Showing papers on "Monsoon published in 1976"

Oscillations of a Monsoon System. Part I. Observational Aspects

Abstract: In this paper the elements of a monsoon system are defined, and its oscillations are determined from spectral analysis of long observational records. The elements of the monsoon system include pressure of the monsoon trough, pressure of the Mascarene high, cross-equatorial low-level jet, Tibetan high, tropical easterly jet, monsoon cloud cover, monsoon rainfall, dry static stability of the lower troposphere, and moist static stability of the lower troposphere. The summer monsoon months over India during normal monsoon rainfall years are considered as guidelines in the selection of data for the period of this study. The salient result of this study is that there seems to exist a quasi-biweekly oscillation in almost all of the elements of the monsoon system. For some of these elements, such as the surface pressure field, monsoon rainfall, low-level cross-equatorial jet and monsoon cloudiness, the amplitude of this oscillation in quasi-biweekly range is very pronounced. For the spectral representati...

Some Climatological Aspects of West African Disturbance Lines During GATE

Abstract: The disturbance lines which occurred during the three phases of GATE over the eastern Atlantic Ocean and West Africa have been identified utilizing the excellent data from the SMS-1 geostationary satellite. The majority of these disturbance lines generated and decayed over land. Genesis occurred predominantly in the afternoon over land and in the early morning over water. They develop to the north of the cloud systems associated with the southwest monsoon, where the moist layer is shallow and the overriding dry air favors the production of downdrafts by the evaporation of precipitation and genesis is to a large extent dependent on insolation and low-level convergence associated with traveling waves.

Climate of Khumbu Himal

Abstract: The climate of the highland in Khumbu Himal is described in analysing the observational data taken at Lhajung (4420 m) in 1973 and 1974. There are marked rainy and dry seasons. 70-80% of annual precipitation (54 cm in 1973 and 35 cm in 1974) is concentrated in 4 months in the summer monsoon. The monsoon activity was somewhat weaker in 1974 than in 1973. Solar insolation is almost twice that of observed at sea level at the same latitude except in the monsoon season. The mean annual temperature at Lhajung is nearly 0°C. The weaker monsoon in 1974 than in 1973 appeared also in the temperature and humidity patterns. Diurnal and daily variations of temperature or humidity are very small in the monsoon season, while they are large, having a periodic change, in dry season. A very stationary valley wind governs the diurnal changes of meteorological parameters at Lhajung through out the year. However, the valley wind is confined to a thin layer of about less than 1500 m thick in the main valley of the Himalayas.

The Agulhas Current System During the Northeast Monsoon Season

Abstract: Data specifically selected from the total available data set have been used for an isentropic analysis of the southwest Indian Ocean. Components of geostrophic velocity at the depths of the various isentropic surfaces have been calculated to aid in the interpretation. It is found that during the northeast monsoon season the Agulhas Current derives its supply of water from different sources at different depths and that at depth a large measure of recirculation of Agulhas Current water takes place. The concept of a southwest Indian Ocean gyre, postulated before, is confirmed.

Monsoonal deposition of sea salt and air pollutants over Bombay

Abstract: Representative sampling of rainwater has been carried out in Greater Bombay and its neighbourhood during the SW monsoon period of 1974. It is estimated that on the average ?200 kg ha ?1 sea salt is deposited here, each monsoon. A high ‘excess’ of Ca is observed throughout Bombay, including relatively unpolluted places. The source of this excess is seen to be non-marine. The mean pH, ionic balance and salinity of rainwater has been used to characterise different areas of Bombay in varying degrees of pollution. DOI: 10.1111/j.2153-3490.1976.tb00676.x

The Mean Troposphere of West Africa

Abstract: Averages of tropospheric aerological data have been prepared from an 11-year period of monthly records for eight stations in the west African region. Due to the relatively large seasonal climatic variations within the region, three mean soundings have been presented: one for the entire area, one for the stations situated about 5°N, i.e., within the monsoon belt, and another for stations located approximately 13°–14°N, i.e., within the zone which the low-level ITCZ traverses. Monthly and annual means have been computed for temperature, specific humidity and heights and tabulated against pressure. Based on these averages, major climatological features of the area are discussed.

Seasonal Weather Variations in Khumbu Himal

Abstract: Seasonal weather variations in Khumbu Himal are described on the basis of two full years of data (April 1973 to March 1975) at Lhajung station (4420 m). The data used are mainly the daily record of cloud, precipitation and moisture content, and the 500 mb weather charts. It is suggested that each stage of seasonal weather variation in the high-altitude Himalayas in Nepal is mainly affected by : i) The Tibetan High in the monsoon season and the subtropical jet stream in the other seasons. ii) The moisture supply to this region from the Indian Ocean. There are also strong year to year variations depending on the strength of the subtropical jet stream and the Tibetan High.

