Vertical Temperature Profiles Research Articles

Three-Dimensional Static Instability of Gravity Waves and a Possible Parameterization of the Associated Wave Breaking

Abstract Parameterizations of subgrid-scale gravity waves (GWs) in atmospheric models commonly involve the description of the dissipation of GWs. Where they dissipate, GWs have an increased effect on the large-scale flow. Instabilities that trigger wave breaking are an important starting point for the route to dissipation. Possible destabilizing mechanisms are numerous, but the classical vertical static instability is still regarded as a key indicator for the disposition to wave breaking. In this work, we investigate how the horizontal variations associated with a GW could alter the criterion for static instability. To this end, we use an extension of the common parcel displacement method. This three-dimensional static stability analysis predicts a significantly larger range of instability than does the vertical static stability analysis. In this case, the Lindzen-type saturation adjustment to a state of marginal stability is perhaps a less suitable ansatz for the parameterization of the GW breaking. To develop a possible ansatz for the GW dissipation due to three-dimensional instability, we apply the methods of irreversible thermodynamics, which are embedded in the Gibbs formalism of dynamics. In this way, the parameterization does not only satisfy the second law of thermodynamics, but it can also be made consistent with the conservation of energy and further (non-)conservation principles. We develop the parameterization for a discrete spectrum of GW packets. Offline computations of GW drag and dissipative heating rates are performed for two vertical profiles of zonal wind and temperature for summer and winter conditions from CIRA data. The results are compared to benchmarks from the literature.

Hierarchical Bayesian modeling of ocean heat content and its uncertainty

The accurate quantification of changes in the heat content of the world’s oceans is crucial for our understanding of the effects of increasing greenhouse gas concentrations. The Argo program, consisting of Lagrangian floats that measure vertical temperature profiles throughout the global ocean, has provided a wealth of data from which to estimate ocean heat content. However, creating a globally consistent statistical model for ocean heat content remains challenging due to the need for a globally valid covariance model that can capture complex nonstationarity. In this paper, we develop a hierarchical Bayesian Gaussian process model that uses kernel convolutions with cylindrical distances to allow for spatial nonstationarity in all model parameters while using a Vecchia process to remain computationally feasible for large spatial datasets. Our approach can produce valid credible intervals for globally integrated quantities that would not be possible using previous approaches. These advantages are demonstrated through the application of the model to Argo data, yielding credible intervals for the spatially varying trend in ocean heat content that accounts for both the uncertainty induced from interpolation and from estimating the mean field and other parameters. Through cross-validation, we show that our model outperforms an out-of-the-box approach as well as other simpler models. The code for performing this analysis is provided as the R package BayesianOHC.

Experimental investigation on RP‐3 aviation kerosene large‐scale pool fires at high altitude

AbstractRP‐3 aviation kerosene is a standard fuel that is used in civil aircraft and is a substitute for Jet‐A fuel. This paper investigates the combustion behaviour of RP‐3 aviation kerosene in an open space in the low‐pressure environment of a plateau. A series of large‐scale pools with diameters ranging from 0.4 m to 2.82 m combustion experiments are performed. Typical combustion characteristic parameters, including combustion rate, flame height and axial plume temperature distribution is measured. Results show that a low‐pressure environment significantly affects pool fires. With combustion rate, there is a linear variation law between oil pool size and combustion rate. The experimental data are fitted as a means of obtaining the large‐scale combustion rate relationship equation at low pressure. Experimental flame height data is compared using classical prediction models. Prediction model coefficients at low pressure are determined. The axial plume temperature distribution is greater than in the literature findings due to flames becoming longer in a low‐pressure environment. The three regimes in McCaffery's model are redefined and correlate well with the vertical temperature profile of the pool centreline. The results of the experimental investigation will help research fire hazards in low‐pressure environments while also contributing to the provision of basic data for the development of firefighting operation strategies.

