The Characteristics of Multi-layer Clouds in Summer over Tibetan Plateau Based on CloudSat Measurements

2020 ◽  
Author(s):  
xiao pan ◽  
Yunfei Fu ◽  
Deqin Li
Keyword(s):  
Tibetan Plateau ◽  
Vertical Structure ◽  
Deep Convection ◽  
Single Layer ◽  
Occurrence Frequency ◽  
Specific Humidity ◽  
Lower Cloud ◽  
Cloud Water Content ◽  
Liquid Precipitation ◽  
Layer Cloud

<p>The characteristics including cloud occurrence frequencies, vertical structure, configuration of cloud type, and microphysical structure of single-layer and multi-layer clouds in Tibetan Plateau (TP) in summer (June-August) during 2007-2010 are investigated based on the CloudSat merged data. The results indicate that cloud over the TP is mainly in the form of single-layer cloud with occurrence frequency of 56.86%, and then followed by the form of double-layer cloud with 24.47%. The spatial distribution of occurrence frequency shows that the single-layer cloud is mainly located in the northern plateau, and fraction of multi-layer cloud decrease gradually from the southeast to the northwest. Single-layer clouds mainly consist of stratocumulus (22.71%), and then followed by altostratus (19.98%) and nimbostratus (19.42%). As for the multi-layer clouds, the upper layers mainly consist of cirrus and altostratus, and the middle layers are mainly dominated by altostratus, cirrus and altocumulus. The lower layers mainly consist of stratocumulus, altocumulus and cumulus. The vertical structure indicates that the averaged cloud thicknesses of single-layer are larger compared with multi-layer clouds. The distributions of microphysical characteristics of multi-level clouds and single-layer clouds are similar, while the averaged values of microphysical characteristics including particle number concentration, cloud water content and effective radius of single-layer are larger. Moreover, the microphysical variable values of upper cloud are lower compared with lower cloud, which are related to the cloud types. The precipitation is mainly in the form of liquid precipitation, and then followed by the solid precipitation, and the drizzle. Furthermore, the drizzle occurs mainly in the multi-layer clouds. The single-layer fraction in the daytime (62.99%) is larger than that at night (51.00%), whereas, multi-layer clouds are opposite. The fraction of liquid precipitation and deep convection are larger during the daytime than those at night. Conversely, the fractions of drizzle and nimbostratus are larger at night. In addition, higher surface temperature, larger surface specific humidity and higher surface pressure is found to be contributed to the formation of multi-layer clouds.</p>

scholarly journals Cloud vertical structure over a tropical station obtained using long-term high resolution Radiosonde measurements

2018 ◽  
Author(s):  
Nelli Narendra Reddy ◽  
Madineni Venkat Ratnam ◽  
Ghouse Basha ◽  
Varaha Ravikiran
Keyword(s):  
Large Scale ◽  
Vertical Structure ◽  
Lower Layer ◽  
Monsoon Season ◽  
Single Layer ◽  
Cloud Base ◽  
High Level ◽  
Tropical Station ◽  
Layer Cloud

Abstract. Cloud vertical structure, including top and base altitudes, thickness of cloud layers, and the vertical distribution of multi-layer clouds affects the large-scale atmosphere circulation by altering gradients in the total diabatic heating/cooling and latent heat release. In this study, long-term (11 years) observations of high vertical resolution radiosondes are used to obtain the cloud vertical structure over a tropical station, Gadanki (13.5° N, 79.2° E), India. The detected cloud layers are verified with independent observations using cloud particle sensor (CPS) sonde launched from the same station. High-level clouds account for 69.05 %, 58.49 %, 55.5 %, and 58.6 % of all clouds during pre-monsoon, monsoon, post-monsoon, and winter seasons, respectively. The average cloud base (cloud top) altitude for low-level, middle-level, high-level and deep convective clouds are 1.74 km (3.16 km), 3.59 km (5.55 km), 8.79 km (10.49 km), and 1.22 km (11.45 km), respectively. Single-layer, two-layer, and three-layer clouds account for 40.80 %, 30.71 %, and 19.68 % of all cloud configurations, respectively. Multi-layer clouds occurred more frequently during the monsoon with 34.58 %. Maximum cloud top altitude and the cloud thickness occurred during monsoon season for single-layer clouds and the uppermost layer of multiple layer cloud configurations. In multi-layer cloud configurations, diurnal variations in the thickness of upper layer clouds are larger than those of lower layer clouds. Heating/cooling in the troposphere and lower stratosphere due to these clouds layers is also investigated and found peak cooling (peak warming) below (above) the Cold Point Tropopause (CPT) altitude. The magnitude of cooling (warming) increases from single-layer to four or more-layer cloud occurrence. Further, the vertical structure of clouds is also studied with respect to the arrival date of Indian summer monsoon over Gadanki.

