Long-range prediction of monsoon activity: A synoptic – Diagnostic study

Abstract

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.

Upper tropospheric monthly mean values of geopotential height; temperature and wind at about sixty Indian and neighbouring stations during the pre-monsoon months of April and May, and monsoon months of June, July and August, have been used to study the inter-annual variation in the upper tropospheric fields for the years 1967 to 1976. Thickness anomalies at selected Indian stations suggest, ( 1) that warming/ cooling of upper troposphere is a large-scale phenomenon over north and northwest Indian region and (2) that the anomalies as observed in the months of April and May (more predominantly in May) , generally persis1 during the subsequent monsoon months. It is found that the years of warmer (cooler) upper troposphere over north and northwest Indian region, beginning from the pre-monsoon month of May (and perhaps from April) and generally persisting during the subsequent monsoon months, are the years when the summer monsoon rainfall over India was good (poor).

The upper tropospheric circulation over Indian sub-continent during the month of May in the contrasting monsoons show marked difference in the wave structure of sub-tropical westerlies over northwest of Indian region.

The study suggests that the upper tropospheric quasi-permanent wave in the westerlies can significantly effect the thermal field over north and northwest Indian region during the pre-monsoon - months, which in turn, may influence the activity of the subsequent summer monsoon over India. This may have value in long-range prediction of monsoon activity.