Synergistic retrieval and complete data fusion methods applied to simulated FORUM and IASI-NG measurements

Abstract. In the frame of Earth observation remote-sensing data analysis, synergistic retrieval (SR) and complete data fusion (CDF) are techniques used to exploit the complementarity of the information carried by different measurements sounding the same air mass and/or ground pixel. While more difficult to implement due to the required simultaneous access to measurements originating from different instruments, the SR method is sometimes preferred over the CDF method as the latter relies on a linear approximation of the retrieved states as functions of the true atmospheric and/or surface state. In this work, we study the performance of the SR and CDF techniques when applied to simulated measurements of the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) and the Infrared Atmospheric Sounding Interferometer – New Generation (IASI-NG) missions that will be operational in a few years, from two polar-orbiting satellites. The study is based on synthetic measurements generated for the two missions in clear-sky atmospheres. The target parameters of the inversion are the vertical profiles of temperature, water vapor and ozone mixing ratios, surface temperature, and spectral emissivity. We find that for exact matching of the measurements, the results of the SR and CDF techniques differ by less than 1/10 of their errors estimated through the propagation of measurement noise. For measurements with a realistic mismatch in space and time, the two methods provide more different results. Still in this case, however, the differences between the results are within the error bars due to measurement noise. We conclude that, when applied to FORUM and IASI-NG missions, the two methods are equivalent from an accuracy point of view.

SIMO v1.0: simplified model of the vertical temperature profile in a small, warm, monomictic lake

Abstract. A simple 1-D energy budget model (SIMO) for the prediction of the vertical temperature profiles in small, monomictic lakes forced by a reduced number of input meteorological variables is proposed. The model estimates the net heat flux and thermal diffusion using only routinely measured hourly mean meteorological variables (namely, the air temperature, relative humidity, atmospheric pressure, wind speed, and precipitation), hourly mean ultraviolet B radiation (UVB), and climatological yearly mean temperature data. Except for the initial vertical temperature profile, the model does not use any lake-specific variables. The model performance was evaluated against lake temperatures measured continuously during an observational campaign in two lakes belonging to the Plitvice Lakes, Croatia (Lake 1 and Lake 12). Temperatures were measured at 15 and 16 depths ranging from 0.2 to 27 m in Lake 1 (maximum depth of 37.4 m) and 0.2 to 43 m in Lake 12 (maximum depth of 46 m). The model performance was evaluated for simulation lengths from 1 to 30 d. The model performed reasonably well, and it was able to satisfactorily reproduce the vertical temperature profile at the hourly scale, the deepening of the thermocline with time, and the annual variation in the vertical temperature profile, which shows its applicability for short-term prognostic simulations. A yearlong simulation initiated with an approximately constant vertical profile of the lake temperature (≈ 4 ∘C) was able to reproduce the onset of stratification and convective overturn. The epilimnion temperature was somewhat overestimated, especially with the onset of the convective overturn. The upper limit of the metalimnion was well captured, while its thickness was overestimated. Nevertheless, the values of the model performance measures obtained for a yearlong simulation were comparable with those reported for other, more complex models. Thus, the presented model can also be used for long-term simulations and the assessment of the onset and duration of lake stratification periods when water temperature data are unavailable, which can be useful for various lake studies performed in other scientific fields, such as biology, geochemistry, and sedimentology.

Upper Ocean Responses to the Tropical Cyclones Ida and Felicia (2021) in the Gulf of Mexico and the Eastern North Pacific

