Cloudy Bands Research Articles

Mesoscale Cyclonic Vortices Embedded in the South Atlantic Convergence Zone Associated with Natural Disasters in the State of São Paulo, Brazil

Natural disasters (NDs) have been observed more frequently and with increasing intensities in Brazil. The South Atlantic Convergence Zone (SACZ) is identified as one of the main meteorological systems responsible for the NDs, however, intense rainfall does not occur along its entire length but is restricted to some locations within the band of cloudiness that defines it. Thus, the objective of this study is to analyze occurrences of mesoscale cyclonic vortices (MCV) in SACZ events that were associated with NDs in the state of São Paulo from 2013 to 2017 using data from the ERA5 Reanalysis, as well as to analyze one case study. To account for SACZ events, surface synoptic charts, observed and estimated precipitation data were used. ND events were selected from the Integrated Disaster Information System (S2ID) database. The methodology used by Quadro (2012) was adapted to identify MCV. The results showed 62 SACZ events, of which 28 were associated with NDs, and, of these, 10 presented MCV. The MCVs were separated into two groups: 1) MCVs in the SACZ events that showed precipitation at the location of the MCV and NDs and 2) MCVs in the SACZ events that did not show precipitation at the location of the MCV and NDs. Group 1 events were characterized by convergence at low levels and divergence at high levels of the atmosphere, vorticity values lower than -8 x 10-4 s-1 predominating at low levels (850–900 hPa), demonstrating a relationship with the highest precipitation accumulations and possibly with the occurrence of NDs. In the events of group 2, there was a predominance of negative values of vorticity in medium and high levels, the lack of a pattern in the field of divergence in the atmospheric levels, as well as lower values in the accumulated precipitation compared to the events of group 1. The case study was from January 11 to 15, 2016, associated with NDs in 8 cities. As a result, it was obtained that MCV was coupled in the atmosphere and the precipitation associated with it represented more than 37% of all the precipitation of the SACZ event, making it possible to attribute to the MCV a contribution in the occurrence of NDs caused by precipitation.

Chemical and visual characterisation of EGRIP glacial ice and cloudy bands within

Abstract. Impurities in polar ice play a critical role in ice flow, deformation, and the integrity of the ice core record. Especially cloudy bands, visible layers with high impurity concentrations, are prominent features in ice from glacial periods. Their physical and chemical properties are poorly understood, highlighting the need to analyse them in more detail. We bridge the gap between decimetre and micrometre scales by combining the visual stratigraphy line scanner, fabric analyser, microstructure mapping, Raman spectroscopy, and laser ablation inductively coupled plasma mass spectrometry 2D impurity imaging. We classified approximately 1300 cloudy bands from glacial ice from the East Greenland Ice-core Project (EGRIP) ice core into seven different types. We determine the localisation and mineralogy of more than 1000 micro-inclusions at 13 depths. The majority of the minerals found are related to terrestrial dust, such as quartz, feldspar, mica, and hematite. We further found carbonaceous particles, dolomite, and gypsum in high abundance. Rutile, anatase, epidote, titanite, and grossular are infrequently observed. The 2D impurity imaging at 20 µm resolution revealed that cloudy bands are clearly distinguishable in the chemical data. Na, Mg, and Sr are mainly present at grain boundaries, whereas dust-related analytes, such as Al, Fe, and Ti, are located in the grain interior, forming clusters of insoluble impurities. We present novel vast micrometre-resolution insights into cloudy bands and describe the differences within and outside these bands. Combining the visual and chemical data results in new insights into the formation of different cloudy band types and could be the starting point for future in-depth studies on impurity signal integrity and internal deformation in deep polar ice cores.