The monsoon forests of the admirality gulf, western australia*

Abstract: Recent investigation has revealed the occurrence of patches of ‘monsoon forest’ (Semi-evergreen and Deciduous Vine Thickets sensu Webb 1959) in the north Kimberley District of Western Australia. Rainfall is much higher in this area than was previously assumed and reaches 1500 mm annually. As in southern Queensland these forests occur only on basic igneous rocks. A description is given of the general vegetation of the Mitchell Plateau and of the monsoon forests found there, based on study of seven sites, three of them ‘high-level’ on the scarps of the bauxite plateau, three ‘low-level’ on the lower basalt country and one riverain. Eleven species not previously listed in published records for Western Australia were found. All were known from the Northern Territory and represent an extension of the known range of species comprised in the Indo-Malaysian element of the Australian flora.

A study of trends and periodicities in the seasonal and annual rainfall of India

Abstract: The seasonal and annual rainfall of India for each year of the 60-year period from 1901 to 15 to1960 have been studied by subjecting them to the latest statistical techniques. This analysis has brought out that the mean annual rainfall is of the order of l19cm with a standard deviation of 9.5cm. Fisher's statistics have shown that the frequency distribution of time series of seasonal and annual rainfall are normal. Significant increase of 5 percent in 30years' mean is observed in the southwest monsoon and the annual rainfall but the increase of 6 per cent in the post monsoon rainfall is not statistically significant. Power spectrum analysis has revealed the presence of 2.3 to 2.5 years' cycle and a weak cycle of about 10.15 years.

Monsoon rains over West Africa

Abstract: Potential mechanisms producing high or low seasonal rainfall in tropical West Africa are investigated for the period 1963–74 using monthly data of precipitation, surface pressure in the South Atlantic and rawinsondes, mainly in Africa. Contrary to widespread opinion, the South Atlantic pressures yielded no correlation; the best connection was between rainfall and upper-level African observations. DOI: 10.1111/j.2153-3490.1976.tb00700.x

Rainfall Minimum in Peninsular Malaysia during the Northeast Monsoon

Abstract: A study. of the pentad rainfall patterns of 29 stations in Peninsular Malaysia reveals that a rainfall minimum exists between late January and mid-February. The causes of this minimum are attributed to two upper air patterns.

Climate of Hidden Valley, Mukut Himal during the Monsoon in 1974

Abstract: For the purpose of understanding climate of the glacier area of the northern side of the Himalayan range, a temporary station was set up at a height of 5055 m in Hidden Valley, Mukut Himal during the monsoon season of 1974. The temperature pattern, especially the trend of minimum temperature and the diurnal temperature range, seems to reflect the monsoonal character and to represent its effect better than the precipitation pattern. At the beginning and the end of the observation period, a rapid change of minimum temperature and large temperature range were recorded, as opposed to the stationary trend of mean temperature from the middle of July to the middle of August, which seems to be the monsoon season in Hidden Valley. At the station, most of the precipitation was in the form of rain and rain-snow mixed. Nocturnal precipitation was more than daytime precipitation, which was less than 5 mm. The daily mean of evaporation slightly exceeded the daily mean of precipitation even in the monsoon period. The diurnal variation of atmospheric pressure shows two maxima and two minima.

Water characteristics and current structure at 65°E during the southwest monsoon

Abstract: Hydrographic data collected aboard R. V. Anton Bruun along 65°E between 18°N and 42°S from 17 May to 4 July 1964 are used to investigate water characteristics and current structure in the upper 500 m in the Indian Ocean. The water characteristics indicate the occurrence of three main water masses,viz., warm, saltier, low-oxyty and nutrient-rich Arabian Sea Surface Water, relatively fresh and high-oxyty Equatorial Indian Ocean Water, and more saline, high-oxyty and nutrient-poor Tropical Water of the South Indian Ocean. The recently discovered South Equatorial Countercurrent and Subtropical Countercurrent (renamed Tropical Countercurrent, at the suggestion of Dr. R. B.Montgomery) are observed in the current structure at 13°S and 22°–26°S respectively, and these could also be identified on the vertical sections of temperature, thermosteric anomaly and salinity. Contrary to the existing concept, the North Equatorial Current continues to be present even after the onset of the southwest monsoon. The Equatorial Undercurrent could not be traced in the Indian Ocean during this period.

