Chowdhury, Swati

Deb, N C

Pal, Amita

IACS Institutional Repository

Indian J. Phys. 75B (3), 259-262 (2001)U P  Ban international JournalAcoustic remote sensing of LPBL over Antarctic environmentN  C  D eb*Electronics & Communication Sciences Unit, Indian Statistical Institute, 203, B T Road, KolkaU-700 035, IndiaE-mail ‘ narayan@isical ac in an dS w ati C h o w d h u ryMachine Intelligence Unit, Indian Statistical Institute, 203, D i Road, Kolkata-700 035, Indiaa n dA m ita  P a lApplied Statistics Unit, Indian Statistical Institute, 203, B T Road, Kolkata-700 035, IndiaAbstract Acoustic sounding experiment and meteorological observations were carried out on simultaneous basis at the Indian Antarctic station Maitri (70 76°S, 11 73*’H) during XV-th Indian Scientific Expedition to Antarctica from January 1995 to January 1997. The entire Antarctic zone is very prone to the sudden occurrence of blizzards during difTercnt month and seasons This stormy activity brings drastic changes m the planetary boundary layer over Antarctica. In order to understand the dynamics of LPBL over this region, all meteorological parameter before onset of blizzard, during and after blizzard have been studied Impact of these blizzards on sodar structures is also highlighted. The effect ot various other phenomena such as katabatic wind, forced convection, etc. arc also visualized.Kf>ivord# LPBl., acoustic sounder, Antarctic environmentl*A(’S Nos. 43 30 -p, 43 50 +\, 93.30 Ca1. I n t ro d u c tio nThe A n tarc tic  c o n tin e n t c o m p r is e s  o n e  te n th  o f  th e  lan d  surface o f  th e  e a r th  a n d  th e  A n ta rc t ic  s e a s  m a k e s  u p  a b o u t one tenth o f  th e  w o r ld 's  o c e a n s . T h is  h u g e  c o n tin e n t is covered w ith  a  p e rm a n e n t  s h e e t  o f  ice . It is  c o n s id e re d  to  be a m ajor h e a ts in k  w h ic h  p la y s  a  v ita l ro le  in  m a in ta in in g  the balance o f  h e a t  e n e rg y  a n d  m o m e n tu m  o f  e n tire  e a r th ’s environment. S c ie n tis ts  f ro m  d if fe re n t c o m e rs  o f  th e  g lo b e  have rea lized  th e  f a c t  a n d  s ta r te d  e x p lo r in g  th e  A n ta rc tic  environm ent s in c e  1 9 5 6 . W e  h a v e  a ls o  p la n n e d  to  in v e s tig a te  the c h a ra c te ris tic s  o f  L P B L  (L o w e r  P la n e ta ry  B o u n d a ry  Layer) o v e r A n ta rc t ic a .  W e  h a v e  in s ta l le d  a  m o n o s ta t ic  s o d a r  system an d  r e c o r d e d  th e  o b s e rv a tio n s  o n  a  re g u la r  b a s is . W e  have c o lle c te d  m e te o ro lo g ic a l  d a ta  u s in g  d if fe re n t in situ m easurem ent te c h n iq u e s . T h e  e n tire  A n ta rc t ic  z o n e  is  v e ry  prone to  th e  o c c u r r e n c e  o f  b l iz z a rd s  th ro u g h o u t th e  y e a r . In  this p a p e r w e  w ill p re s e n t  th e  d if fe re n t ty p e  o f  so d a r  structures o b s e r v e d  o v e r  A n ta rc t ic a  d u r in g  th e  c o u rse  o f  d a ta  collection. M e te o ro lo g ic a l o b se rv a tio n s  a re  re c o rd e d  ca re fu lly  during an d  a f te r  d e p a r tu re  o f  b liz z a rd . In  a d d it io n  to  th is , w e* Corresponding Authorw ill