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MONSOON VARIABILITY

MONSOON VARIABILITY. TEMPORAL SCALES OF MONSOON VARIABILITY. 2010. DURING THE PERIOD OF 1875-2010, NUMBER OF DEFICIENT YEARS (24) IS MORE THAN THE NUMBER OF EXCESS YEARS (19). OSCILLATION OF MONSOON. EPOCHAL PATTERNS OF SUMMER MONSOON RAINFALL

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MONSOON VARIABILITY

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  1. MONSOON VARIABILITY

  2. TEMPORAL SCALES OF MONSOON VARIABILITY

  3. 2010 DURING THE PERIOD OF 1875-2010, NUMBER OF DEFICIENT YEARS (24) IS MORE THAN THE NUMBER OF EXCESS YEARS (19).

  4. OSCILLATION OF MONSOON EPOCHAL PATTERNS OF SUMMER MONSOON RAINFALL • THIRTY-ONE YEAR MOVING AVERAGE OF ALL INDIA SUMMER RAINFALL ANOMALIES SHOWS:- * 1871-1900 WET ** 1901-1930 DRY *** 1931-1960 WET **** 1961-1990 DRY

  5. OSCILLATION OF MONSOON

  6. ALTERNATING SEQUENCE OF MULTIDECADAL PERIODS HAVING FREQUENT DROUGHTS AND FLOOD YEARS.

  7. INTER-ANNUAL VARIABILITY OF EXTREME RAINFALL

  8. QUASI-BIWEEKLY OSCILLAITON IN THE INDIAN MONSOON

  9. DEFINITION OF THE NINE ELEMENTS. (A) MONSOON TROUGH. THIS IS THE LOW PRESSURE TROUGH AT SEA LEVEL THAT IS A PART OF THE GLOBAL EQUATORIAL TROUGH OF THE NORTHERN SUMMER SEASON. OVER LAND AREAS, THE EQUATORIAL TROUGH EXTENDS FROM WEST AFRICA TO EAST COAST OF INDO-CHINA. FIG SHOWS THE MT OVER NORTH INDIA IN JULY. (B) MASCARENE HIGH. (CENTRE OF A’CYCLONE 30°S, 50°E)THIS IS THE HIGH PRESSURE AREA SOUTH OF THE EQUATOR. THE NAME COMES FROM THE MASCARENE ISLANDS EAST OF MADAGASCAR. THE ARC OF THE ANTICYCLONE IS LOCATED NEAR 30°S, 50°E.

  10. DEFINITION OF THE NINE ELEMENTS. (C) LOW-LEVEL CROSS EQUATORIAL JET. ITS IMPORTANCE HAS BEEN RECOGNIZED SINCE OBSERVATIONAL STUDIES OF FINDLATER (1969). THE JET HAS, MAX WINDS NEAR 1.5 KM LEVEL ~ 100 KT NEAR MADAGASCAR AND ON SOMALI COAST. IT IS A VERY NARROW JET. THE AXIS OF THE JET IS KNOWN TO BECOME MORE INTENSE DURING JUN-AUG. IT IS ALSO OBSERVED TO SPLIT INTO TWO BRANCHES. (D) TIBETAN HIGH. THIS IS A LARGE SCALE ANTICYCLONE THAT IS KNOWN TO HAVE ITS LARGEST AMPLITUDE NEAR 200 hPa DURING NORTHERN SUMMER MONTHS..

  11. DEFINITION OF THE NINE ELEMENTS. (E) TROPICAL EASTERLY JET. IT IS FOUND AT 150 hPa, WIND SPEED IS OF THE ORDER OF 80-100 KT WITH THE STRONGEST WIND BEING FOUND JUST TO THE WEST OF THE SOUTHERN TIP OF INDIA OVER ARABIAN SEA. (F) MONSOON CLOUDINESS. (SATELLITE BRIGHTNESS)THE STUDY WAS BASED ON SATELLITE BRIGHTNESS FOR THE ENTIRE TROPICAL BELT BETWEEN 5°N & 15°N AND ITS OSCILLATIONS WERE STUDIED. (G) MONSOON RAINFALL. THE STUDY WAS CONFINED TO MONSOON RAINFALL OVER CENTRAL INDIA AND ITS VARIABILITY DURING AN ACTIVE MONSOON SEASON.

  12. DEFINITION OF THE NINE ELEMENTS. (H) DRY STATIC STABILITY. IN THE MONSOON BELT OVER NORTH INDIA, DURING ACTIVE AND INACTIVE RAINFALL PERIODS, THE SURFACE HEATING GOES FROM SMALL TO VERY HIGH VALUES DUE TO SOLAR INSOLATION. THE DRY STATIC STABILITY FLUCTUATES NEAR THE SURFACE FROM STABLE TO LESS STABLE OR UNSTABLE VALUES DURING THESE PERIODS. THESE FLUCTUATIONS WERE RELATED TO CLOUDINESS CYCLE.

