Cloud Vertical Structure Research Articles

Lagrangian formation pathways of moist anomalies in the trade-wind region during the dry season: two case studies from EUREC<sup>4</sup>A

Abstract. Shallow clouds in the trade-wind region over the North Atlantic contribute substantially to the global radiative budget. In the vicinity of the Caribbean island of Barbados, they appear in different mesoscale organization patterns with distinct net cloud radiative effects (CREs). Cloud formation processes in this region are typically controlled by the prevailing large-scale subsidence. However, occasionally weather systems from remote origin cause significant disturbances. This study investigates the complex cloud–circulation interactions during the field campaign EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) from 16 January to 20 February 2020, using a combination of Eulerian and Lagrangian diagnostics. Based on observations and ERA5 reanalyses, we identify the relevant processes and characterize the formation pathways of two moist anomalies above the Barbados Cloud Observatory (BCO), one in the lower troposphere (∼ 1000–650 hPa) and one in the middle troposphere (∼ 650–300 hPa). These moist anomalies are associated with strongly negative CRE values and with contrasting long-range transport processes from the extratropics and the tropics, respectively. The first case study about the low-level moist anomaly is characterized by an unusually thick cloud layer, high precipitation totals, and a strongly negative CRE. The formation of the low-level moist anomaly is connected to an extratropical dry intrusion (EDI) that interacts with a trailing cold front. A quasi-climatological (2010-2020) analysis reveals that EDIs lead to different conditions at the BCO depending on how they interact with the associated trailing cold front. Based on this climatology, we discuss the relevance of the strong large-scale forcing by EDIs for the low-cloud patterns near the BCO and the related CRE. The second case study about the mid-tropospheric moist anomaly is associated with an extended and persistent mixed-phase shelf cloud and the lowest daily CRE value observed during the campaign. The formation of the mid-level moist anomaly is linked to “tropical mid-level detrainment” (TMD), which refers to detrainment from tropical deep convection near the melting layer. The quasi-climatological analysis shows that TMDs consistently lead to mid-tropospheric moist anomalies over the BCO and that the detrainment height controls the magnitude of the anomaly. However, no systematic relationship was found between the amplitude of this mid-tropospheric moist anomaly and the CRE at the BCO. This is most likely due to the modulation of the CRE by above and below lying clouds and the fact that we used daily mean CREs, thereby ignoring the impact of the timing of the synoptic anomaly with respect to the daily cycle. Overall, this study reveals the important impact of the long-range moisture transport, driven by dynamical processes either in the extratropics or the tropics, on the variability of the vertical structure of moisture and clouds, and on the resulting CRE in the North Atlantic winter trades.

Characteristics of clouds, precipitation, and latent heat in midlatitude frontal system mixed with dust storm from GPM satellite observations and WRF simulations

A heavy dust storm originating in Mongolia and Inner Mongolia traveled to Northeast China and met a midlatitude frontal system on May 3, 2017. The potential ice nuclei (IN) effects of mineral dust aerosols on the vertical structure of clouds, precipitation, and latent heat (LH) were studied using Global Precipitation Mission (GPM) satellite observations and Weather Research and Forecasting (WRF) model simulations. The WRF simulations correctly captured the main features of the system, and the surface rain rate distribution was positively correlated with data retrieved from the GPM Microwave Imager. Moreover, the correlation coefficient increased from 0.31 to 0.54 with increasing moving average window size. The WRF-simulated rainfall vertical profiles are generally comparable to the GPM Dual-Frequency Precipitation Radar (DPR) observations, particularly in low layers. The joint probability distribution functions of the rain rate at different altitudes from the WRF simulation and GPM observations show high positive correlation coefficients of ~0.80, indicating that the assumptions regarding the raindrop size distribution in the WRF model and DPR retrieval were consistent. Atmospheric circulation analysis and aerosol optical depth observations from the Himawari-8 satellite indicated that the dust storm entered only a narrow strip of the northwest edge of the frontal precipitation system. The WRF simulations showed that in carefully selected areas of heavy dust, dust can enhance the heterogeneous ice nucleation process and increase the cloud ice, snowfall, high-altitude precipitation rate, and LH rate in the upper layers. This effect is significant at temperatures of −15 °C to −38 °C and requires dust number concentrations exceeding 10<sup>6</sup> m<sup>−</sup><sup>3</sup>. It is important to accurately classify the dusty region in this type of case study. In the selected vertical cross section, the WRF-simulated and DPR-retrieved LH have comparable vertical shapes and amplitudes. Both results reflect the structure of the tilted frontal surface, with positive LH above it and negative LH below it. The simulated area-averaged LH profiles show positive heating in the entire column, which is a convective-dominated region, and this feature is not significantly affected by dust. DPR-based LH profiles show stratiform-dominated or convective-dominated shapes, depending on the DPR retrieval product.

