ANALYSIS OF VORTEX DEVELOPMENT IN EASTERN INDIAN OCEAN USING POTENTIAL VORTICITY

R P DAMAYANTI^1,2 ,N J TRILAKSONO^2,3, M R ABDILLAH^2,3

 

¹MASTER PROGRAM IN EARTH SCIENCE, FACULTY OF EARTH SCIENCES AND TECHNOLOGY, INSTITUT TEKNOLOGI BANDUNG

 

 

 

²WEATHER AND CLIMATE PREDICTION LABORATORY, FACULTY OF EARTH SCIENCES AND TECHNOLOGY, INSTITUT TEKNOLOGI BANDUNG

³ATMOSPHRIC SCIENCE RESEARCH GROUP, FACULTY OF EARTH SCIENCES AND TECHNOLOGY, INSTITUT TEKNOLOGI BANDUNG

 

RIGGITA17@GMAIL.COM

 

ABSTRACT. THE VORTEX PHENOMENON HAS A SIGNIFICANT INFLUENCE, ESPECIALLY ON WIND CIRCULATION PATTERNS AND EXTREME WEATHER IN INDONESIA. THE FORMATION OF VORTEX ON THIS STUDY IS LOCATED IN THE EASTERN PART OF THE INDIAN OCEAN, WHICH HAS THE HIGHEST FREQUENCY OF VORTEX OCCURRENCE OVER INDONESIA. THIS VORTEX IS ALSO SUSPECTED AS ONE OF CONTRIBUTING FACTOR FOR FLOODING EVENTS AT JAKARTA IN 2002 AND 2007, HENCE BOTH FORMATION AND DEVELOPMENT OF THIS VORTEX IS VERY IMPORTANT TO STUDY. THE EVOLUTION OF VORTEX DEVELOPMENT IS CONDUCTED TO UNDERSTAND THE MAIN CHARACTERISTICS OF THE VORTEX IN THE EASTERN INDIAN OCEAN REGION. THIS STUDY WAS CONDUCTED OVER A PERIOD OF 17 YEARS STARTING FROM 1998 TO 2016 ON EVERY DECEMBER-JANUARY-FEBRUARY (DJF) PERIOD USING ECMWF (EUROPEAN CENTER FOR MEDIUM-RANGE WEATHER FORECAST) ERA-INTERIM REANALYSIS DATA. THE ANALYSIS OF VORTEX EVOLUTION WAS CONDUCTED FOR EACH EVENT USING A COMPOSITE EVOLUTION OF POTENTIAL VORTICITY ANOMALIES IN THE ISENTROPIC LAYER. THE STUDY RESULTS DETECTED 84 SYSTEMS WITH THREE CHARACTERISTIC PATTERNS OF VORTEX MOVEMENT THAT OCCURRED DURING 295 DAYS OF OBSERVATION PERIOD. COMPOSITE ANALYSIS OF POTENTIAL VORTICITY ANOMALIES SHOWS THAT THE INITIAL FORMATION OF VORTICES IN THE EASTERN INDIAN OCEAN IS RELATED TO THE  EMERGENCE OF NEGATIVE POTENTIAL VORTICITY ANOMALIES FROM THE WEST WHICH SUBSEQUENTLY FORM THE VORTICES.

 

 

 

KEYWORDS: VORTEX, POTENTIAL VORTICITY, COMPOSITE POTENTIAL VORTICITY ANOMALIES, EASTERN INDIAN OCEAN

THE DIURNAL CYCLE DOMINATES CONVECTION OVER THE MARITIME CONTINENT, WITH DEEP CONVECTION OCCURRING OVER LAND DURING THE AFTERNOON AND EVENING, AND TENDING TO PROPAGATE OFFSHORE OVERNIGHT, ALTHOUGH THE MECHANISM OF THIS PROPAGATION IS NOT WELL UNDERSTOOD.  DAY-TO-DAY VARIABILITY IN THE DIURNAL CYCLE IS ASSOCIATED WITH SCALE INTERACTIONS WITH LARGE-SCALE FORCINGS INCLUDING THE MJO, ENSO, EQUATORIAL WAVES AND TROPICAL CYCLONES.  USING A COMBINATION OF IN SITU OBSERVATIONS, CONVECTION-PERMITTING MET OFFICE UNIFIED MODEL FORECASTS AND REANALYSIS DATA IT IS SHOWN THAT THESE LARGE-SCALE FORCINGS MODULATE THE LOCAL-SCALE DIURNAL CYCLE VIA THEIR CONTROL ON THE COASTAL WINDS.