  13. DEFINITION OF THE NINE ELEMENTS. (J) MOIST STATIC STABILITY. THE CHANGE OF MOIST STATIC STABILITY BETWEEN SURFACE AND 700HPA WAS STUDIED. THE MOIST STATIC STABILITY PARAMETER IS GIVEN BY WHERE, θ- POTENTIAL TEMPERATURE q – SPECIFIC HUMIDITY - DRY STATIC ENERGY L – LATENT HEAT OF CONDENSATION COMPUTED FOR LKN, JDP, NGP (1000-700 HPA). Q – SP. HUMIDITY

  14. PRESSURE OF MONSOON TROUGH The salient pressure oscillation in the monsoon trough is around 11.5 days.

  15. PRESSURE IN MASCARENE HIGH A broad and large oscillation takes place around 11.5 days. There is a pronounced peak around 15 days with a positive value.

  16. LOW LEVEL CROSS-EQUATORIAL JET-FINDLATER Wind Index – mean wind of the layer between 0.9 & 1.5 km off Garissa, Kenya. Results show a very pronounced peak around 15.3 days

  17. TIBETAN HIGH The Oscillation of the trough is represented by local mean value of the stream function and the peak is seen around 13.1 days.

  18. TROPICAL EASTERLY JET (200hPa WIND) The distinct and isolated peak of the wind oscillations was around 13.1 days.

  19. MONSOON CLOUD COVER The spectra of satellite brightness reveals a significant peak around 13.1 days.

  20. MONSOON RAINFALL The spectral analysis of monsoon rainfall over Central India (1967–near normal monsoon) showed two major peaks around 2 days and 13.1 days.

  21. DRY STATIC STABILITY The fluctuations in dry static stability were examined by θ- Potential temperature T – Temperature P – Pressure gz + Cp T – Dry state energy Computed for LKN, JDP and NGP (Between 1000 and 900 hPa)

  22. MOIST STATIC STABILITY The moist static stability parameter is given by q – Specific humidity L – Latent heat of condensation computed for LKN, JDP, NGP (between 1000-700hPa) gz + Cp T + Lq - Moist state energy A peak was found around 15 days with a negative value.

  23. ELIOT’S 5 DAY STANDING OSCILLATION (A) AREA COVERAGE. 5°S TO 45°N, 45°E TO 105°E (MONSOON AREA) (B) SEASON OF OCCURRENCE: OSCILLATORY CHANGES OF PRESSURE OF SHORT PERIOD ARE SEEN THROUGHOUT THE YEAR. (C) PERIOD OF OSCILLATION. VARIES CONSIDERABLY FROM 2 TO 8 OR 9 DAYS. MEAN ≈ 4 TO 5 DAYS. (D) AMPLITUDE OF OSCILLATION. THE AMPLITUDE DECREASES EQUATORWARD. HE SUGGESTED THAT AMPLITUDE MAY BE 0.6 hPa NEAR 10°N AND 2 hPa NEAR 30°N. (E) MOVEMENT. THE OSCILLATIONS OCCUR OVER THE WHOLE AREA ALMOST SIMULTANEOUSLY. ANY MOVEMENT WESTWARDS OR EASTWARDS MOVES WITHIN A FEW HOURS OVER THE WHOLE AREA. (ROUGHLY LESS THAN 6 HOURS). (F) CAUSE. IT IS LIKELY THAT THE WAVES ARE OF RAREFACTION AND CONDENSATION CAUSED DUE TO VARIATIONS OF THERMAL CONDITIONS.

  24. MADDEN JULIAN OSCILLATIONS (MJO) • Madden and Julian (1971) detected a 40-50 day oscillation of the zonal wind in the lower troposphere over Canton Island (30S, 1720W), in the central equatorial Pacific. • Similar oscillations occur in an extremely large portion of equatorial belt, manifested in zonal wind and surface pressure, with maximum amplitude at equator. • The oscillation basically propagates eastwards at a fairly steady phase speed and at most time exhibits zonal wave number 1. • 40-50 day perturbations move northwards and eastward over the monsoon region north of equator between 600 and 1500E with a phase speed of 0.8 latitude per day. • Krishanamurti et al.(1985) also found a pressure pulse with 30-50 day period, moving from equator to Himalayas.

  25. 30-50 Day Oscillation -Low inversion -More radiation reaching surface -Strong wind = More evaporation -Moisture convergence -more convection Blue= more clouds Red= fewer clouds

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