Elevated Temperature Inversion Research Articles

Concurrence of Temperature and Humidity Inversions in Winter in Qingdao, China

AbstractConcurrence of temperature inversion (TI) and humidity inversion (HI) is a particular configuration of the atmospheric boundary layer with important implications for early warning of fog formation. With a microwave radiometer device deployed in a 2‐month winter campaign at a coastal island in Qingdao, China, we here examine the relationship between TI and HI, and investigate the underneath mechanisms. Cases of temperature inversion are further divided into surface‐based temperature inversion (SBTI) and elevated temperature inversion (ETI), which show different relationship with HI. SBTI typically occurs at night with its strength significantly and positively correlated with HI. ETI also shows a high degree of temporal overlap with HI, but its strength has no obvious relationship with HI. The main explanation for this phenomenon is that ETI may block the vertical diffusion of water vapor, resulting in the formation of HI.

Influences of meteorological conditions in PM2.5 levels in Krasnoyarsk city atmosphere

The relationship between meteorological conditions and the levels of PM2.5 in Krasnoyarsk city atmosphere for the period from 2019 to 2022 were investigated. The meteorological data of the National Centers for Environmental Prediction Global Forecast System (NCEP GFS) reanalysis model was used. PM2.5 data were obtained from the ground monitoring stations. Analysis of variances (one-way and two-way ANOVA) and the Tukey Test showed statistically significant differences for temperature inversions, months in the cold period (November-February), and calm wind. In the case of high daily PM2.5 surface and elevated inversions occurred at 69% cases and strong temperature inversions at 74%. In the reverse case, in the presence of surface and elevated temperature inversions, high daily PM2.5 occurred in 53% of cases, and the presence of strong temperature inversions in 44%.

Impurity distribution in foggy and low cloud cover conditions

The paper discusses the possibilities of modelling the distribution of harmful impurities emitted into the atmosphere by industrial enterprises in conditions of fog and low clouds. With several sources located along a certain line or dispersed over an area, under conditions of elevated temperature inversion, which is often observed in fogs, additional reasons for increasing pollution of the surface air layer may appear. Under such conditions, calculations show that the distance at which the maximum concentration is observed increases substantially, and the concentration decreases very slowly with the distance after its maximum. As a result, the effect of the mutual overlapping of concentration fields from individual sources increases and more uniform pollution than in convective conditions is created in the industrial area. At the same time, even if the concentration from a separate source is relatively small, the total pollution can be very significant.

Spatio-temporally differentiated impacts of temperature inversion on surface PM2.5 in eastern China

Temperature inversion (TI) is one of the meteorological conditions that significantly affect regional air quality. Knowledge gap regarding the impacts of TI on surface PM2.5 in different topographies still existed. In the present study, the occurrence frequency, temperature lapse rate (TLR), depth, and the diurnal variations of TI, surface-based TI (SBTI), elevated TI (ElTI), and multiple layers of TIs (MultiTI) and their impacts on near-surface PM2.5 concentrations over eastern China that covers a range of topographies and climates, are systematically investigated based on global reanalysis ERA5 and the nationwide monitoring PM2.5 dataset from 2014 to 2020. TIs occurred mostly in the early morning. Different types of TIs present distinctive seasonal and spatial patterns. The majority of SBTIs and ElTIs occurred during nighttime in northern China and daytime in southern China, respectively, as the result of their formation mechanisms. SBTIs usually had larger TLR while ElTIs had deeper depth. SBTIs showed strong enhancement effects on PM2.5 concentration over the study domain while ElTIs showed more obvious impacts on northern nocturnal PM2.5. The peak time of PM2.5 was found around 18:00–22:00 LST, and TLR and depth of TIs are thought to be more relevant to PM2.5 peak concentration due to their coincident peak times. The strength of TIs is therefore more crucial in regulating PM2.5 than its occurrence frequency. Based on statistical analysis, our study provided a large picture of the generic spatiotemporal patterns of TIs and illustrated the impacts of different TIs on surface PM2.5 pollution on a diurnal basis. For a deeper understanding of the formation of PM2.5 pollution, more attention needs to be paid to the nocturnal PM2.5 not only at surface level but also at higher levels in the presence of TIs.

