship with LAI. A cluster analysis incorporating the elevational variation of LAI, climate, soil and vegetation clearly classified the TRFs into four ranges of elevation at a linkage distance of 0.75. We conclude that LAI of TRFs in our study decreases with increasing elevation and identify increasing water deficits with elevation as the major climatic factor controlling this reduction.

Variation of floristic diversity, community composition, endemism, and conservation status of tree species in tropical rainforests of Sri Lanka across a wide altitudinal gradient

Tropical rainforests in Sri Lanka are biodiversity hotspots, which are sensitive to anthropogenic disturbance and long-term climate change. We assessed the diversity, endemism and conservation status of these rainforests across a wide altitudinal range (100–2200 m above sea level) via a complete census of all trees having ≥ 10 cm diameter at breast height in ten one-hectare permanent sampling plots. The numbers of tree families, genera and species and community-scale tree diversity decreased with increasing altitude. Tree diversity, species richness and total basal area per ha across the altitudinal range were positively associated with long-term means of maximum temperature, annual rainfall and solar irradiance. Percentage of endangered species increased with increasing altitude and was positively associated with cumulative maximum soil water deficit, day-night temperature difference and high anthropogenic disturbance. Percentage of endemic species was greater in the lowland rainforests than in high-altitude montane forests. Nearly 85% of the species were recorded in three or less plots, which indicated substantial altitudinal differentiation in their distributions. Less than 10 individuals were recorded in 41% of the endemic species and 45% of the native species, which underlined the need for urgent conservation efforts across the whole altitudinal range.

Past and future trends of diurnal temperature range and their correlation with vegetation assessed by MODIS and CMIP6

Temperature anomalies and changes in the diurnal temperature range (DTR) are expected to pose physiological challenges to biota; hence, both spatial and temporal variations in DTR provide important insights into temperature-induced stress in humans, animals, and vegetation. Furthermore, vegetation could dampen temperature variability. Here, we use the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data of Land Surface Temperature (LST) to evaluate the global variation in DTR and its rate of change in spatial and temporal scales for the two decades spanning from 2001 to 2020. We show that North America, Africa, and Antarctica, as well as the global mean, experienced statistically significant DTR rates of change over the last 20 years in either summer, winter, or the annual mean. The rates were all negative, indicating the day-night temperature differences are decreasing in those regions because night temperatures are increasing at a faster rate than day temperatures. MODIS data of the Normalized Difference Vegetation Index (NDVI) revealed a strongly negative correlation with DTR, with a spatial correlation coefficient of −0.61. This correlation demonstrates a prominent dampening effect of vegetation on diurnal temperature oscillations. For future DTR projections, we used 19 models in the Coupled Model Intercomparison Project 6 (CMIP6) to predict global DTR trends from 2021 to 2050 with low and high CO2 concentration scenarios. The high CO2 emission scenario projects significant decreases in DTR in circumpolar regions, central Africa, and India compared to the low CO2 scenario. This difference in the two scenarios underscores the substantial influence of increased global temperatures and elevated CO2 concentration on DTR and, consequently, on the ecosystems in certain regions.

Controlling growth and carbohydrate utilization of tomato seedlings through day-night temperature difference and high light intensity under elevated CO2 conditions

Negative DIF, increasing nighttime temperature relative to daytime temperature, is widely used in the floral industry to reduce plant height. However, negative DIF can also reduce photosynthetic capacity in vegetative seedlings. We investigated the use of negative DIF combined with high light intensity under elevated CO2 and a long photoperiod to produce compact and well-developed tomato seedlings with reduced plant height. Seedlings were grown for 28 days under positive or negative DIF (with daytime/nighttime temperatures of 25 °C/19 °C or 21 °C/27 °C, respectively) combined with low or high light intensity [250 or 500 μmol m−2 s−1 photosynthetic photon flux density (PPFD), PPFD 250 or PPFD 500, respectively] at 1000 ppm CO2 (mean daily temperature: 23 °C across a photoperiod of 16 h d−1). Compared with positive DIF and PPFD 250, negative DIF with PPFD 500 significantly reduced plant height while tending to increase dry matter (DM) but decrease leaf area (LA). Relative growth rate was decreased under negative DIF despite the provision of PPFD 500, but there were no differences in photosynthetic rate and capacity parameters (e.g., total nitrogen and chlorophyll content at the LA level) between DIF treatments. Negative DIF and PPFD 500 might reduce DM by decreasing the amount of intercepted light in tomato seedlings. Negative DIF and PPFD 500 also increased respiration rate during nighttime and led to the consumption of more nonstructural carbohydrates (NSCs) at the LA level. Overall, our results indicate that negative DIF combined with high light intensity can maintain DM, photosynthetic capacity, and plant development while reducing plant height in tomato seedlings.

