Cloud regimes and associated MJO variability over the Maritime Continent in austral summer

2020 ◽  
Author(s):  
Zijie Zhao ◽  
Claire Vincent ◽  
Todd Lane
Keyword(s):  
Rainfall Variability ◽  
Austral Summer ◽  
Maritime Continent ◽  
Convective Clouds ◽  
Scale Modelling ◽  
A New Technique ◽  
Climate Scale ◽  
High Level ◽  
Cloud Patterns ◽  
Cloud Regimes

<p>In this study, a new technique to determine distinct cloud regimes and their variation in space and time is proposed, evaluated, and applied to two satellite products over the Maritime Continent (MC). Compared to previous methods, the method presented here allows different types of cloud to co-exist in the same grid at the same time, giving rise to physically explainable and spatially continuous patterns in cloud regimes. Similar results generated by ISCCP – H and Himawari 8 data suggests that the method is robust. The 4 cloud regimes determined using this method are associated with shallow, mid-level, deep convective and high level clouds respectively. The analysis shows that he MJO–induced variation in total cloud fraction is dominated by day-time high–level clouds, while the diurnal MJO variability is mostly demonstrated by low–level cumulus. Spatial and temporal rainfall variability over the MC during austral summer is dominated by high–level clouds, while most local signatures and land–sea differences are attributed to deep convective clouds. Using an artificial neural network, the cloud patterns over the MC can be classified into nine categories, largely dominated by the MJO-phase. Active MJO activity is shown by systematic propagation around the cloud categories, with one category associated with the inactive MJO phase. The inhomogenous propagation of the MJO can partially be revealed in the generated patterns, which can be physically explained by the enhanced/suppressed convection over the Indian Ocean. This work has implications for understanding the MJO-scale variation in precipitation and diabatic heating associated with different cloud regimes, and its representation in mesoscale and climate scale modelling systems.</p>

Rain and Cloud Perspectives on the Seasonal Cycle over the Western Equatorial Indian Ocean

2020 ◽  
Vol 33 (3) ◽  
pp. 925-940
Author(s):  
Malcolm J. King ◽  
Christian Jakob
Keyword(s):  
Indian Ocean ◽  
Seasonal Cycle ◽  
Large Scale ◽  
Climate Models ◽  
Austral Summer ◽  
Equatorial Indian Ocean ◽  
Boreal Summer ◽  
Annual Peak ◽  
High Level ◽  
Cloud Regimes

AbstractConvection over the western equatorial Indian Ocean (WEIO) is strongly linked to precipitation over Africa and Australia but is poorly represented in current climate models, and its observed seasonal cycle is poorly understood. This study investigates the seasonal cycle of convection in the WEIO through rainfall and cloud measurements. Rainfall shows a single annual peak in early austral summer, but cloud proxies identify convective activity maxima in both boreal and austral summer. These diverging measures of convection during boreal summer are indicative of a reduction in the intensity of precipitation associated with a given cloud regime or cloud-top height during this time of year but an increase in the overall occurrence of high-top clouds and convectively active cloud regimes. The change in precipitation intensity associated with regimes is found to explain most of the changes in total precipitation during the period from May to November, whereas changes in the occurrence of convective regimes explains most of the changes throughout the rest of the year. The reduction in precipitation intensities associated with cloud regimes over the WEIO during boreal summer appears to be related to large-scale monsoon circulations, which suppress convection through forcing air descent in the midtroposphere and increase the apparent occurrence of convectively active cloud regimes through the advection of high-level cloud from monsoon-active areas toward the WEIO region.

scholarly journals A CloudSat–CALIPSO View of Cloud and Precipitation Properties across Cold Fronts over the Global Oceans

2015 ◽  
Vol 28 (17) ◽  
pp. 6743-6762 ◽  
Author(s):  
Catherine M. Naud ◽  
Derek J. Posselt ◽  
Susan C. van den Heever
Keyword(s):  
Large Scale ◽  
Cold Front ◽  
Conveyor Belt ◽  
Low Level ◽  
Scale Parameters ◽  
Convective Clouds ◽  
Cold Fronts ◽  
Surface Front ◽  
High Level ◽  
The Impact