Biomineralization of primary carbonate cements: a new biosignature in the fossil record from the Anisian of Southern Italy

Biomineralization is a generic term used to indicate biological-mediated mineral formation. In carbonate mineralization, nucleation of crystals can be: (1) controlled directly by the organisms, like in the skeletal formation of most metazoans; (2) induced by microbial communities, by indirect precipitation mediated by their metabolic activities; or (3) influenced by organic matter decay, with mineral precipitation on specific non-living organic cell surfaces. Recognition of these products is a direct marker of biological activity in time and space and is a key element in the study of the biological evolution and of its interactions with the geological processes. In this paper, primary carbonate cements from the Anisian microbial build-up of the ‘Monte Facito’ Formation (Basilicata region, Southern Italy) have been studied from a geobiological point of view. Optical microscopy, UV-epifluorescence and micro-Raman spectroscopy have been applied to investigate the organic mediation on their precipitation. The cements formed in microcavities or on grain substrates, and often show a microstromatolite-like pattern of growth. They are composed of alternations of cloudy organic and whitish inorganic bands that point to a double phase of mineralization. In the first phase, a biologically induced/influenced biomineralization is confirmed by the presence of organic matter strictly connected with the cloudy bands. This phase is followed by a pure abiotic mineralization that leads to the formation of whitish bands. This process repeated cyclically, ending at the complete filling of the microcavities or because of changes in the chemical conditions of the microsystem, for example, due to burial processes. This model of mineralization is similar to that proposed for primary cements forming in recent beach rocks. The Monte Facito Formation cements could be considered as the product of unconventional biomineralization, and the understanding of their growth process could provide an innovative tool in the research of biological signatures in the fossil record. The term unconventional is here utilized to discriminate this type of biomineralizations from those related to well-known biotic mineralization processes, like those involved in skeletons and microbialites growth, which can be considered as conventional biomineralizations.

Deep Learning Based Thin Cloud Removal Fusing Vegetation Red Edge and Short Wave Infrared Spectral Information for Sentinel-2A Imagery

Thin clouds seriously affect the availability of optical remote sensing images, especially in visible bands. Short-wave infrared (SWIR) bands are less influenced by thin clouds, but usually have lower spatial resolution than visible (Vis) bands in high spatial resolution remote sensing images (e.g., in Sentinel-2A/B, CBERS04, ZY-1 02D and HJ-1B satellites). Most cloud removal methods do not take advantage of the spectral information available in SWIR bands, which are less affected by clouds, to restore the background information tainted by thin clouds in Vis bands. In this paper, we propose CR-MSS, a novel deep learning-based thin cloud removal method that takes the SWIR and vegetation red edge (VRE) bands as inputs in addition to visible/near infrared (Vis/NIR) bands, in order to improve cloud removal in Sentinel-2 visible bands. Contrary to some traditional and deep learning-based cloud removal methods, which use manually designed rescaling algorithm to handle bands at different resolutions, CR-MSS uses convolutional layers to automatically process bands at different resolution. CR-MSS has two input/output branches that are designed to process Vis/NIR and VRE/SWIR, respectively. Firstly, Vis/NIR cloudy bands are down-sampled by a convolutional layer to low spatial resolution features, which are then concatenated with the corresponding features extracted from VRE/SWIR bands. Secondly, the concatenated features are put into a fusion tunnel to down-sample and fuse the spectral information from Vis/NIR and VRE/SWIR bands. Third, a decomposition tunnel is designed to up-sample and decompose the fused features. Finally, a transpose convolutional layer is used to up-sample the feature maps to the resolution of input Vis/NIR bands. CR-MSS was trained on 28 real Sentinel-2A image pairs over the globe, and tested separately on eight real cloud image pairs and eight simulated cloud image pairs. The average SSIM values (Structural Similarity Index Measurement) for CR-MSS results on Vis/NIR bands over all testing images were 0.69, 0.71, 0.77, and 0.81, respectively, which was on average 1.74% higher than the best baseline method. The visual results on real Sentinel-2 images demonstrate that CR-MSS can produce more realistic cloud and cloud shadow removal results than baseline methods.

Variação da Temperatura da Superfície do Mar no Oceano Atlântico Sul Durante Episódios de Zona de Convergência do Atlântico Sul Oceânica