Analysis of the influence of day and night temperature difference on oxygen concentration in ullage space of fuel tank

PurposeDetermining the variation law of the oxygen concentration in the ullage space of the fuel tank is the key to the design of the inert system. Among various factors affecting the oxygen concentration in the ullage space of the fuel tank, the temperature difference between day and night shows particular importance while relevant analysis and calculation are scarce.Design/methodology/approachThis study establishes a theoretical simulation model of the central wing fuel tank of an aircraft according to the relevant provisions of day-night temperature variation in FAR25 airworthiness regulations, verifies the model with the existing experimental data and discusses the corresponding relationship between the oxygen concentration in the ullage space of the fuel tank and the day-night temperature difference. The influence of day and night temperature difference, fuel type, fuel load rate, initial oxygen concentration, dissolved oxygen evolution and other factors on the oxygen concentration in the ullage space of the fuel tank were analyzed, and the limit of initial oxygen concentration of the fuel tank before the shutdown at night meeting the requirements of the airworthiness provisions was proposed.FindingsThe results show that the temperature difference between day and night, fuel load rate, initial oxygen concentration and other factors have different effects on the oxygen concentration in the ullage space of fuel tank. The initial oxygen concentration limit before shutdown shall be 2% below the 12% oxygen concentration stipulated by FAA.Research limitations/implicationsThe research results in this paper will be of good reference value to the design of the inert system and the calculation of the flammability exposure evaluation time. This paper aims to be good reference of the design of the inert system and the calculation of the flammability exposure evaluation time.Originality/valueThe research results of this paper can provide practical guidance for the current civil airworthiness certification work.

APPLICATION OF A DAY-NIGHT TEMPERATURE DIFFERENCE ENERGY CONVERTER FOR POWER SUPPLY OF REMOTE AGRICULTURAL FACILITIES

Due to the development of information technologies, microelectronics and control systems, all electronic devices are being minimized. In some cases there is a need for electricity supply to remote agricultural facilities, for example, nomadic apiaries, remote pastures, hunting camps, reindeer herder camps. To solve this problem, the article proposes to use power supply devices based on the day-night temperature difference developed by the authors. (Research purpose) The research purpose is increasing the environmental safety and the reliability of energy supply of autonomous hybrid energy complexes based on renewable energy sources using the device of the daily temperature difference in their construction. (Materials and methods) The article proposes a method for producing energy using the day-night temperature difference. The advantages of the method are the absence of harmful environmental influences, safety for humans and nature, the inexhaustibility of the source, the possibility of using the device anywhere and the simplicity of technical implementation at the modern level. The authors have developed a methodology for calculating the device, its structural elements for electrical strength for autonomous power supply of remote agricultural production facilities. Classical methods for calculating charged containers with a dynamic change in their values at ambient temperature drop have been used in the research. (Results and discussion) Equation presented allows the calculation of a converter for a given capacity of autonomous power supply to remote agricultural production facilities. The advantages of the energy converter device, that is free of radioactive materials, there are the absence of combustion processes, gases, odors or volatile fractions. (Conclusions) The service life of the device can be long, up to hundreds of years. This technology can also be successfully used in the power supply on planets and space objects, for example, on the Moon, Mars, and other planets, where the temperature difference can reach up to hundreds of degrees.

