Cold Point Research Articles

ENSO signatures observed in tropical tropopause layer parameters using long-term COSMIC RO data

The El Nino Southern Oscillation (ENSO) signatures interpreted in different tropical tropopause layer (TTL) parameters are investigated by using long-term Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)-1 radio occultation temperature data from July 2006 to March 2019. The TTL parameters include the cold point tropopause height (CPT-H) and corresponding temperature (CPT-T), lapse rate tropopause height (LRT-H) and corresponding temperature (LRT-T), convective outflow level height (COH), and TTL thickness. Results indicate that the warm phase of ENSO is associated with prominent negative CPT-T anomalies, whereas the cold phase of ENSO is associated with positive CPT-T anomalies over the tropical central and eastern Pacific Ocean. Further, correlation analysis is carried out between TTL parameters obtained over the Nino 3.4 region (5°N–5°S, 170°W–120°W) and sea surface temperature Nino 3.4 Index. We found weak positive correlations in CPT-H (0.37) and LRT-H (0.49), and moderate negative correlations in CPT-T (− 0.62), LRT-T (− 0.64), and TTL thickness (− 0.5) with Nino 3.4 Index. Interestingly, a higher correlation of 0.8 is noticed between COH and the Nino 3.4 Index. Furthermore, lag correlation analysis reveals that a 4-month lag is noticed in tropopause heights (CPT-H and LRT-H) and a 2-month lag is evident in tropopause temperatures (CPT-T and LRT-T) with the Nino 3.4 Index. In addition, only 1-month lag is noticed between COH and Nino 3.4 index. With a high correlation and 1-month lag with the Nino 3.4 index, it is concluded that the COH is the most suitable TTL parameter to detect the ENSO signatures among the TTL parameters.

Impact of Convectively Detrained Ice Crystals on the Humidity of the Tropical Tropopause Layer in Boreal Winter

AbstractDeep convection detraining in the uppermost tropical troposphere is capable of transporting water vapor and ice into the tropical tropopause layer (TTL), but the impact of deep convection on the global and regional TTL water vapor budget remains uncertain. In particular, the role of convectively detrained ice crystals that remain suspended after active convection has subsided is not well understood. These ice crystals represent aging cirrus anvils detached from the convective core. We use a cloud microphysical model that tracks individual ice crystals throughout their lifetimes to quantify the impact of detrained ice on the humidity of the TTL during boreal winter. Convective influence of air parcels near the wintertime cold point tropical tropopause is determined by tracing thousands of backward trajectories through satellite‐derived, global, 3‐hourly convective cloud‐top altitude fields. Detrained ice, most of which is found over the tropical western Pacific, experiences cooling on the order of 1 K day−1 downstream of convection. Downstream cooling increases relative humidity and explains the observed supersaturated TTL over this region. Vapor in excess of saturation condenses onto the detrained ice, which ultimately brings the relative humidity down to saturation. Thus, convectively detrained ice crystals in aging anvils predominantly dehydrate the TTL, but the effect is small (0.01 ppmv). Moistening by active convection (0.30 ppmv), including the rapid sublimation of convectively lofted ice crystals near the tops of core anvils, overwhelms the dehydration by aging anvil ice crystals detrained from the core. The net effect is moistening by convective core anvils during boreal winter.

On the Role of Peroxide Compounds in the Cold Zone Heating of Combustion Waves of Methane–Air Mixtures at Atmospheric Pressure

To study the role of the reactions of CH3O2 radicals in the unsteady process of formation and propagation of methane combustion waves in air at P = 1 atm, the reactions were mathematically simulated using a kinetic model complemented with a block of these reactions. The influence of this block is limited by the decomposition reaction СН3О2 → СН3 + О2(II); therefore, the standard calculations were performed for a wide range of compositions at a smaller value of the reaction rate constant k2∞, and additional calculations were performed at a larger value of this constant. For mixtures containing 5, 9, and 16% CH4, the calculations were performed without taking into account the CH3O2 radicals. All the calculated data (according to flame velocities and the structure of their preheating zones) were compared with one another and with the experimental values. Based on the results of standard calculations, the space profiles of temperature and substances were presented for mixtures containing 5, 9, and 16% CH4, and time profiles were additionally given for the case with 9% CH4. To characterize the structure of the combustion wave using these data, two small kinetic schemes were chosen, which are determined by the low-temperature kinetics of the HO2 and CH3O2 radicals. Analytical criteria were obtained based on these schemes; the calculations of self-ignition temperatures using these criteria (including the state of various points of the preheating zone) characterize the change in the activity of the system up to its coldest point.