d isc u ss  a b o u t th e  d isc re p e n c ie s  in th e  b e h a v io r  o f  th e  m e te o ro lo g ic a l p a ra m e te rs  o b se rv e d  d u rin g  th e  n o rm a l and  s to rm y  p e rio d  o v e r  A n ta rc tica .2 . D e s c r ip t io n  o f  th e  s y s te m  a n d  d a t a  c o lle c tio nF ig u re  I sh o w s th e  b lo c k  d ia g ra m  o f  a  m o n o s ta tic  a co u stic  so u n d in g  sy s tem , w o rk in g  su c c e ss fu lly  a t M a itr i , A n ta rc tica .Figure 1. Block diagram of sodar system (1) Antenna system; (a) acoustic shield, (b) parabolic dish made of fiber glass, (c) transducer with cone, (d) transmit receive switch with pre-amplifier. (2) Receiving unit: (a) band pass filter, (b) detector, (c) log amplifier. (3) Power amplifier (4) lx)W pass filter (5) Personal computer. (6) Vedio display unit. (7) Digital printer. (8) Facsimili recorder.© 2001 I ACS260 N C Deb, S^ati Chowdhury and Amita PalA  tra n s-re c e iv in g  an te n n a  h as b e e n  used  to  tran sm it an d  re c e iv e  th e  so u n d  s ig n a l (5 0  m iliseco n d  p u lse  o f  1800 H z  to n e )  a n d  th e  sy s tem  is fu lly  co m p u te r-co n tro lled . T h is  is a  m o n o s ta tic  a c o u s tic  so u n d e r an d  em its  h ig h  p o w er aco u stic  p u lse s  w ith  a  s in g le  p a rab o lic  an ten n a . T h e  sam e an ten n a  p e rfo rm s  as  th e  re c e iv e r  o f  th e  b ack sc a tte re d  s ignals. T h e  sy s tem  em its  so u n d  p u lse s  o f  1800 H z, each  o f  50  m illiseco n d  d u ra tio n , a t in te rv a ls  o f  10 seco n d s . T h e  sca tte red  in ten sity  o f  a c o u s tic  p u ls e s  re f le c te d  b y  s c a t te re r  ( te m p e ra tu re  in h o m o g en itie s )  a t d iffe re n t h e ig h ts  a re  m easu red  at an  in te rv a l o f  2 m e te rs  v e rtic a l d is tan ce  u p to  1 k ilo m ete r. D ig itiz e d  d a ta , a re  s to red  in co m p u te r m em o ry  an d  o n lin e  d isp la y  o f  the  a tm o sp h e ric  s tru c tu re  can  a lso  be o b se rv ed  on  c o m p u te r  sc reen . A t th e  sam e  tim e, th e  th ree  d im en sio n a l (tim e , h e ig lu  an d  in ten sity ) b e h a v io u r o f  th e  an a lo g  s ig n a ls  a lso  a re  re c o rd e d  on  facs im ili c h a rt reco rd e r. A ttem p t h as b e e n  m ad e  to  re c o rd  th e  d a ta  on  a  ro u n d -th e -c lo ck  b asis d u rin g  th e  n o rm a l d ay s (w in d  is less th an  10 kno ts).3 . O b s e r v a t io n s  a n d  a n a ly s isF ig u re s  2 a  an d  2 b  are  d raw n  to  g e t fu r th e r k n o w led g e  o f  b liz z a rd  h is to ry  o v e r  A n ta rc tica . F ig u re  2 a  p re sen ts  theTibic 1. Blizzard observed at Maitri (Antarctica) during the ve 1996. ^Onset of blizzard Off^ of blizzard Duration of b l i^iillllllliii f(b)Figure 2. (a) Total number of blizzard per month and (b) Total duration of blizzard per monthm o n th ly  v a r ia t io n  in  n u m b e r  o f  b l iz z a rd s .  