DEVELOPMENT OF AN AUTONOMOUS HYBRID ELECTRICAL COMPLEX WITH A TEMPERATURE CHANGE SYSTEM

Recently, due to the progress in the development of wind generators and solar panels, autonomous hybrid energy systems based on renewable energy sources, which include solar panels, wind generators and power units, have been used for reliable power supply to remote settlements. The vulnerability of a hybrid power plant is its dependence on external climatic conditions and power units require fuel. To solve this problem, it is proposed to supplement hybrid systems with the use of power systems based on the day-night temperature difference. Today, there are no developed circuit solutions for the structure of a hybrid electrical complex based on renewable energy sources with a system of daily temperature difference in its composition according to a scheme with a common AC bus. (Research purpose) The research purpose is developing electric circuits of an autonomous hybrid power plant based on renewable energy sources with a temperature change system taking into account the load and determining the turn-on time of the gasoline generator. (Materials and methods) Considered an electrical complex of hybrid type with four sources of electrical energy, which includes a system of daily temperature difference. (Results and discussion) We have developed schemes for an autonomous hybrid electrical complex based on renewable energy sources with a temperature change system and an alternating current bus for power supply to remote agricultural facilities. The problems of the complex when using several inverters operating on one AC bus in the circuit and ways to solve them were shown. We calculated the loads for each power system and deduced the condition for switching on the gasoline power unit in adverse weather conditions. (Conclusions) It was determined that the developed electrical circuits with a load control unit and a common master generator of a hybrid energy system based on renewable energy sources with a temperature difference power system allow creating an optimal mode of its operation and managing the entire hybrid system more efficiently.

Graphical Analysis of Day - Night Temperature Difference by Interpolation and Approximation Methods for the Energy Converter of the Environment

Today, a lot of attention is paid to the search for environmentally friendly renewable energy sources. The most frequently considered such energy sources are wind energy, solar technology, the use of the energy of sea waves and biomass.Each of them has a drawback that prevents its widespread adoption. For example, wind farms create noise during their operation, are rigidly tied to the place where there are acceptable wind resources.To date, an energy converter has been developed, which works on the basis of the use of the ambient temperature difference during the day - the temperature is high during the day, and the temperature decreases at nightAs a rule, this temperature difference is in the range of about 5-9 degrees, although there are regions in which this difference is much higher, for example, in winter in Urengoy it can reach up to 30 degrees. An energy converter of this type is considered in works / 1-2/.The basis of the operation of such a converter is the change in the linear size of bodies, for example, plexiglass, with a change in temperature. When the temperature rises during the day, when the temperature is high, the rod lengthens, while at night, when the temperature is low, the linear dimensions of the rod decrease. This is exactly what is used to obtain energy through the use of a container. A conventional capacitor is used, one plate of which is fixed, the second plate of this capacitor is movable and connected to a dielectric plexiglass rod. When the temperature changes, for example, at a high temperature, the rod lengthens, the plates of the container come closer and the capacity will be maximum. At night, when the temperature decreases, the plexiglass rod is shortened, the plate moves away and the capacity decreases.If, at maximum capacity, the capacitor is charged and disconnected from the source, then the charge on it will be constant. At night, when the rod shrinks its linear dimensions, the movable plate moves away, the capacity falls. Since the charge on the container is constant, the voltage increases and we get an increase in energy, which is obtained from the day-night temperature difference and the change in the linear dimensions of the dielectric rod.

FEA of Effects Induced by Diurnal Temperature Variation on Downstream Surface of Xiaowan Arch Dam

In order to make clear the cracking reasons in arch dam of Xiaowan Hydropower Station during operation period, the approach to combine ANSYS with finite element program COCE-3D is adopted. Firstly, the influence by element type and mesh size for the temperature field simulation result is analyzed. Subsequently, the three typical dam segments cut from Xiaowan arch dam are selected and the relevant finite element model is established; the effect of the measured diurnal air temperature on temperature field and temperature stress of arch dam is analyzed thoroughly. The results indicate that the temperature gradient in mass concrete becomes lower, whereas the affecting depth becomes deeper when the mesh size is too large. Therefore, it is advisable to use smaller size mesh to study the influence of the measured diurnal air temperature on the surface temperature distribution in mass concrete. The temperature of downstream zone in arch dam is significantly affected by air temperature; the changing laws of temperature field and temperature stress with the air temperature are basically consistent, which is sensitive to lower temperature. When the temperature sharply decreased, the temperature stress in the downstream zone is mainly in tensile stress state. The calculated results are basically consistent with the measured results, and the temperature stress induced by the day-night temperature difference is the important reason for the horizontal cracks on the downstream surface. The submodel analysis method is an important alternative approach to study the changing laws of temperature field of arch dam. The research results not only provide an evidence for temperature control and crack prevention of Xiaowan arch dam but also provide a reference for temperature field simulation of similar projects.