scholarly journals Comprehensive Characteristics of Summer Deep Convection over Tibetan Plateau and Its South Slope from the Global Precipitation Measurement Core Observatory

Atmosphere ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 9 ◽  
Author(s):  
Guolu Gao ◽  
Quanliang Chen ◽  
Hongke Cai ◽  
Yang Li ◽  
Zhenglin Wang
Keyword(s):  
Tibetan Plateau ◽  
Diurnal Variation ◽  
Vertical Structure ◽  
Deep Convection ◽  
Low Frequency ◽  
The Tibetan Plateau ◽  
Precipitation Measurement ◽  
South Slope ◽  
Global Precipitation Measurement ◽  
Global Precipitation

Observational data from the Global Precipitation Measurement (GPM) Core Observatory during four summers (2014–2017) has been used to investigate deep convection systems (DCSs) over the Tibetan Plateau (TP) and its south slope (SS). The frequency, geographical distribution diurnal variation, and vertical structure of DCSs over the TP and SS are compared among these two regions. The frequency of DCSs over the SS (0.98%) was far higher than over the TP (0.15%), suggesting that stronger DCSs occur to the east and south of the TP. The maximum number of DCS occurred in July and August. A clear diurnal variation in DCS was found over the whole region, DCSs over the TP and SS both have a greatest amplitude in the afternoon. The probability of DCSs from 1200 to 1800 local time (LT) was 76.3% and 44.1% over TP and SS respectively, whereas the probability of DCSs being generated from 2200 (LT) to 0600 on the next day LT was 0.03% and 33.1% over the TP and SS respectively. There was a very low frequency of DCSs over the TP during the night. Five special echo top heights were used to investigate the vertical structure of DCSs. DCSs over the TP were both weaker and smaller than those over the SS.

scholarly journals Moisture Vertical Structure, Column Water Vapor, and Tropical Deep Convection

2009 ◽  
Vol 66 (6) ◽  
pp. 1665-1683 ◽  
Author(s):  
Christopher E. Holloway ◽  
J. David Neelin
Keyword(s):  
Water Vapor ◽  
Vertical Structure ◽  
Deep Convection ◽  
Strong Association ◽  
Lower Troposphere ◽  
Principal Component ◽  
Environmental Water ◽  
Specific Humidity ◽  
Free Troposphere ◽  
Precipitation Gauge

Abstract The vertical structure of the relationship between water vapor and precipitation is analyzed in 5 yr of radiosonde and precipitation gauge data from the Nauru Atmospheric Radiation Measurement (ARM) site. The first vertical principal component of specific humidity is very highly correlated with column water vapor (CWV) and has a maximum of both total and fractional variance captured in the lower free troposphere (around 800 hPa). Moisture profiles conditionally averaged on precipitation show a strong association between rainfall and moisture variability in the free troposphere and little boundary layer variability. A sharp pickup in precipitation occurs near a critical value of CWV, confirming satellite-based studies. A lag–lead analysis suggests it is unlikely that the increase in water vapor is just a result of the falling precipitation. To investigate mechanisms for the CWV–precipitation relationship, entraining plume buoyancy is examined in sonde data and simplified cases. For several different mixing schemes, higher CWV results in progressively greater plume buoyancies, particularly in the upper troposphere, indicating conditions favorable for deep convection. All other things being equal, higher values of lower-tropospheric humidity, via entrainment, play a major role in this buoyancy increase. A small but significant increase in subcloud layer moisture with increasing CWV also contributes to buoyancy. Entrainment coefficients inversely proportional to distance from the surface, associated with mass flux increase through a deep lower-tropospheric layer, appear promising. These yield a relatively even weighting through the lower troposphere for the contribution of environmental water vapor to midtropospheric buoyancy, explaining the association of CWV and buoyancy available for deep convection.

scholarly journals Cloud vertical structure over a tropical station obtained using long-term high-resolution radiosonde measurements

2018 ◽  
Vol 18 (16) ◽  
pp. 11709-11727 ◽  
Author(s):  
Nelli Narendra Reddy ◽  
Madineni Venkat Ratnam ◽  
Ghouse Basha ◽  
Varaha Ravikiran
Keyword(s):  
Large Scale ◽  
Vertical Structure ◽  
Lower Layer ◽  
Single Layer ◽  
Cloud Base ◽  
Heating And Cooling ◽  
High Level ◽  
Tropical Station ◽  
Layer Cloud