Variability and past long-term changes of brominated very short-lived substances at the tropical tropopause

Abstract. Halogenated very short-lived substances (VSLSs), such as bromoform (CHBr3), can be transported to the stratosphere and contribute to the halogen loading and ozone depletion. Given their highly variable emission rates and their short atmospheric lifetimes, the exact amount as well as the spatio-temporal variability of their contribution to the stratospheric halogen loading are still uncertain. We combine observational data sets with Lagrangian atmospheric modelling in order to analyse the spatial and temporal variability of the CHBr3 injection into the stratosphere for the time period 1979–2013. Regional maxima with mixing ratios of up to 0.4–0.5 ppt at 17 km altitude are diagnosed to be over Central America (1) and over the Maritime Continent–west Pacific (2), both of which are confirmed by high-altitude aircraft campaigns. The CHBr3 maximum over Central America is caused by the co-occurrence of convectively driven short transport timescales and strong regional sources, which in conjunction drive the seasonality of CHBr3 injection. Model results at a daily resolution reveal isolated, exceptionally high CHBr3 values in this region which are confirmed by aircraft measurements during the ACCENT campaign and do not occur in spatially or temporally averaged model fields. CHBr3 injection over the west Pacific is centred south of the Equator due to strong oceanic sources underneath prescribed by the here-applied bottom-up emission inventory. The globally largest CHBr3 mixing ratios at the cold point level of up to 0.6 ppt are diagnosed to occur over the region of India, Bay of Bengal, and Arabian Sea (3); however, no data from aircraft campaigns are available to confirm this finding. Inter-annual variability of stratospheric CHBr3 injection of 10 %–20 % is to a large part driven by the variability of coupled ocean–atmosphere circulation systems. Long-term changes, on the other hand, correlate with the regional sea surface temperature trends resulting in positive trends of stratospheric CHBr3 injection over the west Pacific and Asian monsoon region and negative trends over the east Pacific. For the tropical mean, these opposite regional trends balance each other out, resulting in a relatively weak positive trend of 0.017±0.012 ppt Br per decade for 1979–2013, corresponding to 3 % Br per decade. The overall contribution of CHBr3 together with CH2Br2 to the stratospheric halogen loading accounts for 4.7 ppt Br, in good agreement with existing studies, with 50 % and 50 % being injected in the form of source and product gases, respectively.

Mathematical modeling of ohmic heating for inactivation of acid-adapted foodborne pathogens in tomato juice

Abstract The objective of the present study was to predict the inactivation trends of acid-adapted foodborne pathogens in tomato juice by ohmic heating through a numerical analysis method. The mathematical model based on finite element method (FEM) was used to simulate the multiphysics phenomena including electric heating, heat transfer, fluid dynamics, and pathogen inactivation. A cold spot was observed in the corner part of the ohmic heating chamber, where some pathogens survived even though all pathogens were inactivated elsewhere. Challenges of this study were how to reflect the increased resistance of pathogen by acid-adaptation. After simulation, we verified that inactivation level of acid-adapted foodborne pathogens by 25 Vrms/cm ohmic heating (1 kHz), predicted with the developed mathematical model, had no significant differences with experimental results (p > 0.05). Therefore, the mathematical approaches described in the present study will help juice processors determine the processing conditions necessary to ensure microbial safety at the cold point of a rectangular type batch ohmic heater.

