Cold Core Research Articles

Predictions of gas-phase methanimine (CH2NH) abundance in cold cores

ABSTRACT Since the 1930s, more than 250 molecules have been discovered in the interstellar medium. With the development of more sensitive telescopes, we keep detecting new more complex species. Amongst them, methanimine (CH2NH) is considered as a pre-biotic molecule as it can be involved in the synthesis of glycine through aminoacetonitrile. CH2NH has been observed in a variety of interstellar sources (hot cores, circumstellar envelops, external galaxies, and even cold cores). We studied the chemistry of this species at low temperature as previous models failed at reproducing the observed abundance in cold cores. First, using the public version of the gas-grain model nautilus (called pnautilus), we tested the effect of new proposed reactions for the production and destruction for CH2NH from the literature. These reactions, in particular association reactions with atomic hydrogen, increases the gas-phase production of CH2NH to a level in disagreement with the published observed values, putting some doubts on these reactions. Using the KIDA gas-phase network, we studied the sensitivity of the CH2NH gas-phase abundance to temperature, density, visual extinction, and cosmic-ray ionization rate. We show that under typical cold core conditions (10 K, 2 × 104 cm−3), CH2NH is formed on the surface of the grains but also from dissociative recombination of protonated ions in the gas. With this model, we are able to reproduce the level of detections in the cold cores Ori-3N and L183.

Chemical models of adenine precursors cyanamide and carbodiimide in the interstellar medium

ABSTRACT Cyanamide (NH2CN) and its isomer, carbodiimide (HNCNH), may form adenine in the interstellar medium (ISM) via a series of reactions. Therefore, they are considered key prebiotic molecules in the study of the origin of life. We used the three-phase NAUTILUS chemical code, which includes the gas, the dust surface, and the icy mantle, to investigate the formation and destruction of cyanamide and carbodiimide. We added over 200 new chemical reactions of the two isomers and related species and established a relatively complete network. We applied cold core, hot corino/core, and shock models to simulate the different physical environments, and found that the two isomers are mainly produced by the free radical reactions on grain surfaces. Our simulated results suggest that cyanamide and carbodiimide molecules come from surface chemistry at early evolutionary stages. Then they are released back to the gas phase, either by thermal process (in hot cores, hot corinos) or by shock-induced desorption (in shock regions). We speculate that it is an inefficient route to form a tautomer of adenine by starting from molecules cyanoacetylene (C3NH), cyanamide, and carbodiimide in ISM.

The Role of Coupled North Pacific Atmosphere–Ocean Interactions in Impacts of Tibetan Plateau Snow Anomalies on the Northern Hemisphere Winter Atmospheric Circulation

Abstract Previous studies indicate observed influences of autumn and winter Tibetan Plateau (TP) snow-cover anomalies on the winter Pacific–North American (PNA) teleconnection. This study simulates atmospheric and oceanic responses to persistent autumn–winter TP snow forcing using an atmospheric general circulation model (AGCM) and a coupled atmospheric-oceanic general circulation model (AOGCM), and quantifies the role of atmosphere–ocean interactions over North Pacific in TP snow effects. The AOGCM experiment induces a stronger and more realistic remote PNA response to heavy TP snow anomalies, and also a significant winter horseshoe-like North Pacific sea surface temperature (SST) pattern resulting from an anomalous equivalent barotropic cyclone, or a strengthened Aleutian low, with associated cyclonic wind stress anomalies. The horseshoe-like SST anomaly pattern is used as boundary forcing (without prescribed heavy TP snow) in another AOGCM experiment, which simulates an enhanced winter Aleutian low and a PNA-like response similar to the original AOGCM responses, indicating that that the direct Pacific–North American atmospheric response to persistent TP snow forcing in the AGCM is amplified in the AOGCM by the North Pacific midlatitude atmosphere–ocean interactions. This suggests that the mechanisms of the winter PNA responses to TP snow forcing involve dynamical atmospheric processes such as horizontal propagation of Rossby wave energy and transient eddy feedbacks, and also North Pacific atmosphere–ocean interactions, which provide a positive feedback on the development of the remote PNA teleconnection. Significance Statement The Tibetan Plateau has a 2.5 million km2 area and a 4000 m average elevation, and is often called “the third pole” because of its polar-like climate in midlatitude Eurasia. A heavy Tibetan Plateau snow cover increases the albedo effect and causes tropospheric cold temperature and low height changes that can be carried or advected to the North Pacific by the prevailing westerlies. The purpose of this study is to better understand how Tibetan Plateau snow anomalies influence the North Pacific and the remote atmospheric circulation through numerical simulations. Our results find that those North Pacific responses amply the direct atmospheric response to Tibetan Plateau snow-cover anomalies. This greatly improves our understanding of physical mechanisms of Tibetan Plateau snow impacts.