A Zona de Convergência do Atlântico Sul (ZCAS) faz parte dos sistemas meteorológicos presentes no Brasil, ocorrendo nos meses de primavera/verão e consiste em uma banda de nebulosidade com eixo orientado de noroeste-sudeste que se inicia no sul da Amazônia e se estende até o Oceano Atlântico Sudoeste. Este sistema meteorológico contribui significativamente para o aumento dos índices pluviométricos, sendo muito importante para as regiões economicamente desenvolvidas do Brasil. Este trabalho foi desenvolvido com o objetivo de analisar a variação da temperatura da superfície do mar (TSM) devido a atividade deste sistema meteorológico quando ocorre configuração de ZCAS Oceânica, que é quando o sistema posiciona-se sobre o oceano.Para isto, serão comparadas imagens de satélite e variáveis atmosféricas associados a ZCAS com a variação da TSM do antes e após a atividade deste sistema meteorológico. Os resultados constataram que a TSM abaixo das ZCAS estava com uma temperatura mais quente (até 1º C) antes do fenômeno se configurar, e decaiu em até 1º C após a atuação da ZCAS. Estudar as variações de temperatura da superfície do mar da ZCAS e adjacências são indispensáveis para iniciar trabalhos que visam compreender os impactos no ambiente marinho.

Microstructural analysis of Greenland ice using a cryogenic scanning electron microscope equipped with an electron backscatter diffraction detector

Mass loss from ice sheets contributes to global sea level rise, and accelerated ice flow to the oceans is one of the major causes of rapid ice sheet mass loss. To understand flow dynamics of polar ice sheets, we need to understand deformation mechanisms of the polycrystalline ice in ice sheets. Laboratory experiments have shown that deformation of polycrystalline ice occurs largely by dislocation glide, which mainly depends on crystal orientation distribution. Grain size and impurities are also important factors that determine ice deformation mechanisms. Compared with ice formed during interglacial periods, ice formed during glacial periods, especially ice that forms cloudy bands, exhibits finer grain sizes and higher impurity concentrations. A previous report suggests the deformation rate of ice containing cloudy bands is higher than that of ice without cloudy bands. To examine the microstructures and deformation histories of ice in cloudy bands, we applied the electron backscatter diffraction (EBSD) technique to samples from the Greenland Ice Sheet using an environmental scanning electron microscope (ESEM) equipped with cold stages. Prior to the EBSD analysis, we optimised our ESEM/EBSD system and performed angular error assessment using artificial ice. In terms of c- and a-axis orientation distributions and grain orientation spread, we found little difference between samples taken from a cloudy band and those taken from an adjacent layer of clear ice. However, subgrain boundary density and orientation gradients were higher in the cloudy band, suggesting that there are more dislocations in the cloudy band than in the clear ice layer.

Small-scale disturbances in the stratigraphy of the NEEM ice core: observations and numerical model simulations

Abstract. Disturbances on the centimetre scale in the stratigraphy of the North Greenland Eemian Ice Drilling (NEEM) ice core (North Greenland) can be mapped by an optical line scanner as long as the ice has visual layering, such as, for example, cloudy bands. Different focal depths allow, to a certain extent, a three-dimensional view of the structures. In this study we present a detailed analysis of the visible folds, discuss their characteristics and frequency, and present examples of typical fold structures. We also analyse the structures with regard to the deformation boundary conditions under which they formed. The structures evolve from gentle waves at about 1500 m to overturned z folds with increasing depth. Occasionally, the folding causes significant thickening of layers. Their similar fold shape indicates that they are passive features and are probably not initiated by rheology differences between alternating layers. Layering is heavily disturbed and tracing of single layers is no longer possible below a depth of 2160 m. C axes orientation distributions for the corresponding core sections were analysed, where available, in addition to visual stratigraphy. The data show axial-plane parallel strings of grains with c axis orientations that deviate from that of the matrix, which shows a single maximum fabric at the depth where the folding occurs. Numerical modelling of crystal viscoplastic deformation and dynamic recrystallisation was used to improve the understanding of the formation of the observed structures during deformation. The modelling reproduces the development of bands of grains with a tilted-lattice orientation relative to the single maximum fabric of the matrix, and also the associated local deformation. We conclude from these results that the observed folding can be explained by formation of these tilted-lattice bands.

