scholarly journals Correction Method for RS80-A Humicap Humidity Profiles and Their Validation by Lidar Backscattering Profiles in Tropical Cirrus Clouds

2005 ◽  
Vol 22 (1) ◽  
pp. 18-29 ◽  
Author(s):  
Ulrich Leiterer ◽  
Horst Dier ◽  
Dagmar Nagel ◽  
Tatjana Naebert ◽  
Dietrich Althausen ◽  
...  
Keyword(s):  
Evaluation Method ◽  
Time Lag ◽  
Correction Method ◽  
Cirrus Clouds ◽  
Temperature Dependent ◽  
Upper Troposphere ◽  
Statistical Comparison ◽  
Daily Show ◽  
Tropical Tropopause ◽  
Humidity Profiles

Abstract Routine radiosonde relative humidity (RH) measurements are not reliable as they are presently used in the global upper-air network. The new Lindenberg measuring and evaluation method, which provides RH profile measurements with an accuracy of ±1% RΗ in the temperature range from 35° to −70°C near the tropical tropopause is described. This Standardized Frequencies (FN) method uses a thin-film capacitive polymer sensor of a modified RS90-H Humicap radiosonde. These research humidity reference radiosondes (FN sondes) are used to develop a correction method for operational RS80-A Humicap humidity profiles. All steps of correction and quality control for RS80-A radiosondes are shown: ground-check correction, time-lag and temperature-dependent correction, and the recognition of icing during the ascent. The results of a statistical comparison between FN sondes and RS80-A sondes are presented. Corrected humidity data of operational RS80-A sondes used in Lindenberg (4 times daily) show no bias when compared to FN radiosondes and have an uncertainty of about ±3% RH at the 1 σ or 68% confidence level from 1000 to about 150 hPa. Only a small dry bias of at most −2% RH remains in the lowest part of the boundary layer (up to 500-m height). Finally, some examples of corrected RS80-A RH profiles in cirrus clouds validated by lidar backscattering profiles in a region of the intertropical convergence (Maldive Islands) are demonstrated. The soundings indicate that ice-saturated and ice-supersaturated air above 10-km height were connected with cirrus clouds in all 47 investigated cases, and, second, that the corrected RS80-A RH profiles also provide good quality information on water vapor in the upper troposphere.

Dehydration of the upper troposphere and lower stratosphere by subvisible cirrus clouds near the tropical tropopause

1996 ◽  
Vol 23 (8) ◽  
pp. 825-828 ◽  
Author(s):  
Eric J. Jensen ◽  
Owen B. Toon ◽  
Leonard Pfister ◽  
Henry B. Selkirk
Keyword(s):  
Lower Stratosphere ◽  
Cirrus Clouds ◽  
Upper Troposphere ◽  
Tropical Tropopause

scholarly journals Performance of the Vaisala RS80A/H and RS90 Humicap Sensors and the Meteolabor “Snow White” Chilled-Mirror Hygrometer in Paramaribo, Suriname

2006 ◽  
Vol 23 (11) ◽  
pp. 1506-1518 ◽  
Author(s):  
Gé Verver ◽  
Masatomo Fujiwara ◽  
Pier Dolmans ◽  
Cor Becker ◽  
Paul Fortuin ◽  
...  
Keyword(s):  
Relative Humidity ◽  
Time Lag ◽  
Lower Troposphere ◽  
Upper Troposphere ◽  
Weather Forecasts ◽  
Snow White ◽  
Study Results ◽  
The Tropics ◽  
Humidity Profiles ◽  
Dry Bias