The Influence of Temperature Inversion on the Vertical Distribution of Aerosols

Temperature inversion plays an important role in the accumulation and diffusion of aerosols. In this study, the relationship between temperature inversion and the vertical distribution of aerosols is investigated based on Raman lidar observations taken from January 2010 to September 2015 at the Atmospheric Radiation Measurement site in the Southern Great Plains, USA. First, the diurnal and seasonal variations of the surface-based inversion (SBI) and elevated temperature inversion (EI) are investigated. The results indicate that the occurrence frequency of SBI and EI have different seasonal trends. SBI has the highest frequency in summer, while EI has the highest frequency in winter. The diurnal variation of SBI is obvious, with a higher frequency in nighttime and a lower frequency in daytime. The inversion intensity (ΔT) and inversion depth (ΔZ) of SBI and EI have consistent diurnal and seasonal trends. The effects of SBI and EI on the vertical distribution of aerosols are then analyzed. The mean aerosol optical depth (AOD) below the SBI height shows a clear seasonal variation, which is consistent with the seasonal trends of ΔT and ΔZ. This phenomenon also occurs on the AOD below EI top height. The sensitivity analysis shows that the mean AOD below SBI height or EI top height increases with an increase of the ΔT and ΔZ of SBI (EI). It indicates that ΔT and ΔZ are the key factors affecting the vertical distribution of aerosols. In addition, the variation of AOD below and above EI top height is opposite to that of AOD below and above EI bottom height under different ΔT and ΔZ conditions. The correlation coefficients between ΔT (ΔZ) of EI with AOD in EI were 0.62 (0.65). These results indicate that the space between EI bottom height and EI top height can store aerosols. The larger the ΔZ of EI, the more aerosols are stored. These findings contribute to our understanding of the effect of temperature inversion on the vertical distribution of aerosols.

Lidar-Derived Aerosol Properties from Ny-Ålesund, Svalbard during the MOSAiC Spring 2020

In this work, we present Raman lidar data (from a Nd:YAG operating at 355 nm, 532 nm and 1064 nm) from the international research village Ny-Ålesund for the time period of January to April 2020 during the Arctic haze season of the MOSAiC winter. We present values of the aerosol backscatter, the lidar ratio and the backscatter Ångström exponent, though the latter depends on wavelength. The aerosol polarization was generally below 2%, indicating mostly spherical particles. We observed that events with high backscatter and high lidar ratio did not coincide. In fact, the highest lidar ratios (LR > 75 sr at 532 nm) were already found by January and may have been caused by hygroscopic growth, rather than by advection of more continental aerosol. Further, we performed an inversion of the lidar data to retrieve a refractive index and a size distribution of the aerosol. Our results suggest that in the free troposphere (above ≈2500 m) the aerosol size distribution is quite constant in time, with dominance of small particles with a modal radius well below 100 nm. On the contrary, below ≈2000 m in altitude, we frequently found gradients in aerosol backscatter and even size distribution, sometimes in accordance with gradients of wind speed, humidity or elevated temperature inversions, as if the aerosol was strongly modified by vertical displacement in what we call the “mechanical boundary layer”. Finally, we present an indication that additional meteorological soundings during MOSAiC campaign did not necessarily improve the fidelity of air backtrajectories.