Tropical cyclones (TCs) are a significant component of ocean–atmosphere interactions and the climate system. These interactions determine both the development and strength of TCs, as well as various biogeochemical processes in the upper oceans, including vertical mixing and primary production. We investigated the impact of the TCs Felicia and Ida that emerged in 2021 in the eastern North Pacific and the Gulf of Mexico, respectively, using satellite observations of sea-surface temperature (SST) and surface chlorophyll a (chl-a) concentrations, and vertical profiles of temperature and salinity derived from Argo floats. Observations differed between the two study areas. Cooling of SST associated with TC Ida was observed throughout the Gulf of Mexico (<0.5 °C), except for warming in a region off the Mexican coast east of Ida’s track (by about 0.5 °C). The passing of TC Felicia cooled SST in the eastern region (15°N, 115°W) and a central region (15°N, 125°W) by 0.5 °C and 0.36 °C, respectively. The passing of the TCs caused enhanced vertical mixing of the upper ocean layer in the Gulf of Mexico, with a deepening of the mixed layers from 38 m to 68 m (TC Ida). In contrast, the mixed layer in the eastern North Pacific decreased from 50 m to 20 m. For the eastern North Pacific, mixing could be related to an increase in surface chl-a and thus enhanced phytoplankton biomass was observed for 2 months after the passing of TC Felicia with a chl-a increase of 0.15 mg m−3. In the Gulf of Mexico, however, TC Ida caused the injection of a coastal phytoplankton bloom into the open Gulf, resting for more than a month after the cyclone had passed. Our findings contribute to the understanding of potential SST cooling, destratification, and enhanced primary production due to the passage of TCs in two distinct ocean regions, i.e., the open eastern North Pacific and the semi-enclosed Gulf of Mexico.

Two-fluid numerical model of chromospheric heating and plasma outflows in a quiet-Sun

\textbf{Purpose:} This paper addresses long-standing solar physics problems, namely, the heating of the solar chromosphere and the origin of the solar wind. Our aim is to reveal the related mechanisms behind chromospheric heating and plasma outflows in a quiet-Sun. \textbf{Methods:} The approach is based on a two-fluid numerical model that accounts for thermal non-equilibrium (ionization/recombination), non-adiabatic, and non-ideal dynamics of protons+electrons and hydrogen atoms. The model is applied to numerically simulate the propagation and dissipation of granulation-generated waves in the chromosphere and plasma flows inside a quiet region. \textbf{Results:} The obtained results demonstrate that collisions between protons+electrons and hydrogen atoms supplemented by plasma viscosity, magnetic resistivity, and recombination lead to thermal energy release, which compensates radiative and thermal losses in the chromosphere, and sustains the atmosphere with vertical profiles of averaged temperature and periods of generated waves that are consistent with recent observational data. \textbf{Conclusion:} Our model conjectures a most robust and global physical picture of granulation-generated wave motions, plasma flows, and subsequent heating, which form and dynamically couple the various layers of the solar atmosphere.

Mesoscale eddies in the southwestern tropical Atlantic

The southwestern tropical Atlantic is a region of complex ocean dynamic where originates the strong western boundary current system composed of North Brazil current and North Brazil undercurrent. The region includes a variety of features including the Atoll das Rocas (AR) and Fernando de Noronha (FN) ridge that may favour mesoscale eddy dynamics. However, origin, occurrence and characteristics of mesoscale eddies were still not described in the region. Using satellite altimetry data from 1993 to 2018 off Northeast Brazil (37-25°W; 13-1°S), we reconstruct eddy trajectories and analyse the main eddy surface characteristics (e.g., size, amplitude, polarity) and their spatiotemporal variations. The study reveals two distinct dynamic regions before quantifying mesoscale eddies characteristics. Approximately 2000 mesoscale eddies crossed the region during the study period, among which 76% were generated inside the region, with amplitudes and radii ranging between 1 and 2 cm and 25 and 205 km, respectively. Eddies are preferentially formed between August and September and propagate westward. In the region around the FN Archipelago (36-26°W; 6-1°S), the formation of cyclonic eddies is likely favoured by barotropic instabilities of surface currents and the wind stress curl. On the other hand, in the south of the region (36-26°W; 12-8°S), eddies formation is likely associated with the barotropic instabilities, wind stress curl and the meandering of surface currents. Based on vertical temperature and salinity profiles from Argo floats’ data, we determined that in average, the core of cyclonic eddies is centred at ~ 130 m (140 m) in the northern (southern) region while the core of anticyclonic eddies is centred at ~90 m (125 m) in the northern (southern) region. Moreover, mesoscale eddies formed in the tropical Atlantic do not connect the eastern tropical Atlantic and northeast Brazil.

