Wind Climatology at 87 km above the Rocky Mountains at Bear Lake Observatory--Fabry-Perot Observations of OH

This paper presents the neutral -wind climatology at approximately 87-km 53 altitude from Utah State University\u27s Bear Lake Observatory (BLO). a mid-latitude site 54 situated in the middle of the Rocky Mountains. The winds were determined using a very 55 sensitive Fabry-Perot interferometer (FPI) observing the OH Me inel (6-2) PI (3) line al 56 843 nm. The climatology. determined from monthly averages of the nightly evolution of 57 the geographic meridional and zonal wind components over forty· five months, has three 58 distinct seasonal patterns: winter (November- February), summer (May-Jul y), and late 59 Slimmer (August and September). The background zonal wind is eastward the whole year 60 except March and April. The background meridional wind is northward in winter and 61 southward during the rest of the year. In late summer. the winds exhibit a very strong 62 semidiurnal tidal variation almost every night. In summer, they exhibit a similar tidal 63 variation on enough nights that a semi diurnal pattern appears in the climatology. In 64 winter. the nighHo·night variability is so great that little structure is evident in the 65 climatology . These winds are compared to those from other techniques or sites: ~l 66 observations from UARS. FPI observations from Michigan, and MF radar observations. 67 While generally agreeing in relative amplitudes and i.n phase. differences do exist. 68 especially the weak semidiurnal tide at BLO in winter and a greatly reduced {tide at spring 69 equinox compared to late summer. It is likely that these differences arise from the 2 70 topographical generation of gravity waves by winds flowing over the Rocky Mountains. 71 The tidal variations are also compared to results from the global-scale wave model 72 (GSWM): our semidiurnal amplitudes arc considerably bigger except in winter, and our 73 phases vary from showing very good agreement in July, fair agreement in April and 74 January, and disagreement in October. These large differences may be evidence that 11011 - 75 linear effects are more important than realized. The behavior of the background winds is 76 consistent with different populations of gravity waves reaching 87 km in summer and 77 winter. The behavior of the semidiurnal tidal variation is consistent\u27 with a strong 78 interaction between the tidal and gravity·wave wind fields, and is consistent with the 79 different summer and Winter gravity wave population s, and with a fall· spring asymmetry 80 characterized by much weaker gravity wave sources in late summer than near spring 81 equinox

Why are estimates of global isoprene emissions so similar (and why is this not so for monoterpenes)?

International audienceEmissions of biogenic volatile organic compounds (BVOC) are a chief uncertainty in calculating the burdens of important atmospheric compounds like tropospheric ozone or secondary organic aerosol, reflecting either imperfect chemical oxidation mechanisms or unreliable emission estimates, or both. To provide a starting point for a more systematic discussion we review here global isoprene and monoterpene emission estimates to-date. We note a surprisingly small variation in the predictions of global isoprene emission rate that is in stark contrast with our lack of process understanding and the small number of observations for model parameterisation and evaluation. Most of the models are based on similar emission algorithms, using fixed values for the emission capacity of various plant functional types. In some studies these values are very similar, but they differ substantially in others. The models differ also broadly with regard to their representation of net primary productivity, method of biome coverage determination and climate data. Their similarities with regard to the global isoprene emission rate would suggest that the dominant parameters driving the ultimate global estimate, and thus the dominant determinant of model sensitivity, are the specific emission algorithm and isoprene emission capacity. Contrary to isoprene, monoterpene estimates show significantly larger model-to-model variation although variation in terms of leaf algorithm, emission capacities, the way of model upscaling, vegetation cover or climatology used in terpene models are comparable to those used for isoprene. From our summary of published studies there appears to be no evidence that the terrestrial modelling community has been any more successful in "resolving unknowns" in the mechanisms that control global isoprene emissions, compared to global monoterpene emissions. Rather, the proliferation of common parameterization schemes within a large variety of model platforms lends the illusion of convergence towards a common estimate of global isoprene emissions. This convergence might be used to provide optimism that the community has reached the "relief phase", the phase when sufficient process understanding and data for evaluation allows for models to converge, when applying a recently proposed concept. We argue that there is no basis for this apparent "relief" phase. Rather, we urge modellers to be bolder in their analysis to draw attention to the fact that terrestrial emissions, particularly in the area of biome-specific emission capacities, are unknown rather than uncertain

