Improved retrieval of cloud base heights from ceilometer using a non-standard instrument method

Abstract The relationship between the inversion stability and the liquid water path (LWP) tendency of a vertically well-mixed, adiabatic stratocumulus cloud layer is investigated in this study through the analysis of the budget equation for the LWP. The LWP budget is mainly determined by the turbulent fluxes of heat and moisture at the top and the base of the cloud layer, as well as by the source terms due to radiation and precipitation. Through substitution of the inversion stability parameter κ into the budget equation, it immediately follows that the LWP tendency will become negative for increasing values of κ due to the entrainment of increasingly dry air. Large κ values are therefore associated with strong cloud thinning. Using the steady-state solution for the LWP, an equilibrium value κeq is formulated, beyond which the stratocumulus cloud will thin. The Second Dynamics and Chemistry of Marine Stratocumulus field study (DYCOMS-II) is used to illustrate that, depending mainly on the magnitude of the moisture flux at cloud base, stratocumulus clouds can persist well within the buoyancy reversal regime.

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A comparison of ship and satellite measurements of cloud properties with global climate model simulations in the southeast Pacific stratus deck

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-6527-2010 ◽

2010 ◽

Vol 10 (14) ◽

pp. 6527-6536 ◽

Cited By ~ 16

Author(s):

M. A. Brunke ◽

S. P. de Szoeke ◽

P. Zuidema ◽

X. Zeng

Keyword(s):

Diurnal Cycle ◽

Climate Model ◽

Global Climate ◽

Global Climate Model ◽

Cloud Fraction ◽

Cloud Base ◽

Liquid Water Path ◽

Cloud Properties ◽

Southeast Pacific ◽

Cloud Thickness

Abstract. Here, liquid water path (LWP), cloud fraction, cloud top height, and cloud base height retrieved by a suite of A-train satellite instruments (the CPR aboard CloudSat, CALIOP aboard CALIPSO, and MODIS aboard Aqua) are compared to ship observations from research cruises made in 2001 and 2003–2007 into the stratus/stratocumulus deck over the southeast Pacific Ocean. It is found that CloudSat radar-only LWP is generally too high over this region and the CloudSat/CALIPSO cloud bases are too low. This results in a relationship (LWP~h9) between CloudSat LWP and CALIPSO cloud thickness (h) that is very different from the adiabatic relationship (LWP~h2) from in situ observations. Such biases can be reduced if LWPs suspected to be contaminated by precipitation are eliminated, as determined by the maximum radar reflectivity Zmax>−15 dBZ in the apparent lower half of the cloud, and if cloud bases are determined based upon the adiabatically-determined cloud thickness (h~LWP1/2). Furthermore, comparing results from a global model (CAM3.1) to ship observations reveals that, while the simulated LWP is quite reasonable, the model cloud is too thick and too low, allowing the model to have LWPs that are almost independent of h. This model can also obtain a reasonable diurnal cycle in LWP and cloud fraction at a location roughly in the centre of this region (20° S, 85° W) but has an opposite diurnal cycle to those observed aboard ship at a location closer to the coast (20° S, 75° W). The diurnal cycle at the latter location is slightly improved in the newest version of the model (CAM4). However, the simulated clouds remain too thick and too low, as cloud bases are usually at or near the surface.

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Modeling Insights into Precipitation Deuterium Excess as an Indicator of Raindrop Evaporation in Lanzhou, China

Water ◽

10.3390/w13020193 ◽

2021 ◽

Vol 13 (2) ◽

pp. 193

Author(s):

Fenli Chen ◽

Mingjun Zhang ◽

Athanassios A. Argiriou ◽

Shengjie Wang ◽

Qian Ma ◽

...

Keyword(s):

Arid Region ◽

Quantitative Methods ◽

Isotope Composition ◽

Sampling Site ◽

Western China ◽

Cloud Base ◽

Deuterium Excess ◽

Semi Arid Region ◽

Semi Arid

The deuterium excess in precipitation is an effective indicator to assess the existence of sub-cloud evaporation of raindrops. Based on the synchronous measurements of stable isotopes of hydrogen and oxygen (δ2H and δ18O) in precipitation for several sites in Lanzhou, western China, spanning for approximately four years, the variations of deuterium excess between the ground and the cloud base are evaluated by using a one-box Stewart model. The deuterium excess difference below the cloud base during summer (−17.82‰ in Anning, −11.76‰ in Yuzhong, −21.18‰ in Gaolan and −12.41‰ in Yongdeng) is greater than that in other seasons, and difference in winter is weak due to the low temperature. The variations of deuterium excess in precipitation due to below-cloud evaporation are examined for each sampling site and year. The results are useful to understand the modification of raindrop isotope composition below the cloud base at a city scale, and the quantitative methods provide a case study for a semi-arid region at the monsoon margin.