Abstract In climate research there is a strong need for accurate observations of water vapor in the upper atmosphere. Radiosoundings provide relative humidity profiles but the accuracy of many routine instruments is notoriously inadequate in the cold upper troposphere. In this study results from a soundings program executed in Paramaribo, Suriname (5.8°N, 55.2°W), are presented. The aim of this program was to compare the performance of different humidity sensors in the upper troposphere in the Tropics and to test different bias corrections suggested in the literature. The payload of each sounding consisted of a chilled-mirror “Snow White” sensor from Meteolabor AG, which was used as a reference, and two additional sensors from Vaisala, that is, either the RS80A, the RS80H, or the RS90. In total 37 separate soundings were made. For the RS80A a clear, dry bias of between −4% and −8% RH is found in the lower troposphere compared to the Snow White observation, confirming the findings in previous studies. A mean dry bias was found in the upper troposphere, which could be effectively corrected. The RS80H sensor shows a significant wet bias of 2%–5% in RH in the middle and upper troposphere, which has not been reported before. Comparing observations with RS80H sensors of different ages gives no indication of sensor aging or sensor contamination. It is therefore concluded that the plastic cover introduced by Vaisala to avoid sensor contamination is effective. Finally, the RS90 sensor yields a small but significant wet bias of 2%–3% below 7-km altitude. The time-lag error correction from Miloshevich et al. was applied to the Vaisala data, which resulted in an increased variability in the relative humidity profile above 9- (RS80A), 8- (RS80H), and 11-km (RS90) altitude, respectively, which is in better agreement with the Snow White data. The averaged Snow White profile is compared with the average profiles of relative humidity from the European Centre for Medium-Range Weather Forecasts (ECMWF). No significant bias is found in either the analyses or the forecasts. The correlation coefficient for the Snow White and ECMWF data between 200 and 800 hPa was 0.66 for the 36-h forecast and 0.77 for the analysis.

Annual, Interannual, and Intraseasonal Variability of Tropical Tropopause Transition Layer Cirrus

2010 ◽  
Vol 67 (10) ◽  
pp. 3097-3112 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
Transition Layer ◽  
El Nino ◽  
Southern Oscillation ◽  
Cirrus Clouds ◽  
Boreal Winter ◽  
Central Pacific ◽  
Tropical Tropopause ◽  
The Pacific

Abstract Cloud fields based on the first three years of data from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission are used to investigate the relationship between cirrus within the tropical tropopause transition layer (TTL) and the Madden–Julian oscillation (MJO), the annual cycle, and El Niño–Southern Oscillation (ENSO). The TTL cirrus signature observed in association with the MJO resembles convectively induced, mixed Kelvin–Rossby wave solutions above the Pacific warm pool region. This signature is centered to the east of the peak convection and propagates eastward more rapidly than the convection; it exhibits a pronounced eastward tilt with height, suggestive of downward phase propagation and upward energy dispersion. A cirrus maximum is observed over equatorial Africa and South America when the enhanced MJO-related convection enters the western Pacific. Tropical-mean TTL cirrus is modulated by the MJO, with more than twice as much TTL cirrus fractional coverage equatorward of 10° latitude when the enhanced convection enters the Pacific than a few weeks earlier, when the convection is over the Indian Ocean. The annual cycle in cirrus clouds around the base of the TTL is equatorially asymmetric, with more cirrus observed in the summer hemisphere. Higher in the TTL, the annual cycle in cirrus clouds is more equatorially symmetric, with a maximum in the boreal winter throughout most of the tropics. The ENSO signature in TTL cirrus is marked by a zonal shift of the peak cloudiness toward the central Pacific during El Niño and toward the Maritime Continent during La Niña.

scholarly journals Balloon-borne match measurements of midlatitude cirrus clouds

2014 ◽  
Vol 14 (14) ◽  
pp. 7341-7365 ◽  
Author(s):  
A. Cirisan ◽  
B. P. Luo ◽  
I. Engel ◽  
F. G. Wienhold ◽  
M. Sprenger ◽  
...  
Keyword(s):  
Temperature Fluctuations ◽  
Cloud Microphysics ◽  
Cirrus Clouds ◽  
Climate Feedback ◽  
Small Scale ◽  
Model Parameters ◽  
Cirrus Cloud ◽  
Air Mass ◽  
Upper Troposphere ◽  
Weather Model

Abstract. Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg−1) and high crystal number densities (> 1 cm−3) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2–15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the small-scale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudy-sky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30% in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or – much more likely – by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrometers under the special humidity conditions in the upper troposphere.

scholarly journals The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

2015 ◽  
Vol 15 (11) ◽  
pp. 6467-6486 ◽  
Author(s):  
W. Frey ◽  
R. Schofield ◽  
P. Hoor ◽  
D. Kunkel ◽  
F. Ravegnani ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Transport Processes ◽  
Convective System ◽  
Upper Troposphere ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Transport And Mixing ◽  
The Impact

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection with a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward transport from the boundary layer into the cloud anvils and overshooting tops. For example, a passive ozone tracer (i.e. a tracer not undergoing chemical processing) shows an enhancement in the upper troposphere of up to about 30 ppbv locally in the cloud, while the in situ measurements show an increase of 50 ppbv. However, the passive carbon monoxide tracer exhibits an increase, while the observations show a decrease of about 10 ppbv, indicative of an erroneous model representation of the transport processes in the tropical tropopause layer. Furthermore, it could point to insufficient entrainment and detrainment in the model. The simulation shows a general moistening of air in the lower stratosphere, but it also exhibits local dehydration features. Here we use the model to explain the processes causing the transport and also expose areas of inconsistencies between the model and observations.

