DMSP-SSM/I retrieval of proper surface winds during monsoon depression

Recently developed various global microwave algorithms for DMSP-SSM/I satellite data are used for the estimation of surface winds over the Indian ocean. Sea surface wind speeds from these algorithms are compared with sea surface wind speeds reported by coincidental Minicoy island (lowest height 2 m a.s.l.) station over the Arabian sea. A statistical comparison of these algorithms is made in terms of rms error, correlation coefficient, bias and standard deviation. Algorithm of Petty showed best results in the comparison. On the basis of this algorithm a notable characteristic feature such as acquiring of large area of strong surface winds (12-15 ms-1) to the south of dipping of monsoon trough in head Bay and then encircling of these winds during further development of low and depression (22-27 July 1992) is observed. This complete life cycle monitoring assessment of monsoon depression in respect of surface winds based on DMSP-SSM/I satellite data encourages to utilise our IRS-P4 (Oceansat-1) satellite data at different frequencies to emerge more details of various weather systems over the Indian region.

APPLICATION OF REMOTE SENSING IN THE STUDY OF MONSOON ENERGETICS OVER BAY OF BENGAL DURING SUMMER MONSOON

IIAR ~ , rR;\CT All attempt has been made 10 slUd )' tho roon soon c ne rgeucs over Bil)' of Hengal by stu, lying th ecloud and monsoon depression field s during sum mer monsoon using 11 ROS ·N sa telli te ima ge ri es . Th e i UU h Pakinetic ft amn-s. ,-.g . vergen ce. vortic ity and vertical vclochics fur Hfcw selected ph ases in th e Ray ufHen gal .luring 27JUll("-6 Allgn ..l l Q"7lj within the 10° X Ill o grid box (it" . IS-!5 °N & ~5 0 95 ° E ) wt're computed. Next. th e kinematicIeamres o f n rypi cul disturbed phase (5-7 Jul y 1979) we re studied in a Lagrangian frame by using drop wind so n' lednm of 1 S n"!'ic;lr..: h ai rcrutt. The data profiles II a nd I' him:' been drawn 10 idemit'y the evolutiona ry femll~ ." of finassociau- I 111 1111 snnn depression.Fol lr wing Such ruau rr 111 ( I ~77) and the cln ud d lls l" r ~ltJ.t ics of (jnsw:uui t." nt , (I 'J9U): th l"wo plausible lIlod elsof Il1ntt s tlon dL'p lr ..."i n l1 hil\"l' been posmhued in lerms of C lusl er ClJ ~ l eSl.:e n ..:e Theory (CCn and Ginn! e lu slernl ~lr)· (( iCl"!The '(" nl en l 1l1 11. ~' d rClllntiuns 'Ailhin an ll a ruun,t Ihe lllunsuon d lopres..,iol1 wcn.- inl l.-ne,l hy making ll ~e ofGt }F.S im a!:l' l·l ·il-" Th " kinemal ic stud ies have rew ala l that th e h ighe r vH lues of \'ertical veloci ties , posi ti\ 'c \·.. r1icilylind \'t'll.l' C" '11.'1' c n lT,,~p h ll d w jlll lhe max imuUl cooncct in ' cloud ..:o\'e rllge 1';SoO-\'; .f fClnuing and mntu re stages ormo nSllllll d C")lll' , !, icl11

Variations in intensity and structure of a westward-propagating monsoon depression

The study deals with a monsoon depression which developed over the Bay of Bengal, moved westward across central India and turned into a mid-tropospheric disturbance (MTD) over the northeastern : corner of the Arabian Sea. Its interactions with the thermal fields associated with the basic monsoon, subtropical westerly troughs and a new depression over the Bay of Bengal are examined. Evidence suggests the involvement of all the three factors in causing the observed variations in its intensity and structure. The low pressure system turned into a mid-tropospheric disturbance when it re-entered the warm sector of the basic monsoon field and received increased warm advection from the north to the west of its centre and cold advection from the south to the east in mid-troposphere. The importance of thermal advection is confirmed by computation of a heat budget. The role of condensation heating is also briefly discussed.

Some structural characteristics of pre-monsoon depression in the Bay of Bengal

During the period 6 to 16 May. 1995. three deep depressions formed one after another over west Bay of Bengal and moved from south to north. In this paper, structural characteristics of these systems are investigated from the distribution of thermal and thermodynamical field observed around the depression center utilising daily Rs/Rw and other available coastal observations during the period, Major findings of the study are: (i) The depressions have low level cold core and middle and upper tropospheric warm core. (ii) Thermal and moisture fields tilt north ward with height but vertical tilt of contour height is .not uniform at all levels, (iii) During intensification of the system significant increase in temperature and moisutre occurs above 700 hPa and significant fall of contour height occurs below 300 hPa.

Role of tropical mid-latitude interaction in the genesis of a monsoon depression - A detailed case study

During northern summer, a monsoon stationary wave which maintains as part of its baroclinic structure three well-defined troughs, one each in the region of the Arabian sea, the Bay of Bengal and South China sea, frequently interacts with the mid-latitude baroclinic waves which amplify during their eastward passage with profound influence on the development of the monsoon troughs. The paper discusses the mechanism of this wave-wave interaction as suggested by the temporal evolution of the themla1 and wind fields associated with the waves and reports the findings of a detailed study of a case of tropical-mid latitude interaction in which the development of a monsoon trough led to the birth of a westward-propagating monsoon depression over South China.

