Kinetic Temperature Research Articles

Centrality dependency of proton, deuteron, and triton’s temperatures in Au+Au collisions at 200 GeV

The transverse momentum (pT) spectra of protons (p), deuterons (d), and tritons (t) in 200 GeV gold–gold (Au + Au) collisions at RHIC are examined across a range of centrality bins using the Levy Tsallis (TS) statistical model. The model's predictions closely match the experimental results from PHENIX (p) and STAR (d and t) Collaborations. Kinetic freeze-out temperatures of hadrons are obtained from particle spectra. The results showed that the kinetic freeze-out temperature decreases as collisions move from center to the periphery. This work found mass-dependent kinetic freeze-out temperatures, heavier particles arrive to the freeze-out phase before lighter ones. Comparison with same data fitted by blast wave function with Tsallis statistics (BWTS) showed that T0 values are increasing from central to peripheral collisions, while in case of TS function (current analysis) it decreases. This behavior puts a question mark on the reliability of using such functions for temperature extraction.

Calcium Chemistry in Carbon-rich Circumstellar Environments: The Laboratory and Astronomical Discovery of Calcium Dicarbide, CaC2 * * This work is based on observations done using the 100 m Green Bank Telescope (GBT), the Yebes 40 m telescope (projects 19A010, 20A017, 20B014, and 21A019), and the IRAM 30 m telescope. The 100 m GBT is an instrument of the Green Bank

Calcium dicarbide, CaC2, has been characterized at high resolution in the laboratory, and its main isotopologue, 40CaC2, has been assigned to 14 rotational emission lines between 14 and 115 GHz, including 12 previously unassigned lines, in the expanding molecular envelope of the evolved carbon star IRC+10216. Aided by high-level quantum calculations and measurements of multiple isotopologues, CaC2 is determined to be a T-shaped molecule with a highly ionic bond linking the metal atom to the C2 unit, very similar in structure to isovalent magnesium dicarbide (MgC2). The excitation of CaC2 is characterized by a very low rotational temperature of 5.8 ± 0.6 K and a kinetic temperature of 36 ± 16 K, similar to values derived for MgC2. On the assumption that the emission originates from a 30″ shell in IRC+10216, the column density of CaC2 is (5.6 ± 1.7) × 1011 cm−2. CaC2 is only the second Ca-bearing molecule besides CaNC and only the second metal dicarbide besides MgC2 identified in space. Owing to the similarity between the predicted ion–molecule chemistry of Ca and Mg, a comparison of the CaC2 abundance with that of MgC2 and related species permits empirical inferences about the radiative association–dissociative recombination processes postulated to yield metal-bearing molecules in IRC+10216 and similar objects.

Secondary halo bias through cosmic time

Context. The spatial distribution of dark matter halos carries cosmological and astrophysical information. Cosmological information can be considered to be contained in the connection between halo main properties and the large-scale halo bias, while the astrophysical information would be encoded in the scaling relations between halo properties. The combination of these two contributions leads to the effect of secondary halo bias. Aims. Our goal is to measure the signal of secondary halo bias as a function of a variety of intrinsic and environmental halo properties and to characterize its statistical significance as a function of cosmological redshift. Methods. Using fixed and paired N-body simulations of dark-matter halos – the UNIT simulation – with masses above ∼1011 M⊙h−1 identified over a wide range of cosmological redshifts (0 < z < 5), we explored the behavior of the scaling relations among different halo properties. We included novel environmental properties based on the halo distribution as well as the underlying dark-matter field. We implemented an object-by-object estimator of large-scale effective bias and tested its validity against standard approaches. With a bias assigned to each tracer, we performed a statistical analysis aimed at characterizing the distribution of the bias and the signal of the secondary halo bias. Results. We show how the halo scaling relations linking direct probes of the halo potential well do not depend on the environment. On the contrary, links between the halo mass and the so-called set of secondary halo properties are sensitive to the cosmological environment, mainly to under-dense regions. We show that the signal of secondary bias is derived statistically from secondary correlations beyond the standard link to the halo mass. Conclusions. We show that the secondary bias arises through nonlocal and/or environmental properties related either to the halo distribution or to the properties of the underlying dark-matter field. In particular, properties such as the tidal field (a measure of the anisotropy of the density field) and the local Mach number (a measure of the local kinetic temperature of the halo distribution) generate the signals of the secondary bias with the highest significance. We propose applications of the assignment of individual bias for the generation of mock catalogs containing the signal of secondary bias, as well as a series of cosmological analyses aimed at mining large galaxy datasets.