Detecting Multilayer Clouds From the Geostationary Advanced Himawari Imager Using Machine Learning Techniques

This study develops a machine learning (ML)-based multilayer cloud detection algorithm for the passive Advanced Himawari Imager (AHI) aboard the geostationary Himawari-8 satellite. AHI measurements in the 0.64-, 1.6-, 2.3-, 3.9-, 7.3-, 8.6-, 11.2-, and 12.4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> channels, their combinations, geolocations, and observational geometries are used as predictors, and collocated active CloudSat and CALIPSO data are used to accurately label multilayer cloud pixels as the reference/truth of the predictand. We develop an ML-based daytime model (ML-Day) that utilizes all the aforementioned predictors and an all-time one (ML-All) that excludes the solar channel-dependent variables. Among four ML algorithms, the random forest (RF) performs slightly better than the artificial neural network, K-nearest neighbor, and support vector machines. By comparing with the merged CloudSat and CALIPSO product, the ML-Day model correctly identifies ~89% single-layer clouds and ~70% multilayer clouds, outperforming the Moderate Resolution Imaging Spectroradiometer (MODIS) operational multilayer cloud product (~80% and ~40% given by Marchant <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> ). The success rates of ML-All for single-layer and multilayer clouds also reach ~85% and ~64%, respectively. The misclassification of our algorithm is mostly caused by missing optically thin clouds, a drawback of most radiometers without the 1.38- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> channel. Furthermore, with multilayer cloud pixels well detected by our algorithm, the AHI operational cloud top height retrievals are found to be larger biased due to multilayer cloud occurrence and might be improved by considering cloud vertical structures.

A decadal climatology of cloud vertical structure over the Indo-Gangetic Plain using radiosonde and radar observations

The cloud vertical structure (CVS) over any place significantly impacts the boundary layer dynamics and horizontal/vertical temperature gradient at local scale, whereas on the synoptic scale it plays a crucial role in determining the atmospheric circulation and hydrological cycle. There is a notable lack of long-term comprehensive studies on CVS over Indian subcontinent. Here, we have done a comprehensive study of CVS over the Indo-Gangetic plain (IGP), in which we have studied the statistics of CVS over various urban agglomerations (UAs) lying within the IGP (using radiosonde data) coupled with CVS of the entire IGP (EIGP) which majorly includes rural and suburban areas (using CloudSat profiling radar data) from 2006 to 2017. Seasonal analysis shows that CVS is much different in monsoon season as compared to other seasons over both EIGP and UAs. The frequency of single layer clouds is ~91%, 87%, 76% and 91% over EIGP and ~ 81%, 80%, 58% and 82% over UAs in winter, pre-monsoon, monsoon and post-monsoon seasons, respectively. In the monsoon season, both data show significant increase in multi-layer clouds frequency, however, the frequency of multi-layer clouds is significantly higher over UAs (>40%) compared to that over EIGP (<26%). The average depth of single-layer clouds over EIGP (2.3–5 km) is higher than that over UAs (1.8–2.7 km). The average cloud top height of single layer clouds is slightly lower over UAs (6.4–7.8 km) as compared to EIGP (7.3–11.2 km), except in pre-monsoon. We infer that though the aerosol induced warming inhibits the convective cloud formation over UAs; aerosols tend to invigorate the convective clouds whenever sufficient moisture is present for cloud formation. The analysis of present study would be helpful in many applications related to radiation budget and climate studies.