S im ila r ly , F ig u re  2 b  sh o w s th e  m o n th ly  v a ria tio n  in d u ra tio n  o f  b liz z a rd s  d u rin g  d iffe re n t m o n th s. F ig u re  2 a  sh o w s th a t m ax im u m  n u m b e r o f  b liz z a rd s  o c c u r  d u rin g  th e  m o n th  o f  F eb ru a ry  w h e re a s  it is m in im u m  in Jan u a ry . O n  th e  o th e r h an d . F ig u re  2 b  sh o w s th a t to ta l d u ra tio n  o f  b liz z a rd  is m ax im u m  in Ju ly  an d  m in im u m  in  Jan u a ry .T a b le  I sh o w s th e  d a te  a n d  tim e  o f  o n se t, o ffse t an d  d u ra tio n  o f  b liz z a rd s  o b se rv e d  a t M a itr i (A n ta rc tic a )  d u rin g  th e  y e a r 1996. T h e  m in im u m  d u ra tio n  (1 0  h o u rs )  o f  b liz z a rd  w e re  o b se rv e d  o n  2 0 th  F e b ru a ry  1996. W h e re a s  m ax im u m  d u ra tio n  (3 4 7  h o u rs )  o f  b liz z a rd  w e re  o b se rv e d  d u rin g  15th Ju ly  to  3 0 th  Ju ly  1996 re sp e c tiv e ly . It c an  b e  o b se rv e d  fro m  th is  ta b le  th a t a  to ta l o f  38  b liz z a rd s  o c c u rre d  a t o u r s ite  o f  e x p e rim e n t d u rin g  th a t y ear. M a x im u m  w in d  g u st (6 2  m /s) w a s  re c o rd e d  o n  18th Ju ly  1996.F ig u re s  3 a  a n d  3 b  sh o w  th e  v a ria tio n  in  w in d  sp eed  d u rin g  th e  b liz z a rd  d ay s  an d  n o rm a l d ay s  re sp ec tiv e ly . D u r in g  tlie  b liz z a rd  d ay s , w in d  sp e e d  is co m p a ra tiv e ly  m u ch  h ig h e r  (a s  h ig h  a s  25  m /se c ) th a n  th a t o n  n o n n a l d ay s  (5  to  10 m /se c ) .No Date Time Date Time Hour Minute1 31.01.1996 08:45 02.02 1996 09:50 49 052 06.02 1996 OO 00 08 02.1996 03:50 51 503 11.02.1996 23:30 14 02 1996 07:30 56 004 20 02.1996 00:00 20 02.1996 10.00 10 005 23 02.1996 03:00 24.02.1996 09:00 30 006 25 02.1996 01.00 25 02.1996 13.00 12 007 02 03.1996 17 00 05 03 1 996 07:25 62 258 21.03 1996 01 40 21 03.1996 18:55 13 159 24.03.1996 05 45 27 03 1996 13 20 79 3510 30 03.1996 17 50 02.04.1996 07.15 37 2511 04.04 1996 23:25 07.04.1996 02:40 51 1512 10 04 1996 19:50 11 04.1996 17:20 21 3013 14.04.1996 00.00 16.04.1996 16:55 64 5514 17 04 1996 10.35 • 21 04.1996 22.20 107 4515 01 05.1996 11.15 05 05 1996 13.10 97 5516 08 05 1996 08 45 09 05 1996 03.35 18 5017 15 05.1996 00 00 17.05.1996 03.25 51 2518 25.05 1996 02 25 01 06.1996 19 185 1519 04.06.1996 19 35 05 06 1996 14:55 19 2020 08.06.1996 06 25 15.06.1996 04 IS 165 5021 28 06.1996 11.35 08 07 1996 16 20 240 4522 11 07 1996 01:40 13 07 1996 10.15 56 3523 15.07 1996 23 25 30.07 1996 10 30 347 0524 03 08 1996 07.55 06 08 1996 18 45 82 5025 09 08.1996 14 40 10 08.1996 15.35 24 5526 17 08 1996 09.50 19.08 1996 03 35 41 4527 23 08 1996 15 00 01.09.1996 12 00 213 0028 13.09.1996 00.00 14.09.1996 11:25 35 2529 16.09 1996 16:45 23 09.1996 07:10 158 2530 26 09 1996 20:20 30 09.1996 08:25 84 0531 02.10.1996 21.10 05.10.1996 19:25 70 1532 15.10.1996 02:25 18 10.1996 12:30 82 0533 21.10.1996 21:20 23.10.1996 04:55 31 3534 25.10.1996 04:15 01 11 1996 06:50 170 3535 07.11.1996 22:00 12. i r  1996 13:55 111 5536 21.11.1996 11:50 24 11.1996 06:35 66 4537 01.12.1996 00:00 02.12.1996 07:15 31 1538 15.12.1996 00:00 19.12 1996 15:15 111 15IBMM ipHd MMiOeNlm - III N«v«iMr 1M■MM•paM I'F NowMHr ttM1 .