Constraints on the non-thermal desorption of methanol in the cold core LDN 429-C

Context. Cold cores are one of the first steps of star formation, characterized by densities of a few 104–105 cm−3, low temperatures (15 K and below), and very low external UV radiation. In these dense environments, a rich chemistry takes place on the surfaces of dust grains. Understanding the physico-chemical processes at play in these environments is essential to tracing the origin of molecules that are predominantly formed via reactions on dust grain surfaces. Aims. We observed the cold core LDN 429-C (hereafter L429-C) with the NOEMA interferometer and the IRAM 30 m single dish telescope in order to obtain the gas-phase abundances of key species, including CO and CH3OH. Comparing the data for methanol to the methanol ice abundance previously observed with Spitzer allows us to put quantitative constraints on the efficiency of the non-thermal desorption of this species. Methods. With physical parameters determined from available Herschel data, we computed abundance maps of 11 detected molecules with a non-local thermal equilibrium (LTE) radiative transfer model. These observations allowed us to probe the molecular abundances as a function of density (ranging from a few 103 to a few 106 cm−3) and visual extinction (ranging from 7 to over 75), with the variation in temperature being restrained between 12 and 18 K. We then compared the observed abundances to the predictions of the Nautilus astrochemical model. Results. We find that all molecules have lower abundances at high densities and visual extinctions with respect to lower density regions, except for methanol, whose abundance remains around 4.5 × 10−10 with respect to H2. The CO abundance spreads over a factor of 10 (from an abundance of 10−4 with respect to H2 at low density to 1.8 × 10−5 at high density) while the CS, SO, and H2S abundances vary by several orders of magnitude. No conclusion can be drawn for CCS, HC3N, and CN because of the lack of detections at low densities. Comparing these observations with a grid of chemical models based on the local physical conditions, we were able to reproduce these observations, allowing only the parameter time to vary. Higher density regions require shorter times than lower density regions. This result can provide insights on the timescale of the dynamical evolution of this region. The increase in density up to a few 104 cm−3 may have taken approximately 105 yr, while the increase to 106 cm−3 occurs over a much shorter time span (104 yr). Comparing the observed gas-phase abundance of methanol with previous measurements of the methanol ice, we estimate a non-thermal desorption efficiency between 0.002 and 0.09%, increasing with density. The apparent increase in the desorption efficiency cannot be reproduced by our model unless the yield of cosmic-ray sputtering is altered due to the ice composition varying as a function of density.

Imprints of tropical cyclone on three-dimensional structural characteristics of mesoscale oceanic eddies

The impact of tropical cyclones (TCs) on the three-dimensional characteristics of mesoscale oceanic eddies is investigated in this study on the basis of statistical analysis by satellite-based eddy information and Argo data. By comparing the three-dimensional structure of the temperature, salinity, and geostrophic velocity in the upper ocean above 1,000 m depth, it was found that there is a heat pump effect in the changes of eddy structure similar to that in tropical cyclones. Under the forcing of TC, the abnormal signals in the strong cold core (warm core) structure originally existing in the upper layer of the cyclonic eddy (anticyclonic eddy) are transmitted to the middle and lower layers of the eddy and form retention, making the eddy structure not recover to the original state in a short period of time. To a certain extent, this shows that the influence of TC on the eddy structure is not limited to the ocean surface. At the same time, the change of barrier layer in the eddy is explored, and it was found that the barrier layer thickness in both cyclonic eddy and anticyclonic eddy has increased, which also confirms the previous research.