The Contribution of Drifting Snow to Cloud Properties and the Atmospheric Radiative Budget Over Antarctica

AbstractThe Antarctic Ice Sheet experiences perpetual katabatic winds, transporting snow, and moisture from the interior towards the periphery. However, the impacts of Antarctic moisture and drifting snow on cloud structure and surface energy fluxes have not been widely investigated. Here, we use a regional climate model with a newly developed drifting snow scheme to show that accounting for drifting snow notably alters the spatial distribution, vertical structure and radiative effect of clouds over Antarctica. Overall, we find that accounting for drifting snow leads to a greater cloud cover providing an increase of +2.74 Wm−2 in the surface radiative energy budget. Additionally, a comparison with 20 weather stations reveals a 2.17 Wm−2 improvement in representing the radiative energy fluxes. Our results highlight the need to study the impact of drifting snow processes on the future evolution of clouds, the surface energy budget and the vertical atmospheric structure over Antarctica.

Vertical Structure of Ice Clouds and Vertical Air Motion from Vertically Pointing Cloud Radar Measurements

The vertical structure of ice clouds and vertical air motion (Vair) were investigated using vertically pointing Ka-band cloud radar. The distributions of reflectivity (Z), Doppler velocity (VD), and spectrum width (SW) were analyzed for three ice cloud types, namely, cirrus, anvil, and stratiform clouds. The radar parameters of the cirrus clouds showed narrower distributions than those of the stratiform and anvil clouds. In the vertical structures, the rapid growth of Z and VD occurred in the layer between 8 and 12 km (roughly a layer of −40 °C to −20 °C) for all ice clouds. The prominent feature in the stratiform clouds was an elongated “S” shape in the VD near 7–7.5 km (at approximately −16 °C to −13 °C) due to a significant decrease in an absolute value of VD. The mean terminal fall velocity (Vt) and Vair in the ice clouds were estimated using pre-determined Vt–Z relationships (Vt = aZb) and the observed VD. Although the cirrus clouds demonstrated wide distributions in coefficients a and exponents b depending on cloud heights, they showed a smaller change in Z and Vt values compared to that of the other cloud types. The anvil clouds had a larger exponent than that of the stratiform clouds, indicating that the ice particle density of anvil clouds increases at a faster rate compared with the density of stratiform clouds for the same Z increment. The significant positive Vair appeared at the top of all ice clouds in range up to 0.5 m s−1, and the anvil clouds showed the deepest layer of upward motion. The stratiform and anvil clouds showed a dramatic increase in vertical air motion in the layer of 6–8 km as shown by the rapid decrease of VD. This likely caused increase of supersaturation above. A periodic positive Vair linked with a significant reduction in VD appeared at the height of 7–8 km (approximately −15 °C) dominantly in the stratiform clouds. This layer exhibited a bi-modal power spectrum produced by pre-existing larger ice particles and newly formed numerous smaller ice particles. This result raised a question on the origins of smaller ice particles such as new nucleation due to increased supersaturation by upward motion below or the seeder-feeder effect. In addition, the retrieved Vair with high-resolution data well represented a Kelvin-Helmholtz wave development.

Revealing the Vertical Cloud Structure of a Young Low-mass Brown Dwarf, an Analog to the β-Pictoris b Directly Imaged Exoplanet, through Keck I/MOSFIRE Spectrophotometric Variability

