Low Cloud Type over the Ocean from Surface Observations. Part III: Relationship to Vertical Motion and the Regional Surface Synoptic Environment

Abstract. The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS) is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat-AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO-AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km) for clouds ≥7 km (<7 km). The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed.

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Observed Relationships between Cloud Vertical Structure and Convective Aggregation over Tropical Ocean

Journal of Climate ◽

10.1175/jcli-d-16-0125.1 ◽

2017 ◽

Vol 30 (6) ◽

pp. 2187-2207 ◽

Cited By ~ 33

Author(s):

T. H. M. Stein ◽

C. E. Holloway ◽

I. Tobin ◽

S. Bony

Keyword(s):

Cloud Cover ◽

Large Scale ◽

Vertical Structure ◽

Vertical Motion ◽

Sea Surface ◽

Precipitation Rate ◽

Aggregation Index ◽

Tropical Ocean ◽

Low Level ◽

Low Cloud

Abstract Using the satellite-infrared-based Simple Convective Aggregation Index (SCAI) to determine the degree of aggregation, 5 years of CloudSat–CALIPSO cloud profiles are composited at a spatial scale of 10 degrees to study the relationship between cloud vertical structure and aggregation. For a given large-scale vertical motion and domain-averaged precipitation rate, there is a large decrease in anvil cloud (and in cloudiness as a whole) and an increase in clear sky and low cloud as aggregation increases. The changes in thick anvil cloud are proportional to the changes in total areal cover of brightness temperatures below 240 K [cold cloud area (CCA)], which is negatively correlated with SCAI. Optically thin anvil cover decreases significantly when aggregation increases, even for a fixed CCA, supporting previous findings of a higher precipitation efficiency for aggregated convection. Cirrus, congestus, and midlevel clouds do not display a consistent relationship with the degree of aggregation. Lidar-observed low-level cloud cover (where the lidar is not attenuated) is presented herein as the best estimate of the true low-level cloud cover, and it is shown that it increases as aggregation increases. Qualitatively, the relationships between cloud distribution and SCAI do not change with sea surface temperature, while cirrus clouds are more abundant and low-level clouds less at higher sea surface temperatures. For the observed regimes, the vertical cloud profile varies more evidently with SCAI than with mean precipitation rate. These results confirm that convective scenes with similar vertical motion and rainfall can be associated with vastly different cloudiness (both high and low cloud) and humidity depending on the degree of convective aggregation.

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A meteorological overview of the ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) campaign over the southeastern Atlantic during 2016–2018: Part 1 – Climatology

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-16689-2021 ◽

2021 ◽

Vol 21 (22) ◽

pp. 16689-16707

Author(s):

Ju-Mee Ryoo ◽

Leonhard Pfister ◽

Rei Ueyama ◽

Paquita Zuidema ◽

Robert Wood ◽

...

Keyword(s):

Atlantic Ocean ◽

Large Scale ◽

Coastal Region ◽

Vertical Motion ◽

Mixing Ratios ◽

Low Cloud ◽

Upper Level ◽

Upper Level Jet ◽

The Impact ◽

Heat Low

Abstract. In 2016–2018, the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project undertook 3-month-long deployments to the southeastern (SE) Atlantic Ocean using research aircraft to better understand the impact of biomass burning (BB) aerosol transport to the SE Atlantic Ocean on climate. In this (part 1 of the meteorological overview) paper, the climatological features at monthly timescales are investigated. The southern African easterly jet (AEJ-S), defined as the zonal easterlies over 600–700 hPa exceeding 6 m s−1 around 5–15∘ S, is a characteristic feature of the mid-level circulation over southern Africa that was also during the deployment months of August 2017, September 2016, and October 2018. Climatologically, the AEJ-S develops at lower altitudes (∼ 3 km; 700 hPa) between 5–10∘ S in August, while it develops at around 4 km (∼ 600 hPa) and further south (5–15∘ S) in September and October, largely driven by the strong sensible heating over the African plateau. Notable meteorological anomalous characteristics during the 3 deployment months, compared to climatology (2000–2018), include the following: (1) during August 2017, the AEJ-S was weaker than the climatological mean, with an additional anomalous upper-level jet aloft (∼ 6 km) around 10∘ S. August 2017 was also drier over the SE Atlantic at 600–700 hPa than climatology, with a stronger Benguela low-level jet (LLJ) at 925–950 hPa along the Namibian coast of the SE Atlantic. Consistent with this, the southern Atlantic anticyclone was also stronger and closer to the coast than the August climatological mean. (2) During September 2016, the AEJ-S intensity was similar to the climatological mean, although the heat low and vertical motion over the land was slightly stronger compared to the September climatology. The LLJ and the large-scale southern Atlantic anticyclone were stronger than the climatological mean. (3) During October 2018, the AEJ-S was slightly weaker compared to the climatological mean, as was the LLJ and the southern Atlantic anticyclone. October 2018 was wetter over the Benguela coastal region at 600 hPa than the climatological mean. During all the deployment months, the sea surface temperatures (SST) over the SE Atlantic were warmer than the climatological means, but the monthly mean low cloud fraction was only noticeably reduced in August 2017. A weak August 2017 AEJ-S can explain low offshore black carbon (BC) mixing ratios within the European Centre for Medium-Range Weather Forecasts (ECMWF) Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, although the BC peak altitude, at 2–3 km, is below that of the AEJ-S. The upper-level wave disturbance and the associated anomalous circulation also explain the weakening of AEJ-S through the reduction of the strength of the heat low over the land during August 2017.

