Horizontal Temperature Variations Research Articles

Atmospheric Dynamics of Earth‐Like Tidally Locked Aquaplanets

We present simulations of atmospheres of Earth‐like aquaplanets that are tidally locked to their star, that is, planets whose orbital period is equal to the rotation period about their spin axis, so that one side always faces the star and the other side is always dark. Such simulations are of interest in the study of tidally locked terrestrial exoplanets and as illustrations of how planetary rotation and the insolation distribution shape climate. As extreme cases illustrating the effects of slow and rapid rotation, we consider planets with rotation periods equal to one current Earth year and one current Earth day. The dynamics responsible for the surface climate (e.g., winds, temperature, precipitation) and the general circulation of the atmosphere are discussed in light of existing theories of atmospheric circulations. For example, as expected from the increasing importance of Coriolis accelerations relative to inertial accelerations as the rotation rate increases, the winds are approximately isotropic and divergent at leading order in the slowly rotating atmosphere but are predominantly zonal and rotational in the rapidly rotating atmosphere. Free‐atmospheric horizontal temperature variations in the slowly rotating atmosphere are generally weaker than in the rapidly rotating atmosphere. Interestingly, the surface temperature on the night side of the planets does not fall below ∼240 K in either the rapidly or slowly rotating atmosphere; that is, heat transport from the day side to the night side of the planets efficiently reduces temperature contrasts in either case. Rotational waves and eddies shape the distribution of winds, temperature, and precipitation in the rapidly rotating atmosphere; in the slowly rotating atmosphere, these distributions are controlled by simpler divergent circulations. Both the slowly and rapidly rotating atmospheres exhibit equatorial superrotation. Systematic variation of the planetary rotation rate shows that the equatorial superrotation varies non‐monotonically with rotation rate, whereas the surface temperature contrast between the day side and the night side does not vary strongly with changes in rotation rate.

Study of successive contrasting monsoons (2001–2002) in terms of aerosol variability over a tropical station Pune, India

Abstract. The present study suggests that aerosols play a major role in cloud formation and affect significantly the precipitation over a regional scale. The study reveals that there is a high variability of aerosol index during a bad monsoon year 2002, indicating an extension of cycle to more than 100 days from a normal 50 day cycle of absorbing and non-absorbing aerosols over a tropical urban station Pune. Pre-monsoon of 2002 shows a high loading of coarse-mode aerosols (absorbing dust aerosols) which indicate vertical and horizontal temperature variations in turn affecting the seasonal rainfall at a regional scale. Cloud formation highly depends on aerosol concentration, but the activation process is not monotonic. The surface meteorological features help to initiate the cloud process. The surface temperatures were high during the pre-monsoon of 2002 leading to increase of aerosol optical depth as compared to 2001. The effect of surface wind speed, though, complicated to understand, results in low values in 2002 with high aerosol optical depth and vice-versa in 2001.

Felsic highland crust on Venus suggested by Galileo Near‐Infrared Mapping Spectrometer data

We evaluated the spatial variation of Venusian surface emissivity at 1.18 μm wavelength and that of near‐surface atmospheric temperature using multispectral images obtained by the Near‐Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. The Galileo NIMS observed the nightside thermal emission from the surface and the deep atmosphere of Venus, which is attenuated by scattering from the overlying clouds. To analyze the NIMS data, we used a radiative transfer model based on the adding method. Although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere, our analysis revealed that the horizontal temperature variation in the near‐surface atmosphere is no more than ±2 K on the Venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands. One interpretation for the latter result is that highland materials are generally composed of felsic rocks. Since formation of a large body of granitic magmas requires water, the presence of granitic terrains would imply that Venus may have had an ocean and a mechanism to recycle water into the mantle in the past.

Horizontal temperature variation in the Osaka Plain in summer

Horizontal temperature variation in the Osaka Plain in summer

Titan's middle-atmospheric temperatures and dynamics observed by the Cassini Composite Infrared Spectrometer