TOI-150: A transiting hot Jupiter in the TESS southern CVZ

We report the detection of a hot Jupiter ($M_{p}=1.75_{-0.17}^{+0.14}\ M_{J}$,$R_{p}=1.38\pm0.04\ R_{J}$) orbiting a middle-aged star ($\log g=4.152^{+0.030}_{-0.043}$) in the Transiting Exoplanet Survey Satellite (TESS) southern continuous viewing zone ($\beta=-79.59^{\circ}$). We confirm the planetary nature of the candidate TOI-150.01 using radial velocity observations from the APOGEE-2 South spectrograph and the Carnegie Planet Finder Spectrograph, ground-based photometric observations from the robotic Three-hundred MilliMeter Telescope at Las Campanas Observatory, and Gaia distance estimates. Large-scale spectroscopic surveys, such as APOGEE/APOGEE-2, now have sufficient radial velocity precision to directly confirm the signature of giant exoplanets, making such data sets valuable tools in the TESS era. Continual monitoring of TOI-150 by TESS can reveal additional planets and subsequent observations can provide insights into planetary system architectures involving a hot Jupiter around a star about halfway through its main-sequence life.Comment: 13 pages, 3 figures, 2 tables, accepted to ApJ

An eclipsing binary distance to the Large Magellanic Cloud accurate to 2 per cent

In the era of precision cosmology it is essential to determine the Hubble Constant with an accuracy of 3% or better. Currently, its uncertainty is dominated by the uncertainty in the distance to the Large Magellanic Cloud (LMC) which as the second nearest galaxy serves as the best anchor point of the cosmic distance scale. Observations of eclipsing binaries offer a unique opportunity to precisely and accurately measure stellar parameters and distances. The eclipsing binary method was previously applied to the LMC but the accuracy of the distance results was hampered by the need to model the bright, early-type systems used in these studies. Here, we present distance determinations to eight long-period, late- type eclipsing systems in the LMC composed of cool giant stars. For such systems we can accurately measure both the linear and angular sizes of their components and avoid the most important problems related to the hot early-type systems. Our LMC distance derived from these systems is demonstrably accurate to 2.2 % (49.97 +/- 0.19 (statistical) +/- 1.11 (systematic) kpc) providing a firm base for a 3 % determination of the Hubble Constant, with prospects for improvement to 2 % in the future.Comment: 34 pages, 5 figures, 13 tables, published in the Nature, a part of our data comes from new unpublished OGLE-IV photometric dat

The Contribution of Advective Fluxes to Net Ecosystem Exchange in a High-Elevation, Subalpine Forest

The eddy covariance technique, which is used in the determination of net ecosystem CO2 exchange (NEE), is subject to significant errors when advection that carries CO2 in the mean flow is ignored. We measured horizontal and vertical advective CO2 fluxes at the Niwot Ridge AmeriFlux site (Colorado, USA) using a measurement approach consisting of multiple towers. We observed relatively high rates of both horizontal (Fhadv) and vertical (Fvadv) advective fluxes at low surface friction velocities (u*) which were associated with downslope katabatic flows. We observed that Fhadv was confined to a relatively thin layer (0–6 m thick) of subcanopy air that flowed beneath the eddy covariance sensors principally at night, carrying with it respired CO2 from the soil and lower parts of the canopy. The observed Fvadv came from above the canopy and was presumably due to the convergence of drainage flows at the tower site. The magnitudes of both Fhadv and Fvadv were similar, of opposite sign, and increased with decreasing u*, meaning that they most affected estimates of the total CO2 flux on calm nights with low wind speeds. The mathematical sign, temporal variation and dependence on u* of both Fhadv and Fvadv were determined by the unique terrain of the Niwot Ridge site. Therefore, the patterns we observed may not be broadly applicable to other sites. We evaluated the influence of advection on the cumulative annual and monthly estimates of the total CO2 flux (Fc), which is often used as an estimate of NEE, over six years using the dependence of Fhadv and Fvadv on u*. When the sum of Fhadv and Fvadv was used to correct monthly Fc, we observed values that were different from the monthly Fc calculated using the traditional u*-filter correction by -16 to 20 g C·m-2·mo-1; the mean percentage difference in monthly Fc for these two methods over the six-year period was 10%. When the sum of Fhadv and Fvadv was used to correct annual Fc, we observed a 65% difference compared to the traditional u*-filter approach. Thus, the errors to the local CO2 budget, when Fhadv and Fvadv are ignored, can become large when compounded in cumulative fashion over long time intervals. We conclude that the ‘‘micrometeorological’’ (using observations of Fhadv and Fvadv) and ‘‘biological’’ (using the u* filter and temperature vs. Fc relationship) corrections differ on the basis of fundamental mechanistic grounds. The micrometeorological correction is based on aerodynamic mechanisms and shows no correlation to drivers of biological activity. Conversely, the biological correction is based on climatic responses of organisms and has no physical connection to aerodynamic processes. In those cases where they impose corrections of similar magnitude on the cumulative Fc sum, the result is due to a serendipitous similarity in scale but has no clear mechanistic explanation