Simulation of monsoon depression over India using high resolution WRF Model – Sensitivity to convective parameterization schemes

The monsoon depression of September 2008, which crossed Orissa coast near Chandbali on 16th had contributed heavy rainfall over Orissa, Chhattisgarh and northern India along the track of the system. The sensitivity of three cumulus parameterization schemes viz., Kain-Fritch (KF) scheme, Grell-Devenyi (GD) scheme and Betts-Miller-Janjic (BMJ) Scheme are tested using high resolution advanced version (3.0) Weather Research Forecasting (WRF) model in forecasting the monsoon depression. The results of the present study shows that the genesis of the system was almost well captured in the model as indicated in 48hr forecast with all three convective parameterization schemes. It is seen that the track of monsoon depression is quite sensitive to the cumulus parameterization schemes used in the model and is found that the track forecast using three different cumulus schemes are improved when the model was started from the initial condition of a depression stage compared to that when it started from the initial condition of low pressure area. It is also seen that when the system was over land all the schemes performed reasonably well with KF and GD schemes closely followed the observed track compared to that of BMJ track. The performance of KF and GD schemes are almost similar till 72 hrs with lowest landfall error in KF scheme compared to other two schemes, whereas the BMJ scheme gives lowest mean forecast error upto 48 hr and largest mean forecast error at 72 hr. The overall rainfall forecast associated with the monsoon depression is also well captured in WRF model with KF scheme compared to that of GD scheme and BMJ scheme with observed heavy rainfall over Orissa, Chhattisgarh and western Himalayas is well captured in the model with KF scheme compared to that with GD scheme and BMJ scheme.

Development of a Monsoon Depression and Its Interaction with the Large-Scale Background: A Case Study

Structure and time evolution of the large-scale background and an embedded synoptic-scale monsoon depression and their interactions are studied. The depression formation is preceded by a cyclonic circulation around 400 hPa. The Fourier-based scale separation technique is used to isolate large (wavenumbers 0–8) and synoptic-scale (wavenumbers 12–60). The wavelength and depression center is determined objectively. The synoptic-scale depression has an average longitudinal wavelength of around 1900 km and a north–south size of 1100 km; it is most intense with a vorticity of 20.5 × 10 −5 s −1 at 900 hPa. The strongest cold core of −3.0°C below 850 hPa and the above warm core of around 2.0°C are evident. The depression is tilted southwestward in the midtroposphere with no significant vertical tilt in the lower troposphere. The mean maximum intensity and upward motion over the life cycle of depression are in close agreement with the composite values. A strong cyclonic shear zone is developed in the midtroposphere preceding the depression. The necessary condition for barotropic (baroclinic) instability is satisfied in the midtroposphere (boundary layer). Strong northward transport of momentum by the depression against the southward shear is found. The strong growth of the MD in the lower troposphere is due to downward transfer of excess energy gained in the midtroposphere from the barotropic energy conversion and east–west direct thermal circulation as the vertical energy flux. The baroclinic interaction contributes to the maintenance of the cold core in the lower troposphere. The diabatic heating rate is computed and its role in the genesis and growth of MD is investigated.

The Anomalous Weather Parameters that Lead to the Extreme Rainfall of Kerala in August 2018

Extremely heavy rainfall has been occurred over Kerala, southwest coast of India, during mid-August 2018. The meteorological conditions during this period are analysed, and it is found that a combination of many rain favouring conditions prevailed at that time. The positive phase of Madden Julian Oscillation coupled with a monsoon depression in the Bay of Bengal and a weak trough in the south-eastern Arabian Sea strengthened the Monsoon Low Level Jet bringing moisture-laden winds over Kerala. The rising limb of Walker and Hadley circulations was also found over Kerala, which gave favourable updraft for cloud formation. In addition, the core of the Tropical Easterly Jet was found over the Kerala and Karnataka region. The cyclonic circulation in the mid-troposphere observed around the monsoon depression extended up to the west coast of India. Simultaneous occurrences of all these could have contributed to the extreme rainfall events and severe floods over Kerala.

Subseasonal Forecasts of the Northern Queensland Floods of February 2019: Causes and Forecast Evaluation

During the austral summer 2018/19, devastating floods occurred over northeast Australia that killed approximately 625,000 head of cattle and inundated over 3000 homes in Townsville. In this paper, the disastrous event was identified as a record-breaking subseasonal peak rainfall event (SPRE). The SPRE was mainly induced by an anomalously strong monsoon depression that was modulated by the convective phases of an MJO and an equatorial Rossby (ER) wave. The ER wave originated from an active equatorial deep convection associated with the El Niño warm sea surface temperatures near the dateline over the central Pacific. Based on the S2S Project Database, we analyzed the extended-range forecast skill of the SPRE from two different perspectives, the monsoon depression represented by an 850-hPa wind shear index and the 15-day accumulated precipitation characterized by the percentile rank (PR) and the ratio to the three-month seasonal (DJF) totals. The results of four S2S models of this study suggest that the monsoon depression can maintain the same level of skill as the short-range (3 days) forecast up to 8–10 days. For precipitation parameters, the conclusions are similar to the monsoon depression. For the 2019 northern Queensland SPRE, the model forecast was, in general, worse than the expectation derived from the hindcast analysis. The clear modulation of the ER wave that enhanced the SPRE monsoon depression circulation and precipitation is suspected as the main cause for the lower forecast skill. The analysis procedure proposed in this study can be applied to analyze the SPREs and their associated large-scale drivers in other regions.