Chemical compositions of solid particles present in the Greenland NEEM ice core over the last 110,000 years

AbstractThis study reports the chemical composition of particles present along Greenland's North Greenland Eemian Ice Drilling (NEEM) ice core, back to 110,000 years before present. Insoluble and soluble particles larger than 0.45 µm were extracted from the ice core by ice sublimation, and their chemical composition was analyzed using scanning electron microscope and energy dispersive X‐ray spectroscopy and micro‐Raman spectroscopy. We show that the dominant insoluble components are silicates, whereas NaCl, Na2SO4, CaSO4, and CaCO3 represent major soluble salts. For the first time, particles of CaMg(CO3)2 and Ca(NO3)2•4H2O are identified in a Greenland ice core. The chemical speciation of salts varies with past climatic conditions. Whereas the fraction of Na salts (NaCl + Na2SO4) exceeds that of Ca salts (CaSO4 + CaCO3) during the Holocene (0.6–11.7 kyr B.P.), the two fractions are similar during the Bølling‐Allerød period (12.9–14.6 kyr B.P.). During cold climate such as over the Younger Dryas (12.0–12.6 kyr B.P.) and the Last Glacial Maximum (15.0–26.9 kyr B.P.), the fraction of Ca salts exceeds that of Na salts, showing that the most abundant ion generally controls the salt budget in each period. High‐resolution analyses reveal changing particle compositions: those in Holocene ice show seasonal changes, and those in LGM ice show a difference between cloudy bands and clear layers, which again can be largely explained by the availability of ionic components in the atmospheric aerosol body of air masses reaching Greenland.

Location of cation impurities in NGRIP deep ice revealed by cryo-cell UV-laser-ablation ICPMS

AbstractIn polar ice sheets, the average grain size varies with depth. Ice grain size increases due to several factors including ice temperature and impurity content, which in turn varies with climate. The effect of impurities on grain growth is thought to be crucial but has never been observed experimentally. Using a methodology recently developed at Royal Holloway University of London, in situ chemical analysis of frozen ice at sub-ppm concentrations with unprecedented spatial resolution (~150 μm) is achievable using ultraviolet laser ablation inductively coupled plasma mass spectrometry (UV-LA-ICPMS) featuring a two-volume cryo-LA-cell. Following surface cleaning with a custom-built vice equipped with a ceramic blade, NGRIP ice slabs (~86 ka before AD 2000) have been analysed using a series of one-dimensional profiles and two-dimensional maps of laser spots at a resolution of 200–300 μm. Results demonstrate that cation impurities are not uniformly distributed in ice layers and show significant variations in concentration on a sub-millimetre scale. Furthermore, a different pattern of elemental distribution between clear ice and layers enriched in impurities (cloudy bands) has been identified: while concentration differences for cloudy bands are not resolvable between boundaries and inner grain domains, within clear ice, grain boundaries and junctions are significantly (up to 100 times) impurity-enriched relative to corresponding grain interiors.

High-resolution variations in size, number and arrangement of air bubbles in the EPICA DML (Antarctica) ice core

AbstractWe investigated the large-scale (10–1000 m) and small-scale (mm–cm) variations in size, number and arrangement of air bubbles in the EPICA Dronning Maud Land (EDML) (Antarctica) ice core, down to the end of the bubble/hydrate transition (BHT) zone. On the large scale, the bubble number density shows a general correlation with the palaeo-temperature proxy, δ18O, and the dust concentration, which means that in Holocene ice there are fewer bubbles than in glacial ice. Small-scale variations in bubble number and size were identified and compared. Above the BHT zone there exists a strong anticorrelation between bubble number density and mean bubble size. In glacial ice, layers of high number density and small bubble size are linked with layers with high impurity content, identified as cloudy bands. Therefore, we regard impurities as a controlling factor for the formation and distribution of bubbles in glacial ice. The anticorrelation inverts in the middle of the BHT zone. In the lower part of the BHT zone, bubble-free layers exist that are also associated with cloudy bands. The high contrast in bubble number density in glacial ice, induced by the impurities, indicates a much more pronounced layering in glacial firn than in modern firn.