Abstract Young brown dwarfs are analogs to giant exoplanets, as they share effective temperatures, near-infrared colors, and surface gravities. Thus, the detailed characterization of young brown dwarfs might shed light on the study of giant exoplanets that we are currently unable to observe with a sufficient signal-to-noise to allow a precise characterization of their atmospheres. 2MASS J22081363+2921215 is a young L3 brown dwarf, and a member of the β-Pictoris young moving group (23 ± 3 Myr), which shares its effective temperature and mass with the β Pictoris b giant exoplanet. We performed a ∼2.5 hr spectrophotometric J-band monitoring of 2MASS J22081363+2921215 with the MOSFIRE multi-object spectrograph, installed at the Keck I telescope. We measured a minimum variability amplitude of 3.22 ± 0.42% for its J-band light curve. The ratio between the maximum and the minimum flux spectra of 2MASS J22081363+2921215 shows a weak wavelength dependence, and a potentially enhanced variability amplitude in its alkali lines. Further analysis suggests that the variability amplitudes of the alkali lines are higher than its overall variability amplitude (4.5%–11%, depending on the lines). The variability amplitudes of these lines are lower if we degrade the resolution of the original MOSFIRE spectra to R ∼ 100, which explains why this potentially enhanced variability of the alkali lines had not been found previously in Hubble Space Telescope (HST)/WFC3 light curves. Using radiative-transfer models, we obtained the different cloud layers that might be introducing the spectrophotometric variability we observe for 2MASS J22081363+2921215, which further supports the measured enhanced variability amplitudes of the alkali lines. We provide an artistic recreation of the vertical cloud structure of this β-Pictoris b analog.

Mixing time scales of dustiness and some associated effects at middle atmosphere during the 2018 global dust storm

• A vertical mixing timescale of dust is observed during the 2018 global storm. • The timescale is based on the appearance of middle atmospheric dust maximum. • The timescale is similar to that previously observed in a regional dust storm. • The timescale influences middle atmospheric warming and column water ice. • The storm affects the diurnal tides and the vertical structure of clouds. This study analyzes some characteristic features associated with the Mars year 34 (2018) global dust storm (GD18) using the retrievals of Mars Climate Sounder (MCS) and Mars Color Imager (MARCI) onboard Mars Reconnaissance Orbiter (MRO). According to the MRO MARCI's weather report and Mars daily global maps, the GD18 resulted from a large precursor dust storm in the broader Acidalia region at L S ~ 186° and developed into a global scale storm at L S ~ 194°. Dust lifting is reported to continue until L S ~ 207° in MARCI images, and the MCS-derived column dust opacity peaks around L S 208°. However, the middle atmospheric dust loading only peaks around L S 211°, i.e., 3–4° L S after the surface dust lifting maximum. High-altitude dust maximum is evident after L S ~ 190°, a few degrees of L S after the large precursor Acidalia dust storm. These delays probably indicate a vertical mixing timescale similar to that for a regional scale storm, indicating a common mechanism irrespective of the spatial scale of a dust storm. During GD18, the diurnal tide is strongly amplified at high altitudes, away from the tropics (especially over SH), and the vertical extent of clouds is significantly reduced. These changes are consistent with the time scale of the evolving vertical distribution of dust observed by MCS.

Contrasting Responses of Idealised and Realistic Simulations of Shallow Cumuli to Aerosol Perturbations

AbstractShallow clouds remain greatly significant in improving our understanding of the atmosphere. Using the Met Office Unified Model, we compare highly idealised simulations of shallow cumuli with those using more realistic domains, with open lateral boundaries and varying large‐scale forcing. We find that the realistic simulations are more capable of representing the cloud field on large spatial scales, and appear to limit the aerosol perturbations leading to impacts on the thermodynamic conditions. Aerosol perturbations lead to changes in the cloud vertical structure, and thermodynamic evolution of the idealised simulations; a central feature of behavior seen previously in idealised simulations. Modelling approaches with open boundaries and time‐varying forcing may allow for improved representation of shallow clouds in the atmosphere, and greater understanding of how they may respond to perturbations.