Spectral Analysis of Monsoonal Precipitation in the Nepal Himalaya

Abstract: Spectral analysis was performed on records of the daily precipitation during the monsoon season of 1973 at stations in the Nepal Himalaya. Through power spectral analysis on the data at 12 stations and also on the areal averaged data (east, central and west Nepal), a predominant periodicity of around 10 days and secondary periodicity of about 5 days are found. Through cross-spectral analysis between these data, the periodicity around 10 days is found to be correlated with large-scale disturbances causing precipitation simultaneously in all of Nepal, and the periodicity of about 5 days seems to be associated with monsoon lows moving westward along the monsoon trough in northern India. The periodicity of around 10 days also seems to be related to the oscillation of the Tibetan High and or level of activity of the monsoon regime over the Indo-Tibetan region.

Low‐level air flow circulation over the Arabian Sea during the summer monsoon as deduced from satellite‐tracked superpressure balloons. Part I—Balloon trajectories

Abstract: During the northern summer of 1975, 45 superpressure constant-level balloons were released from the Seychelles Islands (4.7°S 55.5°E) for flight at 955mb (500m), 910mb (1000m) and 860mb (1500m) within the tropical boundary layer. The balloons were located by the Random Access Measurement System (RAMS) of the Nimbus-6 satellite. This spacecraft also operated as a data relay system and collected pressure measurements performed by transducers carried by the balloons. The mean lifetime of the balloons was about 4–5 days, some of them lasting more than 8 days. Low-level Lagrangian air trajectories in the southwesterly flow over the Arabian Sea are presented. They show the drastic changes in the airflow direction over the southwestern Arabian Sea associated with high or low activity periods of the monsoon over the western coast of India. During the first period of the experiment, the airflow over the southwestern Arabian Sea joins the low-level jet flowing to the east of the Somali coast. This change, due to intense convective activity near Somalia, can be associated with a break in the monsoon activity. During the second period the air joins the Bay of Bengal branch of the monsoon over the southwest coast of India. Before the end of July a complete reversal of the winds over the Seychelles Islands is observed and some balloons drift towards Madagascar. During the third period the air flow over the Arabian Sea resumes a southwesterly direction and at the beginning of August it seems to join again the Bay of Bengal branch of the monsoon. Thus this experiment shows that low-level ballooning can be used to map air currents over vast unsurveyed areas of the oceans.

Moisture distribution and water vapour flux over the Arabian Sea during an active and weak spell of southwest monsoon, 1973

Abstract: The radiosonde data collected during the Indo-Soviet Monsoon Experiment, 1973 have been utilised to study some aspects of the moisture distribution over the Arabian Sea during an active and weak spell of southwest monsoon in that year, The study shows that there is stratification of moisture field over the Arabian Sea during the weak monsoon except the equatorial region, particularly the eastern parts, During the active monsoon, the stratification is broken to the north of about 10°N and east of 60°E, resulting in the building up of a deep moist layer over this area from surface to 400 mb, The equatorial region is conspicuously dry in the middle layers -during the active spell The moisture build up in the middle layers during both the spells is mainly brought about by large-scale vertical motion associated with synoptic scale disturbances rather than by advective processes During active monsoon, large, scale upward motion is envisaged over north and east central Arabian Sea and subsidence near the equator The moisture flux computations show that there is a large net flux divergence over the Arabian Sea during the active monsoon and small net convergence during the weak monsoon

Structure of low-level Jet-stream over the Arabian Sea and the Peninsula as revealed by observations in June and July during the monsoon experiment (Monex) 1973 and its probable origin