Abstract The distribution of cloud and precipitation properties across oceanic extratropical cyclone cold fronts is examined using four years of combined CloudSat radar and CALIPSO lidar retrievals. The global annual mean cloud and precipitation distributions show that low-level clouds are ubiquitous in the postfrontal zone while higher-level cloud frequency and precipitation peak in the warm sector along the surface front. Increases in temperature and moisture within the cold front region are associated with larger high-level but lower mid-/low-level cloud frequencies and precipitation decreases in the cold sector. This behavior seems to be related to a shift from stratiform to convective clouds and precipitation. Stronger ascent in the warm conveyor belt tends to enhance cloudiness and precipitation across the cold front. A strong temperature contrast between the warm and cold sectors also encourages greater post-cold-frontal cloud occurrence. While the seasonal contrasts in environmental temperature, moisture, and ascent strength are enough to explain most of the variations in cloud and precipitation across cold fronts in both hemispheres, they do not fully explain the differences between Northern and Southern Hemisphere cold fronts. These differences are better explained when the impact of the contrast in temperature across the cold front is also considered. In addition, these large-scale parameters do not explain the relatively large frequency in springtime postfrontal precipitation.

scholarly journals On the Sensitivity of the Simulated Diurnal Cycle of Precipitation to 3-Hourly Radiosonde Assimilation: A Case Study over the Western Maritime Continent

2021 ◽  
Vol 149 (10) ◽  
pp. 3449-3468
Author(s):  
Joshua Chun Kwang Lee ◽  
Anurag Dipankar ◽  
Xiang-Yu Huang
Keyword(s):  
Diurnal Cycle ◽  
High Frequency ◽  
Initial Conditions ◽  
Rainfall Variability ◽  
Weather Prediction ◽  
Radiosonde Data ◽  
Western Coast ◽  
Maritime Continent ◽  
Model Biases ◽  
Diurnal Cycle Of Precipitation

AbstractThe diurnal cycle is the most prominent mode of rainfall variability in the tropics, governed mainly by the strong solar heating and land–sea interactions that trigger convection. Over the western Maritime Continent, complex orographic and coastal effects can also play an important role. Weather and climate models often struggle to represent these physical processes, resulting in substantial model biases in simulations over the region. For numerical weather prediction, these biases manifest themselves in the initial conditions, leading to phase and amplitude errors in the diurnal cycle of precipitation. Using a tropical convective-scale data assimilation system, we assimilate 3-hourly radiosonde data from the pilot field campaign of the Years of Maritime Continent, in addition to existing available observations, to diagnose the model biases and assess the relative impacts of the additional wind, temperature, and moisture information on the simulated diurnal cycle of precipitation over the western coast of Sumatra. We show how assimilating such high-frequency in situ observations can improve the simulated diurnal cycle, verified against satellite-derived precipitation, radar-derived precipitation, and rain gauge data. The improvements are due to a better representation of the sea breeze and increased available moisture in the lowest 4 km prior to peak convection. Assimilating wind information alone was sufficient to improve the simulations. We also highlight how during the assimilation, certain multivariate background error constraints and moisture addition in an ad hoc manner can negatively impact the simulations. Other approaches should be explored to better exploit information from such high-frequency observations over this region.

scholarly journals Secure Data-Encryption Strategy for Big-Data in Mobile Cloud

2019 ◽  
Vol 9 (1S) ◽  
pp. 1-4
Keyword(s):  
Big Data ◽  
Data Privacy ◽  
Data Encryption ◽  
Mobile Cloud ◽  
Timing Constraints ◽  
Privacy And Security ◽  
Secure Data ◽  
Consistent Performance ◽  
A New Technique ◽  
High Level