Vertical structure of cloud radiative heating in the tropics: confronting the EC-Earth v3.3.1/3P model with satellite observations

Abstract. Understanding the coupling of clouds to large-scale circulation is one of the grand challenges for the global climate research community. In this context, realistically modelling the vertical structure of cloud radiative heating (CRH) and/or cooling in Earth system models is a key premise to understand this coupling. Here, we evaluate CRH in two versions of the European Community Earth System Model (EC-Earth) using retrievals derived from the combined radar and lidar data from the CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellites. One model version is also used with two different horizontal resolutions. Our study evaluates large-scale intraseasonal variability in the vertical structure of CRH and cloud properties and investigates the changes in CRH during different phases of the El Niño–Southern Oscillation (ENSO), a process that dominates the interannual climate variability in the tropics. EC-Earth generally captures both the intraseasonal and meridional pattern of variability in CRH over the convectively active and stratocumulus regions and the CRH during the positive and negative phases of ENSO. However, two key differences between model simulations and satellite retrievals emerge. First, the magnitude of CRH, in the upper troposphere, over the convectively active zones is up to twice as large in the models compared to the satellite data. Further dissection of net CRH into its shortwave and longwave components reveals noticeable differences in their vertical structure. The shortwave component of the radiative heating is overestimated by all model versions in the lowermost troposphere and underestimated in the middle troposphere. These over- and underestimates of shortwave heating are partly compensated by an overestimate of longwave cooling in the lowermost troposphere and heating in the middle troposphere. The biases in CRH can be traced back to disagreement in cloud amount and cloud water content. There is no noticeable improvement of CRH by increasing the horizontal resolution in the model alone. Our findings highlight the importance of evaluating models with satellite observations that resolve the vertical structure of clouds and cloud properties.

Cloud vertical structure measurements from a ground-based cloud radar over the southeastern Tibetan Plateau

The southeastern Tibetan Plateau (TP) is the critical region of water vapor transport over the TP. Ground-based Ka-band cloud radar (KaCR) measurements collected at the Motuo National Climate Observatory in 2019 were used to analyze the physical properties of clouds at the front of the water vapor channel over the TP. The cloud top heights (CTHs) measured by the KaCR were verified through a comparison with observations from the Fengyun-4A (FY-4A) satellite at the same location. The KaCR-obtained CTHs were generally consistent with the FY-4A-obtained CTHs, although the KaCR slightly overestimated the CTHs of nonprecipitation clouds and underestimated the CTHs of precipitation clouds. Negative deviations between the KaCR- and FY-4A-obtained CTHs increased with rainfall rate. Cloud cover frequently occurred over Motuo, with an annual mean occurrence frequency of 65.3%. Clouds tended to form frequently at night and dissipate gradually in the daytime. Two peaks in the cloud base height (CBH) distribution were observed in Motuo, located at 0–1 km and 2–3 km, corresponding to precipitation and nonprecipitation clouds, respectively. The CTHs reached a peak at 6–7 km, which might be related to precipitation clouds. Moreover, a maximum CTH probability was observed in the midnight-early morning hours during the rainy season, while the CTH frequency peaked in the evening during the dry season. In addition, low and middle clouds were prevalent in Motuo for the period of observation in 2019. Understanding the characteristics of clouds over the TP will provide key validations of satellite measurements and promote research on cloud forces over the TP.

Relationship between cloud vertical structures inferred from radiosonde humidity profiles and precipitation over Indonesia

Knowledge of cloud vertical structure, including the presence of multiple cloud layers, is important for several climate-related applications such as for understanding the impact of clouds on Earth’s radiation budget. Moreover, the vertical distribution of latent heat release that affects global circulation and precipitation. The characteristics of cloud vertical structure may change as a consequence of climate change. However, study on cloud vertical structure in Indonesia is limited to case study based on short period observation. This study aims to analyse the vertical structure of clouds, such as cloud base height (CBH), the height of the cloud top (CT) and the number of cloud layers due to climate change in Indonesia, based on ∼ 30 years radiosonde observation. The relation between cloud vertical structures and precipitation was investigated. We used the radiosonde data from nine observation stations in Indonesia. On an average, it is observed that over Indonesia one-layer clouds is most frequently observed cloud, more than 60% of the time. This number is much larger than the fraction of single layer clouds over the globe which is about 58 % of the time. The cloud vertical structures in Indonesia vary from month to month. The cloud vertical structure during wet and dry season is different which indicate a strong relationship between cloud vertical structure and precipitation.