Mid-latitude and Tropical Cirrus: Microphysical Properties

Cirrus ◽  
2002 ◽  
Author(s):  
Andrew J. Heymsfield ◽  
Greg M. McFarquhar
Keyword(s):  
Large Scale ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
The Arctic ◽  
Horizontal Wind ◽  
Cloud Type ◽  
Fall Velocity ◽  
Upper Troposphere ◽  
Vertical Extent ◽  
Microphysical Properties

Cirrus, a principal cloud type that forms at low temperatures in the upper troposphere, is composed almost always of ice crystals (Heymsfield and Miloshevich 1989) and on average cover about 20% of the earth's surface (Hartmann et al. 1992). The purpose of this chapter is to characterize the microphysical properties of cirrus clouds. The Glossary of Meteorology (Huschke 1970) defines cirrus clouds as detached clouds in the form of white, delicate filaments, or white or mostly white patches, which are composed of ice crystals. This cloud type forms primarily in the upper troposphere, above about 8km (25,000 feet), where temperatures are generally below -30° C. There are a number of types of cirrus clouds, with the most frequent ones occurring in layers or sheets with horizontal dimensions of hundreds or even thousands of kilometers. Because horizontal dimensions are much greater than vertical extent, this particular type of cirrus cloud is called cirrostratus. Cirrus can also form in a patchy or tufted shape, when the ice crystals are large enough to acquire an appreciable fall velocity (the rate at which ice crystals fall in the vertical) so that trails of considerable vertical extent may form. These trails curve irregularly or slant, sometimes with a commalike shape, as a result of changes in the horizontal wind velocity with height and variations in the fall velocity of the ice crystals. A wispy, layered cloud that forms at the top of a cumulonimbus cloud, termed an “anvil” because of its shape, is a cirrus that consists essentially of ice debris which spreads outward from the convective parts of the storm. Anvils do not include the white, dense portions of thunderstorms or the active convective column. Anvils can spread to form large, widespread cloud layers. Tropical cirrus clouds are thought to arise primarily from cumulonimbus clouds. Unlike the thin, wispy cirrus typifying mid-latitudes, the high altitudes and extensive lateral and vertical development that often characterize tropical cirrus impose substantial large-scale radiative effects in the atmosphere and at the earth's surface (Hartmann et al. 1992; Collins et al. 1996). The cirrus-like low-level ice clouds and ice fogs of the Arctic are not considered cirrus.

scholarly journals Long-term trend analysis and climatology of tropical cirrus clouds using 16 years of lidar data set over Southern India

2015 ◽  
Vol 15 (24) ◽  
pp. 13833-13848 ◽  
Author(s):  
A. K. Pandit ◽  
H. S. Gadhavi ◽  
M. Venkat Ratnam ◽  
K. Raghunath ◽  
S. V. B. Rao ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Radiative Forcing ◽  
Climate Model ◽  
Cirrus Clouds ◽  
Orthogonal Polarization ◽  
Cirrus Cloud ◽  
Data Set ◽  
Tropical Tropopause ◽  
Recent Climate ◽  
Ground Based Lidar