Transitional fluctuations of thermal boundary layer in horizontal convection

Fluctuations of thermal boundary layer (BL) in horizontal convection (HC) strongly affect the global heat transport through the HC sample and predominately determine the flow state. Here, we present a systematic experimental study of vertical profiles of mean temperature and temperature variance in the thermal BL of a HC flow that are heated and cooled from the bottom. Three rectangular HC samples filled with de-ionised water are used in the experiment. They have the same aspect ratios Γ≡L:W:H=10:1:1 but with different L (L, W and H are, respectively the length, width and height of the sample). The Rayleigh number Ra varies in the range 2×1010≲Ra≲1.3×1013, and the Prandtl number Pr is in the range 3.9≲Pr≲6.5. For all Ra in the studied range, we find that the cold thermal BL above the cooling plate remains laminar and the vertical profiles of measured mean temperature follow a universal scaling form predicted for laminar BL by Yan, Shishkina and He (J. Fluid Mech., vol. 915, 2021, R5). Above the heated plate, on the contrary, temperature fluctuations in the hot thermal BL undergo several transitional changes as Ra increases. For Ra≲6×1010, the thermal BL has a stable double-layer structure agreeing with the predicted scaling form for laminar BL and the temperature fluctuations are nearly zero. In the range 6×1010≲Ra≲1.1×1011, temperature fluctuations inside the BL have intermittent decayed oscillations, which results in deviations of the measured mean temperature profiles from the predicted scaling form. For 1.1×1011≲Ra≲1012, the temperature oscillations inside the BL become continuous and stable. Correspondingly, an intermediate layer emerges in the thermal BL, where the mean temperature profile has a sinusoidal variation on the distance z above the heated plate. For 1012≲Ra≲1.3×1013, the temperature fluctuations in the intermediate layer become irregular and intermittent, indicating a growing mixing intensity as Ra increases. When Ra exceeds 7×1012, the vertical distribution of mean temperature in the intermediate layer is uniform because of strong mixing. The temperature-variance vertical profiles follow a power-law function σT2(z)∼z−γ with the exponent γ=0.66, which agrees with the Priestley prediction for thermal convection over a heated horizontal surface. Our results thus reveal a series of transitional changes of temperature fluctuations, from laminar to chaotic states, in the hot thermal BL. They predominately account for the enhancement of global heat transport in the HC flow observed by Reiter and Shishkina (J. Fluid Mech., vol. 892, 2020, R1).

Seasonal Changes in the Vertical Structure of Ozone in the Martian Lower Atmosphere and Its Relationship to Water Vapor

AbstractThe mid‐infrared channel of the Atmospheric Chemistry Suite (ACS MIR) onboard the ExoMars Trace Gas Orbiter is capable of observing the infrared absorption of ozone (O3) in the atmosphere of Mars. During solar occulations, the 003←000 band (3,000‐3,060 cm−1) is observed with spectral sampling of ∼0.045 cm−1. Around the equinoxes in both hemispheres and over the southern winters, we regularly observe around 200–500 ppbv of O3 below 30 km. The warm southern summers, near perihelion, produce enough atmospheric moisture that O3 is not detectable at all, and observations are rare even at high northern latitudes. During the northern summers, water vapor is restricted to below 10 km, and an O3 layer (100–300 ppbv) is visible between 20 and 30 km. At this same time, the aphelion cloud belt forms, condensing water vapor and allowing O3 to build up between 30 and 40 km. A comparison to vertical profiles of water vapor and temperature in each season reveals that water vapor abundance is controlled by atmospheric temperature, and H2O and O3 are anti‐correlated as expected. When the atmosphere cools, over time or over altitude, water vapor condenses (observed as a reduction in its mixing ratio) and the production of odd hydrogen species is reduced, which allows O3 to build up. Conversely, warmer temperatures lead to water vapor enhancements and ozone loss. The LMD Mars Global Climate Model is able to reproduce vertical structure and seasonal changes of temperature, H2O, and O3 that we observe. However, the observed O3 abundance is larger by factors between 2 and 6, indicating important differences in the rate of odd‐hydrogen photochemistry.

