scholarly journals The vertical structure and spatial variability of lower-tropospheric water vapor and clouds in the trades

2020 ◽  
Vol 20 (10) ◽  
pp. 6129-6145
Author(s):  
Ann Kristin Naumann ◽  
Christoph Kiemle
Keyword(s):  
Water Vapor ◽  
Cloud Fraction ◽  
Airborne Lidar ◽  
Cloud Base ◽  
Trade Wind ◽  
Model Resolution ◽  
Grid Spacing ◽  
Model Bias ◽  
Shallow Cumulus ◽  
Vapor Distribution

Abstract. Horizontal and vertical variability of water vapor is omnipresent in the tropics, but its interaction with cloudiness poses challenges for weather and climate models. In this study we compare airborne lidar measurements from a summer and a winter field campaign in the tropical Atlantic with high-resolution simulations to analyze the water vapor distributions in the trade wind regime, its covariation with cloudiness, and their representation in simulations. Across model grid spacing from 300 m to 2.5 km, the simulations show good skill in reproducing the water vapor distribution in the trades as measured by the lidar. An exception to this is a pronounced moist model bias at the top of the shallow cumulus layer in the dry winter season which is accompanied by a humidity gradient that is too weak at the inversion near the cloud top. The model's underestimation of water vapor variability in the cloud and subcloud layer occurs in both seasons but is less pronounced than the moist model bias at the inversion. Despite the model's insensitivity to resolution from hecto- to kilometer scale for the distribution of water vapor, cloud fraction decreases strongly with increasing model resolution and is not converged at hectometer grid spacing. The observed cloud deepening with increasing water vapor path is captured well across model resolution, but the concurrent transition from cloud-free to low cloud fraction is better represented at hectometer resolution. In particular, in the wet summer season the simulations with kilometer-scale resolution overestimate the observed cloud fraction near the inversion but lack condensate near the observed cloud base. This illustrates how a model's ability to properly capture the water vapor distribution does not necessarily translate into an adequate representation of shallow cumulus clouds that live at the tail of the water vapor distribution.

scholarly journals The vertical Structure and spatial Variability of lower tropospheric Water Vapor and Clouds in the Trades

2019 ◽  
Author(s):  
Ann Kristin Naumann ◽  
Christoph Kiemle
Keyword(s):  
Water Vapor ◽  
Winter Season ◽  
Cloud Fraction ◽  
Airborne Lidar ◽  
Cloud Base ◽  
Trade Wind ◽  
Model Resolution ◽  
Grid Spacing ◽  
Shallow Cumulus ◽  
Vapor Distribution

Abstract. Horizontal and vertical variability of water vapor is omnipresent in the tropics but its interaction with cloudiness poses challenges for weather and climate models. In this study we compare airborne lidar measurements from a summer and a winter field campaign in the tropical Atlantic with high-resolution simulations to analyse the water vapor distributions in the trade wind regime, its covariation with cloudiness and their representation in simulations. Across model grid spacing from 300 m to 2.5 km, the simulations show good skill in reproducing the water vapor distribution in the trades as measured by the lidar. An exception to this is a pronounced moist model bias at the top of the shallow cumulus layer in the dry winter season which is accompanied by a too weak humidity inversion at the cloud top. The model's underestimation of water vapor variability in the cloud and subcloud layer occurs in both seasons but is less pronounced. Despite the model's insensitivity to resolution from hecto- to kilometer scale for the distribution of water vapor, cloud fraction decreases strongly with increasing model resolution and is not converged at hectometer grid spacing. The observed cloud deepening with increasing water vapor path is captured well across model resolution but the concurrent transition from cloud-free to low cloud fraction is better represented at hectometer resolution. In particular, in the wet summer season the simulations with kilometer-scale resolution overestimate the observed cloud fraction near the inversion but lack condensate near the observed cloud base. This illustrates how a model's ability to properly capture the water vapor distribution does not need to translate into an adequate representation of shallow cumulus clouds that live at the tail of the water vapor distribution.

scholarly journals Shallow cumulus cloud feedback in large eddy simulations – bridging the gap to storm-resolving models

2021 ◽  
Vol 21 (5) ◽  
pp. 3275-3288
Author(s):  
Jule Radtke ◽  
Thorsten Mauritsen ◽  
Cathy Hohenegger
Keyword(s):  
Cloud Cover ◽  
Horizontal Resolution ◽  
Cloud Fraction ◽  
Cloud Feedback ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty in projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Nonhydrostatic Large Eddy Model in a control and a perturbed 4 K warmer climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened, the base-state cloud fraction increases substantially, especially near cloud base, lateral mixing is weaker, and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of base-state cloud fraction and thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapour availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm-resolving models may exaggerate the trade wind cumulus cloud feedback.