Sensing Horizontally Oriented Frozen Particles With Polarimetric Radio Occultations Aboard PAZ: Validation Using GMI Coincident Observations and Cloudsat a Priori Information

The sensitivity of PAZ’s Polarimetric Radio Occultation (PRO) observations to horizontally oriented frozen particles is assessed using coincident measurements from the Global Precipitation Measurement (GPM) core satellite’s radiometer GPM Microwave Imager (GMI) and ancillary information from Cloudsat. The difference between the horizontal and vertical polarizations of the GMI observed radiances at 166 GHz, indicative of horizontally oriented particles, is compared with the PAZ differential phase shift observations. A clear positive trend is observed, exhibiting a good correlation between the two observations. The radiometer absolute observations and polarization differences (PD) are then used to build a lookup table of ice water content (IWC) vertical profiles, using coincident observations between GPM and Cloudsat. The vertical profiles of IWC, along with the information of the radiometric PDs and some simple assumptions, are used to simulate the expected PAZ differential phase shift observations. The validation with the PAZ and GPM coincident measurements shows a high correlation between the simulated and observed differential phase shift, therefore proving the sensitivity of polarimetric radio occultations to horizontally oriented frozen particles. These results demonstrate that PRO can not only sense the precipitation near the surface (the original goal of the mission) but also the frozen particles near and well above the freezing level, providing additional detail of the cloud vertical structure.

Long-Term Change in Characteristics of Cloud Vertical Structures Over Sumatra from Radiosonde Observations

Study on the vertical structure of cloud in Indonesia in terms of climate change is still very limited. We investigated the long-term change in characteristics of cloud vertical structures over Sumatra from three radiosonde observation stations in this work. The cloud base height (CBH), cloud top height (CT), and the number of cloud layers were retrieved using relative humidity (RH) profiles from radiosonde observation. The height of the cloud base is determined by taking the height of the layer with relative humidity (RH) value &gt; 84% with at least a 3% jump in the RH from the ground level. Sumatra’s most frequently observed cloud layer is a one-layer cloud with an average occurrence rate of &gt; 60%, which is slightly larger than the one-layer cloud globally. The percentage of appearance values at the Padang station, Pangkal Pinang, and Medan are 63.58%, 69.50% and 66.05%. The appearance of low-level clouds also dominates in Sumatra compared to other cloud types. CT and CBH increase with the number of years including all seasons. This is in line with the increase in temperature in Indonesia reported by previous researchers. On the other hand, the clouds’ thickness, especially for the cloud with one layer, varies from one location to another. The thickness of clouds decreases at Padang station and does not change at Pangkal Pinang and Medan stations.

Vertical structures of temperature inversions and clouds derived from high-resolution radiosonde measurements at Ny-Ålesund, Svalbard

The knowledge of the vertical atmospheric structures in the Arctic Region remains elusive, due largely to sparse long-term continuous profiling observations. Based on the temporally high-resolution (1 s) radiosonde measurements from April 2017 to September 2019 collected at the Ny-Ålesund (11.92°E, 78.92°N) station in the Arctic, we analyzed the characteristics of temperature inversion (TI) and clouds, including the diurnal and seasonal variabilities under different atmospheric circulations. Clouds mainly appear in the lower troposphere, with the largest contribution by double-layer clouds. The seasonal variation of vertical cloud distribution above 7 km seems is closely linked to the seasonal variability of tropopause height. Besides, the diurnal variation of TI frequency exhibits significant seasonality, with a bimodal distribution in the vertical, with stronger TI intensity in summer. The lowest temperatures at the top of bottom of the elevated inversion are observed in winter, whereas the lowest temperature of the surface-based inversion top is observed in spring, which may be related to the seasonal variation of sea surface temperature. The characteristics of cloud and TI are further analyzed under the five typical circulation patterns. It is found that the low-pressure system and southerly wind in front of the trough are favorable for cloud formation in the lower troposphere, while the impact of synoptic pattern on clouds in the upper troposphere seems negligible, likely due to the cold environment. The TI associated with cyclone systems tends to be much thinner and weaker, owning to the conditionally unstable conditions. These findings provide key reference for the vertical structure of the inversion and cloud in the Arctic, which is expected to help improve cloud parameterization in numeric model.