Improving the Reconstruction of Vertical Temperature Profiles on Account of Oceanic Front Impacts

The application of remote sensing observations in estimating ocean sub-surface temperatures has been widely adopted. Machine learning-based methods in particular are gaining more and more interest. While there is promising relevant progress, most temperature profile reconstruction models are still built upon the gridded Argo data regardless of the impacts of mesoscale oceanic processes. As a follow-on to the previous study that demonstrates the influence of ocean fronts is negligible, we focus on the improvement of temperature profile reconstruction by introducing the sea surface temperature (SST) gradient into the neural network model. The model sensitivity assessments reveal that the normalization of the input variables achieves a higher estimation accuracy than the original scale. Five experiments are then designed to examine the model performances with or without the SST gradient input. Our results confirm that, for a given model configuration, the one with the input of the SST gradient has the lowest reconstruction bias in comparison to the in situ Argo measurements. Such improvement is particularly pronounced below 200 m depth. We also found that the non-linear activation functions and deeper network structures facilitate the performance of reconstruction models. Results of this work open new insights and challenges to refine the mapping of upper ocean temperature structures. While more relevant machine learning methods are worth further exploitation, how to better characterize the mesoscale oceanic processes from surface observations and bring them into the reconstruction models is the key and needs much attention.

Tethered balloon-borne profile measurements of atmospheric properties in the cloudy atmospheric boundary layer over the Arctic sea ice during MOSAiC: Overview and first results

The tethered balloon-borne measurement system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) was deployed over the Arctic sea ice for 4 weeks in summer 2020 as part of the Multidisciplinary drifting Observatory for the Study of Arctic Climate expedition. Using BELUGA, vertical profiles of dynamic, thermodynamic, aerosol particle, cloud, radiation, and turbulence properties were measured from the ground up to a height of 1,500 m. BELUGA was operated during an anomalously warm period with frequent liquid water clouds and variable sea ice conditions. Three case studies of liquid water phase, single-layer clouds observed on 3 days (July 13, 23, and 24, 2020) are discussed to show the potential of the collected data set to comprehensively investigate cloud properties determining cloud evolution in the inner Arctic over sea ice. Simulated back-trajectories show that the observed clouds have evolved within 3 different air masses (“aged Arctic,” “advected over sea ice,” and “advected over open ocean”), which left distinct fingerprints in the cloud properties. Strong cloud top radiative cooling rates agree with simulated results of previous studies. The weak warming at cloud base is mostly driven by the vertical temperature profile between the surface and cloud base. In-cloud turbulence induced by the cloud top cooling was similar in strength compared to former studies. From the extent of the mixing layer, it is speculated that the overall cloud cooling is stronger and thus faster in the warm oceanic air mass. Larger aerosol particle number concentrations and larger sizes were observed in the air mass advected over the sea ice and in the air mass advected over the open ocean.

A dataset of temperature, humidity, and liquid water path retrievals from a network of ground-based microwave radiometers dedicated to fog investigation

The database presented in this study has been acquired during the SOuth west FOGs 3D (SOFOG3D) experiment for processes study. This international campaign led by Météo-France during the winter 2019–2020 aimed at deploying a unique network of both in situ and remote sensing measurements in order to document spatial and temporal variabilities of fog events. To support this scientific objective but also to conduct first data assimilation experiments within the French convective scale model AROME, an un-precedented network of 8 ground-based microwave radiometers (MWR) has been deployed in 7 different locations known to be prone to fog occurrences. The database gives access to vertical profiles of temperature and humidity (both absolute and relative) from the surface up to 10 km altitude as well as integrated water vapor and liquid water path estimates. The retrieved profiles offer a very large database that can be exploited for several scientific purposes: fog process studies at specific location, documentation on the variability of fog properties at the regional scale, better understanding of the atmospheric boundary layer (ABL) height and dynamics during wintertime conditions, development of nowcasting products dedicated to fog alerts, data assimilation experiments to improve fog forecasts, development of synergetical advanced products, and evaluation of new model configurations with advanced parameterization or resolutions.