FOR THE COASTLINES OF SOUTH-WEST SUMATRA, NORTH-WEST BORNEO, AND THE NORTH AND SOUTH OF JAVA, IT IS SHOWN THAT ONSHORE WIND REGIMES TEND TO SUPPRESS CONVECTION OVER LAND.  CONVERSELY, DAYS WITH OFFSHORE WINDS SEE DEEP CONVECTION TRIGGERED DURING THE AFTERNOON WITH ASSOCIATED OFFSHORE PROPAGATION OF CONVECTION OVERNIGHT.  IT IS OFTEN ASSUMED THAT GRAVITY WAVES ARE RESPONSIBLE FOR THE NOCTURNAL OFFSHORE PROPAGATION, BUT OBSERVATIONAL EVIDENCE FOR THIS REMAINS ELUSIVE.  CONVECTION-PERMITTING FORECASTS OVER SUMATRA SUGGEST TWO MODES OF PROPAGATION, WHICH MAY OCCUR IN COMBINATION.  THE FIRST IS DUE TO A GRAVITY WAVE WHILE THE SECOND IS MUCH SLOWER AND IS CAUSED BY A GRAVITY CURRENT CONVERGING WITH THE ENVIRONMENTAL WINDS.

MADDEN JULIAN OSCILLATION (MJO) AFFECTS ALMOST ALL WEATHER PARAMETERS SUCH AS WIND, HUMIDITY, TEMPERATURE, RAINFALL, AND CLOUDS.  A COMPLETE UNDERSTANDING OF THE MJO PHENOMENON IS STILL DIFFICULT TO CARRY OUT, ILLUSTRATED BY SOME LARGE CIRCULATION MODELS' FAILURE TO ACCURATELY SIMULATE THE MJO. ONE OF THE CRITICAL PARAMETERS RELATED TO THIS IS THE CLOUD'S VERTICAL STRUCTURE, SUCH AS THE CLOUD BASE HEIGHT (CBH), THE CLOUD TOP HEIGHT (CT), AND THE NUMBER OF CLOUD LAYERS. THIS STUDY AIMS TO ANALYZE THE EFFECT OF MJO ON THE VERTICAL STRUCTURE OF CLOUDS IN SUMATRA. THIS STUDY ANALYZED DATA FOR TWO PERIODS OF COUPLING PROCESSES IN THE EQUATORIAL ATMOSPHERE (CPEA), NAMELY CPEA-I (APRIL-MAY 2004) AND CPEA-II (NOVEMBER-DECEMBER 2005). THE CLOUD VERTICAL STRUCTURE WAS STUDIED USING RADISONDE DATA FOLLOWING THE ZHANG ET AL. (2010, 2018) METHOD. IT WAS FOUND THAT THE CLOUD LAYER CONSISTS OF ONE LAYER CLOUD, TWO-LAYER CLOUD, THREE-LAYER CLOUD, AND FOUR-LAYER CLOUD.  CLOUD OCCURRENCE FREQUENCY IS LARGER DURING CPEA-II THAN CPEA-I. DURING CPEA-I, IN WHICH AN ACTIVE MJO EVENT IS CLEARLY OBSERVED, ONE LAYER CLOUD IS DOMINANT. ON THE OTHER HAND, DURING CPEA-II, WHICH IS IN-ACTIVE MJO PERIOD, THE TWO-LAYER CLOUD'S ABUNDANCE IS LARGE AS THE ONE-LAYER CLOUD. THE AVERAGE CLOUD TOP HEIGHT (CT) IN THE ACTIVE MJO PHASE (CPEA-I) IS 3.9 KM, LOWER THAN THE AVERAGE CLOUD TOP HEIGHT IN THE INACTIVE MJO PHASE (~4.7 KM). FURTHERMORE,  THE AVERAGE CLOUD BASE HEIGHT (CBH) IN THE ACTIVE MJO PHASE IS 3.0 KM, LOWER THAN THE MEAN CLOUD BASE HEIGHT DURING THE INACTIVE MJO PHASE (~3.2 KM).