Satellite Multi-Sensor Data Analysis of Unusually Strong Polar Lows over the Chukchi and Beaufort Seas in October 2017

Polar lows (PLs) are intense mesoscale weather systems that often cause severe storm winds in the Nordic Seas but were considered as being exceedingly rare in the Pacific Arctic region before sea ice decline. Here, we explore four PLs observed on 18–22 October 2017 in the Chukchi and Beaufort Seas—an area with an exceptionally sparse observation network. The study is based on the combined use of the satellite microwave measurements, as well as infrared imagery, the ERA5, MERRA-2 and NCEP-CFSv2 reanalysis data sets. An unusually strong PLs pair developed near the marginal ice zone during a marine-cold air outbreak in anomalously low sea ice extent conditions. PLs pair moved southward as a mesocyclonic system called the “merry-go-round”, under the upper-level tropospheric vortex with a cold core. Multi-sensor satellite measurements show that, in the mature stage, a PL pair had near-surface wind speeds (W) close to hurricane force—over 30 m/s. Comparison analysis of W distributions within the strongest PL showed that all reanalysis data sets reasonably reproduce the PL median wind speed but underestimate its extreme values by 15–23%. The reanalysis data sets detected only two PLs with horizontal scales of over 220 km. Tracks of identified PLs for all data sets are in good agreement with the ones obtained from satellite images capturing the main features of the mesoscale weather system propagation. For the track of the strongest PL event, ERA5 exhibited the most accordance with satellite observations with a tracking error of 50–60 km.

The impact of the initial core temperature on protostellar disc fragmentation

ABSTRACT Ground-based and satellite observations have revealed dust temperatures as low as ∼5−7 K in the centre of low-mass, pre-stellar cloud cores, where star formation takes place. However, external heating may rise the outer core temperatures up to ∼15−20 K. Such low temperatures at the centre of pre-stellar cores are a key factor to constrain the conditions that lead to the formation of gravitationally bound protostellar systems as was recently captured by highly-resolved Atacama large millimeter/submillimeter array observations. Here, we report consistent smoothed particle hydrodynamics collapse calculations of cold cores that demonstrate the formation of close protobinary systems via small-scale fragmentation of a gravitationally unstable protostellar disc. The results indicate that mean binary separations, of tens of astronomical units, are a consequence of disc fragmentation in cold pre-stellar cores. Cloud cores initially with temperatures ≤6 K and a low amplitude (a = 0.1), m = 2 density perturbation formed close protobinaries that were followed deep into the non-isothermal collapse for several orbital periods and appeared to survive as independent stellar entities. At temperatures ≥7 K disc fragmentation is no longer observed and the calculations terminate with the formation of a wide protobinary, which may occasionally be accompanied by small substellar objects emerging by fragmentation of the circumbinary disc. When the perturbation amplitude is raised to a = 0.25, disc fragmentation occurs again only in cores with initial temperatures ≤6 K. Therefore, increasing the perturbation amplitude does not necessarily imply that there will be disc fragmentation at higher core temperatures.

Brazil-Malvinas Confluence in the South-West Atlantic Ocean: phytoplankton species, life forms and trophic mode

Abstract The Brazil-Malvinas Confluence (BMC) is characterized by high environmental variability and represents a hotspot of phytoplankton biodiversity. This study has investigated the phytoplankton composition in the BMC and a Cold Core Eddy (CCE), with particular reference to the life forms and trophic modes of the species. Vertical hauls were performed between the maximum chlorophyll depth and the surface with a 20-μm mesh plankton net at six sampling points in the BMC (4 hauls) and CCE (2 hauls) during the austral spring (November 2019). Temperature and salinity were determined in situ. The Brazil Current and Malvinas Current in the BMC had different species compositions, and the CCE had greater similarity with the Malvinas Current. Autotrophic organisms (mainly diatoms) and marine planktonic oceanic and/or neritic life forms were predominant in the BMC and the CCE. Heterotrophic dinoflagellates were predominant in the Brazil Current and the CCE, while mixotrophic dinoflagellates in the Malvinas Current were associated with low temperatures and salinities. A high diversity of species was confirmed in the region, mainly associated with marine planktonic oceanic and/or neritic species, and there was a predominance of autotrophic organisms. The temperature conditions in the CCE promoted an increase in species richness in the region.