Characteristics of Temperature and Humidity Inversions Based on High-Resolution Radiosonde Observations at Three Arctic Stations

AbstractThe Global Climate Observing System Reference Upper-Air Network (GRUAN) with high-vertical-resolution radiosonde data at three Arctic stations and European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA5) were used to investigate the characteristics of multiple temperature inversions (TI) and humidity inversions (HI) in this study. It is found that surface-based inversion (SBI) at two coastal stations exists throughout the whole year, mainly due to the surface cooling in cold months, advection warm months, and the orography of the stations. The seasonal variation of surfaced-based HI (SBHI) frequency is similar to that of SBI, and its intensity is greater in summer because of the larger air moisture content. The frequency of the first elevated TI (EI1) and HI (EHI1) are both higher than that of the surface-based ones. The second elevated TI/HI layer (EI2/EHI2) is shallower and weaker than that of the EI1/EHI1. At two coastal stations, EI1 caused by warm advection is thicker and stronger than that caused by subsidence. At the station farther from the coast, EI1 caused by subsidence is higher, thinner, and stronger. The top height and depth of the EHI2 both show seasonal variations, with larger values in the cold months. EHI1 tends to be formed by the TI, whereas EHI2 is dominant by humidity advection at all studied stations. HI under the influence of TI is usually thicker and stronger than that formed by humidity advection. The coexistence of EI and EHI is the most frequent inversion structure at these stations.

Responses in PM2.5 and its chemical components to typical unfavorable meteorological events in the suburban area of Tianjin, China

Air pollution is the result of enormous emissions and unfavorable meteorological conditions. The role of meteorology, particularly extremely unfavorable meteorological events (EUMEs), in processing atmospheric PM2.5 pollution has not been fully addressed. This work examined the variations of PM2.5 mass and its chemical components associated with various meteorological parameters and three EUMEs based on meteorological observations and analysis combined with one-year long in situ measurement in 2018 in the suburban area of Tianjin, China. Analysis shows that the polluted days in 2018 were mostly related to the increase in sulfate, nitrate, and ammonium (SNA). Temperature between −2 to 13 °C is more favorable for the formation of SNA, while high temperature exceeding 28 °C is favorable for the formation of organic carbon and sulfate. Most of the ions and carbon components showed significant increase in concentrations when relative humidity exceeded 80%. The maximum decreasing rate of PM2.5 concentrations due to increase in wind speed and planetary boundary height could be 15.35 μg m−3 (m s−1)−1, and 34.37 μg m−3 (100 m)−1, respectively. EUMEs showed significant impacts on PM2.5 components, in which PM2.5 concentrations showed the most significant increase under temperature inversion (TI) events, and surface-based TI (SBTI) events usually have much stronger impacts on PM2.5 concentrations than elevated TI (ELTI). Nitrate was found to be the most sensitive component to EUMEs, especially under multiple EUMEs. The synthetic effects of multiple EUMEs could result in an increase of nitrate by 35.53 μg m−3 (523.3%). In addition, OC and sulfate are more sensitive to heat wave events. Our analysis provides improved understanding of the formation of PM2.5 pollution with respect to meteorology, particularly EUMEs. Based on such information, more attention may be needed on the collaborative prediction of EUMEs and air pollution episodes.

Low-tropospheric humidity inversions over Europe: spatiotemporal variability and relations to temperature inversions\u2019 occurrence

Tropospheric humidity inversions are an important component of the Earth’s climate system as well as a significant factor affecting the global radiation budget and cloud formation. Their occurrence enlarges the amount of downward longwave radiation trapped near the Earth’s surface and provides moisture to maintain the top of clouds from evaporation. The aim of this paper is to examine the spatiotemporal variability of the humidity inversions over Europe. For the first time, we provide also a comprehensive analysis of relations between the humidity inversions and temperature inversions over the domain considered. The study is based on data derived from the ERA-Interim reanalysis for the period 1981–2015. We have confirmed that the temporal and spatial variability of the humidity inversions is strongly related to inversion type. The mean seasonal frequency of surface-based humidity inversions (SBHI) usually does not exceed 20%, while the mean seasonal frequency of elevated humidity inversions (EHI) ranges from 5 to 60% depending on the region and season. On average, EHI are substantially deeper and stronger than SBHI. We found also that the low-tropospheric humidity inversions often occur simultaneously with the temperature inversions. Moderate positive correlations exist, however, only among the parameters (depth and strength) of the same inversion type, but not between the humidity inversions and the temperature inversions. Considering the links between EHI and ETI (elevated temperature inversions) parameters, slightly higher values of the Spearman’s rank correlation coefficient (ρs > 0.50) are found between EHI base height and ETI base height. Nonetheless, the simultaneous occurrence of EHI and ETI usually fosters the intensity of both inversion types.