The Composite Infrared Radiometer–Spectrometer (CIRS) instrument, on the NASA Cassini Saturn orbiter, has been acquiring thermal emission spectra from the atmosphere of Titan since orbit insertion in 2004. Observation sequences for measuring stratospheric temperatures have been obtained using both a nadir mapping mode and a limb viewing mode. The limb observations give better vertical resolution, and give information from higher altitudes, while the nadir observations provide more complete longitude coverage. Because the scale height of Titan's atmosphere is large enough so that emission from a grazing ray is influenced by horizontal temperature variations in the atmosphere, we have developed a two-dimensional temperature retrieval algorithm for reducing the limb spectra, which solves simultaneously for meridional and vertical temperature variations. The analyzed nadir mapping data have sampled nearly all longitudes at latitudes from about 90° S to 60° N, providing temperatures between pressure levels of about 5 to 0.2 mbar. The limb data covers latitudes between about 75° S and 85° N, and yields temperatures between about 1 and 0.005 mbar, at a small number of longitudes. The retrieved temperatures are consistent with early results from nadir observations [Flasar, F.M., and 44 colleagues, 2005. Science 308, 975–978] between 0.5 and 5 mbar where both results are valid, with the warmest temperatures at the equator, and much stronger meridional temperature gradients in the northern (winter) hemisphere than in the southern. At higher altitudes not probed by nadir viewing, the limb data reveal that the stratopause is nearly 20 K warmer in the northern polar regions than at the equator and southern hemisphere, and that the altitude of the stratopause shifts from ≈0.1 mbar (300 km) near the equator to 0.01 mbar (400 km) poleward of about 40° N. When the gradient wind equation is used to construct a zonal mean wind, the reversal in sign of the temperature leads to capping of the winter westerly flow. The core of the resulting jet is about 190 m s −1 in magnitude, spans between 30° N and 60° N, and peaks near 0.1 mbar. Estimates of the radiative heating associated with the radiative disequilibrium lead to a meridional overturning timescale of about three Earth years.

A Thermospheric Circulation Model for Extrasolar Giant Planets

Several models of extrasolar giant planet (EGP) atmospheres have been developed recently. Many of them are one-dimensional or concentrate on the lower or middle atmosphere. Three-dimensional hydrodynamic models are needed to study the horizontal variations in temperature and composition of EGP atmospheres. Circulation models for the upper atmosphere are particularly important as they can be used to study the thermal structure due to stellar irradiation, radiative cooling, and atmospheric circulation in the thermospheres of close-in EGPs and hence the rate of evaporation of their atmospheres. We present a generic gas giant model that is capable of generating three-dimensional, self-consistent global simulations of stable EGP thermospheres at different orbital distances. Calculations performed by this model indicate that IR emissions from H ions may play a significant role in cooling the thermospheres of EGPs at least in the range of 0.2-1 AU from a solar-type host star. In this range thermal dissociation of H2 is negligible and ion densities are small compared to the overall neutral density. Inside 0.2 AU thermal dissociation and dissociative photoionization of H2 may prevent the effective formation of H. In the absence of radiative cooling from H the upper atmospheres reach temperatures well above 10,000 K within ~0.5 AU. In this case the upper thermospheres are entirely converted into atomic hydrogen and the temperatures are high enough for significant atmospheric loss to take place. Our model is capable of calculating the IR signal strengths for various vibrational transitions of H based on the thermal state and the composition of the atmosphere. Potential detection of such signals would thus provide a validation of some of our results.

Basic Studies on the Treatment of Volatile Organic Pollutant in Sand by Microwave Radiation

The heating characteristics of water and sand were investigated to understand the basic features of a microwave soil pollution treatment system and the reasonableness of this method was examined. The evaporation and temperature change of water by microwave irradiation were dependent on its volume and sand showed a three-fold temperature change compared with water. When microwave energy was applied, water showed an even variation in temperature on the whole, however, there was approximately 30□ difference according to the location inside the sand. Sand temperature was observed to show a larger difference as it was horizontally and vertically closer to the microwave irradiation point and horizontal temperature variations were more evenly distributed than vertical variations. Heating characteristics according to the particle size of sand showed that the temperature change was larger when the particle size became smaller and the moisture content of sand was found to influence its heating behavior. In the conditions of experiment, about 50% of the benzene in sand was volatized after 23 minutes of heating and 85% of the total benzene was removed from the sand after 60 minutes of microwave irradiation. For real soil test, more than 70% of BTEX was successfully removed from the soil after 120 minutes of heating.