Abstract: Surface and upper air observations recorded by the four Russian ships during Monsoon Experiment (MONEX) 1973 over the Arabian sea and the Indian Ocean upto the equator and by the obsrvatories over Kenya and Peninsular India, have been examined to study details about the jet-speed winds noticed over the area during active or strong monsoon conditions. The following points are brought out by the study: (1) The low-level jet was noticed simultaneously over the Arabian Sea between Lats. 7° and 16° N east of about long. 53° E and over the Peninsula at (i) different levels over the same place, (ii) different latitudes at the same time, and (iii) different latitudes and levels at different times. (2) The extent of the jet in the horizontal and vertical was generally larger over land than oversea. It may be at as high a level as 3.0 km over sea and 3.8 km over land. (3) When a jet-stream persisted over an area for a day or two, the lowest jet over the sea would appear to be at a lower level during the morning than evening hours. (4) The low-level jet over the Peninsula and the Arabian Sea would not appear to originate due to thermal conditions off Somalia an over the Arabian Sea. Jet-speed winds occurred over sea in the moist air and not near the boundary of moist and dry airmasses they occurred below above or in isothermal layer or in the and their airmasses with nearly moist adiabatic lapse and the other moist adiabiatic lapse. (5) The low-level jet over the Peninsular India is a continuation of that over the Arabian Sea, which in turn, would appear to be a coatinuation of that which crosses equator between Longs. 37° and 45°E and has its origin in the southern hemisphere as seen from paper of Findlater (1969) and as discussed by Desai (1972); the cold fronts in the mid latitude of that hemisphere moving eastwards initiate the low-level Jet, the topographical features to the west of the eastern coast of Africa and of Madagascar directing it northwards across the Mozambique channel and also enhancing its speed. (6) The need for closer network of Rawin and Radiosonde observation over the equator between longitude of Nairobi and 45 degrees East in any future MONEX expeditions has been emphasized.

Numerical Experiments with a Primitive Equation Barotropic Model for the Prediction of Movement of Monsoon Depressions and Tropical Cyclones

Abstract: A limited-area primitive equation barotropic model with wind as input has been integrated up to 72 h to predict the movement of a monsoon depression and a tropical cyclone in the Indian region. The forecast up to 48 h is satisfactory in both cases whereas that beyond this period appears to deteriorate rapidly.

Numerical Simulation of the Asian-African Winter Monsoon

Abstract: This paper shows that a general circulation model at the National Center for Atmospheric Research is capable of simulating many aspects of the Asian-African winter monsoon. We concentrate on a climatological descriptive comparison of wind patterns, particularly the reversed flow of the low-level Somalian jet near the east coast of Africa, sea-level pressure, and cloudiness and precipitation over the monsoon region.

Climate of Hidden Valley, Mukut Himal during the Monsoon in 1974:Glaciological Expedition to Nepal, Contribution No. 22

Abstract: For the purpose of understanding climate of the glacier area of the northern side of the Himalayan range, a temporary station was set up at a height of 5055 m in Hidden Valley, Mukut Himal during the monsoon season of 1974. The temperature pattern, especially the trend of minimum temperature and the diurnal temperature range, seems to reflect the monsoonal character and to represent its effect better than the precipitation pattern. At the beginning and the end of the observation period, a rapid change of minimum temperature and large temperature range were recorded, as opposed to the stationary trend of mean temperature from the middle of July to the middle of August, which seems to be the monsoon season in Hidden Valley. At the station, most of the precipitation was in the form of rain and rain-snow mixed. Nocturnal precipitation was more than daytime precipitation, which was less than 5 mm. The daily mean of evaporation slightly exceeded the daily mean of precipitation even in the monsoon period. The diurnal variation of atmospheric pressure shows two maxima and two minima.

Synoptic Analyses of the Precipitation in Nepal in 1974

Abstract: A synoptic analyses were done of the precipitation in August and December in 1974. Types of precipitation in this August were much different between those in the northern coast of the Bengal Bay, the plain and high mountain area in Nepal. The monsoon currents come from the equatorial region, but the possibility of the intrusion of the monsson wind into the mountain area is affected by the behaviour of the westerly current in middle latitudes. When the Tibetan High move to the north, the monsoon wind easily flows into the Himalayan region. The position of the trough line of the wave in middle latitudes is also important. In the winter season, the precipitation in the plain area of Nepal is of the showery type, but rainfall in the high mountain area is relatively continuous. The relation between the precipitation and the behavior of the middle latitude upper level wind is more intimate in the winter season. To understand the precipitation in Nepal, the interaction of the middle and the low latitude atmospheric circulation, and also the local behavior of the mountain and valley winds in relation to the orographic conditions must be studied.

Structure of the southwest monsoon near the equator during Monex 1973

Abstract: The structure, of, the southwest monsoon near the equator over the west Indian Ocean during June 1973 has been studied by utilising MONEX 1973 data. It is found that the equatorial belt extending from the east African coast to about 75°E can broadly be divided into three regions, viz., (i) the western region-extending from the east African coast to, about 56°E (ii) the central region -from 56° to about 65°E and (iii) the eastern region-east of 650 E. The vertical fields of wind, temperature and moisture markedly differ from each other over these region . While over the western, and eastern regions deep convective activity is observed, the central region is characterized by a large-scale sinking of air in the mid-tropospheric levels. Due to this dynamic process, the mid-tropospheric westerlies suffer considerable modification and become increasingly warm and dry downstream over the central region.