Inhibition of PDE4 Induces Hypothermia in Mice

Type 4 cyclic nucleotide phosphodiesterases (PDE4s), a group of isoenzymes that hydrolyze and inactivate the second messenger cAMP, are established targets for development of enzyme inhibitors with anti‐inflammatory properties. While testing the anti‐inflammatory effects of a nonselective PDE4 inhibitor in a murine model of bacterial lung infection, we noticed that PDE4 inhibition per se induced significant hypothermia in the animals in the absence of bacterial infection. Because drug‐induced hypothermia may critically impact our animal model, and the role cAMP‐phosphodiesterases play in the regulation of body temperature is poorly understood, we further explored this observation. We found that treatment with a number of structurally distinct PAN‐PDE4 inhibitors, including Rolipram, Roflumilast and RS25344 (all 1 mg/kg, i.p.), but not the PDE3‐selective inhibitor Cilostamide, induced a rapid decrease in core body temperature of C57Bl6 mice as measured with a rectal thermometer at 30 min after drug application, suggesting that hypothermia in mice is a class‐effect of PDE4 inhibitors. PDE4 inhibitor‐induced hypothermia was considerable (~4°C drop), rapid in onset (max effect is reached within 20–30 min), and long lasting (core body temperature remains below controls for up to 5 h). As little as 40 μg/kg of the archetypal PDE4 inhibitor Rolipram induced a hypothermic effect. Similar or higher doses of Rolipram were used in most published animal studies. Thus, the reported findings are likely associated with, or at least paralleled by, drug‐induced hypothermia. The initial decrease in body temperature after PDE4 inhibitor injection is so rapid that it is no different from heat dissipation after euthanasia, suggesting that PDE4 inhibition affects central body temperature regulation so that both heat‐generating (e.g. shivering/non‐shivering thermogenesis) as well as heat‐preserving (e.g. skin vasoconstriction) mechanisms are simultaneously suspended, either by lowering the cold defense set point or by impairing its enforcement. Indeed, PDE4 inhibitor treatment induced a temporary heat‐loss via tail vasodilation as assessed by thermography. Consistent with the idea of an effect on central body temperature regulation, hypothermia was induced by moderate doses (≤1 mg/kg) of various brain‐penetrant PDE4 inhibitors. Conversely, YM976, a PDE4 inhibitor that does not cross the blood‐brain barrier, had no effect. Finally, to begin delineating the mechanism of drug‐induced hypothermia, we show that a blockade of serotonergic‐ and dopaminergic‐, but not β‐adrenergic‐, histaminergic‐ or opiate receptors, can alleviate PDE4 inhibitor‐induced hypothermia.Support or Funding InformationSupported by grants from the Cystic Fibrosis Foundation (SALEH18H0,RICHTE16GO) and the NIH (HL76125, HL141473, HL066299).

Temperature and tropopause characteristics from reanalyses data in the tropical tropopause layer

Abstract. The tropical tropopause layer (TTL) is the transition region between the well-mixed convective troposphere and the radiatively controlled stratosphere with air masses showing chemical and dynamical properties of both regions. The representation of the TTL in meteorological reanalysis data sets is important for studying the complex interactions of circulation, convection, trace gases, clouds, and radiation. In this paper, we present the evaluation of climatological and long-term TTL temperature and tropopause characteristics in the reanalysis data sets ERA-Interim, ERA5, JRA-25, JRA-55, MERRA, MERRA-2, NCEP-NCAR (R1), and CFSR. The evaluation has been performed as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The most recent atmospheric reanalysis data sets (ERA-Interim, ERA5, JRA-55, MERRA-2, and CFSR) all provide realistic representations of the major characteristics of the temperature structure within the TTL. There is good agreement between reanalysis estimates of tropical mean temperatures and radio occultation data, with relatively small cold biases for most data sets. Temperatures at the cold point and lapse rate tropopause levels, on the other hand, show warm biases in reanalyses when compared to observations. This tropopause-level warm bias is related to the vertical resolution of the reanalysis data, with the smallest bias found for data sets with the highest vertical resolution around the tropopause. Differences in the cold point temperature maximize over equatorial Africa, related to Kelvin wave activity and associated disturbances in TTL temperatures. Interannual variability in reanalysis temperatures is best constrained in the upper TTL, with larger differences at levels below the cold point. The reanalyses reproduce the temperature responses to major dynamical and radiative signals such as volcanic eruptions and the quasi-biennial oscillation (QBO). Long-term reanalysis trends in temperature in the upper TTL show good agreement with trends derived from adjusted radiosonde data sets indicating significant stratospheric cooling of around −0.5 to −1 K per decade. At 100 hPa and the cold point, most of the reanalyses suggest small but significant cooling trends of −0.3 to −0.6 K per decade that are statistically consistent with trends based on the adjusted radiosonde data sets. Advances of the reanalysis and observational systems over the last decades have led to a clear improvement in the TTL reanalysis products over time. Biases of the temperature profiles and differences in interannual variability clearly decreased in 2006, when densely sampled radio occultation data started being assimilated by the reanalyses. While there is an overall good agreement, different reanalyses offer different advantages in the TTL such as realistic profile and cold point temperature, continuous time series, or a realistic representation of signals of interannual variability. Their use in model simulations and in comparisons with climate model output should be tailored to their specific strengths and weaknesses.