Characteristics and meteorological mechanisms of transboundary air pollution in a persistent heavy PM2.5 pollution episode in Central-East China

Previous research has shown the significant transboundary air pollution (TAP) in China. Despite its adverse environmental and human health impacts, the characteristics and mechanisms of TAP have yet to be fully understood. This study comprehensively analyzed intensive ground and upper levels measurements along with the atmospheric modeling approach to determine the driving meteorological conditions responsible for the formation and evolution of a persistent severe PM2.5 pollution episode in Central-East China (CEC, 112°E −118°E, 30°N −34°N) starting from 18:00 on Dec. 3 to 18:00 on Dec. 5, 2017, which had obvious characteristics of TAP and explosive increases in PM2.5 concentration. We assessed and quantified contributions of local and nonlocal emissions to PM2.5 in the region and different cities during the episode and determined the altitude level at which TAP occurred. Results show that PM2.5 concentration in most cities in CEC region experienced two major increases: the first increase was due to the change in wind direction from south to north, transporting pollutants from north China to CEC; the second increase was driven by several important meteorological factors, including warm/cold advection at different altitudes, large-scale subsidence, and radiative cooling, jointly resulting in a deep (reaching around 800 m) and strong elevated temperature inversion with a significant reduction in mixing layer thickness and thus causing a rapid increase in PM2.5 concentration in CEC region. On average, TAP accounted for 42% of total PM2.5 concentration in the region during the event, in which the TAP impact varied by cities, ranging from ~26% to ~70%. Our findings demonstrate the synergetic effect of TAP and large-scale subsidence, providing a critical reference for air pollution forecast and assessment in the eastern China.

Analysis of Low-level Temperature Inversions and Their Effects on Aerosols in the Lower Atmosphere

High-quality and continuous radiosonde, aerosol and surface meteorology datasets are used to investigate the statistical characteristics of meteorological parameters and their effects on aerosols. The data were collected at the Atmospheric Radiation Measurement Southern Great Plains climate research facility during 2000–15. The parameters and vertical distribution of temperature inversion layers were found to have strong diurnal and seasonal changes. For surface-based temperature inversion (SBI), the mean frequency and depth of temperature inversion layers were 39.4% and 198 m, respectively. The temperature difference between the top and bottom of SBI was 4.8°C, and so the temperature gradient was 2.4°C (100 m)−1. The detailed vertical distributions of temperature inversion had been determined, and only the temperature inversion layers below 1000 m showed diurnal and seasonal variations. Mean surface aerosol number concentrations increased by 43.0%, 21.9% and 49.2% when SBIs were present at 0530, 1730 and 2330 LST, respectively. The effect of SBI on surface aerosol concentration was weakest in summer (18.1%) and strongest in winter (58.4%). During elevated temperature inversion events, there was no noticeable difference in surface aerosol number concentrations. Temperature differences and temperature gradients across SBIs correlated fairly well with aerosol number concentrations, especially for temperature gradients. The vertical distribution of aerosol optical properties with and without temperature inversions was different. Surface aerosol measurements were representative of the air within (below), but not above, SBIs and EIs. These results provide a basis for developing a boundary layer aerosol accumulation model and for improving radiative transfer models in the lower atmosphere.