scholarly journals Shallow Cumulus Cloud Feedback in Large Eddy Simulations – Bridging the Gap to Storm Resolving Models

2020 ◽  
Author(s):  
Jule Radtke ◽  
Thorsten Mauritsen ◽  
Cathy Hohenegger
Keyword(s):  
Cloud Cover ◽  
Horizontal Resolution ◽  
Cloud Fraction ◽  
Cloud Feedback ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Cloud ◽  
Shallow Cumulus ◽  
Large Eddy ◽  
Carry Over

Abstract. The response of shallow trade cumulus clouds to global warming is a leading source of uncertainty to interpretations and projections of the Earth's changing climate. A setup based on the Rain In Cumulus over the Ocean field campaign is used to simulate a shallow trade wind cumulus field with the Icosahedral Non-hydrostatic Large Eddy Model in a control and a perturbed 4 K warmed climate, while degrading horizontal resolution from 100 m to 5 km. As the resolution is coarsened the basic state cloud fraction increases substantially, especially at cloud base, lateral mixing is weaker and cloud tops reach higher. Nevertheless, the overall vertical structure of the cloud layer is surprisingly robust across resolutions. In a warmer climate, cloud cover reduces, alone constituting a positive shortwave cloud feedback: the strength correlates with the amount of basic state cloud fraction, thus is stronger at coarser resolutions. Cloud thickening, resulting from more water vapor availability for condensation in a warmer climate, acts as a compensating feedback, but unlike the cloud cover reduction it is largely resolution independent. Therefore, refining the resolution leads to convergence to a near-zero shallow cumulus feedback. This dependence holds in experiments with enhanced realism including precipitation processes or warming along a moist adiabat instead of uniform warming. Insofar as these findings carry over to other models, they suggest that storm resolving models may exaggerate the trade wind cumulus cloud feedback.

scholarly journals Climatology of stratocumulus cloud morphologies: microphysical properties and radiative effects

2014 ◽  
Vol 14 (13) ◽  
pp. 6695-6716 ◽  
Author(s):  
A. Muhlbauer ◽  
I. L. McCoy ◽  
R. Wood
Keyword(s):  
Physical Properties ◽  
Global Scale ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Radiative Effects ◽  
Regional Variability ◽  
Microphysical Properties ◽  
Low Clouds ◽  
Low Cloud

Abstract. An artificial neural network cloud classification scheme is combined with A-train observations to characterize the physical properties and radiative effects of marine low clouds based on their morphology and type of mesoscale cellular convection (MCC) on a global scale. The cloud morphological categories are (i) organized closed MCC, (ii) organized open MCC and (iii) cellular but disorganized MCC. Global distributions of the frequency of occurrence of MCC types show clear regional signatures. Organized closed and open MCCs are most frequently found in subtropical regions and in midlatitude storm tracks of both hemispheres. Cellular but disorganized MCC are the predominant type of marine low clouds in regions with warmer sea surface temperature such as in the tropics and trade wind zones. All MCC types exhibit a pronounced seasonal cycle. The physical properties of MCCs such as cloud fraction, radar reflectivity, drizzle rates and cloud top heights as well as the radiative effects of MCCs are found highly variable and a function of the type of MCC. On a global scale, the cloud fraction is largest for closed MCC with mean cloud fractions of about 90%, whereas cloud fractions of open and cellular but disorganized MCC are only about 51% and 40%, respectively. Probability density functions (PDFs) of cloud fractions are heavily skewed and exhibit modest regional variability. PDFs of column maximum radar reflectivities and inferred cloud base drizzle rates indicate fundamental differences in the cloud and precipitation characteristics of different MCC types. Similarly, the radiative effects of MCCs differ substantially from each other in terms of shortwave reflectance and transmissivity. These differences highlight the importance of low-cloud morphologies and their associated cloudiness on the shortwave cloud forcing.

scholarly journals The Environment of Precipitating Shallow Cumulus Convection

2009 ◽  
Vol 66 (7) ◽  
pp. 1962-1979 ◽  
Author(s):  
Louise Nuijens ◽  
Bjorn Stevens ◽  
A. Pier Siebesma
Keyword(s):  
Surface Flux ◽  
Airborne Lidar ◽  
Trade Wind ◽  
Lidar Data ◽  
Cumulus Convection ◽  
Total Precipitation ◽  
Quantitative Estimates ◽  
Shallow Cumulus ◽  
Reflectivity Data ◽  
Airborne Lidar Data

Abstract Quantitative estimates of precipitation in a typical undisturbed trade wind region are derived from 2 months of radar reflectivity data and compared to the meteorological environment determined from soundings, surface flux, and airborne-lidar data. Shallow precipitation was ubiquitous, covering on average about 2% of the region and contributing to at least half of the total precipitation. Echo fractions on the scale of the radar domain range between 0% and 10% and vary greatly within a period from a few hours to a day. Variability in precipitation relates most strongly to variability in humidity and the zonal wind speed, although greater inversion heights and deeper clouds are also evident at times of more rain. The analysis herein suggests that subtle fluctuations in both the strength of the easterlies and in subsidence play a major role in regulating humidity and hence precipitation, even within a given meteorological regime (here, the undisturbed trades).