Improving Snow‐Process Modeling by Evaluating Reanalysis Vertical Temperature Profiles Using a Distributed Hydrological Model

AbstractThe use of the Japanese 55‐year Reanalysis (JRA55) vertical temperature profile (VTP) has been suggested in previous studies for estimating gridded air temperatures at high elevations in data‐scarce regions to conduct hydrological simulations. In this study, we investigate and further enhance the applicability of VTP for hydrological simulations through several experimental sets using a distributed hydrological model with improved snow physics (WEB‐DHM‐S) based on water and energy budget to simulate the hydrology of a snowfed river basin in Japan, Kurobe Basin, while simultaneously correcting the snow precipitation estimates through optimization. We examined the simulated discharge, point snow depth, and snow cover, finding that the snow processes were highly sensitive to the individual station used with VTP for extrapolating air temperature to higher elevations, with corrected snowfall estimates differing by as much as 18%. We further compared this with simulations based on linear regression‐based lapse rates derived from station observations (scarce and often distributed at low elevations). It was found that the use of VTP improved discharge simulations but deteriorated point snow depth simulations at low elevations, compared with linear regression‐based lapse rates. A hybrid of the two methods led to better discharge and point snow depth simulations with reasonable snow cover simulations. The study advances the application of snow‐process models in data‐scarce regions by enhancing our understanding about the usage of VTP.

Photosynthetic Active Solar Radiation in Lake Teletskoye During the Open Water Period

Spatial and temporal variability of flux density of photosynthetic active solar radiation (PAR) in the waters of large deep-water oligotrophic Lake Teletskoye (Republic of Altai) is considered based on the analyzed experimental data for the years 2016-2021. Probing of the lake water column was implemented using Satlanic PAR sensor as a part of CTD of the SBE 25plus probe at the beginning and the end of the summer heating period. During various years of studying, PAR magnitude monotonically decreased with lake depth increase and practically became zero at horizons from 3 to 14,8 m according to the data received from two weather stations at the reservoir, i.e. in the pelagic zone of rivers Chulyshman and Kokshi. Flux density of photosynthetic active solar radiation in the upper layer made up to 27-1000 μmol/(m2·s) during the observation period. The photic depth zone (at one percent irradiation) in Lake Teletskoye at the Chulyshman station on sunny days reached 14.8 m, while at the Kokshi one — 11.7 m. According to PAR measurements, the attenuation coefficient (extinction coefficient) along the vertical was estimated as 0.1-2.6 m-1. The maximum weakening coefficient at the Chulyshman station was recorded in June 2016 in the surface 3-m layer of the lake (1.8-2.6 m-1), while below 3 m it had values of 0.1-1.9 m-1. The attenuation coefficient varied within 0.1-1.6 m-1 at the Kokshi station. Relative transparency of the Secchi white disk at the Chulyshman and Kokshi stations ranged within 1.3-5.3 and 2.4-6.5 m, respectively. The paper also presents vertical lake profiles of water temperature in June-July — characteristic of direct summer stratification of the reservoir.