Partial ionization of plasma in solar prominences.

The plasma in cool cores of solar prominences is partially ionized and its ionization degree, in general, depends on the actual kinetic temperature and density of the plasma and the ions considered. However, we demonstrate that under typical prominence conditions, the dominant mechanism contributing to partial ionization is photoionization by radiation diffusing through the plasma. This mechanism strongly depends on the radiation illuminating prominences from the surrounding solar atmosphere. The understanding of the partial ionization of prominence plasma thus requires a complex solution of the non-LTE radiative-transfer problem. In this paper, we discuss the ionization of hydrogen, helium and some other important species. We also demonstrate the role of non-equilibrium ionization. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

The First Spatially Resolved Detection of 13CN in a Protoplanetary Disk and Evidence for Complex Carbon Isotope Fractionation

Recent measurements of carbon isotope ratios in both protoplanetary disks and exoplanet atmospheres have suggested a possible transfer of significant carbon isotope fractionation from disks to planets. For a clearer understanding of the isotopic link between disks and planets, it is important to measure the carbon isotope ratios in various species. In this paper, we present a detection of the 13CN N = 2 − 1 hyperfine lines in the TW Hya disk with the Atacama Large Millimeter/submillimeter Array. This is the first spatially resolved detection of 13CN in disks, which enables us to measure the spatially resolved 12CN/13CN ratio for the first time. We conducted nonlocal thermal equilibrium modeling of the 13CN lines in conjunction with previously observed 12CN lines to derive the kinetic temperature, H2 volume density, and column densities of 12CN and 13CN. The H2 volume density is found to range between (4 − 10) × 107 cm−3, suggesting that CN molecules mainly reside in the disk's upper layer. The 12CN/13CN ratio is measured to be 70−6+9 at 30 < r < 80 au from the central star, which is similar to the 12C/13C ratio in the interstellar medium. However, this value differs from the previously reported values found for other carbon-bearing molecules (CO and HCN) in the TW Hya disk. This could be self-consistently explained by different emission layer heights for different molecules combined with preferential sequestration of 12C into the solid phase toward the disk midplane. This study reveals the complexity of the carbon isotope fractionation operating in disks.

Kinetic glass transition in granular gases and nonlinear molecular fluids.

In this paper, we investigate, both analytically and numerically, the emergence of a kinetic glass transition in two different model systems: a uniformly heated granular gas and a molecular fluid with nonlinear drag. Despite the profound differences between these two physical systems, their behavior in thermal cycles share strong similarities, which stem from the relaxation time diverging algebraically at low temperatures for both systems. When the driving intensity--for the granular gas-or the bath temperature-for the molecular fluid-is decreased to sufficiently low values, the kinetic temperature of both systems becomes "frozen" at a value that depends on the cooling rate through a power law with the same exponent. Interestingly, this frozen glassy state is universal in the following sense: for a suitable rescaling of the relevant variables, its velocity distribution function becomes independent of the cooling rate. Upon reheating, i.e., when either the driving intensity or the bath temperature is increased from this frozen state, hysteresis cycles arise and the apparent heat capacity displays a maximum. The numerical results obtained from the simulations are well described by a perturbative approach.