The Coordinated Relationship between Investment Potential and Economic Development and Its Driving Mechanism: A Case Study of the African Region

In order to analyze the coordination relationship between investment potential and economic development and its driving mechanisms, this study integrated the entropy weight method, coupling coordination degree model, exploratory spatial data analysis, geographic detector, and geographically weighted regression model. The developed approach was applied using data from 51 African countries from 2008 to 2016. The results showed that: (1) While the level of economic development in the African continent has increased steadily, the overall investment potential needs to be improved. The mean economic development index rose from 0.116 to 0.151, but the economic gap among countries was still highly evident. (2) Uncoordinated development and barely coordinated development level were the dominant types of relationship between investment potential and economic development in African countries. The spatial distribution showed significant agglomeration characteristics; the sub-hot spot and sub-cold point regions maintained strong dependence with their hot spot and cold point counterparts. The hot spot areas gradually formed an agglomeration in Southern Africa and highly fragmented distribution in other areas. The cold spot areas formed a spatial distribution pattern of “one core and one belt” with some countries in Western Africa forming the core, while some Central and East African countries constituting the belt. (3) The coordination relationship between investment potential and economic development was influenced mainly by factors including economic base, residents’ living standard, industrial construction level, information support level, and business friendliness. Using geographically weighted regression coefficient distribution of indicators, the driving mechanisms of spatial distribution could be divided into five types: economic base driven, industry-driven, information application-driven, business convenience-driven, and consumer market-driven.

Inductive Medium Pressure UV-Source

In this paper, an efficient inductively coupled medium pressure source for ultraviolet radiation (UV-source) is demonstrated. The lamp was operated with powers up to 3 kW while the radiation and the coldest point temperature were measured. In addition, different coil geometries were investigated. Here a symmetrical and asymmetrical winding density were compared. Also the operation pressures and DC to radiation efficiencies are presented. In this work, an operation pressure of one atmosphere and an UV-efficiency (200–380 nm) of 15.5% was achieved. This is comparable to conventional medium pressure Hg-lamp technology. The main advantage of the presented inductive lamp is the electrodeless operation and therefore the longer service life, since an electrode failure is eliminated.

Influence of Oxidant Agent on Syngas Composition: Gasification of Hazelnut Shells through an Updraft Reactor

This work aims to study the influence of an oxidant agent on syngas quality. A series of tests using air and steam as oxidant agents have been performed and the results compared with those of a pyrolysis test used as a reference. Tests were carried out at Sapienza University of Rome, using an updraft reactor. The reactor was fed with hazelnut shells, waste biomass commonly available in some parts of Italy. Temperature distribution, syngas composition and heating value, and producible energy were measured. Air and steam gasification tests produced about the same amount of syngas flow, but with a different quality. The energy flow in air gasification had the smallest measurement during the experiments. On the contrary, steam gasification produced a syngas flow with higher quality (13.1 MJ/Nm3), leading to the best values of energy flow (about 5.4 MJ/s vs. 3.3 MJ/s in the case of air gasification). From the cold gas efficiency point of view, steam gasification is still the best solution, even considering the effect of the enthalpy associated with the steam injected within the gasification reactor.

Numerical analysis of rectangular type batch ohmic heater to identify the cold point.

