LASE Measurements of Water Vapor, Aerosol, and Cloud Distributions in Saharan Air Layers and Tropical Disturbances

Abstract The Lidar Atmospheric Sensing Experiment (LASE) on board the NASA DC-8 measured high-resolution profiles of water vapor and aerosols, and cloud distributions in 14 flights over the eastern North Atlantic during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) field experiment. These measurements were used to study African easterly waves (AEWs), tropical cyclones (TCs), and the Saharan air layer (SAL). These LASE measurements represent the first simultaneous water vapor and aerosol lidar measurements to study the SAL and its interactions with AEWs and TCs. Three case studies were selected for detailed analysis: (i) a stratified SAL, with fine structure and layering (unlike a well-mixed SAL), (ii) a SAL with high relative humidity (RH), and (iii) an AEW surrounded by SAL dry air intrusions. Profile measurements of aerosol scattering ratios, aerosol extinction coefficients, aerosol optical thickness, water vapor mixing ratios, RH, and temperature are presented to illustrate their characteristics in the SAL, convection, and clear air regions. LASE extinction-to-backscatter ratios for the dust layers varied from 35 ± 5 to 45 ± 5 sr, well within the range of values determined by other lidar systems. LASE aerosol extinction and water vapor profiles are validated by comparison with onboard in situ aerosol measurements and GPS dropsonde water vapor soundings, respectively. An analysis of LASE data suggests that the SAL suppresses low-altitude convection. Midlevel convection associated with the AEW and transport are likely responsible for high water vapor content observed in the southern regions of the SAL on 20 August 2008. This interaction is responsible for the transfer of about 7 × 1015 J (or 8 × 103 J m−2) latent heat energy within a day to the SAL. Initial modeling studies that used LASE water vapor profiles show sensitivity to and improvements in model forecasts of an AEW.

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Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-12313-2020 ◽

2020 ◽

Vol 20 (20) ◽

pp. 12313-12327

Author(s):

Manuel Gutleben ◽

Silke Groß ◽

Martin Wirth ◽

Bernhard Mayer

Keyword(s):

Water Vapor ◽

Radiative Transfer ◽

Heating Rate ◽

Mineral Dust ◽

Short Wave ◽

Radiative Effect ◽

Mixing Ratios ◽

Long Wave ◽

Lidar Measurements ◽

Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high-spectral-resolution and differential-absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers, increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found at altitudes of highest dust concentration (short wave: +0.5 K d−1; long wave: −0.2 K d−1; net: +0.3 K d−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations, the maximum heating/cooling rates shift to the top of the dust layer (short wave: +2.2 K d−1; long wave: −6.0 to −7.0 K d−1; net: −4.0 to −5.0 K d−1). Additionally, the net heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter-radiation of Saharan air layers is found to reduce cooling at the tops of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 W m−2 at surface level and a maximum of −25 W m−2 at the top of the atmosphere.

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Radiative effects of long-range-transported Saharan air layers as determined from airborne lidar measurements

10.5194/acp-2020-420 ◽

2020 ◽

Author(s):

Manuel Gutleben ◽

Silke Groß ◽

Martin Wirth ◽

Bernhard Mayer

Keyword(s):

Water Vapor ◽

Radiative Transfer ◽

Heating Rate ◽

Mineral Dust ◽

Short Wave ◽

Radiative Effect ◽

Mixing Ratios ◽

Long Wave ◽

Lidar Measurements ◽

Air Layers

Abstract. The radiative effect of long-range-transported Saharan air layers is investigated on the basis of simultaneous airborne high spectral resolution and differential absorption lidar measurements in the vicinity of Barbados. Within the observed Saharan air layers increased water vapor concentrations compared to the dry trade wind atmosphere are found. The measured profiles of aerosol optical properties and water vapor mixing ratios are used to characterize the atmospheric composition in radiative transfer calculations, to calculate radiative effects of moist Saharan air layers and to determine radiative heating rate profiles. An analysis based on three case studies reveals that the observed enhanced amounts of water vapor within Saharan air layers have a much stronger impact on heating rate calculations than mineral dust aerosol. Maximum mineral dust short-wave heating and long-wave cooling rates are found in altitudes of highest dust concentration (short-wave: +0.5 Kd−1, long-wave: −0.2 Kd−1, net: +0.3 Kd−1). However, when considering both aerosol concentrations and measured water vapor mixing ratios in radiative transfer calculations the maximum heating/cooling rates shift to the top of the dust layer (short-wave: +2.2 Kd Kd−1, long-wave: −6.0 to −7.0 Kd−1, net: −5.0 to −4.0 Kd−1). Additionally, the net-heating rates decrease with height – indicating a destabilizing effect in the dust layers. Long-wave counter radiation of Saharan air layers is found to reduce cooling at the top of the subjacent marine boundary layers and might lead to less convective mixing in these layers. The overall short-wave radiative effect of mineral dust particles in Saharan air layers indicates a maximum magnitude of −40 Wm−2 at surface level and a maximum of −25 Wm−2 at the top of the atmosphere.