Motility-induced coexistence of a hot liquid and a cold gas

If two phases exist at the same time, such as a gas and a liquid, they have the same temperature. This fundamental law of equilibrium physics is known to apply even to many non-equilibrium systems. However, recently, there has been much attention in the finding that inertial self-propelled particles like Janus colloids in a plasma or microflyers could self-organize into a hot gas-like phase that coexists with a colder liquid-like phase. Here, we show that a kinetic temperature difference across coexisting phases can occur even in equilibrium systems when adding generic (overdamped) self-propelled particles. In particular, we consider mixtures of overdamped active and inertial passive Brownian particles and show that when they phase separate into a dense and a dilute phase, both phases have different kinetic temperatures. Surprisingly, we find that the dense phase (liquid) cannot only be colder but also hotter than the dilute phase (gas). This effect hinges on correlated motions where active particles collectively push and heat up passive ones primarily within the dense phase. Our results answer the fundamental question if a non-equilibrium gas can be colder than a coexisting liquid and create a route to equip matter with self-organized domains of different kinetic temperatures.

Nitrate denitrification rate response to temperature gradient change during river bank infiltration.

Nitrate attenuation during river bank infiltration is the key process for reducing nitrogen pollution. Temperature is considered to be an important factor affecting nitrate attenuation. However, the magnitude and mechanism of its impact have not been clear for a long time. In this study, the effects of temperature and temperature gradient on the nitrate denitrification rate were investigated via static batch and dynamic soil column simulation experiments. The results showed that temperature had a significant effect on the denitrification rate. Temperature effects were first observed in denitrifying bacteria. At low temperatures, the microorganism diversity was low, resulting in a lower denitrification rate constant. The static experimental results showed that the denitrification rate at 19°C was approximately 2.4 times that at 10°C. The dynamic soil column experiment established an exponential positive correlation between the nitrate denitrification decay kinetic constant and temperature. The affinity of denitrifying enzymes for nitrate in the reaction substrate was ordered as follows: decreasing temperature gradient (30°C → 10°C) > zero temperature gradient (10°C) > increasing temperature gradient condition (0°C → 10°C). This study provides a theoretical basis for the biogeochemical processes underlying river bank infiltration, which will help aid in the development and utilization of groundwater resources.

K*(892)± resonance production in Pb-Pb collisions at sNN=5.02 TeV

The production of K*(892)± meson resonance is measured at midrapidity (|y|&lt;0.5) in Pb−Pb collisions at sNN=5.02 TeV using the ALICE detector at the CERN Large Hadron Collider. The resonance is reconstructed via its hadronic decay channel K*(892)±→KS0π±. The transverse momentum distributions are obtained for various centrality intervals in the pT range of 0.4−16 GeV/c. Measurements of integrated yields, mean transverse momenta, and particle yield ratios are reported and found to be consistent with previous ALICE measurements for K*(892)0 within uncertainties. The pT-integrated yield ratio 2K*(892)±/(K++K−) in central Pb−Pb collisions shows a significant suppression at a level of 9.3σ relative to pp collisions. Thermal model calculations result in an overprediction of the particle yield ratio. Although both hadron resonance gas in partial chemical equilibrium (HRG-PCE) and + simulations consider the hadronic phase, only HRG-PCE accurately represents the measurements, whereas + simulations tend to overpredict the particle yield ratio. These observations, along with the kinetic freeze-out temperatures extracted from the yields measured for light-flavored hadrons using the HRG-PCE model, indicate a finite hadronic phase lifetime, which decreases with increasing collision centrality percentile. The pT-differential yield ratios 2K*(892)±/(K++K−) and 2K*(892)±/(π++π−) are presented and compared with measurements in pp collisions at s=5.02 TeV. Both particle ratios are found to be suppressed by up to a factor of five at pT&lt;2.0 GeV/c in central Pb−Pb collisions and are qualitatively consistent with expectations for rescattering effects in the hadronic phase. The nuclear modification factor (RAA) shows a smooth evolution with centrality and is found to be below unity at pT&gt;8 GeV/c, consistent with measurements for other light-flavored hadrons. The smallest values are observed in most central collisions, indicating larger energy loss of partons traversing the dense medium. ©2024 CERN, for the ALICE Collaboration 2024 CERN