GNSS Radio Occultation Infilling of the African Radiosonde Data Gaps Reveals Drivers of Tropopause Climate Variability

AbstractRadiosonde data are important for understanding and monitoring the upper troposphere and lower stratosphere (UTLS) region. Over much of Africa, however, such data are lacking; consequently, the African UTLS is understudied, and potential proxies such as climate models and reanalysis products fail to fully capture the behavior of the UTLS. This study pioneers the use of Global Navigation Satellite System‐Radio Occultation (GNSS‐RO) data from 2001 to 2020 to address the radiosonde data gap over Africa and contributes to a better understanding of the tropopause (TP) characteristics under the influence of global and regional climate drivers over the continent. As a first step to using GNSS‐RO for infilling the radiosonde data gap over Africa, we analyzed the performance of GNSS‐RO (2001–2020) and reanalysis products (European Centre for Medium‐Range Weather Forecasts Reanalysis 5 (ERA5) and Modern‐Era Retrospective analysis for Research and Applications version 2 (MERRA‐2)) against radiosonde observations applying the Kling‐Gupta Efficiency metric. The analyses show that GNSS‐RO data from Challenging Mini‐satellite Payload, Gravity Recovery and Climate Experiment, Meteorological Operational, Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC), and COSMIC‐2 are in good agreement with radiosonde measurements with differences being smaller than 1 K in the UTLS, thereby enabling infilling of missing radiosonde data in Africa during 2001–2020. By contrast, the smoothed vertical temperature profiles of reanalysis products lead to a warm bias of +0.8 K in ERA5 and +1.2 K in MERRA‐2 and these biases alter some vertical and temporal structure details, with possible implications on climate change detection and attribution. Furthermore, the analysis of GNSS‐RO data over Africa revealed: (a) the teleconnections of El Niño‐Southern Oscillation (ENSO), Quasi‐Biennial Oscillation (QBO), Indian Ocean Dipole (IOD), Madden‐Julian Oscillation (MJO), North Atlantic Oscillation (NAO) and Southern Annular Mode (SAM) at the tropopause boundary; (b) multiple coupled global climate drivers such as ENSO‐IOD, ENSO‐MJO, ENSO‐NAO, QBO‐IOD, and ENSO‐NAO‐MJO; (c) coupled global and regional climate drivers that influence the TP variability, for example, ENSO‐Inter Tropical Convergence Zone; and (d), the deep convection associated with the Asian Summer Monsoon and Tropical/African Easterly Jet also locally influence TP height. In conclusion, this study demonstrates the capability of GNSS‐RO to fill the vast radiosonde data gap over Africa. This opens the opportunity for further detailed studies toward a better understanding of the tropopause characteristics including localization, quantification of trends, and influences of global, regional, and coupled climate drivers.

Variability in the vertical temperature profile within crevasses at an alpine glacier

AbstractTasman Glacier, a temperate maritime glacier in the New Zealand Southern Alps, is rapidly receding. Climate warming is resulting in lengthening of the ablation season, meaning crevasses in the accumulation area are becoming exposed at the surface for longer. We combine measurements of air temperature and wind speed from inside crevasses with surface meteorological data, finding that during summer, in-crevasse air temperature is frequently positive, and can at times exceed surface air temperature. Greatest warming occurred in the widest crevasses during clear-sky conditions, but full depth warming of crevasses also occurred at night. Net shortwave radiation contributes to heating of air in the upper regions of crevasses, but turbulent sensible heat transfer was responsible for driving warm air deeper into crevasses. Crevasses orientated to maximise radiation retrieval, and running parallel to wind flow, have the greatest potential for warming and heat storage. We hypothesise a positive feedback loop in the surface energy-balance system, where crevasses entrain and trap heat, which enhances melting, that in turn enlarges the crevasses, enabling greater heat storage and further melting. Energy-balance models that treat accumulation areas of alpine glaciers as homogeneous surfaces will therefore underestimate snow melt and overestimate mass balance.

