On the decreasing frequency of monsoon depressions over the Indian region RESEARCH COMMUNICATIONS

Transcription

1 9. Shrd, A. C., Solomon, F. E., Um Devi, P., Udup, N. nd Srinivsn, K. K., Act Oncol., 1996, 35, Kmth, R., Ro, B. S. S. nd Um Devi, P., Phrm. Phrmcol. Commun., 1999, 5, Um Devi, P. nd Kmth, R., J. Rdit. Res., 2003, 44, Um Devi, P., Akgi, K., Ostpenko, V., Tnk, Y. nd Sughr, T., Int. J. Rdit. Biol., 1996, 69, Surmnin, S. S. nd Sethi, P. D., Curr. Sci., 1969, 38, Hill, R. P. nd Bush, R. S., Int. J. Rdit. Biol., 1969, 15, Um Devi, P. nd Ro, B. S. S., Strhlenther. Onkol., 1993, 10, Vrind, B. nd Um Devi, P., Mutt. Res., 2001, 498, Vrind, B., Ph D thesis, Mnipl Acdemy of Higher Eduction, Mnipl, Indi, Yuhs, J. M., Cncer Res., 1980, 40, Nyk, V. nd Um Devi, P., Rdit. Res., 2003 (communicted). 20. Yuhs, J. M. nd Storer, J. B., Int. J. Rdit. Biol., 1969, 15, ACKNOWLEDGEMENTS. This work ws supported y reserch grnt from the Defence Reserch nd Development Orgniztion, Ministry of Defence, Government of Indi. We thnk the Medicl Director nd Den, Kstur Medicl College, Mnipl for providing lortory fcilities for this work. We lso thnk Zndu Phrmceuticl Co, Mumi, for free supply of Withni root powder. Received 29 August 2003; revised ccepted 8 Jnury 2004 On the decresing frequency of monsoon depressions over the Indin region S. K. Dsh 1, *, Jenmni Rjendr Kumr 2 nd M. S. Shekhr 1 1 Centre for Atmospheric Sciences, Indin Institute of Technology Delhi, Huz Khs, New Delhi , Indi 2 Office of the Director Generl of Meteorology, Musm Bhvn, Indi Meteorologicl Deprtment, Lodi Rod, New Delhi , Indi *For correspondence. (e-mil: skdsh@cs.iitd.ernet.in) 1404 Studies on the occurrence of monsoon depressions over long period such s 1889 to 2002 show significnt decrese of their sesonl frequencies. Also, exmintion of monthly frequencies indictes tht the decresing trend ws mximum in July followed y August nd Septemer. There is no trend in the month of June. Therefore, n ttempt hs een mde in the present study, to exmine whether ny such vriility lso exists in the dynmicl prmeters representing the monsoon circultion such s horizontl nd verticl wind shers, men se-level pressure (MSLP), middle level temperture, moisture, se surfce temperture (SST) nd outgoing longwve rdition over the By of Bengl. NCEP/NCAR renlysed dt ville for the period hve een used for this study. Results show similr decrese in the horizontl nd verticl wind shers of the men monsoon flow over Indi s well s over the By of Bengl nd decrese in the moisture nd convection over the By re. There re corresponding incresing tendencies in the MSLP, temperture t 500 hp nd SST over the By of Bengl. Thus, in the present study, the decresing trend in the numer of monsoon depressions hs een supported y the fct tht the tmospheric dynmicl prmeters which fvour formtion of monsoon depressions hve wekened in recent yers. AMONGST ll the monsoonl wether systems, monsoon depressions re recognized s the min rinfll-producing synoptic wether systems over Indi. Intrsesonl nd internnul vritions 1 of monsoon depressions nd their effect 2 4 on intrsesonl nd internnul vrition of Indin summer monsoon rinfll (ISMR) hve een discussed y mny uthors. In ddition to the internnul vrition, ISMR exhiits strong interdecdl vritions Chrcteristics of the monsoon disturnces nd their reltionship with ISMR in longer timescles such s decdl to 30-yers, hve lso een exmined 11. These studies show the existence of dominnt interdecdl shifts in the chrcteristics of monsoon disturnces nd their reltionship with ISMR. Results lso indicte significnt decrese in the frequencies of occurrence of monsoon depressions. Figure 1 shows the 11-yer running mens of frequency nomlies of cyclonic storms nd depressions over the Indin region in the summer monsoon seson for the period The decresing trend since the seventies is well mrked. Such decresing trend in the frequency of occurrence of monsoon depressions over the Indin region is so predominnt in recent yers tht their verge sesonl frequency hs come down to 2 or 3 in the most recent decde of , from its longperiod verge vlue of 7 to 8. It my e noted tht for the first time in the lst 115 yers of dt ville with Indi Meteorologicl Deprtment (IMD), not single depression or cyclonic storm formed over the Indin region, including the By of Bengl nd Arin Se during the monsoon seson of Bsed on oserved dt from IMD, the occurrence of low-pressure res (LOPARS) is lso exmined nd their 11-yer running mens re shown in Figure 1. Interestingly, the study shows tht the numer of LOPARS hs incresed significntly from 1970s to the recent decde. Since the numer of LOPARS shows incresing tendency nd tht of depressions nd cyclonic storms indictes decresing trend, it my e inferred tht the dynmicl prmeters of the monsoon flow re not fvourle for the intensifiction of lows into depressions nd cyclonic storms. CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY 2004