Size of maturity for blue king crab Paralithodes platypus in the northern part of the Sea of Okhotsk

We determined the size of sexual maturity of male and female blue crabs in the northwestern part of the sea (zone of cold core action), as well as in the northeastern part of the sea and the local cluster near the Iona bank (zone of comparatively warm waters). Morphological 50% maturation of males in the northwestern part of the Sea of Okhotsk was observed at the carapace width of 73.3 mm. Similar width were demonstrated for the northeastern part of the sea and for the Iona Bank area – respectively 88.5 mm and 91.0 mm. Females in samples from the northwestern part of the sea reached functional 50% maturity at the carapace width of 71.7 mm, from the northeastern part – of 79.4 mm, and from the Iona Bank – of 81.0 mm. Comparison with available literature data showed that blue crab in the northwestern part of the Sea of Okhotsk has probably the slowest growth rate, and the crabs have the smallest size at maturity compared to individuals in the other areas.

Impacts of Mesoscale Eddies on Biogeochemical Variables in the Northwest Pacific

Mesoscale eddies play an important role in regulating biogeochemical cycles. However, the response of biogeochemical variables to cold and warm eddies has not been well elucidated, mainly due to most previous studies relying on remote sensing techniques and lacking in situ observations below the surface water. Here, we used hydrographic and biochemical data from one survey in the northwestern Pacific to document the vertical biogeochemical structure of one cold and two warm eddies. We first compared the changes of key variables in the eddy core relative to eddy outside, explained the role of key layers (the mixing depth, pycnocline, nutricline, euphotic) in causing these changes, and then analyzed the main environmental factors affecting chlorophyll a (Chla) and phytoplankton communities. Finally we focused on the response mechanisms of key biogeochemical variables to the cold and warm eddies. The results showed that biological variables (Chla, microphytoplankton, picophytoplankton), salinity, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP), and dissolved inorganic silicate (DSi) in the cold eddy core increased by 0.2–134%, while in the warm eddy core, they decreased by 0.2–70% relative to the eddy outside. The cold and warm eddies were able to force the deep chlorophyll maximum (DCM), which rose or fell with the pycnocline, nutricline and euphotic depth (Zeu) as a whole. Cold eddies with a raised thermocline could lead to about 20 m elevated DCM and enhanced phytoplankton biomass when the nutricline and thermocline were coincident. In contrast, warm eddies drove isopycnals downward, resulting in a 10–25 m drop in DCM and a decrease in nutrient and Chla concentrations at the center of the eddies. The significant difference in the vertical structure of the phytoplankton community between the center and the outside of the eddy might be explained by the direct influence of both nutrient concentrations and stoichiometry changes. The contribution of microphytoplankton to total biomass was much smaller than that of picophytoplankton in oligotrophic waters where the DIN:DIP and DSi:DIN ratios are significantly low. Compared to nutrients, photosynthetically active radiation (PAR) might not be the main factor controlling phytoplankton biomass and abundance attributed to Zeu being consistently deeper than the mixed depth (Zm), whereas it was likely to be the key limiting factor affecting the vertical distribution of the phytoplankton community.

Stability of urea in astrophysical ices. A laboratory study of VUV irradiation and high-energy electron bombardment

ABSTRACT The recent detection of urea in the interstellar medium raises questions about its stability in different astronomical environments. In this work, we have studied the stability of urea ices and urea/water ice mixtures under vacuum-ultraviolet (VUV; 6.3–10.9 eV) irradiation and high-energy (5 keV) electron bombardment at 30, 100, and 200 K. The evolution of the ices was monitored with infrared spectroscopy. CO2, HNCO, and OCN− were identified as reaction products in the 30 K samples. At the higher temperatures CO2 and HNCO were hardly found in the processed ices. The measurements provided destruction cross-sections and allowed the derivation of radiation yields, G100, and half-life doses for urea. G100 values were found to be low (≈3.6–0.3 molecules/100 eV) both for VUV photons and high-energy electrons with electrons being slightly more efficient for the destruction of the molecule. These low G100 values are likely due to favourable mechanisms of energy dissipation or urea recombination. The stability of urea under irradiation increases with temperature which suggests that higher mobility improves the repair mechanisms. Estimates based on these laboratory data indicate that urea should be stable (≈108–109 yr) against irradiation in cold dense clouds and hot cores. It would not survive long (≈103–104 yr) on the bare surface of a Kuiper belt object, but would be well protected (≈109 yr) against radiation below a 30 $\mu$m ice layer. The high resistance of the molecule to radiation damage makes it a good candidate for prebiotic chemistry.