The Impact of Nonzenith Elevation Angles on Ground-Based Infrared Thermodynamic Retrievals

Abstract Observing thermodynamic profiles within the planetary boundary layer is essential to understanding and predicting atmospheric phenomena because of the significant exchange of sensible and latent heat between the land and atmosphere within that layer. The Atmospheric Emitted Radiance Interferometer (AERI) is a ground-based infrared spectrometer used to obtain the vertical profiles of temperature and water vapor mixing ratio. Most AERIs are only capable of zenith views, although the Marine AERI (M-AERI) has a design that allows it to view various elevation angles. In this study, we quantify the improvement in the information content and accuracy of the retrieved profiles when nonzenith angles are included, as is common with microwave radiometer profilers. The impacts of the additional scan angles are quantified through both a synthetic study and with M-AERI observations from the ARM Cloud Aerosol Precipitation Experiment (ACAPEX) campaign. The simulation study shows that low elevation angles contain more information content for temperature whereas high elevation angles have more information content for water vapor. Outside of very humid environments, the addition of low elevation angles also results in lower root-mean-square errors when compared with high angles for both temperature and water vapor mixing ratio, although this is primarily a result of averaging multiple observations together to reduce instrument noise. Real-world results from the ACAPEX dataset indicate similar results as were found for the simulation study, although not all predicted benefits are realized because of the small sample size and observational uncertainties.

Extreme temperature events monitored by Raman lidar: Consistency and complementarity with spaceborne observations and modelling

AbstractTwo extreme temperature events (ETEs), both triggered by atmospheric blocking situations, were monitored by a pure rotational Raman lidar 20 km south of Paris. The first ETE lasted 6 days in late February 2018 with the onset of a cold wave surging from Siberia, and the second was a short heatwave that occurred at the end of July 2020. After calibration using simultaneous radiosoundings, lidar vertical profiles of temperature are derived with an uncertainty of less than 1 °C within both the planetary boundary layer and the lower/middle free troposphere (~3/6 km above ground level [a.g.l.] for day/night), with a final vertical resolution of 50 m and a temporal resolution of 30 min. Such capabilities fulfil the observational requirements of the World Meteorological Organisation and contribute to fill a gap left behind by current operational instruments, which struggle to follow the diurnal cycle of the planetary boundary layer due to insufficient spatial and temporal resolutions in the low troposphere. These case studies allow to assess how such weather events are represented by numerical weather prediction modelling and whether they can be correctly observed by the Infrared Atmospheric Sounding Interferometer (IASI) spaceborne mission. Our results demonstrate that during these events both ECMWF reanalyses and forecasts are in overall very good accordance with lidar observations (correlation >0.9 in average). Still, they show warm biases (~1°C–2°C) compared with the lidar and improvable temperature field representation in the boundary layer. The radiances measured by IASI, assimilated in the operational model, do not capture temperature profiles adequately below ~2–3 km a.g.l., mainly due to the altitude location of its weighting functions. The bias computed against the lidar reaches 2°C during the heatwave and 4°C during the cold wave case in the first 2 km of the atmosphere, beyond expected errors found in the literature.

Martian Atmospheric Thermal Structure and Dust Distribution During the MY 34 Global Dust Storm From ACS TIRVIM Nadir Observations

AbstractThe Thermal InfraRed channel in honor of professor Vassili Ivanovich Moroz (TIRVIM) of the Atmospheric Chemistry Suite onboard ExoMars Trace Gas Orbiter has continuously monitored the Martian atmosphere from 13 March 2018 until 2 December 2019, covering almost a complete Martian Year (MY). In the nadir mode of observations, infrared spectra obtained by TIRVIM in the spectral range 600–1,300 cm−1 permit retrievals of vertical temperature profiles from the surface up to 60 km of altitude, surface temperatures and column aerosol optical depths. Here we report the retrieved atmospheric thermal structure and the column dust content during the global dust storm (GDS) of MY 34 monitored from Ls = 182.2° to Ls = 211.8° (Solar Longitude), capturing the evolution of the GDS and the response of the atmospheric thermal structure to the changing dust loading. The global storm caused asymmetric atmosphere heating, predominantly in the southern hemisphere, and changed diurnal contrast of atmospheric thermal structure. We also observe a reduced diurnal contrast of surface temperatures at the peak of the GDS.