2 Figure 1. nomlies nd their 11-yer running mens of () totl cyclonic storms nd depressions nd () low pressure res over the Indin region during June to Septemer for the period Monsoon depressions re importnt synoptic-scle tropicl disturnces which form periodiclly on the Indin summer monsoon circultion. According to the definition of IMD, in cse of depressions 12, the pressure grdient etween the centre nd distnce of 250 km from it rnges etween 5 nd 13 hp nd the surfce winds in cyclonic circultions re etween 8.5 nd 16.5 m/s. LOPARS re weker thn depressions, with surfce-wind speeds less thn 8.5 m/s. Cyclonic storms re more intense thn depressions, with surfce-wind speeds more thn 16.5 m/s. Monsoon depressions usully hve horizontl wvelengths of out 2000 km nd in their most intense stge, they cn hve verticl extension 12 up to out km. Depressions re like verticl tues of cyclonic vorticity, with well-defined cold core in the lower troposphere nd wrm core ove. The depression centre is either nerly verticl or hs smll westwrd 13 tilt with height. The kinetic energy of such disturnces is mintined y comined rotropic roclinic instility in the presence of the conditionl instility of the second kind (CISK). Mny studies show tht strong horizontl nd verticl wind shers support the growth of LOPARS to monsoon depressions nd cyclonic storms through the conversion of sic-flow kinetic energy nd ville potentil energy into perturtion kinetic energy. In the presence of convective heting, the horizontl nd verticl wind shers of the men monsoon flow to lrge extent, determine the growth rte, horizontl structure nd the phse speed of the monsoon depressions. Monthly frequencies of cyclonic storms nd depressions during the summer monsoon seson over the Indin region re collected from IMD for the period Frequencies of LOPARS re tken from erlier pulictions 2,11. In this study, the numer of cycolonic storms is clculted y including ll disturnces with intensities of cyclonic storms nd ove. Monthly Reynolds SST t 2 2 grids nd NCEP/NCAR renlysed dt t grid for the period re used to compute the nomlies in SST, wind shers, moisture, men se-level pressure (MSLP), outgoing longwve rdition (OLR) nd temperture t 500 hp over the By of Bengl within the ltitude elt N, where the depressions usully occur. Horizontl wind shers t 850 hp nd verticl wind shers etween 850 nd 200 hp levels re lso cl- CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY

3 Figure 2. Eleven-yer running mens of frequency nomlies of cyclonic storms nd depressions over the Indin region in () June nd Septemer nd () July nd August. culted over the Indin region. -wise nomlies re computed on the sis of men vlue. Elevenyer running mens of the nomlies re computed for nlysis. Figure 2 nd show 11-yer running mens of frequency nomlies of cyclonic storms nd depressions for June nd Septemer, nd July nd August respectively. As shown in Figure 2, in the month of June, there is no significnt vrition in the frequency of cyclonic storms nd depressions for the entire period of study, the fluctution eing within ±. The highest nd lowest numer of systems in June ws oserved during nd respectively. In Septemer (Figure 2 ), there is little chnge during the period , with decresing trend therefter. The highest nd lowest numer of systems in Septemer ws oserved during nd respectively. As shown in Figure 2, in the month of July, the frequency nomly of cyclonic storms nd depressions hs decresed from in 1898 to in Therefter, steep increse up to is oserved till Afterwrds, decresing trend is oserved till recent yers, with mximum fll of frequency to 1.2. The highest nd 1406 lowest numer of systems in July ws oserved during nd respectively. In August, the vrition in frequency of occurrence of cyclonic storms nd depressions (Figure 2 ) is similr to tht in July, except tht there is n incresing trend from 1966 to The highest nd lowest numer of systems in August ws oserved during nd respectively. Bsed on climtology, one my infer tht July nd August re fvourle months for more depressions nd storms. However, there is exctly no preferred month to hve mximum numer of systems every yer. During some yers, even June nd Septemer were hving mximum numer of cyclonic storms nd depressions. In generl, June hs the lowest numer of cyclonic storms nd depressions, while the numer of cyclonic storms nd depressions during other months shows vritions from period to period. We consider July nd August to e the most importnt months for monsoon depressions nd exmine the chrcteristics of dynmicl nd convective prmeters during these two months. Figure 3 nd shows the monthly zonl men wind in July t 850 nd 200 hp respectively, verged over the Indin ltitudes etween 55 nd 95 E, sed on NCEP/ CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY 2004