TURBULENCE IS A PRIMARY FACTOR IN THE STRATOSPHERE–TROPOSPHERE EXCHANGE (STE) THAT OCCURRED IN A LAYER CALLED TROPICAL TROPOSPHERE LAYER (TTL), THE TRANSITION LAYER BETWEEN TROPOSPHERE AND STRATOSPHERE AT 14-18.5 KM ABOVE SEA LEVEL. THE STATE OF TTL IS ONE OF KEY ANSWER ON HOW PHENOMENA IN TROPOSPHERE AND STRATOSPHERE INTERACT. THE INTERACTION BETWEEN QUASI-BIENNIAL OSCILLATION (QBO) AND MADDEN-JULIAN OSCILLATION (MJO) IN PREVIOUS STUDY IS CLOSELY LINKED IN BOREAL WINTER. QBO IS ZONAL WIND OSCILLATION IN STRATOSPHERE WHILE MJO IS AN EASTWARD MOVING DISTURBANCE OF CONVECTIVE SYSTEM THAT TAKES PART ON CLIMATE VARIABILITIES IN INDONESIA. HOWEVER, THE CHARACTERISTIC OF TURBULENCE INTENSITY IN TTL TOWARDS INTERACTION OF QBO-MJO REMAIN UNKNOWN BECAUSE OF THE SCARCITY OF OBSERVATION DATA. THIS STUDY PRESENT INTENSITY VARIATION OF TURBULENCE TOWARD QBO-MJO INTERACTION IN TTL USING EQUATORIAL ATMOSPHERE RADAR (EAR) DATA LOCATED IN AGAM, WEST SUMATRA (0.2°S, 100.32°E). THE INTERACTION IS FOCUSED IN EXTENDED BOREAL WINTER PERIOD (NDJFM; 5 MONTHS) AND ACTIVE PHASE MJO IS DEFINED BY PHASE 4. TURBULENCE INTENSITY IN TTL TEND TO HAVE INVERSELY PROPORTIONAL VALUE TOWARD ZONAL WIND IN 50 HPA. GENERALLY, ENHANCEMENT OF TUBRULENCE IS OBSERVED ON ACTIVE PHASE MJO WITH MAXIMUM ADDED VALUE 0.075 M/S IN 17 KM HEIGHT. THE VALUE OF TURBULENCE INTENSITY, ZONAL WIND, AND VERTICAL WIND STRENGTHEN DURING QBOE (QBO EASTERLY) RATHER THAN QBOW (QBO WESTERLY). THIS ENHANCEMENT ASSOCIATED WITH STRONGER CONVECTIVE AND PRECIPITATION SYSTEM BEFORE THAT CAUSED BY MORE UNSTABLE ATMOSPHERE IN QBOE.

 