Complex organic molecules formation in cold cores on stochastically heated grains

ABSTRACT We investigate the roles of stochastic grain heating in the formation of complex organic molecules (COMs) in cold cores, where COMs have been detected. Two different types of grain-size distributions are used in the chemical models. The first one is the MRN distribution, and the second one considers grain coagulation to study its effects on the chemical evolution in these environments. The macroscopic Monte Carlo method is used to perform the two-phase chemical model simulations. We find that (1) grain coagulation can affect certain gas-phase species, such as CO2 and N2H+, in the cold core environments, which can be attributed to the volatile precursors originating from the small grains with temperature fluctuations; (2) grains with radii around 4.6 × 10$^{-3}\, \mu$m contribute most to the production of COMs on dust grains under cold core conditions, while few species can be formed on even smaller grains with radii less than 2 × 10$^{-3}\, \mu$m; (3) COMs formed on stochastically heated grains could help explain the observed abundances of gas-phase COMs in cold cores.

The Intrusion of Spicy Water Favours the Intensification of Arabian Sea Cyclones

ABSTRACT The intensity of the cyclones in the Arabian Sea has been increasing in recent years. Approximately ten storms were intensified into severe cyclones over spicy waters of the northern Arabian Sea during 1998-2019. Reduction in upwelling was observed due to decreasing wind speed, which raised the sea surface temperature (SST) and the intrusion of spicy waters from the Red Sea and the Persian Gulf acted as a barrier to mixing in the top layers, especially in May. Consequently, there was a noticeable increase in the heat content of the 50 m surface layer. This research presents two main rationales that explain the intensification of these cyclones. The first rationale explores the increasing trends in SST and ocean internal energy, while the second investigates the influence of the intrusion of spicy Persian Gulf waters into the Oman coast. The results showed that spicy water from the north suppressed the upwelling in the cold core eddy off the Oman coast and that higher SSTs and high latent heat flux almost double the climatological values off the Oman coast in May.

A New Perspective on the Development of the Great Arctic Cyclone in August 2012

AbstractThe evolutionary process of “The Great Arctic Cyclone (AC) of August 2012” (hereafter named as AC2) was investigated by using the Arctic System Reanalysis version 2 data, from a new perspective of two cyclones' merging. The evolution of AC2 was affected by the merging process with a pre‐existing AC (hereafter named as AC1) at lower‐levels, and the impact of the two tropopause polar vortices (TPVs). The AC2's development showed a slowdown at the early stage of merging (before 00 UTC 5), and a rapid intensification at the later stage (after 00 UTC 5). The diagnostic results based on Zwack‐Okossi equation showed that, at the early stage of merging when two TPVs had not merged, despite AC2's intensification was favored by vorticity advection provided by the upper‐level jet stream, the warm advection supporting AC2's development, which was prevented by TPV2. AC2 weakened due to the joint influences of cold advection induced by the cold core beneath the TPV2 and AC1's cyclonic circulation at lower‐levels. At the later stage of merging, AC2 rapidly intensified due to the joint influences of warm advection produced by the warm air advected from warm core above the merged TPV by the upper‐level jet stream, and the warm advection induced by enhanced lower‐level baroclinicity near the warm front. Diabatic heating near the upper‐ and lower‐level fronts also played an important role in promoting AC2's development through its whole time.