Abstract. Cloud vertical structure, including top and base altitudes, thickness of cloud layers, and the vertical distribution of multilayer clouds, affects large-scale atmosphere circulation by altering gradients in the total diabatic heating and cooling and latent heat release. In this study, long-term (11 years) observations of high-vertical-resolution radiosondes are used to obtain the cloud vertical structure over a tropical station at Gadanki (13.5∘ N, 79.2∘ E), India. The detected cloud layers are verified with independent observations using cloud particle sensor (CPS) sonde launched from the same station. High-level clouds account for 69.05 %, 58.49 %, 55.5 %, and 58.6 % of all clouds during the pre-monsoon, monsoon, post-monsoon, and winter seasons, respectively. The average cloud base (cloud top) altitudes for low-level, middle-level, high-level, and deep convective clouds are 1.74 km (3.16 km), 3.59 km (5.55 km), 8.79 km (10.49 km), and 1.22 km (11.45 km), respectively. Single-layer, two-layer, and three-layer clouds account for 40.80 %, 30.71 %, and 19.68 % of all cloud configurations, respectively. Multilayer clouds occurred more frequently during the monsoon with 34.58 %. Maximum cloud top altitude and cloud thickness occurred during the monsoon season for single-layer clouds and the uppermost layer of multiple-layer cloud configurations. In multilayer cloud configurations, diurnal variations in the thickness of upper-layer clouds are larger than those of lower-layer clouds. Heating and cooling in the troposphere and lower stratosphere due to these cloud layers are also investigated and peak cooling (peak warming) is found below (above) the cold-point tropopause (CPT) altitude. The magnitude of cooling (warming) increases from single-layer to four- or more-layer cloud occurrence. Further, the vertical structure of clouds is also studied with respect to the arrival date of the Indian summer monsoon over Gadanki.

scholarly journals Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

2013 ◽  
Vol 26 (8) ◽  
pp. 2417-2431 ◽  
Author(s):  
Qiongqiong Cai ◽  
Guang J. Zhang ◽  
Tianjun Zhou
Keyword(s):  
Boundary Layer ◽  
Deep Convection ◽  
Lower Troposphere ◽  
Longwave Radiation ◽  
Reanalysis Data ◽  
Specific Humidity ◽  
Moist Static Energy ◽  
Shallow Convection ◽  
Budget Analysis ◽  
Static Energy

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

scholarly journals How frequent is natural cloud seeding from ice cloud layers ( < −35 °C) over Switzerland?

2021 ◽  
Vol 21 (6) ◽  
pp. 5195-5216
Author(s):  
Ulrike Proske ◽  
Verena Bessenbacher ◽  
Zane Dedekind ◽  
Ulrike Lohmann ◽  
David Neubauer
Keyword(s):  
Prediction Models ◽  
Water Cycle ◽  
Weather Prediction ◽  
Ice Crystals ◽  
Occurrence Frequency ◽  
Climate Projections ◽  
Cirrus Cloud ◽  
Cloud Seeding ◽  
Cloud Properties ◽  
Layer Cloud

Abstract. Clouds and cloud feedbacks represent one of the largest uncertainties in climate projections. As the ice phase influences many key cloud properties and their lifetime, its formation needs to be better understood in order to improve climate and weather prediction models. Ice crystals sedimenting out of a cloud do not sublimate immediately but can survive certain distances and eventually fall into a cloud below. This natural cloud seeding can trigger glaciation and has been shown to enhance precipitation formation. However, to date, an estimate of its occurrence frequency is lacking. In this study, we estimate the occurrence frequency of natural cloud seeding over Switzerland from satellite data and sublimation calculations. We use the DARDAR (radar lidar) satellite product between April 2006 and October 2017 to estimate the occurrence frequency of multi-layer cloud situations, where a cirrus cloud at T < −35 ∘C can provide seeds to a lower-lying feeder cloud. These situations are found to occur in 31 % of the observations. Of these, 42 % have a cirrus cloud above another cloud, separated, while in 58 % the cirrus is part of a thicker cloud, with a potential for in-cloud seeding. Vertical distances between the cirrus and the lower-lying cloud are distributed uniformly between 100 m and 10 km. They are found to not vary with topography. Seasonally, winter nights have the most multi-layer cloud occurrences, in 38 % of the measurements. Additionally, in situ and liquid origin cirrus cloud size modes can be identified according to the ice crystal mean effective radius in the DARDAR data. Using sublimation calculations, we show that in a significant number of cases the seeding ice crystals do not sublimate before reaching the lower-lying feeder cloud. Depending on whether bullet rosette, plate-like or spherical crystals were assumed, 10 %, 11 % or 20 % of the crystals, respectively, could provide seeds after sedimenting 2 km. The high occurrence frequency of seeding situations and the survival of the ice crystals indicate that the seeder–feeder process and natural cloud seeding are widespread phenomena over Switzerland. This hints at a large potential for natural cloud seeding to influence cloud properties and thereby the Earth's radiative budget and water cycle, which should be studied globally. Further investigations of the magnitude of the seeding ice crystals' effect on lower-lying clouds are necessary to estimate the contribution of natural cloud seeding to precipitation.