Influence of a basal thermal anomaly on mantle convection

We perform laboratory experiments to study the effects of a variable basal thermal anomaly on convection. In the regime of cellular convection ( Ra < 10 7), the convection pattern changes as the horizontal temperature variation in the bottom boundary increases. When the temperature variation is less than the critical value, there is no effect to the convection pattern. Above this critical value, an upwelling is fixed at the site of the thermal anomaly. For a larger temperature variation, the upwelling region becomes wider. For the cases above the critical value, the time-averaged temperature in the isothermal core above the thermal anomaly becomes higher than that in the other regions. In the regime of plume dominant convection ( Ra ≥ 10 7), when the horizontal temperature variation exceeds the critical value, the location of a hot plume is similarly affected. For this case, the plume generated by the thermal anomaly straddles around the site of the thermal anomaly rather than being fixed. For a larger temperature variation, multiple plumes cluster together which also straddle around the anomaly. The straddling nature of the hot plumes generated by the thermal anomaly causes the time-averaged temperature above the thermal anomaly to remain unchanged. We also find that different from the cellular convection cases, the temperature variation less than critical is capable of generating intermittent hot plumes, but they do not dominate the convection pattern. The critical horizontal temperature variation needed to affect the convection pattern is found to be scaled by the maximum standard deviation of the time variation of the temperature σ max * around the lower thermal boundary layer in the absence of thermal anomaly. We estimate the possible temperature variation which can be generated by a partially molten region at the CMB. We find that assuming that σ max * for mantle is the same as that obtained from the experiment, a region less viscous than the surrounding region by an order of magnitude, can generate a hotspot.

The vertical structure of Titan's upper atmosphere from Cassini Ion Neutral Mass Spectrometer measurements

Data acquired by the Ion Neutral Mass Spectrometer (INMS) on the Cassini spacecraft during its close encounter with Titan on 26 October 2004 reveal the structure of its upper atmosphere. Altitude profiles of N 2, CH 4, and H 2, inferred from INMS measurements, determine the temperature, vertical mixing rate, and escape flux from the upper atmosphere. The mean atmospheric temperature in the region sampled by the INMS is 149 ± 3 K , where the variance is a consequence of local time variations in temperature. The CH 4 mole fraction at 1174 km is 2.71 ± 0.1 % . The effects of diffusive separation are clearly seen in the data that we interpret as an eddy diffusion coefficient of 4 −3 +4 × 10 9 cm 2 s −1 , that, along with the measured CH 4 mole fraction, implies a mole fraction in the stratosphere of 2.2 ± 0.2 % . The H 2 distribution is affected primarily by upward flow and atmospheric escape. The H 2 mole fraction at 1200 km is 4 ± 1 × 10 −3 and analysis of the altitude profile indicates an upward flux of 1.2 ± 0.2 × 10 10 cm −2 s −1 , referred to the surface. If horizontal variations in temperature and H 2 density are small, this upward flux also represents the escape flux from the atmosphere. The CH 4 density exhibits significant horizontal variations that are likely an indication of dynamical processes in the upper atmosphere.

A global circulation model of Saturn's thermosphere

We present the first 3-dimensional self-consistent calculations of the response of Saturn's global thermosphere to different sources of external heating, giving local time and latitudinal changes of temperatures, winds and composition at equinox and solstice. Our calculations confirm the well-known finding that solar EUV heating alone is insufficient to produce Saturn's observed low latitude thermospheric temperatures of 420 K. We therefore carry out a sensitivity study to investigate the thermosphere's response to two additional external sources of energy, (1) auroral Joule heating and (2) empirical wave heating in the lower thermosphere. Solar EUV heating alone produces horizontal temperature variations of below 20 K, which drive horizontal winds of less than 20 m/s and negligible horizontal changes in composition. In contrast, Joule heating produces a strong dynamical response with westward winds comparable to the sound speed on Saturn. Joule heating alone, at a total rate of 9.8 TW, raises polar temperatures to around 1200 K, but values equatorward of 30° latitude, where observations were made, remain below 200 K due to inefficient meridional energy transport in a fast rotating atmosphere. The primarily zonal wind flow driven by strong Coriolis forces implies that energy from high latitudes is transported equatorward mainly by vertical winds through adiabatic processes, and an additional 0.29–0.44 mW/m 2 thermal energy are needed at low latitudes to obtain the observed temperature values. Strong upwelling increases the H 2 abundances at high latitudes, which in turn affects the H + 3 densities. Downwelling at low latitudes helps increase atomic hydrogen abundances there.

Wave Flow Simulations Over Arctic Leads

We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons. The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of the lead appear far downstream.