High turbulence in the IM Lup protoplanetary disk

Context. Constraining turbulence in disks is key to understanding their evolution via the transport of angular momentum. Measurements of high turbulence remain elusive, and methods for estimating turbulence mostly rely on complex radiative transfer models of the data. Using the disk emission from IM Lup, a source proposed to be undergoing magneto-rotational instabilities (MRIs) and to possibly have high turbulence values in the upper disk layers, we present a new way of directly measuring turbulence without the need of radiative transfer or thermochemical models. Aims. Through the characterization of the CN and C2H emission in IM Lup, we aim to connect the information on the vertical and thermal structure of a particular disk region to derive the turbulence at that location. By using an optically thin tracer, it is possible to directly measure turbulence from the nonthermal broadening of the line. Methods. The vertical layers of the CN and C2H emission were traced directly from the channel maps using ALFAHOR. By comparing their position to that of optically thick CO observations, we were able to characterize the kinetic temperature of the emitting region. Using a simple parametric model of the line intensity with DISCMINER, we accurately measured the emission linewidth and separated the thermal and nonthermal components. Assuming that the nonthermal component is fully turbulent, we were able to directly estimate the turbulent motions at the studied radial and vertical location of CN emission. Results. IM Lup shows a high turbulence of Mach 0.4–0.6 at z/r ~ 0.25. Considering previous estimates of low turbulence near the midplane, this may indicate a vertical gradient in the disk turbulence, which is a key prediction in MRI studies. CN and C2H are both emitting from a localized upper disk region at z/r = 0.2–0.3, in agreement with thermochemical models.

REMOTE SENSING ANALYSIS AND NUMERICAL MODELLING OF SURFACE TEMPERATURE ANOMALIES OVER PETROLEUM ACCUMULATIONS: A CASE STUDY OF THE ALBORZ OILFIELD, CENTRAL IRAN

Petroleum accumulations may coincide with either positive or negative temperature anomalies, which are conventionally detected using in situ temperature measurements made in shallow boreholes 1‐3 m deep. Data gathered in this way, however, can be sparse and costly, and may require intensive fieldwork over a long time period. This article explores the possibility of detecting thermal anomalies associated with petroleum entrapment using satellite‐derived land surface temperature data. For this aim, a robust correction scheme based on a physically‐based land surface model was applied to night‐time kinetic temperature data derived from NASA's ASTER instrument. The numerical model, known as SKinTES, attempts to simulate diurnal effects and to remove them from the measured temperature data to yield a residual temperature anomaly map. The performance of this methodology was tested over the Alborz oilfield located on an anticline of the same name in the Qom region of Central Iran. The study area has an arid to semi‐arid climate and the surface geology is dominated by outcrops of the Lower Miocene Upper Red Formation. The modelling approach used successfully highlighted several negative temperature anomalies over the oil‐bearing parts of the Alborz structure. In comparison to the uncorrected data, the anomalies were shown to be highly enhanced in both spatial and magnitude terms. In addition, time series analysis indicated that the temperature anomalies were consistent over time. The authenticity of the anomalies was confirmed by a suite of in situ temperature measurements made at shallow boreholes. In conclusion, a unifying framework is proposed to explain the occurrence of both negative and positive temperature anomalies over petroleum accumulations. The new modelling and correction scheme is expected to broaden the application of remote sensing land surface temperature data not only in petroleum exploration but also in other types of geothermic investigations including geothermal exploration.