Comparative analysis of four types of mesoscale eddies in the Kuroshio-Oyashio extension region

Oceanic mesoscale cyclonic (anticyclonic) eddies usually have cold (warm) cores and counterclockwise (clockwise) flow fields in the Northern Hemisphere. However, “abnormal” cyclonic (anticyclonic) eddies with warm (cold) cores and counterclockwise (clockwise) flow fields have recently been identified in the Kuroshio-Oyashio Extension (KOE) region. Here, traditional cyclonic cold-core eddies (CCEs) and anticyclonic warm-core eddies (AWEs) are termed normal eddies, and cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) are called abnormal eddies. Applying a vector geometry-based automatic eddy detection method to the Ocean General Circulation Model for the Earth Simulator reanalysis data (OFES), a three-dimensional eddy dataset is obtained and used to quantify the statistical characteristics of these eddies. Results illustrate that the number of CCEs, AWEs, CWEs, and ACEs accounted for 38.46, 36.15, 13.40, and 11.99%, respectively. In the vertical direction, normal eddies are concentrated in the upper 2,000 m, while abnormal eddies are mainly found in the upper 600 m of the ocean. On seasonal scales, normal eddies are more abundant in winter and spring than in summer and autumn, with the opposite trend found for abnormal eddies. Potential density changes modulated by normal eddies are dominated by eddies-induced temperature anomalies, while salinity anomalies dominate the changes modulated by abnormal eddies. This study expands the types of eddies and enriches their understanding in the KOE region.

A lens-shaped, cold-core anticyclonic surface eddy in the northern South China Sea

Typically, compared with the normal ocean, an anticyclonic eddy has higher sea surface temperature (SST), greater surface mixed-layer depth (MLD), and a bowl-shaped structure under the action of geostrophy. This study is the first to report an abnormal anticyclonic eddy characterized by a lens-shaped structure, cold core, and shallower MLD, which were observed in situ in the northern South China Sea (SCS) in September 2021. The SST at core of the anticyclonic eddy was 0.4°C lower than that in its peripheral region. The MLD at the center of the eddy was about half of that outside the eddy. Below the surface mixed layer, a lens-shaped structure containing relatively well-mixed water was observed between the two high-gradient layers. Within this lens-shaped structure, the isothermal layers were stretched, but accompanied by water mixing that was about one third of that at the upper and lower bounds of the structure. This eddy originated from a Kuroshio Current intrusion in late October 2020 and died in November 2021, such that its lifespan exceeded 1 year. The shedding of the Kuroshio Loop into the SCS under strong air–sea interactions under continuous sea surface cooling in winter was considered a key mechanism for the generation of the cold core of the eddy. The lens-shaped structure formed below the surface mixed layer and was maintained through geostrophic balance by the subsurface maximum speeds of the Kuroshio Current intrusion (50–100 m), thereby forming a shallower MLD in the eddy center. The subsurface speed maximum within the eddy was also observed by a shipborne acoustic Doppler current profiler at 10 months after its formation, confirming the hypothesized mechanism. This type of abnormal anticyclonic may be a common phenomenon in the northern SCS and has potential implications for the local biogeochemistry, local heat budget, and regional oceanic models.

Grain-Surface Hydrogen-Addition Reactions as a Chemical Link Between Cold Cores and Hot Corinos: The Case of H2CCS and CH3CH2SH.

Recently, searches were made for H2CCS and HCCSH in a variety of interstellar environments─all of them resulted in nondetections of these two species. Recent findings have indicated the importance of destruction pathways, e.g., with atomic hydrogen, in explaining the consistent nondetection of other species, such as the H2C3O family of isomers. We have thus performed ab initio calculations looking at reactions of H2CCS, HCCSH, and related species with atomic hydrogen. Our results show that H2CCS and HCCSH are both destroyed barrierlessly by atomic hydrogen, thus providing a plausible explanation for the nondetections. We further find that subsequent reactions with atomic hydrogen can barrierlessly lead to CH3CH2SH, which has been detected. Astrochemical simulations including these reactions result not only in reproducing the observed abundance of H2CCS in TMC-1 but also show that CH3CH2SH, produced via our H-addition pathways and subsequently trapped on grains, can desorb in warmer sources up to abundances that match previous observations of CH3CH2SH in Orion KL. These results, taken together, point to the importance of grain-surface H-atom addition reactions and highlight the chemical links between cold prestellar cores and their subsequent, warmer evolutionary stages.