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Contrasting the Co-variability of Daytime Cloud and Precipitation over Tropical Land and Ocean

10.5194/acp-2017-612 ◽

2017 ◽

Author(s):

Daeho Jin ◽

Lazaros Oreopoulos ◽

Dongmin Lee ◽

Nayeong Cho ◽

Jackson Tan

Keyword(s):

Correlation Coefficients ◽

Tropical Rainfall Measuring Mission ◽

Cloud Type ◽

Convective Systems ◽

Low Cloud ◽

Moderate Resolution Imaging Spectroradiometer ◽

The Difference ◽

Histogram Bins ◽

Positive Correlations ◽

The Relationship

Abstract. The co-variability of cloud and precipitation in the extended tropics (35° N–35° S) is investigated using contemporaneous datasets for a 13-year period. The goal is to quantify the relationship between cloud types and precipitation events of particular strength. Particular attention is paid to whether the relationship exhibits different characteristics over tropical land and ocean. A major analysis metric is correlation coefficients between fractions of individual cloud types and frequencies within precipitation histogram bins that have been matched in time and space. The cloud type fractions are derived from Moderate Resolution Imaging Spectroradiometer (MODIS) joint histograms of cloud top pressure and cloud optical thickness in one-degree grid cells, and the precipitation frequencies come from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) dataset aggregated to the same grid. It is found that the strongest coupling (positive correlation) between clouds and precipitation occurs for cumulonimbus clouds and heaviest rainfall over ocean. While the same cloud type and rainfall bin are also best correlated over land compared to other combinations, the correlation magnitude over land is weaker than over ocean. The difference is attributed to the greater size of convective systems over ocean. It is also found both over ocean and land that the anti-correlation of strong precipitation with weak (i.e., thin and/or low) cloud types is of greater absolute strength than positive correlations between weak cloud types and weak precipitation. Cloud type co-occurrence relationships explain some of the cloud-precipitation anti-correlations. Couplings between weaker rainfall and clouds are also distinct in ocean vs. land, with precipitation predictability when cloud type is known being quite poor in general, particularly over land.

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Instantaneous Linkages between Clouds and Large-Scale Meteorology over the Southern Ocean in Observations and a Climate Model

Journal of Climate ◽

10.1175/jcli-d-17-0156.1 ◽

2017 ◽

Vol 30 (23) ◽

pp. 9455-9474 ◽

Cited By ~ 15

Author(s):

Casey J. Wall ◽

Dennis L. Hartmann ◽

Po-Lun Ma

Keyword(s):

Southern Ocean ◽

Large Scale ◽

Climate Models ◽

Climate Model ◽

Austral Summer ◽

Vertical Motion ◽

Cloud Properties ◽

Low Clouds ◽

Community Atmosphere Model ◽

Low Cloud

Instantaneous, coincident, footprint-level satellite observations of cloud properties and radiation taken during austral summer over the Southern Ocean are used to study relationships between clouds and large-scale meteorology. Cloud properties are very sensitive to the strength of vertical motion in the midtroposphere, and low-cloud properties are sensitive to estimated inversion strength, low-level temperature advection, and sea surface temperature. These relationships are quantified. An index for the meteorological anomalies associated with midlatitude cyclones is presented, and it is used to reveal the sensitivity of clouds to the meteorology within the warm and cold sectors of cyclones. The observed relationships between clouds and meteorology are compared to those in the Community Atmosphere Model, version 5 (CAM5), using satellite simulators. Low clouds simulated by CAM5 are too few, are too bright, and contain too much ice. In the cold sector of cyclones, the low clouds are also too sensitive to variations in the meteorology. When CAM5 is coupled with an updated boundary layer parameterization known as Cloud Layers Unified by Binormals (CLUBB), bias in the ice content of low clouds is dramatically reduced. More generally, this study demonstrates that examining the instantaneous time scale is a powerful approach to understanding the physical processes that control clouds and how they are represented in climate models. Such an evaluation goes beyond the cloud climatology and exposes model bias under various meteorological conditions.