Abstract. Sixteen-year (1998–2013) climatology of cirrus clouds and their macrophysical (base height, top height and geometrical thickness) and optical properties (cloud optical thickness) observed using a ground-based lidar over Gadanki (13.5° N, 79.2° E), India, is presented. The climatology obtained from the ground-based lidar is compared with the climatology obtained from 7 and a half years (June 2006–December 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. A very good agreement is found between the two climatologies in spite of their opposite viewing geometries and the differences in sampling frequencies. Nearly 50–55 % of cirrus clouds were found to possess geometrical thickness less than 2 km. Ground-based lidar is found to detect a higher number of sub-visible clouds than CALIOP which has implications for global warming studies as sub-visible cirrus clouds have significant positive radiative forcing. Cirrus clouds with mid-cloud temperatures between −50 to −70 °C have a mean geometrical thickness greater than 2 km in contrast to the earlier reported value of 1.7 km. Trend analyses reveal a statistically significant increase in the altitude of sub-visible cirrus clouds which is consistent with the recent climate model simulations. The mid-cloud altitude of sub-visible cirrus clouds is found to be increasing at the rate of 41 ± 21 m year−1. Statistically significant decrease in optical thickness of sub-visible and thick cirrus clouds is observed. Also, the fraction of sub-visible cirrus cloud is found to have increased by 9 % in the last 16 years (1998 to 2013). This increase is mainly compensated by a 7 % decrease in thin cirrus cloud fraction. This has implications for the temperature and water vapour budget in the tropical tropopause layer.

Research on Risk Assessment Method and System Development of Small Ammonia Refrigeration Units

2019 ◽  
Author(s):  
Xiang Li ◽  
Weihua Wang ◽  
Weike Jing ◽  
Jin Shi ◽  
Fakun Zhuang
Keyword(s):  
Risk Assessment ◽  
Evaluation Method ◽  
System Development ◽  
Correction Method ◽  
Assessment Method ◽  
Scientific Basis ◽  
Assessment System ◽  
Assessment Model ◽  
Mitigation Measures ◽  
Risk Assessment Method

Abstract In recent years, ammonia leakage accidents occur frequently, which causes a great concern in China. Based on traditional risk analysis methods and the equipment characteristics, a risk evaluation method for small ammonia refrigeration units is proposed. The method includes a risk assessment model based on area division, a failure probability assessment method based on expert scoring system, a failure consequence assessment method based on regional population density and consequence mitigation measures, and a HAZOP risk correction method. Based on the proposed method, a risk assessment system of small ammonia refrigeration units is developed. This risk assessment method and system will provide a scientific basis to carry out the cold storage management in China.

scholarly journals An empirical method to correct for temperature-dependent variations in the overlap function of CHM15k ceilometers

2016 ◽  
Vol 9 (7) ◽  
pp. 2947-2959 ◽  
Author(s):  
Maxime Hervo ◽  
Yann Poltera ◽  
Alexander Haefele
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Correction Method ◽  
Empirical Method ◽  
Cloud Base ◽  
Atmospheric Conditions ◽  
Cloud Detection ◽  
Temperature Dependent ◽  
Night Time ◽  
Gradient Based

Abstract. Imperfections in a lidar's overlap function lead to artefacts in the background, range and overlap-corrected lidar signals. These artefacts can erroneously be interpreted as an aerosol gradient or, in extreme cases, as a cloud base leading to false cloud detection. A correct specification of the overlap function is hence crucial in the use of automatic elastic lidars (ceilometers) for the detection of the planetary boundary layer or of low cloud. In this study, an algorithm is presented to correct such artefacts. It is based on the assumption of a homogeneous boundary layer and a correct specification of the overlap function down to a minimum range, which must be situated within the boundary layer. The strength of the algorithm lies in a sophisticated quality-check scheme which allows the reliable identification of favourable atmospheric conditions. The algorithm was applied to 2 years of data from a CHM15k ceilometer from the company Lufft. Backscatter signals corrected for background, range and overlap were compared using the overlap function provided by the manufacturer and the one corrected with the presented algorithm. Differences between corrected and uncorrected signals reached up to 45 % in the first 300 m above ground. The amplitude of the correction turned out to be temperature dependent and was larger for higher temperatures. A linear model of the correction as a function of the instrument's internal temperature was derived from the experimental data. Case studies and a statistical analysis of the strongest gradient derived from corrected signals reveal that the temperature model is capable of a high-quality correction of overlap artefacts, in particular those due to diurnal variations. The presented correction method has the potential to significantly improve the detection of the boundary layer with gradient-based methods because it removes false candidates and hence simplifies the attribution of the detected gradients to the planetary boundary layer. A particularly significant benefit can be expected for the detection of shallow stable layers typical of night-time situations. The algorithm is completely automatic and does not require any on-site intervention but requires the definition of an adequate instrument-specific configuration. It is therefore suited for use in large ceilometer networks.

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