Now-a-days data plays a key role in Information Technology and while coming to privacy of that data it has become a considerable issue to maintain data security at high level. Large amounts of data generated through devices are considered as a major obstacle and also tough to handle in real time scenarios. To meetwith consistent performance applications at present abandon encryptions techniquesbecausethe time for the execution and the completion of encryption techniques plays a key role during processing and transmissions of data. In this paper our moto is to secure data and proposed a new technique called Dynamic Data Encryption Strategy (DDES)which selectively encrypts data and uses some algorithms which provides a perfect encryption strategy for the data packages under some timing constraints. By this method we can achieve data privacy and security for big-data in mobile cloud-computing by using an encryption strategy respective to their requirements during execution time.

scholarly journals Ozone mixing ratios inside tropical deep convective clouds from OMI satellite measurements

2008 ◽  
Vol 8 (4) ◽  
pp. 16381-16407
Author(s):  
J. R. Ziemke ◽  
J. Joiner ◽  
S. Chandra ◽  
P. K. Bhartia ◽  
A. Vasilkov ◽  
...  
Keyword(s):  
Radar Data ◽  
Mixing Ratio ◽  
Ozone Monitoring Instrument ◽  
Upper Troposphere ◽  
Mixing Ratios ◽  
Convective Clouds ◽  
Deep Convective Clouds ◽  
A New Technique ◽  
Oceanic Boundary Layer ◽  
Column Ozone

Abstract. We have developed a new technique for estimating ozone mixing ratio inside deep convective clouds. The technique uses the concept of an optical centroid cloud pressure that is indicative of the photon path inside clouds. Radiative transfer calculations based on realistic cloud vertical structure as provided by CloudSat radar data show that because deep convective clouds are optically thin near the top, photons can penetrate significantly inside the cloud. This photon penetration coupled with in-cloud scattering produces optical centroid pressures that are hundreds of hPa inside the cloud. We use the measured column ozone and the optical centroid cloud pressure derived using the effects of rotational-Raman scattering to estimate O3 mixing ratio in the upper regions of deep convective clouds. The data are obtained from the Ozone Monitoring Instrument (OMI) aboard NASA's Aura satellite. Our results show that low O3 concentrations in these clouds are a common occurrence throughout much of the tropical Pacific. Ozonesonde measurements in the tropics following convective activity also show very low concentrations of O3 in the upper troposphere. These low amounts are attributed to vertical injection of ozone poor oceanic boundary layer air during convection into the upper troposphere followed by convective outflow. Over South America and Africa, O3 mixing ratio inside deep convective clouds often exceeds 50 ppbv which is comparable to mean background (cloud-free) concentrations. These areas contain higher amounts of ozone precursors due to biomass burning and lightning. Assuming that O3 is well mixed (i.e. constant mixing ratio with height) up to the tropopause, we can estimate the stratospheric column O3 over clouds. Stratospheric column ozone derived in this manner agrees well with that retrieved independently with the Aura Microwave Limb Sounder (MLS) instrument and thus provides a consistency check of our method.

scholarly journals Interdecadal Variability of Southeastern South America Rainfall and Moisture Sources during the Austral Summertime

2016 ◽  
Vol 29 (18) ◽  
pp. 6751-6763 ◽  
Author(s):  
Verónica Martín-Gómez ◽  
Emilio Hernández-Garcia ◽  
Marcelo Barreiro ◽  
Cristóbal López
Keyword(s):  
South America ◽  
Rainfall Variability ◽  
Austral Summer ◽  
Eastern Shore ◽  
Central Brazil ◽  
Moisture Sources ◽  
Tropical Oceans ◽  
Eastern Brazil ◽  
Central Eastern ◽  
Atmospheric Circulation Anomalies