GRAVITY WAVES (GWS) ARE BELIEVED TO PLAY IMPORTANT ROLE IN THE GENERATION OF THE DRIVING FORCE OF THE STRATOSPHERIC QUASI BIENNIAL OSCILLATION (QBO). DEEP CONVECTIONS IN THE EQUATORIAL REGION CAN GENERATE LARGE AMOUNT OF GWS WITH SHORT VERTICAL WAVELENGTH (&LAMBDA;_Z <1 KM) BUT STUDIES OF THESE WAVE ACTIVITIES IN THE UPPER TROPOSPHERE LOWER STRATOSPHERE (UTLS) REGION ARE STILL LIMITED DUE TO THE SCARCITY OF HIGH RESOLUTION ATMOSPHERIC PROFILE WITH GLOBAL COVERAGE. BUT, RECENT ADVANCES IN GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS) RADIO OCCULTATION (RO) RETREIVAL TECHNIQUES HAVE MADE IT POSSIBLE TO DERIVE GLOBAL TEMPERATURE PROFILE WITH VERTICAL RESOLUTION OF LESS THAN 1 KM. IN THIS RESEARCH, ACTIVITIES OF GWS WITH &LAMBDA;_Z FROM 0.5 TO 3.5 KM IN THE UTLS REGION OF 20-27 KM HEIGHTS ARE IDENTIFIED BY CALCULATING THE GW POTENTIAL ENERGY (E_P). CORRELATION BETWEEN GW ACTIVITIES AND QBO PHASES IS EXAMINED USING 50 HPA ZONAL WIND AS THE QBO INDEX. THE RESULTS SHOW THAT DURING BOTH EASTERLY AND WESTERLY QBO PHASES, THE GW E_P VALUE INCREASES GRADUALLY WITH TIME AND REACHES ITS PEAK IN THE TRANSITION PERIODS. THIS PATTERN IS SEEN IN E_P WITH ALL VERTICAL WAVELENGTHS BETWEEN 0.5-3.5 KM BUT THE PERCENTAGE VALUE OF E_P FOR &LAMBDA;_Z < 1 KM IS HIGHER DURING THE TRANSITION FROM WESTERLY TO EASTERLY QBO. THE GW EP VALUES EXHIBIT DOWNWARD PROPAGATION WITH THE QBO PHASE BUT THERE ARE ALSO DISCERNIBLE UPWARD PROPAGATIONS OF GW ACTIVITIES BELOW 24 KM HEIGHT. FURTHERMORE, LARGE CHANGES IN QBO PHASE SEEM TO OCCUR WHEN UPWARD GW ACTIVITIES INTERSECT THE DOWNWARD PROPAGATING EP. ADDITIONALLY, BY COMPARING WITH EL NINO SOUTHERN OSCILLATION (ENSO) INDEX, EVEN HIGHER PERCENTAGE OF E_P WITH &LAMBDA;_Z<1 KM IS ALSO FOUND TO BE ASSOCIATED WITH EL NINO EVENTS.

&NBSP;

HADLEY CELLS ARE THERMALLY DRIVEN CELL IN THE TROPICS. ON ITS OCCURRENCE, THESE CELLS ARE STRONGLY INFLUENCED BY THE SEA SURFACE TEMPERATURE (SST) DISTRIBUTION ACROSS THE TROPICAL OCEAN OR THE PACIFIC OCEAN AS THE INVESTIGATED LOCATION IN THIS STUDY. THE SST SHIFTING IN THE PACIFIC OCEAN IS MAINLY DUE TO THE ENSO. AN OPPOSITE SST POLARITY BETWEEN THE WESTERN AND EASTERN PACIFIC OCEAN ARE CAPTURED DURING ENSO EVENTS. THIS MEANS THAT ENSO COULD TRIGGER AN ANOMALOUS REGIONAL HADLEY CELLS THAT BEHAVE OPPOSITELY BETWEEN INDONESIA OR THE WESTERN PACIFIC AND THE EASTERN PACIFIC. THIS STUDY EXAMINES THE STRENGTH OF THE REGIONAL HADLEY CELLS RELATED TO THE ENSO EVENT ACROSS THE INDONESIAN REGION AND THE PACIFIC OCEAN. A SIGNIFICANT CORRELATION BETWEEN THE HADLEY CELLS AND ENSO AS THE TROPICAL CLIMATE VARIABILITY IN THE PACIFIC OCEANS ARE FOUND. THE STRENGTH OF THE HADLEY CELLS ASSOCIATED WITH ENSO EVENT IS EXAMINED BY USING THE ZONALLY AVERAGE VERTICAL VELOCITY ACROSS THE PACIFIC OCEAN. DURING LA NINA, THE REGIONAL HADLEY CELLS OVER INDONESIA OR THE WESTERN PACIFIC STRENGTHENED, WHEREAS THE REGIONAL CELLS OVER THE EASTERN PACIFIC WEAKENED. IN CONTRAST, DURING THE EL NINO WHERE THE WARM POOL SHIFTED TO THE EASTERN PACIFIC, THE REGIONAL CELL IN THE EASTERN PACIFIC STRENGTHENED, WHILE THE CELL OVER THE WESTERN PACIFIC WEAKENED. THESE ANOMALOUS CONDITIONS CLEARLY SHOW THAT THE MERIDIONAL TEMPERATURE GRADIENT IS STRONGLY AFFECTING THE REGIONAL HADLEY CELLS STRENGTH. THE STRONGER THE MERIDIONAL TEMPERATURE GRADIENT, THE STRONGER THE REGIONAL HADLEY CELLS.