Extracting Kinetic Freeze-Out Properties in High-Energy Collisions Using a Multisource Thermal Model

We study the transverse momentum (pT) spectra of neutral pions and identified charged hadrons produced in proton–proton (pp), deuteron–gold (d–Au), and gold–gold (Au–Au) collisions at the center of mass energy sNN=200 GeV. The study is made in the framework of a multisource thermal model used in the partonic level. It is assumed that the contribution to the pT-value of any hadron comes from two or three partons with an isotropic distribution of the azimuthal angle. The contribution of each parton to the pT-value of a given hadron is assumed to obey any one of the standard (Maxwell-Boltzmann, Fermi-Dirac, and Bose-Einstein) distributions with the kinetic freeze-out temperature and average transverse flow velocity. The pT spectra of the final-state hadrons can be fitted by the superposition of two or three components. The results obtained from our Monte Carlo method are used to fit the experimental results of the PHENIX and STAR Collaborations. The results of the present work serve as a suitable reference baseline for other experiments and simulation studies.

Can Recurrence Quantification Analysis Be Useful in the Interpretation of Airborne Turbulence Measurements?

AbstractIn airborne data or model outputs, clouds are often defined using information about Liquid Water Content (LWC). Unfortunately LWC is not enough to retrieve information about the dynamical boundary of the cloud, that is, volume of turbulent air around the cloud. In this work, we propose an algorithmic approach to this problem based on a method used in time series analysis of dynamical systems, namely Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA). We construct RPs using time series of turbulence kinetic energy, vertical velocity and temperature fluctuations as variables important for cloud dynamics. Then, by studying time series of laminarity (LAM), a variable which is calculated using RPs, we distinguish between turbulent and non‐turbulent segments along a horizontal flight leg. By selecting a single threshold of this quantity, we are able to reduce the number of subjective variables and their thresholds used in the definition of the dynamical cloud boundary.

System-size dependence of collective transverse flow in relativistic nuclear collisions

The transverse momentum distributions of identified hadrons (π±, K±, p, p, K0S, Λ, Λ, Ξ−, Ξ+, φ, Ω−, and Ω+) produced in Au+Au collisions at RHIC-BES energies are analyzed with Blast-Wave model and with Boltzmann-Gibbs statistics. The kinetic freeze-out temperature, the average transverse flow velocity and the flow profile exponent are extracted from the transverse momentum spectra of the particles. The study of system-size dependence of the kinetic freeze-out parameters showed that kinetic freeze-out temperature increases, while average transverse flow ve- locity decreases from central to peripheral collisions. The larger freeze-out temperature for peripheral collisions may indicate an earlier decoupling of the expanding system. For the same centrality class, it is observed that the transverse flow velocity and flow profile exponent have an increasing trend with increasing collision energy.

Unlocking the Thermal Efficiency of Irregular Open-Cell Metal Foams: A Computational Exploration of Flow Dynamics and Heat Transfer Phenomena

An open-cell metal foam has excellent characteristics such as low density, high porosity, high specific surface area, high thermal conductivity, and low mass due to its unique internal three-dimensional network structure. It has gradually become a new material for enhanced heat transfer in industrial equipment, new compact heat exchangers, microelectronic device cooling, etc. This research established a comprehensive three-dimensional structural model of open-cell metal foams utilizing Laguerre–Voronoi tessellations and employed computational fluid dynamics to investigate its flow dynamics and coupled heat transfer performance. By exploring the impact of foam microstructure on flow resistance and heat transfer characteristics, the study provided insights into the overall convective heat transfer performance across a range of foam configurations with varying pore densities and porosities. The findings revealed a direct correlation between convective heat transfer coefficient (h) and pressure drop (ΔP) with increasing Reynolds number (Re), accompanied by notable changes in fluid turbulence kinetic energy (e) and temperature (T), ultimately influencing heat transfer efficiency. Furthermore, the analysis demonstrated that alterations in porosity (ε) and pore density significantly affected unit pressure drop (ΔP/L) and convective heat transfer coefficient (h). This study identified an optimal configuration, highlighting a metal foam with a pore density of 20 PPI and a porosity of 95% as exhibiting superior overall convective heat transfer performance.