Day/night temperature differences (DNTD) trigger changes in nutrient removal and functional bacteria in membrane bioreactors

Temperature is a well-known environmental stress that influences both microbial metabolism and community structure in the biological wastewater treatment systems. In this study, responses of biological performance and sludge microbiota to the long-term day/night temperature differences (DNTD) were investigated in membrane bioreactors (MBRs). The results showed that the functional bacteria could sustained their ecological functions at low DNTD (20/30 °C), resulting in relatively stable performance with respect to nutrient removal. However, when the activated sludge was subjected to a high DNTD (17/33 °C), the effluent concentrations of COD, TN and TP were significantly higher in MBR-B than that in MBR-A. In addition, more severe membrane fouling occurred under the perturbation of high DNTD as revealed by the transmembrane pressure (TMP) profile, which was mainly attributed to the accumulation of extracellular polymeric substances (EPS). The results of 16S rRNA gene sequencing showed that DNTD showed negligible effect on the bacterial community structures. Nonetheless, the functional bacteria responded differently to DNTD, which were in accordance with the bioreactor performances. Specifically, Nitrospina (NOB) and Tetrasphaera (PAOs) appeared to be sensitive to both low and high DNTD. In contrast, a low DNTD showed marginal effects on the denitrifiers, while a high DNTD significantly decreased their abundances. More strikingly, filamentous bulking bacteria were found to be well-adapted to DNTD, indicating their tolerance to the daily temperature fluctuation. This study will advance our knowledge regarding the response of microbial ecology of activated sludge to daily temperature variations in full-scale MBRs.

Study on the Tensile Creep Model of the Admixture of Early-Age Concrete and Application Simulation

With respect to the recent issue related to the lack of research on tensile creep model of the admixture concrete at early age and simulation, the admixture influence function with factor of the admixture dosage was established based on composite exponential function as reference model based on existed creep rules and appropriate assumption. It has been proposed that contributing factor, c, quantitatively represented the sensitivity of concrete creep changes to the admixture and correlation between concrete creep and the admixture. The model fitting was then made after tensile creep experiment by adding different admixtures such as fly ash, slag, silica fume and polypropylene fiber in contract to reference concrete test. It indicated that the model exhibited a good fitting performance, which is practical and useful as well as readily adopted by simulation. Meanwhile, the contributing factor also demonstrated quantitatively the variation among the effect of the admixtures (fly ash, slag, silica fume and polypropylene fiber) on the tensile creep of the concrete. Finally, the model was applied to an as-built concrete project for extended simulation, the results indicated that tensile creep can effectively improve the distribution of surface tensile stress and alleviate detrimental effect due to day-night temperature differences.

Thermoperiodic control of hypocotyl elongation depends on auxin-induced ethylene signaling that controls downstream PHYTOCHROME INTERACTING FACTOR3 activity.

We show that antiphase light-temperature cycles (negative day-night temperature difference [-DIF]) inhibit hypocotyl growth in Arabidopsis (Arabidopsis thaliana). This is caused by reduced cell elongation during the cold photoperiod. Cell elongation in the basal part of the hypocotyl under -DIF was restored by both 1-aminocyclopropane-1-carboxylic acid (ACC; ethylene precursor) and auxin, indicating limited auxin and ethylene signaling under -DIF. Both auxin biosynthesis and auxin signaling were reduced during -DIF. In addition, expression of several ACC Synthase was reduced under -DIF but could be restored by auxin application. In contrast, the reduced hypocotyl elongation of ethylene biosynthesis and signaling mutants could not be complemented by auxin, indicating that auxin functions upstream of ethylene. The PHYTOCHROME INTERACTING FACTORS (PIFs) PIF3, PIF4, and PIF5 were previously shown to be important regulators of hypocotyl elongation. We now show that, in contrast to pif4 and pif5 mutants, the reduced hypocotyl length in pif3 cannot be rescued by either ACC or auxin. In line with this, treatment with ethylene or auxin inhibitors reduced hypocotyl elongation in PIF4 overexpressor (PIF4ox) and PIF5ox but not PIF3ox plants. PIF3 promoter activity was strongly reduced under -DIF but could be restored by auxin application in an ACC Synthase-dependent manner. Combined, these results show that PIF3 regulates hypocotyl length downstream, whereas PIF4 and PIF5 regulate hypocotyl length upstream of an auxin and ethylene cascade. We show that, under -DIF, lower auxin biosynthesis activity limits the signaling in this pathway, resulting in low activity of PIF3 and short hypocotyls.