Towards operational use of aircraft‐derived observations: a case study at London Heathrow airport

Mode‐Selective Enhanced Surveillance (Mode‐S EHS) aircraft reports can be collected at a low cost and are readily available around busy airports. The new work presented here demonstrates that observations derived from Mode‐S EHS reports can be used to study the evolution of temperature inversions since the data have a high spatial and temporal frequency. This is illustrated by a case study centred around London Heathrow airport for the period January 4–5, 2015. Using Mode‐S EHS reports from multiple aircraft and after applying quality control criteria, vertical temperature profiles are constructed by aggregating these reports at discrete intervals between the surface and 3,000 m. To improve these derived temperatures, four smoothing methods using low‐pass filters are evaluated. The effect of smoothing reduces the variance in the aircraft derived temperature by approximately half. After smoothing, the temperature variance between the altitudes 3,000 and 1,000 m is 1–2 K; below 1,000 m, it is 2–4 K. Although the differences between the four smoothing methods are small, exponential smoothing is favoured because it uses all available Mode‐S EHS reports. The resulting vertical profiles may be useful in operational meteorology for identifying elevated temperature inversions above 1,000 m. However, below 1,000 m they are less useful because of the reduced precision of the reported Mach number. A better source of in situ temperature observations would be for aircraft to use the meteorological reporting function of their automatic dependent surveillance system.

The Intraseasonal and Interannual Variability of Arctic Temperature and Specific Humidity Inversions

Temperature and humidity inversions are common in the Arctic’s lower troposphere, and are a crucial component of the Arctic’s climate system. In this study, we quantify the intraseasonal oscillation of Arctic temperature and specific humidity inversions and investigate its interannual variability using data from the Surface Heat Balance of the Arctic (SHEBA) experiment from October 1997 to September 1998 and the European Centre for Medium-Range Forecasts (ECMWF) Reanalysis (ERA)-interim for the 1979–2017 period. In January 1998, there were two noticeable elevated inversions and one surface inversion. The transitions between elevated and surface-based inversions were associated with the intraseasonal variability of the temperature and humidity differences between 850 and 950 hPa. The self-organizing map (SOM) technique is utilized to obtain the main modes of surface and elevated temperature and humidity inversions on intraseasonal time scales. Low (high) pressure and more (less) cloud cover are related to elevated (surface) temperature and humidity inversions. The frequency of strong (weak) elevated inversions over the eastern hemisphere has decreased (increased) in the past three decades. The wintertime Arctic Oscillation (AO) and Arctic Dipole (AD) during their positive phases have a significant effect on the occurrence of surface and elevated inversions for two Nodes only.

A climatological view of the vertical stratification of RH, O<sub>3</sub> and CO within the PBL and at the interface with free troposphere as seen by IAGOS aircraft and ozonesondes at northern mid-latitudes over 1994–2016

Abstract. This paper investigates in an innovative way the climatological vertical stratification of relative humidity (RH), ozone (O3) and carbon monoxide (CO) mixing ratios within the planetary boundary layer (PBL) and at the interface with the free troposphere (FT). The climatology includes all vertical profiles available at northern mid-latitudes over the period 1994–2016 in both the IAGOS (In-service Aircraft for a Global Observing System) and WOUDC (World Ozone and Ultraviolet Radiation Data Centre) databases, which represents more than 90 000 vertical profiles. For all individual profiles, apart from the specific case of surface-based temperature inversions (SBIs), the PBL height is estimated following the elevated temperature inversion (EI) method. Several features of both SBIs and EIs are analysed, including their diurnal and seasonal variations. Based on these PBL height estimates (denoted h), the novel approach introduced in this paper consists of building a so-called PBL-referenced vertical distribution of O3, CO and RH by averaging all individual profiles beforehand expressed as a function of z∕h rather than z (with z the altitude). Using this vertical coordinate system allows us to highlight the features existing at the PBL–FT interface that would have been smoothed otherwise. Results demonstrate that the frequently assumed well-mixed PBL remains an exception for both chemical species. Within the PBL, CO profiles are characterized by a mean vertical stratification (here defined as the standard deviation of the CO profile between the surface and the PBL top, normalized by the mean) of 11 %, with moderate seasonal and diurnal variations. A higher vertical stratification is observed for O3 mixing ratios (18 %), with stronger seasonal and diurnal variability (from ∼ 10 % in spring–summer midday–afternoon to ∼ 25 % in winter–fall night). This vertical stratification is distributed heterogeneously in the PBL with stronger vertical gradients observed at both the surface (due to dry deposition and titration by NO for O3 and due to surface emissions for CO) and the PBL–FT interface. These gradients vary with the season from the lowest values in summer to the highest ones in winter. In contrast to CO, the O3 vertical stratification was found to vary with the surface potential temperature following an interesting bell shape with the weakest stratification for both the lowest (typically negative) and highest temperatures, which could be due to much lower O3 dry deposition in the presence of snow. Therefore, results demonstrate that EIs act as a geophysical interface separating air masses of distinct chemical composition and/or chemical regime. This is further supported by the analysis of the correlation of O3 and CO mixing ratios between the different altitude levels in the PBL and FT (the so-called vertical autocorrelation). Results indeed highlight lower correlations apart from the PBL–FT interface and higher correlations within each of the two atmospheric compartments (PBL and FT). The mean climatological O3 and CO PBL-referenced profiles analysed in this study are freely available on the IAGOS portal for all seasons and times of day (https://doi.org/10.25326/4).