Observed effects of horizontal radiative surface temperature variations on the atmosphere over a midwest watershed during CASES 97

The association between ∼10‐km scale horizontal variation of radiometric surface temperature (Ts) and aircraft‐derived fluxes of sensible heat (H) and moisture (LE) is the focus of this work. We use aircraft, surface, and satellite data from a Cooperative Atmospheric‐Surface Exchange Studies (CASES) field program, which took place in the southern part of the 60 × 100 km Walnut River (Kansas) watershed from 22 April to 22 May 1997, when winter wheat matured and prairie grass greened up. Aircraft Ts observed along repeated flight tracks above the surface layer showed a persistent pattern: maxima over ridges characterized by shallow soil and rocky outcroppings and minima over riparian zones. H and Ts reached maxima in the same longitude zone on two flight tracks 40 km apart. Satellite Ts data from March to June reveal similar persistent patterns with minima more persistent than maxima. Two mechanisms are suggested to explain the association of H and Ts maxima: (1) for winds between 6 and 8 ms−1, modulation of the surface energy budget by vegetation effects; or (2) for winds equal to or below 4 ms−1, a thermally driven circulation centered on Ts maxima. Both mechanisms were possibly enhanced by increased static instability over the Ts maxima. Owing to the small sample available, these results are suggestive rather than conclusive. Effects of rainfall and vegetation on watershed‐scale Ts gradients are also explored.

The impacts of spatial variability on the development of convection

AbstractA cloud‐resolving model is used to investigate the impact of spatial variability in moisture and temperature on the timing of deep convection over land. Using a simulation of a diurnal cycle of convection, horizontal variations in moisture and temperature are shown to have a significant impact on the development of convection. The onset of deep convection can change by several hours and total rainfall amounts can change by up to 70%.Further sensitivity studies are carried out to investigate the impacts of vertical location, horizontal scale and magnitude of the variability. It is shown that variability of relative humidity in the boundary layer has the most significant impact and this is linked to its strong influence on local convective inhibition. Horizontal scales larger than 10 km are shown to have the strongest influence on the timing of convection, and the strongest amplitude of convectively generated fluctuations is shown to be on these larger scales. © Royal Meteorological Society, 2004. J. C. Petch's contribution is Crown copyright

Solitons Northeast of Tung-Sha Island During the ASIAEX Pilot Studies

In a recent study, satellite images have shown that internal solitons are active in the northern South China Sea (SCS). During the Asian Seas International Acoustic Experiment (ASIAEX) pilot studies, current profiler and thermistor chain moorings were deployed in the spring of 1999 and 2000 to investigate internal solitons northeast of Tung-Sha Island on the continental slope of the northern SCS. Most of the observed internal solitons were first baroclinic mode depression waves. The largest horizontal current velocity, vertical displacement, and temperature variation induced by the internal solitons were around 240 cm/s, 106 m, and 11/spl deg/C, respectively, while the estimated nonlinear phase speed was primarily westward at 152 /spl plusmn/ 4 cm/s. The observed internal solitons could be categorized as four types. The first type is the incoming wave from deep water and can be described reasonably well with the KdV equation. The second and third types are in the transition zone before and close to the turning point (where the upper and lower layer depths are equal), respectively. These two types of solitons were generally near the wave-breaking stage. The fourth type of soliton is a second baroclinic mode and probably was locally generated. The time evolutions are asymmetric, especially at the middle depths. A temperature kink following the main pulse of the soliton is often seen. Higher order nonlinear and shallow topographic effects could be the primary cause for these features. The appearance/disappearance of internal solitons coincides mostly with spring/neap tide. The internal soliton is irregularly seen during the neap tide period and its amplitude is generally small. The time interval between two leading solitons is generally around 12 h. The first baroclinic mode of the semidiurnal tide has a larger amplitude than the diurnal tide and could redistribute its energy into the soliton.

High frequency intensity fluctuations: Comparison of theory with experiment

Amplitude fluctuations were measured during August 2002 near San Diego using 20 and 40 kHz cw and fm signals. Source–receiver separation was 1 km; source depths were 10 m to 67 m; receiver hydrophone depths were 44 m to 217 m. A 15-element chain of CTD sensors was towed to measure horizontal temperature and salinity variation with 1m resolution. Theory exists explaining the relationship between amplitude fluctuations and acoustic frequency, source–receiver separation, and index of refraction patch size in the ocean [e.g., Flatte et al., Sound Transmission Through a Fluctuating Ocean (Cambridge Press, 1979); Uscinsky et al., ‘‘Intensity Fluctuations. Part 1: Theory,’’ J. Acoust. Soc. Am. 74 (1983)]. However, the amplitude fluctuations we observe are much lower than that predicted by theory [J. Acoust. Soc. Am. 113, 2333 (2003)]. Our frequencies are 1 to 2 orders of magnitude higher than those used in the experiments upon which the theory is based and our propagation ranges are considerable shorter 1 km versus many km. Results will be discussed from a more detailed analysis of the ray path locations within the water column activity (Langmuir cell formation and internal wave passage).