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A study on the aerosol extinction-to-backscatter ratio with combination of micro-pulse LIDAR and MODIS over Hong Kong

Atmospheric Chemistry and Physics ◽

10.5194/acp-6-3243-2006 ◽

2006 ◽

Vol 6 (11) ◽

pp. 3243-3256 ◽

Cited By ~ 38

Author(s):

Q. S. He ◽

C. C. Li ◽

J. T. Mao ◽

A. K. H. Lau ◽

P. R. Li

Keyword(s):

Hong Kong ◽

Aerosol Extinction ◽

Scattering Coefficients ◽

Aerosol Scattering ◽

Microphysical Parameters ◽

Lidar Measurements ◽

Moderate Resolution ◽

Moderate Resolution Imaging Spectroradiometer ◽

Lidar Equation ◽

Micro Pulse Lidar

Abstract. The aerosol extinction-to-backscatter ratio is an important parameter for inverting LIDAR signals in the LIDAR equation. It is a complicated function of the aerosol microphysical characteristics. In this paper, a method to retrieve the column-averaged aerosol extinction-to-backscatter ratio by constraining the aerosol optical depths (AOD) from a Micro-pulse LIDAR (MPL) by the AOD measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) is presented. Both measurements were taken on cloud free days between 1 May 2003 and 30 June 2004 over Hong Kong, a coastal city in south China. Simultaneous measurements of aerosol scattering coefficients with a forward scattering visibility sensor are compared with the LIDAR retrieval of aerosol extinction coefficients. The data are then analyzed to determine seasonal trends of the aetrosol extinction-to-backscatter ratio. In addition, the relationships between the extinction-to-backscatter ratio and wind conditions as well as other aerosol microphysical parameters are presented. The mean aerosol extinction-to-backscatter ratio for the whole period was found to be 29.1±5.8 sr, with a minimum of 18 sr in July 2003 and a maximum of 44 sr in March 2004. The ratio is lower in summer because of the dominance of oceanic aerosols in association with the prevailing southwesterly monsoon. In contrast, relatively larger ratios are noted in spring and winter because of the increased impact of local and regional industrial pollutants associated with the northerly monsoon. The extended LIDAR measurements over Hong Kong provide not only a more accurate retrieval of aerosol extinction coefficient profiles, but also significant substantial information for air pollution and climate studies in the region.

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First-Year Operation of a New Water Vapor Raman Lidar at the JPL Table Mountain Facility, California

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2007jtecha978.1 ◽

2008 ◽

Vol 25 (8) ◽

pp. 1454-1462 ◽

Cited By ~ 26

Author(s):

Thierry Leblanc ◽

I. Stuart McDermid ◽

Robin A. Aspey

Keyword(s):

Water Vapor ◽

Current System ◽

First Year ◽

Raman Lidar ◽

Upper Troposphere ◽

Mixing Ratios ◽

Table Mountain ◽

Lidar Measurements ◽

Better Than ◽

Good Agreement

Abstract A new water vapor Raman lidar was recently built at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL) in California and more than a year of routine 2-h-long nighttime measurements 4–5 times per week have been completed. The lidar was designed to reach accuracies better than 5% anywhere up to 12-km altitude, and with the capability to measure water vapor mixing ratios as low as 1 to 10 ppmv near the tropopause and in the lower stratosphere. The current system is not yet fully optimized but has already shown promising results as water vapor profiles have been retrieved up to 18-km altitude. Comparisons with Vaisala RS92K radiosondes exhibit very good agreement up to at least 10 km. They also revealed a wet bias in the lidar profiles (or a dry bias in the radiosonde profiles), increasing with altitude and becoming significant near 10 km and large when approaching the tropopause. This bias cannot be explained solely by well-known too-dry measurements of the RS92K in the upper troposphere and therefore must partly originate in the lidar measurements. Excess signal due to residual fluorescence in the lidar receiver components is among the most likely candidates and is subject to ongoing investigation.