Abstract Sea surface temperature (SST) anomalies over the tropical oceans are able to generate extratropical atmospheric circulation anomalies that can induce rainfall variability and changes in the sources of moisture. The work reported here evaluates the interdecadal changes in the moisture sources for southeastern South America (SESA) during austral summer, and it is divided into two complementary parts. In the first part the authors construct a climate network to detect synchronization periods among the tropical oceans and the precipitation over SESA. Afterward, taking into account these results, the authors select two periods with different degrees of synchronization to compare the spatial distribution of the SESA moisture sources. Results show that during the last century there were three synchronization periods among the tropical oceans and the precipitation over SESA (during the 1930s, 1970s, and 1990s) and suggest that the main moisture sources of SESA are the recycling over the region, the central-eastern shore of Brazil together with the surrounding Atlantic Ocean, and the southwestern South Atlantic surrounding the SESA domain. Comparison of SESA moisture sources for the 1980s (a period of nonsignificant synchronization) and the 1990s (a synchronized period) shows that the principal differences are in the intensity of the recycling and in the strength of the central-eastern shore of Brazil. Moreover, the authors find that a region centered at (20°S, 300°E) is a moisture source for SESA only during the 1990s. These differences can be associated with the development of a low-level anticyclonic (cyclonic) anomaly circulation over central-eastern Brazil that favors the transport of moisture from central Brazil (central-eastern shore of Brazil) toward SESA in the 1990s (1980s).

scholarly journals Coupling of Precipitation and Cloud Structures in Oceanic Extratropical Cyclones to Large-Scale Moisture Flux Convergence

2018 ◽  
Vol 31 (23) ◽  
pp. 9565-9584 ◽  
Author(s):  
Sun Wong ◽  
Catherine M. Naud ◽  
Brian H. Kahn ◽  
Longtao Wu ◽  
Eric J. Fetzer
Keyword(s):  
Large Scale ◽  
Moisture Flux ◽  
Extratropical Cyclones ◽  
Flux Divergence ◽  
Moisture Flux Convergence ◽  
Convective Clouds ◽  
Moisture Advection ◽  
Deep Convective Clouds ◽  
Stratiform Clouds ◽  
High Level

Precipitation (from TMPA) and cloud structures (from MODIS) in extratropical cyclones (ETCs) are modulated by phases of large-scale moisture flux convergence (from MERRA-2) in the sectors of ETCs, which are studied in a new coordinate system with directions of both surface warm fronts (WFs) and surface cold fronts (CFs) fixed. The phase of moisture flux convergence is described by moisture dynamical convergence Qcnvg and moisture advection Qadvt. Precipitation and occurrence frequencies of deep convective clouds are sensitive to changes in Qcnvg, while moisture tendency is sensitive to changes in Qadvt. Increasing Qcnvg and Qadvt during the advance of the WF is associated with increasing occurrences of both deep convective and high-level stratiform clouds. A rapid decrease in Qadvt with a relatively steady Qcnvg during the advance of the CF is associated with high-level cloud distribution weighting toward deep convective clouds. Behind the CF (cold sector or area with polar air intrusion), the moisture flux is divergent with abundant low- and midlevel clouds. From deepening to decaying stages, the pre-WF and WF sectors experience high-level clouds shifting to more convective and less stratiform because of decreasing Qadvt with relatively steady Qcnvg, and the CF experiences shifting from high-level to midlevel clouds. Sectors of moisture flux divergence are less influenced by cyclone evolution. Surface evaporation is the largest in the cold sector and the CF during the deepening stage. Deepening cyclones are more efficient in poleward transport of water vapor.

Cloud Patterns as Seen from Altitudes of 250 to 850 Miles — Preliminary Results

1960 ◽  
Vol 41 (6) ◽  
pp. 291-297 ◽  
Author(s):  
John H. Conover ◽  
James C. Sadler
Keyword(s):  
Large Scale ◽  
Vertical Motion ◽  
Time Lapse ◽  
Squall Line ◽  
Low Level ◽  
The Earth ◽  
Stationary Front ◽  
Ballistic Missiles ◽  
High Level ◽  
Cloud Patterns