4 Ltitude ( 0 N) Ltitude ( 0 N) Wind (m/s) Wind (m/s) Figure 3. Ltitudinl vrition of zonl wind component in July over the Indin region etween 55 nd 95 E t () 850 hp nd () 200 hp. Sher Sher - Sher (m/s) / frequency Figure 4., Eleven-yer running mens of nomlies of horizontl wind sher t 850 hp in July etween ltitudes 0 nd 25 N verged over longitudes E;, Eleven-yer running mens of horizontl wind sher nomlies in July etween 850 nd 200 hp levels, verged over the Indin region 0 25 N nd E. Sher (m/s) / frequency Sher Sher (m/s) / frequency Sher - - Figure 5., Sme s in Figure 4, ut for the month of August., Sme s in Figure 4, ut for the month of August. NCAR renlysed dt for the period The lrge vlues of horizontl wind sher over the Indin ltitudes re evident in Figure 3. For exmple, t 850 hp (Figure 3 ), the wind sher etween 5 nd 15 N ltitudes is out 7 m/s. Similrly, t the upper level (Figure 3 ), the wind sher etween the sme two ltitudes is out 10 m/s. Studies hve shown tht lrge horizontl wind sher in the men monsoon flow supplies kinetic energy to the CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY

5 Sher (m/s) / frequency Sher Sher (m/s) / frequency - Sher Figure 6., Eleven-yer running mens of horizontl wind sher nomlies in July etween 50 nd 25 N lt, verged over the By of Bengl., Eleven-yer running mens of verticl wind sher nomlies in July etween 850 nd 200 hp, verged over the By of Bengl region 15 nd 25 N. Figure 7. Sptil distriution of difference in the vlues of verticl wind sher ( hp) nomly etween nd during () July nd () August. Temperture ( C) / frequency - - Temperture Temperture ( C) / frequency - - Temperture Figure 8. August. Eleven-yer running mens of temperture nomlies t 500 hp verged over the By of Bengl region during () July nd () monsoon disturnces for their growth. Similrly, the lrge verticl wind shers help in converting the ville potentil energy of the men flow to the perturtion 1408 kinetic energy for the intensifiction of monsoon disturnces. Figure 4 shows the 11-yer running mens of horizontl wind sher nomly in July t 850 hp etween CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY 2004

6 MSLP (hp) / frequency - MSLP MSLP (hp) / frequency - - MSLP - Figure 9. Sme s in Figure 8, ut for men se level pressure (MSLP) nomly. Moisture (g / kg) / frequency - - Moisture Moisture (g / kg) / frequency Moisture Figure 10. Sme s in Figure 8, ut for moisture nomly. the ltitude circles 0 nd 25 N, verged over the Indin longitudes E. For convenience of comprison, the 11-yer running mens of frequency nomlies of cyclonic storms re lso plotted in the sme figure. Simultneous decrese of horizontl wind sher nd frequency nomlies during the lst two decdes is clerly visile. Similrly, Figure 4 shows the verticl wind sher nomly in July etween 850 nd 200 hp, verged over the region 0 25 N nd E long with the frequency nomly of storms. The verticl wind sher nomly hd decresing trend during 1960s nd 1970s nd during the lst three decdes it lmost remined constnt, with some internnul fluctutions. Figure 5 nd shows similr nomlies s in Figure 4 nd respectively, ut for the month of August. Simultneous decrese of oth horizontl nd verticl wind sher nomlies with the decrese in frequency nomlies of depressions during the lst three decdes, is clerly indicted in the figure. Since depressions nd cyclones occur mostly over the By of Bengl, the dynmicl prmeters over this region re exmined in conjunction with the frequency of storms. Figure 6 shows the 11-yer running mens of horizontl wind sher nomlies in July etween the ltitudes 15 nd 25 N, verged over the longitudes of the By of Bengl region long with the 11-yer running mens of frequency nomlies of cyclones. In generl, oth the curves indicte decresing tendency, except tht fter 1988 there is some increse in the horizontl wind sher nomly for four yers. However, towrds the end there is n indiction of decrese gin. Figure 6 shows the 11-yer running mens of verticl wind sher nomlies in July etween 850 nd 200 hp levels, verged over the By of Bengl region, long with the corresponding curve for depression frequency. Both the curves exhiit similr internnul vritions up to the erly eighties, fter which the verticl wind sher nomly incresed for out decde. However, there is shrp decrese during the pst decde long with decrese in depression frequency. The sptil distriution of the difference in the men vlues of verticl wind sher ( hp) in July, verged over the period to the recent two decdes, , is depicted in Figure 7 to study the sptil chrcteris- CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY

7 OLR (W/m 2 ) / frequency OLR OLR (W/m 2 ) / frequency OLR Figure 11. Sme s in Figure 8, ut for OLR nomly. SST 1.2 SST SST ( C) / frequency - - SST ( C) / frequency - - Figure 12. Sme s in Figure 8, ut for SST nomly. tics of chnges in verticl wind sher over Indi. Figure 7 shows similr field in the month of August. Figure 7 nd exhiit similr chnges in the verticl wind sher etween the two decdes nd the recent two decdes The difference is more in the month of August thn in July, specilly over the By of Bengl region. Figure 8 nd shows the 11-yer running mens of temperture nomlies t 500 hp, verged over the By of Bengl re in July nd August respectively, long with the 11-yer running mens of depression frequency. The figure indictes tht s the mid-level temperture nomlies increse since the seventies, the frequency of occurrence of depressions decreses. Figure 9 nd shows the 11-yer running mens of MSLP over the By of Bengl in July nd August respectively. The opposite chrcteristics of chnges in MSLP nd frequency of depressions re visile. Similrly, Figure 10 nd depict the 11-yer running mens of moisture nomlies over the By of Bengl in July nd August respectively. The moisture in the By re shows decresing trend 1410 long with the decrese in the frequency of depressions. Figure 11 nd shows the 11-yer running mens of OLR nomlies over the By re in July nd August respectively. OLR nomlies exhiit vritions opposite to those of the frequency of depressions. Figure 12 nd shows the 11-yer running mens of SST nomlies verged over the By re in July nd August respectively. The SST nomlies show incresing tendency s the frequency of depressions decrese during the seventies. Erlier results 19 lso indicte out-of-phse reltionship etween By of Bengl SST nd storm frequency since mid-1980s. Hence decresing frequency of monsoon depressions over the Indin region my not e due to the chnge in SST, ut due to unfvourle tmospheric dynmicl prmeters which do not support the formtion of more depressions over the Indin region. The decrese in the occurrence of depressions my lso e due to the movement of lesser numer of remnnts from djoining west Pcific to the By of Bengl in recent decdes. It my e noted tht the decrese in the frequency of monsoon depressions my not e due to ny sptil shifting to CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY 2004