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Comparison of in-situ FISH measurements of water vapor in the UTLS with ECMWF (re)analysis data

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-14399-2014 ◽

2014 ◽

Vol 14 (10) ◽

pp. 14399-14438 ◽

Cited By ~ 1

Author(s):

A. Kunz ◽

N. Spelten ◽

P. Konopka ◽

R. Müller ◽

R. M. Forbes ◽

...

Keyword(s):

Water Vapor ◽

Analysis Data ◽

High Water ◽

Reanalysis Data ◽

Polar Regions ◽

Large Set ◽

Data Set ◽

Mixing Ratios ◽

Time Periods

Abstract. An evaluation of water vapor in the UTLS in the atmospheric ERA-Interim reanalysis data set is presented by using in-situ measurements from a large set of airborne measurement campaigns from 2001 to 2011 in the tropics, midlatitudes and polar regions. Water vapor measurements are derived from the Fast In-situ Stratospheric Hygrometer (FISH) and cover isentropic layers from 300–400 K (5–18 km). At the same time, the improvement of the ECMWF assimilation scheme representation of water vapor is addressed for time periods representing different cycles of the Integrated Forecast System (IFS). The ratio Δ(H2O) = H2OERA / H2OFISH is used as a simple measure for the difference between observations and the reanalyses. Overall, the reanalysis data reproduce around 87% of all FISH measurements within Δ(H2O) = 0.5–2, and 30% are within Δ(H2O) = 1.0 ± 0.1. Nevertheless, also strong over- and underestimations occur both in the troposphere and in the stratosphere. Δ(H2O) values indicate deviations of factors up to 10, with lower deviations in the stratosphere (Δ(H2O) = 0.5–4) than in the troposphere (Δ(H2O) = 0.5–10). In the tropical stratosphere the ratio is closer to 1 (Δ(H2O) = 0.5–2) than in the extratropical stratosphere where strong deviations occur (Δ(H2O) = 0.1–4). When considering operational analysis data, the agreement with FISH improves over the time, in particular when comparing water vapor fields for time periods before 2004 and after 2010. It appears that influences of tropical tropospheric and extratropical lower stratospheric processes on the water vapor distribution in the UTLS are particularly challenging, resulting in an overestimation of low and underestimation of high water vapor mixing ratios.

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Torrefaction of Woody and Agricultural Biomass: Influence of the Presence of Water Vapor in the Gaseous Atmosphere

Processes ◽

10.3390/pr9010030 ◽

2020 ◽

Vol 9 (1) ◽

pp. 30

Author(s):

María González Martínez ◽

Estéban Hélias ◽

Gilles Ratel ◽

Sébastien Thiéry ◽

Thierry Melkior

Keyword(s):

Water Vapor ◽

Water Content ◽

Wheat Straw ◽

Beech Wood ◽

High Water ◽

High Water Content ◽

Biomass Degradation ◽

Moist Atmosphere ◽

Thermochemical Transformation ◽

Degradation Reactions

Biomass preheating in torrefaction at an industrial scale is possible through a direct contact with the hot gases released. However, their high water-content implies introducing moisture (around 20% v/v) in the torrefaction atmosphere, which may impact biomass thermochemical transformation. In this work, this situation was investigated for wheat straw, beech wood and pine forest residue in torrefaction in two complementary experimental devices. Firstly, experiments in chemical regime carried out in a thermogravimetric analyzer (TGA) showed that biomass degradation started from lower temperatures and was faster under a moist atmosphere (20% v/v water content) for all biomass samples. This suggests that moisture might promote biomass components’ degradation reactions from lower temperatures than those observed under a dry atmosphere. Furthermore, biomass inorganic composition might play a role in the extent of biomass degradation in torrefaction in the presence of moisture. Secondly, torrefaction experiments on a lab-scale device made possible to assess the influence of temperature and residence time under dry and 100% moist atmosphere. In this case, the difference in solid mass loss between dry and moist torrefaction was only significant for wheat straw. Globally, an effect of water vapor on biomass transformation through torrefaction was observed (maximum 10%db), which appeared to be dependent on the biomass type and composition.

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