Measuring the variability of the shallow convective mass flux profiles in the tropical trade wind region

2020 ◽  
Author(s):  
Marcus Klingebiel ◽  
Heike Konow ◽  
Bjorn Stevens
Keyword(s):  
Boundary Layer ◽  
Vertical Velocity ◽  
Mass Flux ◽  
Doppler Radar ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Geophysical Research ◽  
Wind Region ◽  
Convective Mass Flux

<p>Mass flux is a key parameter to represent shallow convection in global circulation models. To estimate the shallow convective mass flux as accurately as possible, observations of this parameter are necessary. Prior studies from Ghate et al. (2011) and Lamer et al. (2015) used Doppler radar measurements over a few months to identify a typical shallow convective mass flux profile based on cloud fraction and vertical velocity. In this study, we extend their observations by using long term remote sensing measurements at the Barbados Cloud Observatory (13° 09’ N, 59° 25’ W) over a time period of 30 months and check a hypothesis by Grant (2001), who proposed that the cloud base mass flux is just proportional to the sub-cloud convective velocity scale. Therefore, we analyze Doppler radar and Doppler lidar measurements to identify the variation of the vertical velocity in the cloud and sub-cloud layer, respectively. Furthermore, we show that the in-cloud mass flux is mainly influenced by the cloud fraction and provide a linear equation, which can be used to roughly calculate the mass flux in the trade wind region based on the cloud fraction.</p><p> </p><p>References:<br>Ghate,  V.  P.,  M.  A.  Miller,  and  L.  DiPretore,  2011:   Vertical  velocity structure of marine boundary layer trade wind cumulus clouds. Journal  of  Geophysical  Research: Atmospheres, 116  (D16), doi:10.1029/2010JD015344.</p><p>Grant,  A.  L.  M.,  2001:   Cloud-base  fluxes  in  the  cumulus-capped boundary layer. Quarterly Journal of the Royal Meteorological Society, 127 (572), 407–421, doi:10.1002/qj.49712757209.</p><p>Lamer, K., P. Kollias, and L. Nuijens, 2015:  Observations of the variability  of  shallow  trade  wind  cumulus  cloudiness  and  mass  flux. Journal of Geophysical Research: Atmospheres, 120  (12), 6161–6178, doi:10.1002/2014JD022950.</p>

Using airborne lidar and weather radar measurements to characterize the interplay between aerosol and shallow marine trade wind clouds

2021 ◽  
Author(s):  
Florian Ewald ◽  
Silke Groß ◽  
Martin Wirth ◽  
Martin Hagen ◽  
Manuel Gutleben
Keyword(s):  
Water Vapor ◽  
Temporal Evolution ◽  
Weather Radar ◽  
Airborne Lidar ◽  
Windward Side ◽  
Trade Wind ◽  
Shallow Marine ◽  
Cloud Radar ◽  
Radar Measurements ◽  
Precipitation Formation

<p>The interaction of aerosol, clouds, and water vapor is still a major source of uncertainty in projections of Earth’s future climate. Especially in the trades, the response of shallow marine trade wind convection to external forcings is poorly understood. These low-level clouds have an important cooling effect on surface temperatures, while their amount and height are directly influenced by the radiative cooling by aerosols and water vapor aloft. Furthermore, there is evidence that aerosols can modify the microphysical properties (e.g., by glaciation) and the precipitation formation inside these clouds while water vapor above the trade inversion influences the atmospheric stability in which they form. Due to the small horizontal scale of these clouds, the vertical separation of atmospheric layers, and the temporal evolution of precipitation, the observation of this interplay by geostationary satellites is scarce.</p><p>To alleviate this observational data gap over the tropical North-Atlantic region, airborne lidar and cloud radar measurements were performed in the vicinity of Barbados and complemented with dedicated weather radar measurements during the EUREC4A campaign in February 2020. Aerosol properties and the vertical water vapor profile were characterized with simultaneous high spectral resolution and differential absorption measurements using the WALES lidar onboard the German research aircraft HALO. On the same platform, the vertical cloud extent and the presence of precipitation were sampled with the high-power Ka-band cloud radar HAMP MIRA. To capture the temporal evolution of precipitation patterns, these measurements were complemented with measurements of the C-band polarimetric weather radar POLDIRAD which was installed on the windward side of Barbados. During EUREC4A, measurements flights were conducted in high and low aerosol loads to sample its influence on the marine trade wind convection.</p><p>This presentation will briefly introduce the instrumentation, data processing, and availability and give an overview of gained insights and ongoing studies. By means of case studies, we will give first impressions of the complementary nature of the collocated, highly resolved airborne measurements and the POLDIRAD measurements which provide the horizontal context and temporal evolution of the precipitation formation. By combining the cross-sectional snapshots with the temporal evolution of the precipitation pattern we will provide a detailed insight into the interplay between the aerosol and water vapor layer and the precipitation formation in the shallow marine trade wind convection.</p>