Assessment of the atmospheric mixing layer height and its effects on pollutant dispersion.

The atmospheric mixing layer height (MLH) is an important parameter of the planetary boundary layer (PBL) because it affects the transportation and dispersion processes of pollutants emitted from different sources. This study investigated the relationship between the surface temperature inversion, elevated temperature inversion, and MLH within the PBL of the Kuwait by collecting and analyzing measurements of the temperature and the air quality of upper air during 2013. The upper air temperature and the MLH were derived using a microwave temperature profiler. Hourly concentrations of SO2, O3, particulate matter (PM10), NO2, CO, NO x , and non-methane hydrocarbons (NMHCs) in ambient air were measured by air quality monitoring stations. The collected data were used to estimate the hourly MLH for the transportation and dispersion of critical pollutants. The results showed that concentrations of SO2 and PM10 have direct correlation with MLH during the day, whereas they have the reverse relationship at night. Conversely, concentrations of CO, NMHCs, and NO x showed negative correlation with MLH during both day and night, whereas concentrations of O3 showed direct correlation with MLH during both day and night. In addition, the relationship between the PBL and concentrations of critical pollutants in residential areas was clarified. These findings indicate the influence of the MLH on SO2 and PM10 is much greater during the day than at night. The findings of the present study could help improve our understanding of the effects of MLH on air quality.

Elevated temperature inversion phenomenon in fracture properties of concrete and its application to maturity model

The effect of elevated curing temperature on the fracture properties of concrete was investigated. Fracture experiments were carried out on wedge splitting specimens exposed to temperatures ranging from 5 to 60 °C. A new maturity model was then proposed for describing the combined influence of the temperature and aging on the fracture properties of concrete. The results show that the fracture energy of concrete subjected to high temperature is high at early ages; however, the effect of curing temperature on the fracture energy was reversed after 14 days, with greater later-age fracture energy corresponding to lower temperature and vice-versa. The effective fracture toughness of concrete also exhibited the same temperature inversion phenomenon. The optimum curing temperature was found to be approximately 40 °C for development of concrete fracture properties. The value of activation energy changed with fracture properties, temperature ranges and the development stage of a given fracture property. The proposed model accurately predicts the fracture properties of concrete and significantly simplifies the calculation process of the maturity index relative to the existing maturity method.

Climatology of low-level temperature inversions at the Prague-Libuš aerological station

Temperature inversions (TIs) have been closely studied for a variety of reasons. Here, we present an analysis of low-level TIs, based on a dataset of atmospheric soundings from the aerological station at Prague-Libus (Czech Republic). Measurements have been carried out here since 1974, at the four main synoptic hours. First, the homogeneity of both the radiosonde data and sounding-derived time series was investigated. Since the homogeneity of the derived time series was affected by changes in the observation routine, only the period of 1992–2012 was further analysed. Second, diurnal and annual regimes of surface-based (SBTIs) and elevated (ETIs) temperature inversions were described. Maximum frequency of the SBTIs occurred at 00 UTC and in September and October. During autumn, persistent SBTIs also often occurred, which could be linked to decreased cyclonicity. Third, changes in TIs were evaluated, and the strongest trends were compared with the nearby station at Kummersbruck (Germany). In all seasons except spring, nocturnal SBTIs decreased almost identically at both stations. Morning SBTIs decreased as well; however, the trend was considerably stronger at Prague; and it was also mirrored by an increase in ETIs. Since only a part of these trends could be explained by changes in the large-scale circulation, other factors (low tropospheric warming, suburbanisation) are hypothesized to have affected the trends.