8 the South By, since oservtions do not indicte ny such signl either in terms of frequency of depressions or OLR nomlies over oth north nd south By of Bengl. The interction etween SST in north Indin Ocen nd the convection or monsoon depression formtion is complex 20. Wrm SST nomlies lone re not sufficient for initition of intense convection over the By of Bengl or Arin Se re, leding to the genesis of meso-scle systems nd hence their intensifiction to monsoon depressions or cyclonic storms. Rther, fvourle tmospheric environmentl conditions like low-level convergence nd verticl wind sher re foremost conditions. The results of the present study indicte tht lthough the numer of LOPARS hs een incresing during the lst two decdes, the dynmic conditions such s wind shers, MSLP, moisture, etc. re not fvourle for their intensifiction to depressions nd cyclones. Thus, there is decrese in the numer of depressions nd cyclones during the lst two decdes. However, it is essentil to exmine why convection ecomes weker in spite of incresed SST over the By of Bengl during the pst yers. 1. Chen, T. C. nd Weng, S. P., Mon. Wether Rev., 1999, 127, Mooley, D. A. nd Shukl, J., Musm, 1989, 40, Jenmni, R. K. nd Dsh, S. K., Musm, 1999, 50, Jenmni, R. K. nd Desi, D. S., Musm, 1999, 50, Thpliyl, V. nd Kulshresth, S. M., Musm, 1991, 42, Thpliyl, V., J. Arid Environ., 1997, 36, Kriplni, R. H., Kulkrni, A. nd Singh, S. V., Int. J. Climtol., 1997, 17, Krishnmurthy, V. nd Goswmi, B. N., J. Climte, 2000, 13, Wester, P. J., Mgn, V. O., Plmer, T. N., Shukl, J., Thoms, R. A., Yni, M. nd Ysunri, T., J. Geophys. Res. C, 1998, 103, Srivsthv, A. K., Sinh Ry, K. C. nd De, U. S., Musm, 2000, 51, Jenmni, R. K. nd Dsh, S. K., Int. J. Climtol., 2001, 21, Sikk, D. R., Pgeoph, 1977, 115, Keshvmurty, R. N., J. Atmos. Sci., 1972, 29, Dsh, S. K. nd Keshvmurty, R. N., Beitr. Phys. Atmos., 1982, 55, Mishr, S. K. nd Slvekr, P. S., J. Atmos. Sci., 1980, 37, Shukl, J., J. Atmos. Sci., 1978, 35, Keshvmurty, R. N., Styn, V. nd Goswmi, B. N., Nture, 1978, 274, Goswmi, B. N., Keshvmurty, R. N. nd Styn, V., Proc. Indin Acd. Sci. (Erth Plnet. Sci.), 1980, 87, Rjeevn, M., De, U. S. nd Prsd, R. K., Curr. Sci., 2000, 79, Wester, P. J., Clrk, C., Cherkov, G., Fsullo, J., Hn, W., Loschnigy, J. nd Shmi, K., Meteorology t the Millennium (ed. Perce, R.), Acdemic Press, 2002, pp Received 26 My 2003; revised ccepted 1 Jnury 2004 Genetic diversity of lck grm (Vign mungo) lndrces s evluted y mplified frgment length polymorphism mrkers K. R. Sivprksh, S. R. Prshnth, B. P. Mohnty nd Ajy Prid* M. S. Swminthn Reserch Foundtion, III Cross Street, Institutionl Are, Trmni, Chenni , Indi Twenty-six lndrces of lck grm collected from Oriss, Indi were nlysed for genetic diversity using mplified frgment length polymorphism (AFLP) mrkers. Seven primer comintions were used for AFLP nlysis. The percentge polymorphism cross the smples vried from 74.5 to 93%. The level of rre nd common lleles contriuting to the diversity in the smple ws nlysed using the Shnnon Weiner (SW) diversity index. The SW index reveled tht three smples of the entire twenty-six contriuted significntly to the overll diversity of the smple set. A dendrogrm ws constructed sed on the UPGMA clustering method, which reveled three mjor clusters. A principl component nlysis of the sme dtset reveled similr results to tht of the dendrogrm, with the first principle component ccounting for 58% of the totl vrition. The nlysed smples formed five significnt groups. Three smples were distinct in their clustering nd remined seprte from the other smples. Influence of soil pttern nd topogrphy in the genetic mke up of the lndrces ws visile nd seemed to contriute to the genetic distinctness of the lndrces. This genetic diversity could well e utilized for future reeding work. BLACK grm (Vign mungo) is tropicl leguminous plnt, which elongs to the Asitic Vign species long with V. rdit, V. trilot, V. conitifoli nd V. glerecence. It is cultivted s fllow crop fter rice cultivtion in Indi. It is grown in vrious gro-ecologicl conditions nd cropping systems with diverse griculturl prctices 1. In vrious prts of Indi, prticulrly in the hilly regions, numer of trditionl lndrces re still eing cultivted s inter crops etween rice, sugrcne, cotton, groundnut nd sorghum cultivting sesons. These lndrces possess unique trits (e.g. disese tolernce, iotic stress tolernce, pest tolernce), which hve een identified y the frmers. The frmers hve een conserving these lndrces for genertions through in situ on-frm conservtion prctices where they collect the seeds of the germplsm nd use the sme seeds for rising the next seson. This prctice is commonly seen in lrge prt of Oriss. In recent yers, there hs een significnt decline in the pulse production in Indi. Lck of suitle vrieties nd *For correspondence. (e-mil: mngrove genes@mssrf.res.in) CURRENT SCIENCE, VOL. 86, NO. 10, 25 MAY