Heat transfer and thermal–hydraulic evaluations of cross-circular grooved rectangular flow ducts depending on rectangular baffle design parameters

The cross-grooved rectangular flow ducts are largely used for plate heat exchangers. In this work, so as to better the heat transfer in cross-grooved rectangular ducts with circular grooves, rectangular baffles were located in the flow duct, and the influences of the rectangular baffle angles and heights on the features of heat transfer were numerically performed in detail. Equations of Navier–Stokes and energy were resolved by employing a program of Ansys-Fluent with k–ε turbulence model as steady and three-dimensional. Air employed as working fluid has a temperature of inlet 293 K while the circular groove’s wall temperature is 373 K. Rectangular baffles have various angles of 30°, 60°, and 90°, and heights of 0.25 H, 0.5 H, and 0.75 H. The mean Nusselt number (Num), temperature, turbulence kinetic energy (TKE), pressure, and PEC (Performance Evaluation Criterion) number of the flow duct with rectangular baffles were evaluated by comparing it with the cross-circular grooved channel non-baffle. Besides, the contours of velocity, turbulence kinetic energy, temperature, and velocity vector were exhibited for the cross-circular grooved rectangular channels with different baffle angles and height arrangements. Results were matched with experimental and numerical outcomes of the study found in the literature, and it was observed that they were fairly coherent. For Re = 6000, the number of Num increases by 180.48% in the duct with a 90° angle and 0.75 H baffle height compared to the duct non-baffle, and for 30° baffle angle, the PEC value at 0.25 H baffle height is 66.88% higher than that in the 0.5 H.Graphical Compared to the temperature contour distribution in the non-baffle state, the temperature gradient increases due to the turbulence intensity created by the inserting of baffles to the circular grooved ducts. When the baffle height is increased to 0.75 H, the increase in fluid temperatures toward the end of the ducts is the clearest evidence of this situation. Thus, while cooling increases in circular grooves, the temperature gradient in the duct above the circular grooved section gets better, especially in the case of 0.75 H height and 90° baffle angle. Temperature distribution contours of the ducts for non-baffle and with baffle of 90° angle and 0.75 H height for Re = 6000.

Study of Plasma Heating Processes in a Coronal Mass Ejection–driven Shock Sheath Region Observed with the Metis Coronagraph

On 2021 September 28, a C1.6 class flare occurred in active region NOAA 12871, located approximately at 27°S and 51°W on the solar disk with respect to Earth’s point of view. This event was followed by a partial halo coronal mass ejection (CME) that caused the deflection of preexisting coronal streamer structures, as observed in visible-light coronagraphic images. An associated type II radio burst was also detected by both space- and ground-based instruments, indicating the presence of a coronal shock propagating into interplanetary space. By using H i Lyα (121.6 nm) observations from the Metis coronagraph on board the Solar Orbiter mission, we demonstrate for the first time the capability of UV imaging to provide, via a Doppler dimming technique, an upper limit estimate of the evolution of the 2D proton kinetic temperature in the CME-driven shock sheath as it passes through the field of view of the instrument. Our results suggest that over the 22 minutes of observations, the shock propagated with a speed decreasing from about 740 ± 110 km s−1 to 400 ± 60 km s−1. At the same time, the postshock proton temperatures peaked at latitudes around the shock nose and decreased with time from about 6.8 ± 1.01 MK to 3.1 ± 0.47 MK. The application of the Rankine–Hugoniot jump conditions demonstrates that these temperatures are higher by a factor of about 2–5 than those expected from simple adiabatic compression, implying that significant shock heating is still going on at these distances.