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Cloud type comparisons of AIRS, CloudSat, and CALIPSO cloud height and amount

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-13915-2007 ◽

2007 ◽

Vol 7 (5) ◽

pp. 13915-13958 ◽

Cited By ~ 8

Author(s):

B. H. Kahn ◽

M. T. Chahine ◽

G. L. Stephens ◽

G. G. Mace ◽

R. T. Marchand ◽

...

Keyword(s):

Lower Layer ◽

Cloud Amount ◽

Satellite Observation ◽

Retrieval Algorithm ◽

Cloud Type ◽

Atmospheric Infrared Sounder ◽

Cloud Height ◽

Wide Range ◽

Low Cloud ◽

Height Fields

Abstract. The precision of the two-layer cloud height fields derived from the Atmospheric Infrared Sounder (AIRS) is explored and quantified for a five-day set of observations. Coincident profiles of vertical cloud structure by CloudSat, a 94 GHz profiling radar, and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), are compared to AIRS for a wide range of cloud types. Bias and variability in cloud height differences are shown to have dependence on cloud type, height, and amount, as well as whether CloudSat or CALIPSO is used as the comparison standard. The CloudSat–AIRS biases and variability range from −4.3 to 0.5±1.2–3.6 km for all cloud types. Likewise, the CALIPSO–AIRS biases range from 0.6–3.0±1.2–3.6 km (−5.8 to −0.2±0.5–2.7 km) for clouds ≥7 km (<7 km). The upper layer of AIRS has the greatest sensitivity to Altocumulus, Altostratus, Cirrus, Cumulonimbus, and Nimbostratus, whereas the lower layer has the greatest sensitivity to Cumulus and Stratocumulus. Although the bias and variability generally decrease with increasing cloud amount, the ability of AIRS to constrain cloud occurrence, height, and amount is demonstrated across all cloud types for many geophysical conditions. In particular, skill is demonstrated for thin Cirrus, as well as some Cumulus and Stratocumulus, cloud types infrared sounders typically struggle to quantify. Furthermore, some improvements in the AIRS Version 5 operational retrieval algorithm are demonstrated. However, limitations in AIRS cloud retrievals are also revealed, including the existence of spurious Cirrus near the tropopause and low cloud layers within Cumulonimbus and Nimbostratus clouds. Likely causes of spurious clouds are identified and the potential for further improvement is discussed.

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Diurnal Cycles of Cumulus, Cumulonimbus, Stratus, Stratocumulus, and Fog from Surface Observations over Land and Ocean

Journal of Climate ◽

10.1175/jcli-d-13-00352.1 ◽

2014 ◽

Vol 27 (6) ◽

pp. 2386-2404 ◽

Cited By ~ 37

Author(s):

Ryan Eastman ◽

Stephen G. Warren

Keyword(s):

Diurnal Cycle ◽

Cloud Cover ◽

Cloud Amount ◽

Early Morning ◽

Local Climate ◽

Diurnal Cycles ◽

Low Cloud ◽

Weather Stations ◽

Low Cloud Cover ◽

Surface Observations

Abstract A worldwide climatology of the diurnal cycles of low clouds is obtained from surface observations made eight or four times daily at 3- or 6-h intervals from weather stations and ships. Harmonic fits to the daily cycle are made for 5388 weather stations with long periods of record, and for gridded data on a 5° × 5° or 10° × 10° latitude–longitude grid over land and ocean areas separately. For all cloud types, the diurnal cycle has larger amplitude over land than over ocean, on average by a factor of 2. Diurnal cycles of cloud amount appear to be proprietary to each low cloud type, showing the same cycle regardless of whether that type dominates the diurnal cycle of cloud cover. Stratiform cloud amounts tend to peak near sunrise, while cumuliform amounts peak in the afternoon; however, cumulonimbus amounts peak in the early morning over the ocean. Small latitudinal and seasonal variation is apparent in the phase and amplitude of the diurnal cycles of each type. Land areas show more seasonality compared to ocean areas with respect to which type dominates the diurnal cycle. Multidecadal trends in low cloud cover are small and agree between day and night regardless of the local climate. Diurnal cycles of base height are much larger over land than over the ocean. For most cloud types, the bases are highest in the midafternoon or early evening.

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