Polar ice structure and the integrity of ice-core paleoclimate records

Polar ice is a unique archive of the climatic conditions in the past. However, ice sheets flow, and this flow may affect the integrity of paleoclimate records. A useful method to analyze the effect of ice flow upon climate records is the combination of microstructure mapping with ice-core line-scanning. Microstructure and stratigraphy have been mapped along the entire EPICA-DML ice core with this combined method. On the macroscale the stratigraphy seems perfectly preserved down to ca 1700 m depth (MIS4), below which minor undulations start to develop. Layers inclined up to 15° and millimeter-scale z-folds are observed below 2050 m depth. Notwithstanding, the EPICA-DML climate record appears not seriously disturbed down to ca 2400 m depth, which marks the climatic transition from the last interglacial (MIS5e) to the MIS6 glacial period. Below this depth the synchronization with the EPICA-Dome C record is lost, and stratigraphic disturbances appear up to the meter scale. On the microscopic scale, we observe dynamic recrystallization already in deep firn, leading to substantial microstructural changes prior to bubble close-off. The concentration of visible micro-inclusions in the Holocene part of the core seems to increase with depth, which could possibly indicate post-depositional formation of salts. In glacial period ice the concentration of visible micro-inclusions in certain layers is so high that these strata appear as light-scattering bands, often called “cloudy bands”. Another interesting stratigraphic feature is what we call “bubble-free bands”, viz. millimeter-thick strata deprived of bubbles and rich in clathrate hydrates, which are found within the bubble–hydrate transition zone (800–1200 m depth) and are probably caused by anomalously fast clathration. While there is hardly any interaction between visible micro-inclusions and grain boundaries down to 2500 m depth, in the deeper ice (warmer than −10 °C) many grain boundaries seem to harvest micro-inclusions. Here we discuss these observations and their relevance for the interpretation of climate records.

Lightning activity analyses with respect to the SPCZ location

The South Pacific Convergence Zone (SPCZ) stretches over the West Pacific warm pool Southeastward to French Polynesia. The Island Climate Update monthly publishes the mean location deduced from the total rainfall. On the other hand, the World Wide Lightning Location Network monthly provides data from which the lightning activity distribution in the 0°–30° South latitude and 150°–240° West longitude area can be drawn. Scanning this rectangle from West to East allows the spots of maximum lightning activity to be located versus the longitude. Fitting the location of these maxima with a polynomial function leads to a curve comparable with the monthly mean position of the SPCZ, showing that this band of cloudiness is one of the main sources of lightning in this whole area.

Properties of GRIP ice crystals from around Greenland interstadial 3

AbstractIce-crystal textures (sizes and shapes) and fabrics (c-axis orientations) have been determined in 3 m of vertical thin sections from the Greenland Icecore Project (GRIP) ice core. the samples cover ice from before, during and after Greenland interstadial 3 (IS3) that occurred about 25 kyr BP. the texture of 60 000 crystals has been obtained from stacked digital images by semi-automated methods, and the fabric of 5000 selected crystals has been measured on the Automatic Ice Fabric Analyzer at the Alfred Wegener Institute, Bremerhaven. the area distribution function of the crystals is close to a log normal distribution, and the mean area is found to be 3.36 mm2 in ice from IS3, and 3.04 mm2 in ice from colder periods before and after IS3. the overall c-axis orientations show a strong single maximum with vertical orientation. These results agree well with earlier GRIP fabric studies obtained by manual methods. from comparisons of crystal areas with the concentrations of dust, Ca2+, SO42–, Cl– and NO3– in the ice we determine that NO3– correlates best with crystal areas. Crystals within clearly visible cloudy bands are significantly smaller than the surrounding crystals, and their c-axis orientations are less well confined than the average.

Ice-sheet flow conditions deduced from mechanical tests of ice core

AbstractUniaxial compression tests were performed on samples of the Greenland Ice Gore Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45° from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability When the Schmid factor was > 0.46, the enhancement factor obtained was higher than expected from the .-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.

Tephra layers in the Dome Fuji (Antarctica) deep ice core

AbstractA deep ice core drilled to 2503 m depth at Dome Fuji, Antarctica, contains 25 visible tephra layers during the past 340 ka. The thickness of tephra layers is in the range 1-24 mm. The thickness and duration at deposition, determined by a simple ice-flow model, suggests that a violent volcanic eruption caused ash to fall onto the Antarctic ice sheet for ~5 years and to form a ~100 mm thick tephra layer at 117 ka BE Two tephra layers at depths of 573 and 2202 m probably originated from volcanoes in the South Sandwich Islands, Southern Ocean, given the size of tephra shards, >20μm in diameter, and their major chemical composition. Only eight of the 25 tephra layers can also be recognized in the Vostok (Antarctica) ice core, but all correspond to the Vostok tephras if we consider cloudy bands to be volcanic.