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Mind the gap – Part 1: Accurately locating warm marine boundary layer clouds and precipitation using spaceborne radars

Atmospheric Measurement Techniques ◽

10.5194/amt-13-2363-2020 ◽

2020 ◽

Vol 13 (5) ◽

pp. 2363-2379 ◽

Cited By ~ 3

Author(s):

Katia Lamer ◽

Pavlos Kollias ◽

Alessandro Battaglia ◽

Simon Preval

Keyword(s):

Boundary Layer ◽

Cloud Cover ◽

Marine Boundary Layer ◽

Short Pulse ◽

Pulse Mode ◽

Cloud Base ◽

Boundary Layer Clouds ◽

Highly Sensitive ◽

Eastern North Atlantic ◽

Long Pulse

Abstract. Ground-based radar observations show that, over the eastern North Atlantic, 50 % of warm marine boundary layer (WMBL) hydrometeors occur below 1.2 km and have reflectivities of < −17 dBZ, thus making their detection from space susceptible to the extent of surface clutter and radar sensitivity. Surface clutter limits the ability of the CloudSat cloud profiling radar (CPR) to observe the true cloud base in ∼52 % of the cloudy columns it detects and true virga base in ∼80 %, meaning the CloudSat CPR often provides an incomplete view of even the clouds it does detect. Using forward simulations, we determine that a 250 m resolution radar would most accurately capture the boundaries of WMBL clouds and precipitation; that being said, because of sensitivity limitations, such a radar would suffer from cloud cover biases similar to those of the CloudSat CPR. Observations and forward simulations indicate that the CloudSat CPR fails to detect 29 %–43 % of the cloudy columns detected by ground-based sensors. Out of all configurations tested, the 7 dB more sensitive EarthCARE CPR performs best (only missing 9.0 % of cloudy columns) indicating that improving radar sensitivity is more important than decreasing the vertical extent of surface clutter for measuring cloud cover. However, because 50 % of WMBL systems are thinner than 400 m, they tend to be artificially stretched by long sensitive radar pulses, hence the EarthCARE CPR overestimation of cloud top height and hydrometeor fraction. Thus, it is recommended that the next generation of space-borne radars targeting WMBL science should operate interlaced pulse modes including both a highly sensitive long-pulse mode and a less sensitive but clutter-limiting short-pulse mode.

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Cloud Base Height and Effective Cloud Emissivity Retrieval with Ground-Based Infrared Interferometer

Atmospheric and Oceanic Science Letters ◽

10.1080/16742834.2012.11447021 ◽

2012 ◽

Vol 5 (5) ◽

pp. 439-444

Author(s):

Pan Lin-Jun ◽

Lu Da-Ren

Keyword(s):

Cloud Base ◽

Cloud Base Height

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A Statistical Model of Cloud Vertical Structure Based on Reconciling Cloud Layer Amounts Inferred from Satellites and Radiosonde Humidity Profiles

Journal of Climate ◽

10.1175/jcli3479.1 ◽

2005 ◽

Vol 18 (17) ◽

pp. 3587-3605 ◽

Cited By ~ 44

Author(s):

William B. Rossow ◽

Yuanchong Zhang ◽

Junhong Wang

Keyword(s):

Statistical Model ◽

Vertical Structure ◽

Atmospheric Temperature ◽

Radiative Flux ◽

Cloud Layer ◽

Cloud Base ◽

Polar Regions ◽

Flux Divergence ◽

Climate Scale ◽

Humidity Profiles

Abstract To diagnose how cloud processes feed back on weather- and climate-scale variations of the atmosphere requires determining the changes that clouds produce in the atmospheric diabatic heating by radiation and precipitation at the same scales of variation. In particular, not only the magnitude of these changes must be quantified but also their correlation with atmospheric temperature variations; hence, the space–time resolution of the cloud perturbations must be sufficient to account for the majority of these variations. Although extensive new global cloud and radiative flux datasets have recently become available, the vertical profiles of clouds and consequent radiative flux divergence have not been systematically measured covering weather-scale variations from about 100 km, 3 h up to climate-scale variations of 10 000 km, decadal inclusive. By combining the statistics of cloud layer occurrence from the International Satellite Cloud Climatology Project (ISCCP) and an analysis of radiosonde humidity profiles, a statistical model has been developed that associates each cloud type, recognizable from satellite measurements, with a particular cloud vertical structure. Application of this model to the ISCCP cloud layer amounts produces estimates of low-level cloud amounts and average cloud-base pressures that are quantitatively closer to observations based on surface weather observations, capturing the variations with latitude and season and land and ocean (results are less good in the polar regions). The main advantage of this statistical model is that the correlations of cloud vertical structure with meteorology are qualitatively similar to “classical” information relating cloud properties to weather. These results can be evaluated and improved with the advent of satellites that can directly probe cloud vertical structures over the globe, providing statistics with changing meteorological conditions.