The objective of this research was to precisely simulate the temperature distribution and inactivation of Escherichia coli O157:H7 by batch ohmic heating pasteurization of orange juice based on a time‐dependent numerical model. A finite element method (FEM) embedded with pathogen inactivation codes using Java language simultaneously solved electric heating, k‐ε turbulent flow, and heat transfer equations and dealt with natural heat losses through the walls and air as the boundary conditions. The simulated temperature distribution and populations of E. coli O157:H7 did not differ from the experimental data for every treatment time within a relative error of 6.0%. A cold point problem was observed in the bottom corner, which was more severe for large orange juice samples, leading to an increased treatment time in order to ensure a 5‐log reduction of E. coli O157:H7.

Ozone Transport‐Radiation Feedbacks in the Tropical Tropopause Layer

AbstractThe tropical tropopause layer (TTL) temperature balance is of considerable interest for its control over the amount of water entering the stratosphere. The upwelling branch of the Brewer‐Dobson circulation (BDC) directly affects these temperatures through adiabatic cooling. BDC upwelling also indirectly affects TTL temperatures through the influence of ozone transport on radiative heating. We investigate this latter feedback using a single‐column radiative‐convective equilibrium model coupled with a model of simplified stratospheric ozone chemistry and vertical transport. We find that BDC ozone transport is of first‐order importance for TTL temperatures. Additionally, we estimate the effect of ozone transport on cold point tropopause temperature responses to changes in upwelling. We find that the feedback is responsible for approximately 20% of the response to perturbations on time scales longer than about half a year but that this contribution can be neglected for time scales shorter than about a week.

The Temporal and Spatial Evolution of Marathons in China from 2010 to 2018.

The purpose of this study is to explore the spatial distribution pattern and influencing factors of the Chinese marathon. Geographic Information System (GIS) related spatial analysis tools were used to calculate the following—averaged nearest neighbor index, nuclear density analysis and hot spot analysis among others. The spatial distribution evolution characteristics and the influencing factors of eighteen Chinese marathon events in 2010, 129 in 2015 and 342 in 2018 were analyzed. The results show that (a) in 2010 the nearest neighbor ratio was 1.164714, Moran’s I was −0.010165 (type: Random), in 2015 it was 0.502146, Moran’s I was 0.066267 (type: Clustered) and in 2018 it was 0.531149 and Moran’s I was 0.083485 (type: Clustered); (b) in 2010 there was a 333.6 km search radius; the core circle of the Yangtze River Delta was adopted. In 2015 and 2018, a search radius of 556 km was adopted, which was respectively obtained from the core circle of the Yangtze River Delta, the core circle of Beijing-Tianjin-Hebei and the core circle of East China; (c) according to the Z-value data, East China and North China in 2015 passed 95% confidence in five provinces and municipal hot spots, passed 90% confidence in three hot spots and passed 95% confidence in Chongqing Cold Point. In 2018, East China, North China, Central Region and eight other provinces and cities’ hot spots passed 95% confidence, four hot spots passed 90% confidence, the Tibet Autonomous Region cold spot passed 90% confidence. Conclusion: The overall distribution of marathon events is greater in the eastern region than the western region, greater in the southern region than the northern region and greater in coastal regions than the inland regions; the nuclear density distribution has spread from the Yangtze River Delta mononuclear circle in 2010 to the core circle of the entire East China region. Moreover, it spread to North China, Central China and South China; the distribution of hot spots spread from Shanghai, Jiangsu and Zhejiang to the entire North China and East China regions. During the past thirty-eight years of development of the Chinese marathon, it has been divided into three stages due to different political, economic and social environments.

Mathematical Model of the Evaporation of Amalgam Components in Discharge Radiation Sources

The urgency of creating a mathematical model of the evaporation of amalgam components in discharge radiation sources (lamps) is due to the dependence of the parameters of the infrared (IR) radiation of special discharge sources on the vapor pressure of an emitting additive. The pressure in turn depends on the sizes and temperature of the discharge, cathode, and anode volumes. In connection with the diverse range of designs of gas-discharge lamps, a set of equations is proposed, which makes it possible to determine the vapor pressure of amalgam components taking into account the specific design of the discharge tube (the burner) and its temperature profile. The design of a discharge source of IR radiation for safety systems of aircraft, for which the calculation of cesium and mercury vapors is presented, is described. As a result of calculations, the dependences of the vapor pressure of cesium and mercury on the temperature of the discharge-tube cold point at various amalgam weights are obtained. The features of the increase in the cesium pressure on the transition from saturated vapors into unsaturated are revealed.