Comparison of Cloud Vertical Structure Retrieved from Radiosonde and Millimeter Wave Cloud Radar

Owing to the synchronizing continuous observation of Ka-band millimeter-wave cloud radar (MMCR), L-band radiosonde, ceilometer, Himawari-8 satellite, and Total Sky Imager (TSI) from 13 December 2016 to 13 March 2017, at Beijing Nanjiao Weather Observatory (BNWO), the cloud vertical structure (CVS, including cloud bottom height, cloud top height, cloud layers, etc.) derived from radiosonde and MMCR is compared, and the causes of observation deviation are analyzed. The results show that cloud top heights observed by MMCR are lower by 422.0 m on average, while cloud base heights are higher by 350.7 m. Generally, there is a good consistency between them. The difference of physical theory, balloon drifting, attenuation of MMCR during precipitation, and the limitations of algorithm for retrieving CVS, among others, are found to be the main causes of the deviation.

Cloud radar observations of multi-scale variability of cloud vertical structure associated with Indian summer monsoon over a tropical location

Tropics nurture three different types of convective clouds, i.e., shallow cumulus, cumulus congestus, and deep cumulonimbus. The vertical structure of clouds holds a crucial metric in studying tropical clouds. Ground-based high-resolution cloud radar measurements are the potential candidate in exploring the characteristics of various types of tropical clouds and their evolution. Quality-controlled cloud radar data containing a total of five million vertical profiles of equivalent reflectivity factor (VPR) are used to examine the intra-seasonal variation of cloud vertical structure (VSC) during the Indian summer monsoon (ISM) over Mandhardev (18.04° N, 73.87° E, and ~ 1.3 km AMSL) in the Indian Western Ghats. The cumulus congestus (Cc) in the transition of shallow to deep clouds is investigated for the first time using the hourly VPR data for 60 consecutive ISM days. Mid-level moistening plays a vital role in this non-precipitating shallow to precipitating congestus transformation and increment of the rain accumulation. Low cloud reflectivity distribution can distinguish precipitating and non-precipitating clouds that help to classify the observed monsoon as normal or below normal. More than 150 mm of rain accumulation during ISM is associated with more than 22% of high clouds. This particular aspect indicates that cold rain processes are essential to assess the ISM over the observational site. FFT analysis on the time series of low-, mid-, and high-level cloud regions with the VPR shows prominent intra-seasonal variability of 5–10, 10–20, and 30–60 days periodicities. This study highlights the significance of VSC over tropics pertinent to the monsoon large scale atmospheric condition.

Clouds and Radiation Processes in Regional Climate Models Evaluated Using Observations Over the Ice‐free Arctic Ocean

AbstractThe presence of clouds in the Arctic regulates the surface energy budget (SEB) over the sea‐ice surface and the ice‐free ocean. Following several previous field campaigns, the cloud‐radiation relationship, including cloud vertical structure and phase, has been elucidated; however, modeling of this relationship has matured slowly. In recognition of the recent decline in the Arctic sea‐ice extent, representation of the cloud system in numerical models should consider the effects of areas covered by sea ice and ice‐free areas. Using an in situ stationary meteorological observation data set obtained over the ice‐free Arctic Ocean by the Japanese Research Vessel Mirai (September 2014), coordinated evaluation of six regional climate models (RCMs) with nine model runs was performed by focusing on clouds and the SEB. The most remarkable findings were as follows: (1) reduced occurrence of unstable stratification with low‐level cloud water in all models in comparison to the observations, (2) significant differences in cloud water representations between single‐ and double‐moment cloud schemes, (3) extensive differences in partitioning of hydrometeors including solid/liquid precipitation, and (4) pronounced lower‐tropospheric air temperature biases. These issues are considered as the main sources of SEB uncertainty over ice‐free areas of the Arctic Ocean. The results from a coupled RCM imply that the SEB is constrained by both the atmosphere and the ocean (and sea ice) with considerable feedback. Coordinated improvement of both stand‐alone atmospheric and coupled RCMs would promote a more comprehensive and improved understanding of the Arctic air‐ice‐sea coupled system.