Why Do Inverse Eddy Surface Temperature Anomalies Emerge? The Case of the Mediterranean Sea

It is widely accepted that the signature of anticyclonic (cyclonic) eddies on the sea surface temperature corresponds to a warm (cold) core anomaly. Nevertheless, this statement has been put to question by recent regional studies showing the existence of inverse eddy SST anomalies: Cold Core anticyclones and, respectively, Warm Core cyclones. This study shows that the emergence of these inverse anomalies is a seasonal phenomenon that affects the life cycle of mesoscale eddies in the Mediterranean Sea. We use remote sensing observations and in situ data to analyse the eddy-induced SST anomaly over a 3-year period (2016–2018). We build an eddy core SST anomaly index to quantify the amount of Cold Core anticyclones and Warm Core cyclones all over the year and especially during the spring re-stratification period. We find that 70% of eddy anomalies are inverse in May and June both for cyclones and anticyclones. Regular temperature anomalies could reach 1.5 °C, while inverse ones are only present in the first 50 m of the oceanic layer and hardly exceed 1 °C. In order to understand the underlying dynamical processes, we construct a simple vertical column model to study the impact of the seasonal air–sea fluxes on the surface stratification inside and outside eddies. It is only by taking into account a differential diapycnal eddy mixing—increased in anticyclones and reduced in cyclones—that we reproduce correctly, in agreement with the observations, the surface temperature inversion in the eddy core. This simplified model suggests that vertical mixing modulation by mesoscale eddies might be the key mechanism that leads to the eddy–SSTA seasonal inversion in the ocean.

Discovery of CH2CCHC4H and a rigorous detection of CH2CCHC3N in TMC-1 with the QUIJOTE line survey

Using the QUIJOTE line survey in the 32.0–50.4 GHz range, we report the discovery of the molecule CH2CCHC4H towards the prestellar cold core TMC-1 in the Taurus region. We also present a rigorous detection of CH2CCHC3N, along with its detailed analysis. We identified a total of twenty rotational transitions for each one of these molecules. The rotational quantum numbers range from Ju = 17 up to 24 and Ka≤ 3. The column density for CH2CCHC4H is N = (2.2 ± 0.2) × 1012 cm−2, while for CH2CCHC3N, we derived N = (1.2 ± 0.15) × 1011 cm−2. The rotational temperature is 9.0 ± 0.5 K for both species. The abundance ratiobetween CH2CCHC4H and CH2CCHC3N is 18 ± 4. We also compared the column densities of these species with those of their isomers CH3C6H and CH3C5N, derived from their J = 20 − 10 up to J = 31 − 30 rotational transitions observed with the QUIJOTE line survey. The observed abundances for all these species are reasonably well explained by state-of-the-art chemical models of TMC-1. The observed astronomical frequencies were merged with laboratory frequencies from the literature to derive improved spectroscopic parameters.

The Relationship of the Spatial Structure of the Total Suspended Matter Concentration and Hydrological Parameters in the Northern Black Sea According to Contact Measurements

Here we describe the features of the horizontal and vertical distribution of total suspended matter in the northern part of the Black Sea and their relationships with the water temperature, salinity, and density fields measured at the identical grid during hydro-optical surveys from 2016 to 2020. The results show that the primary sources of increased total suspended matter concen trations in the northern part of the Black Sea are low-salinity and turbid waters of the Kerch Strait; runoffs of the Rioni, Enguri, and other rivers in the east of the survey area; together with freshened waters of the Dnieper, Dniester, and Danube runoff from the northwestern shelf. Higher turbidity was observed in the deep-water part of the sea, associated with the cyclonic gyres and meanders of the Rim Current effects. The total suspended matter vertical structure features an upper mixed layer, which usually coincides in thickness with the upper thermohaline upper mixed layer. Significant negative correlations were found for this layer comparing total suspended matter concentration versus temperature and salinity, while the correlation appears positive with density values. Below, a total suspended matter subsurface maximum was observed in the seasonal thermocline and pycnocline layer. The high turbidity layer appeared almost an order of magnitude thinner in the regions of maximum temperature gradients versus the areas where the temperature gradient was weak. A local total suspended matter minimum occurred below the cold intermediate core, corresponding to the main thermocline, halocline, and pycnocline layer. Beneath this minimum, there was a local increase of total suspended matter coinciding with the upper boundary of the hydrogen sulfide zone.