scholarly journals EUREC<sup>4</sup>A observations from the SAFIRE ATR42 aircraft

2022 ◽  
Author(s):  
Sandrine Bony ◽  
Marie Lothon ◽  
Julien Delanoë ◽  
Pierre Coutris ◽  
Jean-Claude Etienne ◽  
...  
Keyword(s):  
Lower Troposphere ◽  
Cloud Fraction ◽  
Cloud Base ◽  
Trade Wind ◽  
Flight Pattern ◽  
Cloud Radar ◽  
Base Level ◽  
Microphysical Properties ◽  
Research Aircraft

Abstract. As part of the EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign, which took place in January and February 2020 over the western tropical Atlantic near Barbados, the French SAFIRE ATR42 research aircraft conducted 19 flights in the lower troposphere. Each flight followed a common flight pattern that sampled the atmosphere around the cloud-base level, at different heights of the subcloud layer, near the sea surface and in the lower free troposphere. The aircraft's payload included a backscatter lidar and a Doppler cloud radar that were both horizontally oriented, a Doppler cloud radar looking upward, microphysical probes, a cavity ring-down spectrometer for water isotopes, a multiwavelength radiometer, a visible camera and multiple meteorological sensors, including fast rate sensors for turbulence measurements. With this instrumentation, the ATR characterized the macrophysical and microphysical properties of trade-wind clouds together with their thermodynamical, turbulent and radiative environment. This paper presents the airborne operations, the flight segmentation, the instrumentation, the data processing and the EUREC4A datasets produced from the ATR measurements. It shows that the ATR measurements of humidity, wind and cloud-base cloud fraction measured with different techniques and samplings are internally consistent, that meteorological measurements are consistent with estimates from dropsondes launched from an overflying aircraft (HALO), and that water isotopic measurements are well correlated with data from the Barbados Cloud Observatory. This consistency demonstrates the robustness of the ATR measurements of humidity, wind, cloud-base cloud fraction and water isotopic composition during EUREC4A. It also confirms that through their repeated flight patterns, the ATR and HALO measurements provided a statistically consistent sampling of trade-wind clouds and of their environment. The ATR datasets are freely available at the locations specified in Table 11.

scholarly journals Remote Sensing of Sea Salt Aerosol below Trade Wind Clouds

2019 ◽  
Vol 76 (5) ◽  
pp. 1189-1202 ◽  
Author(s):  
Marcus Klingebiel ◽  
Virendra P. Ghate ◽  
Ann Kristin Naumann ◽  
Florian Ditas ◽  
Mira L. Pöhlker ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Relative Humidity ◽  
Sea Salt ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Clouds ◽  
Ka Band ◽  
Sea Salt Aerosol ◽  
Cloud Radar ◽  
Shallow Cumulus

Abstract Sea salt aerosol in the boundary layer below shallow cumulus clouds is remotely observed with a Ka-band cloud radar at the Barbados Cloud Observatory and is detected in 76% of the measurements over 1 year. Carried by convection, sea salt particles with a diameter larger than 500 nm show an upward motion of 0.2 m s−1 below shallow cumulus clouds for a 2-day case study. Caused by an increasing relative humidity with increasing altitude, the sea salt particles become larger as they move closer to the cloud base. By using combined measurements of a Ka-band cloud radar and a Raman lidar, the retrieved equivolumetric diameter of the hygroscopically grown sea salt particles is found to be between 6 and 11 μm with a total number concentration of 20 cm−3 near cloud base. Assuming a fixed shape parameter, a size distribution of sea salt particles under high-relative-humidity conditions below cloud base is estimated and agrees with measurements taken by a dry-deposition sampler and online aerosol observations. The methods outlined in this paper can be used in future studies to get a better understanding of the vertical and temporal sea salt distribution in the boundary layer and sea salt aerosol–cloud interaction processes.

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