Pairwise‐rotated EOFs of global cloud cover and their linkages to sea surface temperature

AbstractSea surface temperature (SST) could significantly affect the dynamic and thermodynamic conditions of the atmospheric circulation and consequently the cloud variations. Here we use several different satellite records to extract the spatial‐time modes of total cloud cover (TCC) by employing a pairwise rotation of Empirical Orthogonal Function analysis. The results show that the first two principal oscillation modes of TCC are closely associated with the Central Pacific El Niño Southern Oscillation (CP ENSO) and Eastern Pacific (EP) ENSO during the 1980s–2000s, while the ENSO‐like mode of TCC can provide an evident contribution to the TCC change during the 2000s–2010s. In CP El Niño, the cloud vertical structure decomposed from CloudSat observations shows an increase of cloud occurrence frequency near the equator and around 40°, and a decrease around 10° in both hemispheres, suggesting a symmetric tightening of Hadley cell (HC). In addition, cloud occurrence frequency increases around 180°, which is accompanied by an eastward shift of Walker circulation (WC). In EP El Niño, TCC increases (decreases) over the Equatorial Eastern Pacific (Western Pacific warm pool), and decreases asymmetrically over the subtropical Pacific Ocean, indicating a weakening of WC and an asymmetric tightening of HC, respectively. The different responses of circulation and clouds to CP and EP El Niño highlight the nonlinearity of El Niño SST forcing. We also construct a trend mode of TCC to investigate cloud long‐term responses to SST warming by transferring the linear trends of the rest modes to a specific mode. The principal components (PCs) of TCC trend modes are strongly correlated with global‐mean SST (GSST) with correlation a coefficient of about 0.60 during the 1980s–2000s and 0.45 during the 2000s–2010s, suggesting a continued influence of global SST warming on TCC. The global TCC change is mainly influenced by the combined effects of Atlantic Multi‐decadal Oscillation (AMO), Pacific Decadal Oscillation (PDO) and Indian Ocean Dipole (IOD). The variation about the trend mode of TCC is closely associated with PDO and IOD.

Comparative Analysis of the Cloud Behavior over Inland and Coastal Regions within Single Climate Characteristics

Continuous and accurate ceilometer measurements can provide the sky-condition such as cloud base height (CBH), cloud vertical structure (CVS), and cloud cover at around the sites of meteorological stations. In this study, ceilometer measurement data over a period of 3 years (January 2017 to December 2019) were analyzed to compare the characteristics of CBH at inland and coastal stations sharing the same climate characteristics in Korea. The annual averaged frequency of cloud occurrence between 0 and 7750 m at the first CBH is similar in both inland (41.8 ± 10.2%) and coastal (40.3 ± 9.5%) areas. However, there are differences in monthly and seasonal trends. The maximum cloud occurrence appears in summer (winter) of 64.3% (60.1%) in inland (coastal) areas, while the minimum of 25.6% (21.9%) shows in transient seasons of spring and autumn. In winter, the cold surge of northwest wind tends to increase the cloud occurrence from the ocean at coastal rather than in the inland area. It is shown that monthly cloud occurrence in each station is closely related to its monthly precipitation variation. The CVS frequency calculated from the total number of CBH with 250 m vertical bins shows the maximum between 500 to 1500 m (0 to 1000 m) in inland (coastal) areas, indicating more frequent occurrence at a lower height in the coastal area. It is mainly caused by the seasonal variability of the low-level clouds in the coastal region, which occurs two to three times higher in spring and summer than in other seasons. The study implies that long-term measurements of ceilometer would provide a better understanding of the characteristics of cloud behaviors in inland and coastal areas.