scholarly journals Tropical convection regimes in climate models: evaluation with satellite observations

2017 ◽  
Author(s):  
Andrea K. Steiner ◽  
Bettina C. Lackner ◽  
Mark A. Ringer
Keyword(s):  
Climate Models ◽  
Lower Stratosphere ◽  
Deep Convection ◽  
Atmospheric Temperature ◽  
Tropical Convection ◽  
Specific Humidity ◽  
Moist Convection ◽  
Tropopause Region ◽  
Tropical Troposphere ◽  
Unique Source

Abstract. High quality observations are powerful tools for the evaluation of climate models towards improvement and reduction of uncertainty. Particularly at low latitudes, the most uncertain aspect lies in the representation of moist convection and interaction with dynamics, where rising motion is tied to deep convection and sinking motion to dry regimes. Since humidity is closely coupled with temperature feedbacks in the tropical troposphere a proper representation of this region is essential. Here we demonstrate the evaluation of atmospheric climate models with satellite-based observations from Global Positioning System (GPS) radio occultation (RO), which feature high vertical resolution and accuracy in the troposphere to lower stratosphere. We focus on the representation of the vertical atmospheric structure in tropical convection regimes, defined by high updraft velocity over warm surfaces, and investigate atmospheric temperature and humidity profiles. Results reveal that some models do not fully capture convection regions, particularly over land, and only partly represent high updraft or downdraft velocities. Models show large biases in tropical mean temperature of more than 4 K in the tropopause region and the lower stratosphere. Reasonable agreement with observations is given in mean specific humidity in the lower to mid-troposphere. In moist convection regions, models tend to underestimate moisture by 10 % to 30 % over oceans whereas in dry downdraft regions they overestimate moisture by 100 %. Our findings provide evidence that RO observations are a unique source of information, with a range of further atmospheric variables to be exploited, for the evaluation and advancement of next generation climate models.

scholarly journals Observational Evidence of the Transition from Shallow to Deep Convection in the Western Caribbean Trade Winds

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 700 ◽  
Author(s):  
Yanet Díaz-Esteban ◽  
Graciela B. Raga
Keyword(s):  
Deep Convection ◽  
Meridional Wind ◽  
Specific Humidity ◽  
Wind Component ◽  
Regime Transition ◽  
Shallow Convection ◽  
Trade Winds ◽  
Convection Regime ◽  
Shallow Cumulus ◽  
Short Period

The present study aims to determine the factors influencing the transition from shallow to deep convection in the trade winds region using an observational approach, with emphasis in the Yucatan Peninsula in eastern Mexico. The methodology is based on a discrimination of two regimes of convection: a shallow cumulus regime, usually with little or no precipitation associated, and an afternoon deep convection regime, with large amounts of precipitation, preceded by a short period of shallow convection. Then, composites of meteorological fields at surface and several vertical levels, for each of the two convection regimes, are compared to infer which meteorological factors are involved in the development of deep convection in this region. Also, the relationship between meteorological variables and selected regime-transition parameters is evaluated only for deep convection regime days. Results indicate the importance of dynamic factors, such as the meridional wind component, in the transition from shallow to deep convection. As expected, thermodynamic variables, such as the low-level specific humidity in the shallow cumulus layer, also contribute to the regime transition. The presence of a southerly component of wind at low- to mid-levels during the early morning in deep convection days provides the shallow cumulus with a more favorable environment so that transition can occur, since abundant moisture from the Caribbean is supplied through this prevailing southern wind. The results can be relevant for reducing uncertainties regarding some important parameters in global and regional models, which could lead to improved simulations of the transition from shallow to deep convection and precipitation.

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