Double bright band observations with high-resolution vertically pointing radar, lidar, and profilers

On 11 May 2010, an elevated temperature inversion associated with an approaching warm front produced two melting layers simultaneously, which resulted in two distinct bright bands as viewed from the ER-2 Doppler radar system, a vertically pointing, coherent X band radar located in Greenbelt, MD. Due to the high temporal resolution of this radar system, an increase in altitude of the melting layer of approximately 1.2 km in the time span of 4 min was captured. The double bright band feature remained evident for approximately 17 min, until the lower atmosphere warmed enough to dissipate the lower melting layer. This case shows the relatively rapid evolution of freezing levels in response to an advancing warm front over a 2 h time period and the descent of an elevated warm air mass with time. Although observations of double bright bands are somewhat rare, the ability to identify this phenomenon is important for rainfall estimation from spaceborne sensors because algorithms employing the restriction of a radar bright band to a constant height, especially when sampling across frontal systems, will limit the ability to accurately estimate rainfall.

Influence of water ice clouds on nighttime tropical temperature structure as seen by the Mars Climate Sounder

AbstractAn analysis of nighttime temperature and water ice cloud extinction profiles from the Mars Climate Sounder aboard the Mars Reconnaissance Orbiter provides evidence for the close relationship between tropical temperature structure and water ice clouds. The tropical temperature structure that evolves over the spring and summer seasons is closely coupled to the waxing and waning of tropical cloud activity. The presence of strong elevated nighttime temperature inversions in the Tharsis region is a robust feature of the equatorial atmosphere during the Ls = 0–135° season, with little interannual variation seen in the three Mars years examined. Mars global circulation model simulations imply that cloud radiative forcing plays a dominant role in the seasonal modulation of the observed longitude distribution of warm and cold anomalies in surface and low‐altitude air temperatures, respectively.

Advances in Predicting Continental Low Stratus with a Regional NWP Model

Abstract In the eastern Alpine region, subinversion cloudiness associated with elevated temperature inversions is a frequent phenomenon in autumn and winter, which often persists for several days. Although the prediction of fog and low stratus by numerical weather prediction (NWP) models has improved in recent years, these models still show deficiencies in the spatial and temporal evolution of such wintertime weather phenomena. In spite of sophisticated current assimilation schemes or simply due to unknown conditions, even the analysis shows large discrepancies compared to the true atmospheric state. Inversions are often “smeared out” and the moist layer below the inversion is too far from saturation. Model integration from such an initial state leads to strong biases in the total cloudiness and, due to erroneous radiative response, in 2-m temperature forecasts. In the present paper, an empirical enhancement scheme for subinversion cloudiness is introduced within the framework of Aire Limitée Adaptation Dynamique Développement International (ALADIN), the operational limited area model (LAM) at the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). The scheme attempts to compensate for model deficiencies in the vertical temperature and humidity profiles in order to enhance or keep preexisting signals of inversions and associated low cloudiness. Thus, a positive feedback due to radiative reaction is activated, which finally leads to more realistic vertical profiles, low (and total) cloudiness, and improved 2-m temperature predictions. Case studies demonstrate the impacts of the scheme on predictions of the spatial distribution of low cloudiness and on the vertical profiles of temperature and humidity. Verification over stratus episodes within a 2-month period comparing a reference model run without the scheme with a modified model version with the subinversion cloudiness scheme confirms the ability of the scheme to improve stratus-related wintertime weather prediction.