Deep ice-core drilling at Dome Fuji and glaciological studies in east Dronning Maud Land, Antarctica

The Dome Fuji Project is a comprehensive study of present and past glaeiological/climatological features of the Antarctic ice sheet in east Dronning Maud Land. Field observations on a 100U km traverse route from the coast to Dome Fuji slum changes in various glaciological parameters with surface elevation and distance from the coast. Deep ice-core drilling at Dome Fuji was started in August 1995 and reached a depth of 2503.52 m in December 1996. in situ core analyses revealed 25 visible tephra layers and a number of distinct cloudy bands in the ice.

Pattern variations of polyclonal and monoclonal immunoglobulins of different isotypes analyzed by high-resolution two-dimensional electrophoresis.

High-resolution two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was used to analyze serum samples and purified immunoglobulins (Ig) obtained from "normal" individuals and from patients diagnosed with monoclonal gammopathies (MG) (n = 47; 5 IgA, 15 IgM, 15 IgG, 4 biclonal IgG, 1 IgD, 7 Bence Jones proteins). Polyclonal and monoclonal heavy (H) chains were located at different restricted gel positions according to their isotype. Monoclonal H chains appeared as sets of spots characterized by charge (pI) and size (M(r)) microheterogeneity. Most of the monoclonal gamma chains were not seen on the gels (12/15). Supplementary polypeptides of 45-48 kDa were detected in serum samples containing monoclonal IgM, but were not seen in MG of other isotypes. However, these polypeptides were not specifically associated with monoclonal IgM because they were also found on protein maps of purified polyclonal IgM. Polyclonal light (L) chains appeared as cloudy bands containing several zones of higher density, whereas monoclonal L chains were usually resolved as single sharp spots. In 6 samples, monoclonal L chains were not seen, and in 9 samples, they appeared as two or more spots, characterized by different pI and/or M(r). In one sample obtained from a patient with a biclonal gammopathy, the L chains were resolved as 4 different spots. Our results confirm that 2-D PAGE is an excellent tool to study Ig. Analysis of the L chain region of the gels was particularly informative. Several monoclonal L chains exhibited heterogeneous two-dimensional spot patterns, suggesting that "subtile" clonal mutations of B-cell lineage and/or posttranslational modifications were involved in their production.

Spatial and temporal variations in Australo‐Indonesian region cloudiness

AbstractSpatial and temporal variations in cloudiness of the Australo‐Indonesian region are examined with the help of a newly created cloudiness data set, based on GMS‐IR imagery. As represented by the first Varimax rotated principal component pattern of the Australo‐Indonesian region cloudiness, the band of tropical cloudiness is dominated by a clearly defined eastward cluster propagation, as well as a more complicated 40–50‐day oscillation pattern. Details of these phenomena are discussed.

Topographically Forced Convergence in Western Washington State

Abstract Several times a year when the low-level winds from off the Pacific Ocean are within a narrow range of speed and direction, air passes both north and south of the Olympic Mountains of Washington State and is forced to converge in Puget Sound by the north-south oriented Cascade Range. This phenomenon, termed the Puget Sound convergence zone, often results in a band of cloudiness and precipitation in northern and central Puget Sound with clear, subsiding air to the north and south. This paper presents the results of a series of case studies in which the structure of the zone, its meteorological manifestations, and the environmental conditions necessary for its formation are explored. It is shown that the convergence zone is skillfully forecast by surface coastal winds and undergoes a strong annual and diurnal cycle, being most frequent during the late spring and early summer months and during the afternoon and early evening. It is also found that the zone is structurally similar to a shallow cold fr...

Weather and Equatorial Waves Over Southeast Asia During the Summer Monsoon

Analysis of wind, pressure and cloudiness patterns shows that the weather of Southeast Asia during the southwest monsoon relates best to westward-moving equatorial waves. These waves are basically the same as those found over the western Pacific by other investigators although they are often not perceived without special analysis as they move through the vigorous monsoonal circulation. They are characterized by average wavelength of 3100 km, average period of 5½ days or speed of 6.5 m sec−1, a deep cool center from the surface to about the 300-mb level, and a deep band of convergence and cloudiness which feeds into the center from the southwest and south. Relatively good weather with lower amounts of cloudiness and areal precipitation coverage is normally found in the area of synoptic-scale subsidence between waves.