ATMOSPHERIC HEAT REDISTRIBUTION ON HOT JUPITERS

Infrared lightcurves of transiting hot Jupiters present a trend in which the atmospheres of the hottest planets are less efficient at redistributing the stellar energy absorbed on their daysides---and thus have a larger day-night temperature contrast---than colder planets. No predictive atmospheric model has been published that identifies which dynamical mechanisms determine the atmospheric heat redistribution efficiency on tidally locked exoplanets. Here we present a two-layer shallow water model of the atmospheric dynamics on synchronously rotating planets that explains the observed trend. Our model shows that planets with weak friction and weak irradiation exhibit a banded zonal flow with minimal day-night temperature differences, while models with strong irradiation and/or strong friction exhibit a day-night flow pattern with order-unity fractional day-night temperature differences. To interpret the model, we develop a scaling theory that shows that the timescale for gravity waves to propagate horizontally over planetary scales, t_wave, plays a dominant role in controlling the transition from small to large temperature contrasts. This implies that heat redistribution is governed by a wave-like process, similar to the one responsible for the weak temperature gradients in the Earth's tropics. When atmospheric drag can be neglected, the transition from small to large day-night temperature contrasts occurs when t_wave ~ sqrt(t_rad/Omega), where t_rad is the radiative relaxation time and Omega is the planetary rotation frequency. Alternatively, this transition criterion can be expressed as t_rad ~ t_vert, where t_vert is the timescale for a fluid parcel to move vertically over the difference in day-night thickness. These results subsume the commonly used timescale comparison for estimating heat redistribution efficiency between t_rad and the global horizontal advection timescale, t_adv.

3D mixing in hot Jupiters atmospheres

Context. Hot Jupiters exhibit atmospheric temperatures ranging from hundreds to thousands of Kelvin. Because of their large day-night temperature differences, condensable species that are stable in the gas phase on the dayside – such as TiO and silicates – may condense and gravitationally settle on the nightside. Atmospheric circulation may counterbalance this tendency to gravitationally settle. This three-dimensional (3D) mixing of condensable species has not previously been studied for hot Jupiters, yet it is crucial to assess the existence and distribution of TiO and silicates in the atmospheres of these planets.

An Efficient Method for Plant Regeneration from Calli of &amp;lt;i&amp;gt;Swertia mussotii&amp;lt;/i&amp;gt;, an Endangered Medicinal Herb

Swertia mussotii Franch is an endangered medicinal plant in the Qinghai-Tibet Plateau. Its regeneration from callus culture is very difficult. In this study, an efficient method for plant regeneration was developed from its calli. The calli derived from young stem explants of S. mussotii were cultured at two types of temperature treatments to test their efficiency of shoot regeneration. When the calli were cultured at variable temperature (VT, 20℃ during the day and 10℃ at night) treatment, the adventitious shoots were formed at each combination tested. However, that did not occur when the calli were cultured at constant temperature (CT, 25℃) treatment. The best response (53.7%) of plantlet regeneration was obtained on Murashige and Skoog (MS) medium containing 3 mg·l-1 6-benzylaminopurine with 0.5 mg·l-1 α-naphthaleneacetic acid in the VT treatment. The regenerated plantlets were rooted on half-strength MS medium without growth regulators. They flowered in the following subculture. The results indicate that the treatment of day-night temperature difference is a critical factor to callus differentiation in S. mussotii. This protocol can be used for conservation as well as mass propagation of this medicinal plant.

Mapping the Spatial and Temporal Pattern of Day-Night Temperature Difference in Greece from MODIS Imagery

The regional temporal and spatial multi-temporal land surface temperature (LST) MODIS dataset and elevation data are used to compute the day and night temperature variation in Greece in 2008. Clustering was applied and eight cluster centroids captured the temporal pattern of near-diurnal temperature (01:30 a.m. and 01:30 p.m.) variability while elevation statistics were computed per cluster. The spatial distribution of the clusters indicate that mean elevation, elevation variability, proximity to the sea, and the major inland water bodies were the key factors controlling the near-diurnal LST variability in Greece.