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). X. Hot Gas Reveals Deeply Embedded Star Formation

Massive infrared dark clouds (IRDCs) are considered to host the earliest stages of high-mass star formation. In particular, 70 μm dark IRDCs are the colder and more quiescent clouds. At a scale of about 5000 au using formaldehyde (H2CO) emission, we investigate the kinetic temperature of dense cores in 12 IRDCs obtained from the pilot Atacama Large Millimeter/submillimeter Array Survey of 70 μm dark High-mass clumps in Early Stages (ASHES). Compared to the 1.3 mm dust continuum and other molecular lines, such as C18O and deuterated species, we find that H2CO is mainly sensitive to low-velocity outflow components rather than to quiescent gas expected in the early phases of star formation. The kinetic temperatures of these components range from 26 to 300 K. The Mach number reaches about 15 with an average value of about 4, suggesting that the velocity distribution of gas traced by H2CO is significantly influenced by a supersonic nonthermal component. In addition, we detect warm line emission from HC3N and OCS in 14 protostellar cores, which requires high excitation temperatures (E u /k ∼ 100 K). These results show that some of the embedded cores in the ASHES fields are in an advanced evolutionary stage, previously unexpected for 70 μm dark IRDCs.

Collisional excitation of propyne (CH3CCH) by He atoms

Context. A detailed interpretation of the detected emission lines of environments where propyne (or methyl acetylene, CH3CCH) is observed requires access to its collisional rate coefficients with the most abundant species in the interstellar medium, namely, helium (He) or molecular hydrogen (H2). Aims. We present the first three-dimensional potential energy surface (3D PES) for the CH3CCH-He molecular complex. We study the dynamics of the collision and report the first set of rate coefficients for temperatures up to 100 K for the collisional excitation of the lowest 60 ortho rotational levels and 60 para rotational levels of CH3CCH by He atoms. Methods. We computed the 3D PES with the explicitly correlated coupled-cluster with a single-, double-, and perturbative triple-excitation method in conjunction with the augmented correlation-consistent triple zeta basis set (CCSD(T)-F12a/aug-cc-pVTZ). The 3D PES was then fitted to an analytical function and scattering computations of pure rotational (de-)excitation of CH3CCH by collision with He atoms were performed. State-to-state cross-sections were computed using the close coupling method for total energies up to 100 cm−1 and with the coupled states approximation at higher energies for both the ortho- and para- symmetries of CH3CCH. Results. The PES we obtained is characterised by a large anisotropy and a potential well depth of 51.04 cm−1. By thermally averaging the collisional cross-sections, we determined the quenching rate coefficients for kinetic temperatures up to 100 K. A strong and even Δj propensity rule at almost all collision energies is present for CH3CCH-He complex. To evaluate the impact of rate coefficients on the analysis of observations, we carried out non-local thermodynamic equilibrium radiative transfer computations of the excitation temperatures and we demonstrate that local thermodynamic equilibrium conditions are not typically fulfilled for the propyne molecule.

Effects of Solar Intrusion on the Calibration of the Metop-C Advanced Microwave Sounding Unit-A2 Channels

This study presents our first discovery about two abnormal problems in the blackbody calibration target associated with the antenna unit A2 in the Metop-C AMSU-A instrument. The problems include the anomalous patterns in both blackbody kinetic temperature Tw and radiative temperature (measured in warm count or Cw), and the time lag between orbital cycles of Tw and Cw. This study further determines solar intrusion as the root cause of the anomalous pattern problem. According to our analysis, solar illumination is constantly observed during each orbit near the satellite terminator, causing anomalous changes in Cw and Tw, characterized by sudden and abnormal increases typically for more than 16 min. The resultant maximum antenna temperature errors due to abnormal increases in Cw are approximately in the range from 0.15 K to 0.25 K, while the maximum errors due to the abnormal increase in Tw are in the range from 0.04 K to 0.07 K, varying with orbit, season, and channel. The time shift feature is characterized with a changeable time lag with the season in the Tw orbital cycle in comparison with the Cw cycle. The longest time lag up to about 18 min occurs in summer through early fall, while the time lag can be decreased down to about 9 min in winter through early spring. Hence, this study underscores the imperative need for future research to rectify radiance errors and reconstruct a more accurate long-term Metop-C AMSU-A radiance data set for channels 1 and 2, crucial for climate studies.