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Biogeography of Tropical Montane Cloud Forests. Part II: Mapping of Orographic Cloud Immersion

Journal of Applied Meteorology and Climatology ◽

10.1175/2007jamc1819.1 ◽

2008 ◽

Vol 47 (8) ◽

pp. 2183-2197 ◽

Cited By ~ 22

Author(s):

Udaysankar S. Nair ◽

Salvi Asefi ◽

Ronald M. Welch ◽

D. K. Ray ◽

Robert O. Lawton ◽

...

Keyword(s):

Costa Rica ◽

Cloud Forest ◽

United Nations Environment Programme ◽

Cloud Base ◽

Trade Wind ◽

Cloud Forests ◽

Study Region ◽

Modis Data ◽

Monitoring Centre ◽

Tropical Montane Cloud Forests

Abstract This study details two unique methods to quantify cloud-immersion statistics for tropical montane cloud forests (TMCFs). The first technique uses a new algorithm for determining cloud-base height using Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, and the second method uses numerical atmospheric simulation along with geostationary satellite data. Cloud-immersion statistics are determined using MODIS data for March 2003 over the study region consisting of Costa Rica, southern Nicaragua, and northern Panama. Comparison with known locations of cloud forests in northern Costa Rica shows that the MODIS-derived cloud-immersion maps successfully identify known cloud-forest locations in the United Nations Environment Programme (UNEP) World Conservation Monitoring Centre (WCMC) database. Large connected regions of cloud immersion are observed in regions in which the trade wind flow is directly impinging upon the mountain slopes; in areas in which the flow is parallel to the slopes, a fractured spatial distribution of TMCFs is observed. Comparisons of the MODIS-derived cloud-immersion map with the model output show that the MODIS product successfully captures the important cloud-immersion patterns in the Monteverde region of Costa Rica. The areal extent of cloud immersion is at a maximum during morning hours and at a minimum during the afternoon, before increasing again in the evening. Cloud-immersion frequencies generally increase with increasing elevation and tend to be higher on the Caribbean Sea side of the mountains. This study shows that the MODIS data may be used successfully to map the biogeography of cloud forests and to quantify cloud immersion over cloud-forest locations.

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A Polar Low Pair over the Norwegian Sea

Monthly Weather Review ◽

10.1175/2009mwr2864.1 ◽

2009 ◽

Vol 137 (8) ◽

pp. 2559-2575 ◽

Cited By ~ 14

Author(s):

Burghard Brümmer ◽

Gerd Müller ◽

Gunnar Noer

Keyword(s):

Heat Budget ◽

Cloud Layer ◽

Sea Surface ◽

Cloud Base ◽

Aircraft Measurements ◽

Polar Lows ◽

The North ◽

Polar Low ◽

Upper Level Jet ◽

Almost All

Abstract During the Lofotes cyclone experiment (LOFZY 2005), two polar lows developed one behind the other inside a cold-air outbreak from the north in the lee of Spitsbergen on 7 March 2005. Buoys, ship, and aircraft measurements as well as satellite imagery are applied to analyze the polar low bulk properties, the horizontal and vertical structure, and the mass, moisture, and heat budget. The lifetime of the system until landfall at northern Norway was 12 h. The generation occurred under the left exit region of an upper-level jet with 70 m s−1. Both polar lows had a radius of 100–130 km and extended to a height of about 2.5 km. The propagation speeds were within 14–17 m s−1 and correspond to the vertically averaged wind velocity of the lowest 2.5 km. In the polar low centers the pressure was about 2–3 hPa lower and the air was 1–2 K warmer and drier than in the surroundings. Aircraft measurements in the second of the two polar lows show an embedded frontlike precipitation band north of the center. Here, the highest low-level winds with 25 m s−1 and the largest fluxes of sensible and latent heat with 290 and 520 W m−2, respectively, were measured (areal averages amounted to 115 and 190 W m−2). Aircraft data show mass convergence in the subcloud layer (0–900 m) and divergence in the cloud layer (900–2500 m). Moisture supply by evaporation from the sea surface was about twice as large as that by convergence in the subcloud layer. The condensation rate in the cloud layer nearly equaled the rate of evaporation at the sea surface. Almost all condensed cloud water was converted to precipitation water. Only half of the precipitation at the cloud base reached the sea surface.

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