Numerical simulation of Martian dust devils

Large eddy simulations of vertical convective vortices and dust devils in the Martian convective boundary layer are presented, employing a version of the Mars MM5 mesoscale model, adapted to use periodic boundary conditions and run at resolutions of 10 to 100 m. The effects of background horizontal wind speed and shear on dust devil development are studied in four simulations, each extending over the daytime portion of one Martian day. The general vorticity development in all cases is similar, with roughly equal positive and negative vorticity extrema. Two dust devils were found to develop in the highest wind speed case and in a case run without background wind. The dust devil structures were found to agree well qualitatively with terrestrial dust devil observations, including the prediction of greatly diminished vertical velocities in the vortex core. Thermodynamic scaling theory of dust devils was found to provide good prediction of the relationship between central pressure and temperature in the modeled vortices. Examination of the turbulent kinetic energy budgets suggests balance between buoyancy generation and loss through dissipation and transport. The vorticity for the dust devils is provided by twisting of horizontal vorticity into the vertical. The horizontal vorticity originates from horizontal variations in temperature at the lower boundary (thermal buoyancy). While the horizontal winds generated by the modeled dust devils were likely insufficient to lift dust, this study provides a solid starting point for dynamic modeling of what may be an important component of the Martian dust cycle.

First XMM-Newton observations of strongly magnetic cataclysmic variables -- II. Timing studies of DP Leo and WW Hor

XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.

Influence of the thermoelectric effect on the Rayleigh-Bénard instability inside a magnetic field.

We investigate the influence of thermoelectric effect on the onset of thermal instability in the Rayleigh-Bénard system with vertical magnetic field. An electrically conducting fluid is confined in an infinite horizontal layer between thick thermally and electrically conducting walls. A horizontal temperature variation resulting from convective instability leads to horizontal temperature gradients along the liquid-solid interface acting as a source of thermoelectric currents. Through interaction with the applied magnetic field, the Lorentz force is created modifying the instability. We find that the critical Rayleigh number for onset of convection is not changed by the thermoelectric effect. However, the thermal gradient on the liquid-solid boundary leads to a change of the shape of the unstable mode creating helical flow in the evolving convection rolls because of the Lorentz force parallel to their axis. The created kinetic helicity depends linearly on the dimensionless parameter K(TE) characterizing the strength of the thermoelectric effect.

Characteristics of marine boundary layers during two Lagrangian measurement periods: 1. General conditions and mean characteristics

Two sets of Lagrangian measurements were made during the southern Aerosol Characterization Experiment (ACE1) south of Tasmania, Australia, in December 1995. This paper intends to provide an overview of the general conditions encountered during the two intensive observational periods. The measurements by the NCAR C‐130 provide the main data set for this study. We also use the sea surface temperature obtained from the R/V Discoverer and the European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses field for the large‐scale divergence field. Emphases of the paper are on the atmospheric and oceanic environment and the boundary layer mean structure during the six flights in the two Lagrangian measurement periods. The large scale features, such as variations of sea surface temperature, synoptic conditions, and large‐scale velocity fields, are discussed. These large‐scale environments had significant influences on boundary layer turbulence and the inversion structure. The boundary layer mean structure and its evolution along the Lagrangian trajectory are also studied using two‐dimensional cross‐section plots of vertical and horizontal (along the flight track) variation of potential temperature, water vapor, wind components, and ozone concentration. The most prominent feature of the boundary layer is the two‐layered structure observed throughout Lagrangian B and during the last flight of Lagrangian A. The two layers have detectable differences in potential temperature, water vapor, and, to a lesser extent, ozone concentration. These differences make it necessary to study the exchange between the two layers. Low‐level cloud structure and cloud microphysics are also discussed. We emphasize, though, that the results on cloud fractions should be used with caution due to the variable nature of the cloud bands observed during ACE1.

Dating topography of the Sierra Nevada, California, using apatite (U–Th)/He ages

The upward motion of rock masses relative to the Earth's surface has been documented for most of the main mountain belts using thermochronological and petrological techniques. More fundamental to the physical processes of mountain building, however, is the motion of the Earth's surface itself, which remains elusive. Here we describe a technique for estimating the age of topographic relief by mapping the low-temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium, thorium and helium contents. The technique exploits horizontal variations in temperature in the shallow crust that result from range-normal river drainages, because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges. Our results from the Sierra Nevada, California, indicate that two of the modern transverse drainages, the Kings and the San Joaquin, had developed deep canyons by the Late Cretaceous period, suggesting that the high topography of the range is ~50–60 million years older than generally thought.