EFFECTS OF INITIAL FLOW ON CLOSE-IN PLANET ATMOSPHERIC CIRCULATION

We use a general circulation model to study the three-dimensional (3-D) flow and temperature distributions of atmospheres on tidally synchronized extrasolar planets. In this work, we focus on the sensitivity of the evolution to the initial flow state, which has not received much attention in 3-D modeling studies. We find that different initial states lead to markedly different distributions-even under the application of strong forcing (large day-night temperature difference with a short "thermal drag time") that may be representative of close-in planets. This is in contrast with the results or assumptions of many published studies. In general, coherent jets and vortices (and their associated temperature distributions) characterize the flow, and they evolve differently in time, depending on the initial condition. If the coherent structures reach a quasi- stationary state, their spatial locations still vary. The result underlines the fact that circulation models are currently unsuitable for making quantitative predictions (e.g., location and size of a "hot spot") without better constrained, and well posed, initial conditions.

MULTIWAVELENGTH CONSTRAINTS ON THE DAY-NIGHT CIRCULATION PATTERNS OF HD 189733b

We present new Spitzer observations of the phase variation of the hot Jupiter HD 189733b in the MIPS 24 μm bandpass, spanning the same part of the planet's orbit as our previous observations in the IRAC 8 μm bandpass (Knutson et al. 2007). We find that the minimum hemisphere-averaged flux from the planet in this bandpass is 76% ± 3% of the maximum flux; this corresponds to minimum and maximum hemisphere-averaged brightness temperatures of 984 ± 48 K and 1220 ± 47 K, respectively. The planet reaches its maximum flux at an orbital phase of 0.396 ± 0.022, corresponding to a hot region shifted 20°-30° east of the substellar point. Because tidally locked hot Jupiters would have enormous day-night temperature differences in the absence of winds, the small amplitude of the observed phase variation indicates that the planet's atmosphere efficiently transports thermal energy from the day side to the night side at the 24 μm photosphere, leading to modest day-night temperature differences. The similarities between the 8 and 24 μm phase curves for HD 189733b lead us to conclude that the circulation on this planet behaves in a fundamentally similar fashion across the range of pressures sensed by these two wavelengths. One-dimensional radiative transfer models indicate that the 8 μm band should probe pressures 2-3 times greater than at 24 μm, although the uncertain methane abundance complicates the interpretation. If these two bandpasses do probe different pressures, it would indicate that the temperature varies only weakly between the two sensed depths, and hence that the atmosphere is not convective at these altitudes. We also present an analysis of the possible contribution of star spots to the time series at both 8 and 24 μm based on near-simultaneous ground-based observations and additional Spitzer observations. Accounting for the effects of these spots results in a slightly warmer night-side temperature for the planet in both bandpasses, but does not otherwise affect our conclusions.

The structure of Venus’ middle atmosphere and ionosphere

The atmosphere and ionosphere of Venus have been studied in the past by spacecraft with remote sensing or in situ techniques. These early missions, however, have left us with questions about, for example, the atmospheric structure in the transition region from the upper troposphere to the lower mesosphere (50-90 km) and the remarkably variable structure of the ionosphere. Observations become increasingly difficult within and below the global cloud deck (<50 km altitude), where strong absorption greatly limits the available investigative spectrum to a few infrared windows and the radio range. Here we report radio-sounding results from the first Venus Express Radio Science (VeRa) occultation season. We determine the fine structure in temperatures at upper cloud-deck altitudes, detect a distinct day-night temperature difference in the southern middle atmosphere, and track day-to-day changes in Venus' ionosphere.

Atmospheric Dynamics of Short‐Period Extrasolar Gas Giant Planets. I. Dependence of Nightside Temperature on Opacity

More than two dozen short-period Jupiter-mass gas giant planets have been discovered around nearby solar-type stars in recent years, several of which undergo transits, making them ideal for the detection and characterization of their atmospheres. Here we adopt a three-dimensional radiative hydrodynamical numerical scheme to simulate atmospheric circulation on close-in gas giant planets. In contrast to the conventional GCM and shallow water algorithms, this method does not assume quasi-hydrostatic equilibrium, and it approximates radiation transfer from optically thin to thick regions with flux-limited diffusion. In the first paper of this series, we consider synchronously spinning gas giants. We show that a full three-dimensional treatment, coupled with rotationally modified flows and an accurate treatment of radiation, yields a clear temperature transition at the terminator. Based on a series of numerical simulations with varying opacities, we show that the nightside temperature is a strong indicator of the opacity of the planetary atmosphere. Planetary atmospheres that maintain large interstellar opacities will exhibit large day-night temperature differences, while planets with reduced atmospheric opacities due to extensive grain growth and sedimentation will exhibit much more uniform temperatures throughout their photospheres. In addition to numerical results, we present a four-zone analytic approximation to explain this dependence.