Time-lapse films of the earth from high-flying ballistic missiles have provided the meteorologist with the first synoptic detailed coverage of cloud patterns over large areas. Analysis of the film obtained on 24 August 1959 shows the cloud patterns over an area corresponding to one-twentieth of the earth's total surface. Comparison of the rectified cloud positions with, the high- and low-level synoptic charts shows large-scale cloud patterns directly associated with high-level vortices and troughs as well as patterns associated with a quasi-stationary front and the intertropical convergence zone. Details suggesting low-level vortices, frontal waves, and a squall line appear, but they cannot be verified due to sparse surface observations. Other details, such as the effects of large and small islands, coastlines and rivers upon the pattern of vertical motion are indicated by the clouds.

scholarly journals Formation of Convective Clouds at the Foothills of the Tropical Eastern Andes (South Ecuador)

2009 ◽  
Vol 48 (8) ◽  
pp. 1682-1695 ◽  
Author(s):  
Jörg Bendix ◽  
Katja Trachte ◽  
Jan Cermak ◽  
Rütger Rollenbeck ◽  
Thomas Nauß
Keyword(s):  
San Francisco ◽  
Cell Formation ◽  
Austral Summer ◽  
Convective Cloud ◽  
Early Morning ◽  
Spatial Extent ◽  
Small Cells ◽  
Target Area ◽  
Convective Clouds ◽  
Mesoscale Convective

Abstract This study examines the seasonal and diurnal dynamics of convective cloud entities—small cells and a mesoscale convective complex–like pattern—in the foothills of the tropical eastern Andes. The investigation is based on Geostationary Operational Environmental Satellite-East (GOES-E) satellite imagery (2005–07), images of a scanning X-band rain radar, and data from regular meteorological stations. The work was conducted in the framework of a major ecological research program, the Research Unit 816, in which meteorological instruments are installed in the Rio San Francisco valley, breaching the eastern Andes of south Ecuador. GOES image segmentation to discriminate convective cells and other clouds is performed for a 600 × 600 km2 target area, using the concept of connected component labeling by applying the 8-connectivity scheme as well as thresholds for minimum blackbody temperature, spatial extent, and eccentricity of the extracted components. The results show that the formation of convective clouds in the lowland part of the target area mainly occurs in austral summer during late afternoon. Nocturnal enhancement of cell formation could be observed from October to April (particularly February–April) between 0100 and 0400 LST (LST = UTC − 5 h) in the Andean foothill region of the target area, which is the relatively dry season of the adjacent eastern Andean slopes. Nocturnal cell formation is especially marked southeast of the Rio San Francisco valley in the southeast Andes of Ecuador, where a confluence area of major katabatic outflow systems coincide with a quasi-concave shape of the Andean terrain line. The confluent cold-air drainage flow leads to low-level instability and cellular convection in the warm, moist Amazon air mass. The novel result of the current study is to provide statistical evidence that, under these special topographic situations, katabatic outflow is strong enough to generate mainly mesoscale convective complexes (MCCs) with a great spatial extent. The MCC-like systems often increase in expanse during their mature phase and propagate toward the Andes because of the prevailing upper-air easterlies, causing early morning peaks of rainfall in the valley of the Rio San Francisco. It is striking that MCC formation in the foothill area is clearly reduced during the main rainy season [June–August (JJA)] of the higher eastern Andean slopes. At a first glance, this contradiction can be explained by rainfall persistence in the Rio San Francisco valley, which is clearly lower during the time of convective activity (December–April) in comparison with JJA, during which low-intensity rainfall is released by predominantly advective clouds with greater temporal endurance.

Maritime Continent rainfall variability during the TRMM era: The role of monsoon, topography and El Niño Modoki

2016 ◽  
Vol 75 ◽  
pp. 58-77 ◽  
Author(s):  
Abd. Rahman As-syakur ◽  
Takahiro Osawa ◽  
Fusanori Miura ◽  
I. Wayan Nuarsa ◽  
Ni Wayan Ekayanti ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Rainfall Variability ◽  
Maritime Continent ◽  
El Niño Modoki
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