Recent trends in the UTLS temperature and tropical tropopause parameters over tropical South Indian region

The Upper Troposphere and Lower Stratosphere (UTLS) region plays an important role in the climate system. Quantifying the processes that control UTLS represents a crucial task. We assess UTLS trends and associated tropopause parameters (Cold Point Tropopause temperature/altitude (CPT/CPH), Lapse Rate Tropopause temperature/altitude (LRT/LRH), Convective outflow level temperature/altitude (COT/COH) and Tropical Tropopause Layer (TTL) thickness). This study is based on high-resolution daily radiosonde data from 2006 to 2018 over a tropical station Gadanki in south India supported by satellite measurements. The results show an increase of CPH (LRH) of ~0.06 km (~0.10 km), decrease of CPT (LRT) of ~1.09 K (1.16 K), increase of COH of ~0.29 km and decrease of TTL thickness of ~0.23 km in the recent decade. The vertical temperature trends show a strong cooling trend at lower stratosphere (17–19 km) with a maximum cooling rate of 1.3 ± 0.86 K per decade at 19.4 km altitude unlike reported recently using global radiosonde network. A warming trend is observed in the entire troposphere (0–15 km) with maximum warming rate of 0.44 ± 0.55 K at 11.6 km during the last decade. Distinct variability in the temperature is noticed below and above the tropopause with the strong seasonal change above the tropical tropopause (18 and 19 km) compared to the below the tropopause (15–17 km). The observed trends are explained in relation to the ozone (O3) and water vapor (WV) trends over Gadanki. Compare to the ozone changes, the WV increasing trend was found strongly influencing the LS cooling trend in the recent decade over Indian monsoon region.

The Impact of Prescribed Ozone in Climate Projections Run With HadGEM3‐GC3.1

AbstractThe Coupled Model Intercomparison Project 6 protocol suggests prescribing preindustrial ozone concentrations in abrupt‐4xCO2 simulations. This leads to a mismatch between the thermal tropopause, which rises due to climate change, and the ozone tropopause, which remains fixed. The result is unphysically high ozone concentrations in the upper troposphere, leading to a warm bias in cold point temperature and increased stratospheric water vapor. In the U.K. physical climate model HadGEM3‐GC3.1 this increases the surface climate sensitivity. In the future, other climate models without interactive ozone schemes may face similar problems. We describe a method to interactively redistribute ozone in climate simulations, which removes the inconsistency between the thermal and ozone tropopause heights while retaining the prescribed ozone distribution as closely as possible. This removes unphysical consequences of the tropopause mismatch, while still allowing a fair comparison against other Coupled Model Intercomparison Project 6 model simulations. After each model year, the monthly mean, zonal mean, thermal tropopause is formed based on the previous two model years. The ozone tropopause is defined at 1 km below the thermal tropopause by setting ozone concentrations there to 80 ppbv, and smoothing appropriately. The mass of ozone removed from the troposphere is added to the stratosphere thus conserving the total mass of ozone. This redistribution is then applied proportionally to the 3‐D monthly mean ozone concentrations. The climate model is run for the following year, using this redistributed ozone, and then the whole process is repeated. Results are presented from preindustrial and abrupt‐4xCO2 simulations, but this method can be used for any climate simulation.

Studi Beban Pendinginan Ikan Menggunakan Brine Dengan Jenis Garam Berbeda

The purpose of this study was to determine the effect of using brine with different types of salt on cooling fish and its effect on cooling load, so that a combination of treatments that produced the lowest cold point and maximum ability were obtained to eliminate the total heat energy in fish. The raw materials used in this study are salts of NaCl, KCl, CaCl2 and tuna. The cooling process in this study uses ice and salt (brine) solutions with concentrations of each type of salt, namely 2%, 7%, and 12% of the weight of the cooling media. In this research, the first two stages were carried out, namely with air load, then continued with the hot load of fish for each cooling medium on different styrofoam boxes. From the results of this experiment, a decrease in the maximum cooling point of brine temperature of -2,46 °C was found in the treatment of NaCl salt concentration of 12% (a1b3), then brine solution which was able to keep the fish temperature at the lowest is -1.4 ° C from treatment a1b3 (NaCl salt) concentration of 12%.