Scaling study of the pion electroproduction cross sections and the pion form factor

The $^{1}$H($e,e^\prime \pi^+$)n cross section was measured for a range of four-momentum transfer up to $Q^2$=3.91 GeV$^2$ at values of the invariant mass, $W$, above the resonance region. The $Q^2$-dependence of the longitudinal component is consistent with the $Q^2$-scaling prediction for hard exclusive processes. This suggests that perturbative QCD concepts are applicable at rather low values of $Q^2$. Pion form factor results, while consistent with the $Q^2$-scaling prediction, are inconsistent in magnitude with perturbative QCD calculations. The extraction of Generalized Parton Distributions from hard exclusive processes assumes the dominance of the longitudinal term. However, transverse contributions to the cross section are still significant at $Q^2$=3.91 GeV$^2$.Comment: 6 pages, 3 figure

Nuclear transparency and effective kaon-nucleon cross section from the A(e, e'K+) reaction

We have determined the transparency of the nuclear medium to kaons from $A(e,e^{'} K^{+})$ measurements on $^{12}$C, $^{63}$Cu, and $^{197}$Au targets. The measurements were performed at the Jefferson Laboratory and span a range in four-momentum-transfer squared Q$^2$=1.1 -- 3.0 GeV$^2$. The nuclear transparency was defined as the ratio of measured kaon electroproduction cross sections with respect to deuterium, ($\sigma^{A}/\sigma^{D}$). We further extracted the atomic number ($A$) dependence of the transparency as parametrized by $T= (A/2)^{\alpha-1}$ and, within a simple model assumption, the in-medium effective kaon-nucleon cross sections. The effective cross sections extracted from the electroproduction data are found to be smaller than the free cross sections determined from kaon-nucleon scattering experiments, and the parameter $\alpha$ was found to be significantly larger than those obtained from kaon-nucleus scattering. We have included similar comparisons between pion- and proton-nucleon effective cross sections as determined from electron scattering experiments, and pion-nucleus and proton-nucleus scattering data.Comment: 7 pages, 5 figure

Study of the A(e,e'π+\pi^+) Reaction on 1^1H, 2^2H, 12^{12}C, 27^{27}Al, 63^{63}Cu and 197^{197}Au

Cross sections for the p($e,e'\pi^{+}$)n process on $^1$H, $^2$H, $^{12}$C, $^{27}$Al, $^{63}$Cu and $^{197}$Au targets were measured at the Thomas Jefferson National Accelerator Facility (Jefferson Lab) in order to extract the nuclear transparencies. Data were taken for four-momentum transfers ranging from $Q^2$=1.1 to 4.8 GeV$^2$ for a fixed center of mass energy of $W$=2.14 GeV. The ratio of $\sigma_L$ and $\sigma_T$ was extracted from the measured cross sections for $^1$H, $^2$H, $^{12}$C and $^{63}$Cu targets at $Q^2$ = 2.15 and 4.0 GeV$^2$ allowing for additional studies of the reaction mechanism. The experimental setup and the analysis of the data are described in detail including systematic studies needed to obtain the results. The results for the nuclear transparency and the differential cross sections as a function of the pion momentum at the different values of $Q^2$ are presented. Global features of the data are discussed and the data are compared with the results of model calculations for the p($e,e'\pi^{+}$)n reaction from nuclear targets.Comment: 28 pages, 19 figures, submited to PR

Measurement of Nuclear Transparency for the A(e,e' pi^+) Reaction

We have measured the nuclear transparency of the A(e,e' pi^+) process in ^{2}H,^{12}C, ^{27}Al, ^{63}Cu and ^{197}Au targets. These measurements were performed at the Jefferson Laboratory over a four momentum transfer squared range Q^2 = 1.1 - 4.7 (GeV/c)^2. The nuclear transparency was extracted as the super-ratio of $(\sigma_A/\sigma_H)$ from data to a model of pion-electroproduction from nuclei without pi-N final state interactions. The Q^2 and atomic number dependence of the nuclear transparency both show deviations from traditional nuclear physics expectations, and are consistent with calculations that include the quantum chromodynamical phenomenon of color transparency.Comment: 5 pages, 3 figs Changes to figure 2 and 3 (error band updated and theory curves updated