Venus mesosphere and thermosphere temperature structure: II. Day-night variations

A two-dimensional nonlinear hydrodynamic model has been developed for studying the global scale winds, temperature, and compositional structure of the mesosphere and thermosphere of Venus. The model is driven by absorption of solar radiation. Ultraviolet radiation produces both heating and photodissociation. Infrared solar heating and thermal cooling are also included with an accurate NLTE treatment. The most crucial uncertainty in determining the solar drive is the efficiency by which $\text{λ < 1080}\text{A}\text{?}$ solar radiation is converted to heat. This question was analyzed in Part I, where it was concluded that essentially all hot atom and O(¹D) energy may be transferred to vibrational-rotational energy of CO₂ molecules. If this is so, the minimum possible euv heating occurs and is determined by the quenching of the resulting excess rotational energy. The hydrodynamic model is integrated with this minimum heating and neglecting any small-scale vertical eddy mixing. The results are compared with predictions of another model with the same physics except that it assumes that 30% of $\text{λ < 1080}\text{A}\text{?}$ radiation goes into heat and that the heating from longer-wavelength radiation includes the O(¹D) energy. For the low-efficiency model, exospheric temperatures are ?300°K on the dayside and drop to < 180°K at the antisolar point. For the higher-efficiency model, the day-to-night temperature variation is from ?600°K to ?250°K. Both versions of the model predict a wind of several hundred meters per second blowing across the terminator and abruptly weakening to small values on the nightside with the mass flow consequently going into a strong tongue of downward motion on the nightside of the terminator. The presence of this circulation could be tested observationally by seeing if its signature can be found in temperature measurements. Both versions of the model indicate that a self-consistent large-scale circulation would maintain oxygen concentrations with ?5% mixing ratios near the dayside F-1 ionospheric peak but ?40% at the antisolar point at the same pressure level.     

Evaluating Lost Person Behavior Models

US wilderness search and rescue consumes thousands of person‐hours and millions of dollars annually. Timeliness is critical: the probability of success decreases substantially after 24 hours. Although over 90% of searches are quickly resolved by standard “reflex” tasks, the remainder require and reward intensive planning. Planning begins with a probability map showing where the lost person is likely to be found. The MapScore project described here provides a way to evaluate probability maps using actual historical searches. In this work we generated probability maps the Euclidean distance tables in (Koester 2008 ), and using Doke's ( 2012 ) watershed model. Watershed boundaries follow high terrain and may better reflect actual barriers to travel. We also created a third model using the joint distribution using Euclidean and watershed features. On a metric where random maps score 0 and perfect maps score 1, the Euclidean distance model scored 0.78 (95%CI: 0.74–0.82, on 376 cases). The simple watershed model by itself was clearly inferior at 0.61, but the Combined model was slightly better at 0.81 (95%CI: 0.77–0.84).     

Nonlinear least-squares method via an isomorphic geometrical setup

The resolution of a nonlinear parametric adjustment model is addressed through an isomorphic geometrical setup with tensor structure and notation, represented by a u-dimensional “model surface” embedded in a flat n-dimensional “observational space”. Then observations correspond to the observational-space coordinates of the pointQ, theu initial parameters correspond to the model-surface coordinates of the “initial” pointP, and theu adjusted parameters correspond to the model-surface coordinates of the “least-squares” point . The least-squares criterion results in a minimum-distance property implying that the vector Q must be orthogonal to the model surface. The geometrical setup leads to the solution of modified normal equations, characterized by a positive-definite matrix. The latter contains second-order and, optionally, thirdorder partial derivatives of the observables with respect to the parameters. This approach significantly shortens the convergence process as compared to the standard (linearized) method.     