An Evaluation of the Representation of Tropical Tropopause Cirrus in the CESM/CARMA Model Using Satellite and Aircraft Observations

AbstractObservations from the third campaign of the National Aeronautics and Space Administration Airborne Tropical Tropopause Experiment (ATTREX 3) field mission and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite mission are used to evaluate simulations of tropical tropopause layer (TTL) cirrus clouds in the Community Earth System Model's (CESM) Community Atmosphere Model, CAM5. In this study, CAM5 is coupled with a sectional ice cloud model, the Community Aerosol and Radiation Model for Atmospheres (CARMA). We find that both model variants underrepresent cloud frequency along the ATTREX 3 flight path and both poorly represent relative humidity in the TTL. Furthermore, simulated in‐cloud ice size distributions contained erroneous amounts of ice crystals throughout the distribution. In response, we present a modified ice cloud fraction scheme that boosts the cloud fraction within the TTL. Due to coarse vertical model resolution in the TTL, we also prescribe a 2‐K decrease in cold point tropopause temperatures to better align with observed temperatures. Our modifications improve both CAM5 and CAM5/CARMA's in‐cloud ice size and mass distributions. However, only CAM5/CARMA has a significant improvement in cloud frequency and relative humidity. An investigation of cloud extinction in the ATTREX 3 region found that each model variant struggles to reproduce observed extinctions. As a first‐order approximation, we introduce randomly generated temperature perturbations to simulate the effect of gravity waves into the CAM5/CARMA simulation. These gravity waves significantly increase the incidence of low extinction (<0.02 km−1) values, ice cloud fraction between 16 and 18 km, and ice crystal smaller than 100‐μm concentrations but provided only small changes to high extinction values.

Tropopause altitude determination from temperature profile measurements of reduced vertical resolution

Abstract. Inference of the lapse rate tropopause or the cold point from temperature profiles of finite vertical resolution entails an uncertainty of the tropopause altitude. For tropical radiosonde profiles the tropopause altitude inferred from coarse-grid profiles was found to be lower than that inferred from the original profiles. The mean (median) displacements of the lapse rate tropopause altitude when inferred from a temperature profile of 3 km vertical resolution and a Gaussian kernel are −130, −400, −730, and −590 m (−70, −230, −390, and −280 m) for Nairobi, Hilo, Munich, and Greifswald, respectively. In the case of a Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) averaging kernel, the displacement of the lapse rate tropopause altitude is −640 m. The mean (median) displacement of the cold point tropopause inferred from a temperature profile of 3 km vertical resolution (Gaussian kernels) was found to be −510, −610, −530, and −390 m (−460, −510, −370, and −280 m) for the stations mentioned above. Unsurprisingly, the tropopause altitude displacement is larger for coarser resolutions. The effect of the tropopause displacement on the water vapor saturation mixing ratio is roughly proportional to the vertical resolution. In tropical latitudes the resulting error is about 1 to 2 ppmv per vertical resolution in kilometers. The spread of the tropopause displacements within each sample of profiles seems too large as to recommend a correction scheme for tropical temperature profiles, while for midlatitudinal temperature profiles of vertical resolutions of 1 to 5 km a lapse rate of −1.3 K km−1 reproduces tropopause altitudes determined from high-resolution temperature profiles with the nominal lapse rate criterion of −2 K km−1 fairly well.

Observational Evidence of Horizontal Transport‐Driven Dehydration in the TTL

AbstractA recent airborne study obtained extensive measurements in the tropical tropopause layer (TTL) over the western Pacific and provided the first opportunity to examine the relationship between water vapor and temperature in the coldest region and season of the TTL using high‐resolution in situ data. Analysis of this data set verifies key hypotheses in Lagrangian simulations of TTL transport and freeze drying. Furthermore, the observations provide a number of new insights into the transport process: In the layer below the lapse rate tropopause, vertical transport from upward motion dominates the relative humidity structure; final dehydration, dominated by large‐scale horizontal advection, occurs in the layer transacting the cold point tropopause that is often above the lapse rate tropopause, resulting in water vapor mixing ratios with corresponding frost points consistent with the coldest temperatures of the region, lower than the temperatures of the local cold points.