Combined Digital Photogrammetry and Time-of-Flight Laser Scanning for Monitoring Cliff Evolution

Although cliffs form approximately 75% of the world's coastline, the understanding of the processes through which they evolve remains limited because of a lack of quantitative data on the morphological changes they undergo. In this paper the combination of terrestrial time-of-flight laser scanning with high-resolution digital photogrammetry is examined to generate high-quality data-sets pertaining to the geomorphic processes governing cliff development. The study was undertaken on a section of hard rock cliffs in North Yorkshire, UK, which has been monitored over a 12-month period. High-density, laser-scanned point clouds have been used to produce an accurate representation of these complex surfaces, free from the optical variations that degrade photographic data. These data-sets have been combined with high-resolution photographic monitoring, resampled with the fixed accuracies of the terrestrial laser survey, to generate a new approach to recording the volumetric changes in complex coastal cliffs. This has led to significant improvements in the understanding of the activity patterns of coastal cliffs.     

Some approaches for location of centroids of quartz grain outlines to increase homology between Fourier amplitude spectra

The ability to test for similarities and differences among families of shapes by closed-form Fourier expansion is greatly enhanced by the concept of homology. Underlying this concept is the assumption that each term of a Fourier series, when compared to the same term in another series, represents the same thing. A method that ensures homology is one which minimizes the centering error, as reflected in the first harmonic term of the Fourier expansion. The problem is to chose a set of edge points derived from a much larger, but variable, number of edge points such that a valid homologous Fourier series can be calculated. Methods are reviewed and criteria given to define a proper solution. An algorithm is presented which takes advantage of the fact that minimization of the error term can be accomplished by minimizing the distance between the origin of the polar coordinate system in the calculation of the Fourier series and the shape centroid. The use of this algorithm has produced higher quality solutions for quartz grain provenance studies.     

Temporal Pointing Variations of the Solar Dynamics Observatory’s HMI and AIA Instruments on Subweekly Time Scales

Achieving subarcsecond co-registration across varying time-lines of multi-wavelength and instrument images is difficult and requires an accurate characterization of the instrument pointing jitter. We investigated the internal pointing errors on daily and yearly time-scales that occur across the Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI). Using cross-correlation techniques on the AIA 1700 Å passband and the HMI line-of-sight magnetograms from three years of observational image pairs at approximately three-day intervals, internal pointing errors were quantified. Pointing variations of ±?0.26″ (jitter-limited) and ±?0.50″ in the solar East–West (x) and North–South (y) directions, respectively, were measured. AIA observations of the Venus transit in June 2012 were used to measure existing coalignment offsets in all passbands. We found that the AIA passband pointing variations are 〈ΔX _CO〉=1.10″±1.41″ and 〈ΔY _CO〉=1.25″±1.24″ when aligned to the HMI nominal image center, referred to here as the CutOut technique. Minimal long-term pointing variations found between limb and correlation derived pointings provide evidence that the image-center positions provided by the instrument teams achieve single-pixel accuracy on time scales shorter than their characterization. However, daily AIA passband pointing variations of ??1.18″ indicate that autonomous subarcsecond co-registration is not fully achieved yet.     

The solar surface differential rotation from disk-integrated chromospheric fluxes

Disk-integrated solar chromospheric Caii K-line (3933.68 ) fluxes have been measured almost daily at Sacramento Peak Observatory since 1977. Using observing windows selected to mimic seasonal windows for chromospheric measurements of lower Main-Sequence stars such as those observed by Mount Wilson Observatory's HK Project, we have measured the solar rotation from the modulation of the Caii K-line flux. We track the change of rotation period from the decline of cycle 21 through the maximum of cycle 22. This variation in rotation period is shown to behave as expected from the migration of active regions in latitude according to Maunder's butterfly diagram, including an abrupt change in rotation period at the transition from cycle 21 to cycle 22. These results indicate the successful detection of solar surface differential rotation from disk-integrated observations. We argue that the success of our study compared to previous investigations of the solar surface differential rotation from disk-integrated fluxes lies primarily with the choice of the length of the time-series window. Our selection of 200 days is shorter than in previous studies whose windows are typically on the order of one year. The 200-day window is long enough to permit an accurate determination of the rotation period, yet short enough to avoid complications arising from active region evolution. Thus, measurements of the variation of rotation period in lower Main-Sequence stars, especially those that appear to be correlated with long-term changes in chromospheric activity (i.e., cycles), are probably evidence for stellar surface differential rotation.