|:.Tl K , m K r > iTJa ■ t « t ■ K * 1(a) (b)Figure 3. (a) B lisvd days and (bj nonnal days.Acoustic remote sensing o f LPBL over Antarctic environment 261Figures 4a and 4b depict the direction ofwind during the sometimes it is associated with multilayered structuresblizzard and normal days respectively. It can be observed appearing in the at 700 to 1000 m range. A noticeable4 i--H«Mr ->i c i i B t c a i i f i s i i i s i i i ;N«Mr(a) (b)Figure 4. (a) Blizzard days and (b) normal daysT«np«um 14thOctob« - 111 Htmmbm im  Twitpamun 2-7 NovamiMr I996i i ' w v v ^(a) H o u r  - >(b)Figure 5. (a) Blizzard days and (b) normal daysR H um M y J4H1 O c lo ta r  111 H o v a m ta r  I M  Humw«y 2 7 N ovam bar i MHour -»(«) (b)r'lsurc 6. (a) Blizzard days and (b) normal days.P iaa iu ro  31  Ih  O clotaor 10 1st N o v a m lw r  P i v m i m  2-7 Noaom bor I MMow.->(a)Figure 7. (a) Blizzard days and (b) normal days (b)that d u rin g  th e  b liz z a rd  d a y s , w in d  d ire c tio n  re m a in e d  constant a t 150° w h e re a s  o n  n o rm a l d a y s , it v a r ie d  b e tw een  0" to 300°.4. C o n c lu s io n  a n d  a p p l i c a t i o nExperim ental o b s e rv a tio n s  o n  A n ta rc t ic a  sh o w  th a t fo r  m o re  than one th ird  o f  a  y e a r , th is  a re a  re m a in s  u n d e r  th e  in flu en ce  of storm y a c tiv ity  w h ic h  in  tu rn , b r in g s  d ra s tic  c h a n g e s  in the c h a rac te ris tic s  o f  lo w e r p la n e ta ry  b o u n d a ry  layer. S o d a r observations re v e a l th a t th e  m e c h a n ic a l tu rb u le n c e  in tro d u c e d  ui LPBL d u e  to  s to rm y  a c tiv it ie s  an d  fro n ta l d is tu rb a n c e s  (generated fro m  th e  A n ta rc t ic  o c e a n )  a ffe c ts  th e  u n ifo rm  formation o f  g ro u n d  b a se d  in v e rs io n  la y e rs  s ig n ific a n tly . In  addition to  th is , fo rm a tio n  o f  m u lti la y e re d  s tru c tu re s  a t th e(a)■ L(b)(c)(c)(0(g)(b)Figure 8. (a) May 5. time 0050 to 0850 hours, (b) May 21. time ; 1020 to 1820 hours; (c) May 12. time 0720 to 1520 hours; (d) May 22,elevated lev e l a rc  a ls o  a b s e n t d u r in g  th is  p e r io d . O n  th e  o th e r  . 1 9 0 0  10 0300 hours; (c) August 22. time . 1030 to 1830 hours, hand, d u rin g  th e  n o rm a l d a y s  a  th ic k  (a b o u t 5 0 0  m ) g ro u n d  (f) September 25. time ; I6 IO to 0010hours, (g)November I7, time : 1015based in v e rs io n  la y e r  w ith  u n ifo rm  to p  is fo rm e d  an d  t8i5 hours and (h) December 6, time ; 09io to i 7 i o  hours262 N C Deb, Swati Chowdhury and Amita Pald if fe re n c e  h a s  a ls o  b e e n  o b se rv e d  in th e  b e h a v io u r  o f  v a rio u s  References m e te o ro lo g ic a l p a ra m e te rs  re c o rd e d  d u rin g  th e  s to rm y  an d  li)  n o rm a l p e r io d s .  T h e s e  d is c re p a n c ie s  can  b e  u s e d  to  d e v e lo p  a n  a p p r o p r ia t e  m a th e m a t ic a l  m o d e l  fo r  th e  A n ta rc t ic  e n v iro n m e n t. A t th e  sa m e  tim e  th is  ty p e  o f  s tu d y  |2l c a n  p ro v e  e x tr e m e ly  u se fu l in d e te rm in in g  th e  m e rits  a n d  d e m e r its  o f  ra d io  c o m m u n ic a tio n  an d  o th e r  re la te d  |3| f ie ld s .W I) Neff Remote Sensing of Atmospheric Processes over Complex Terrain by W Blumen (Boston, MA * AMS) P173 (1991)W Schwerdtfegcr Weather and Climate o f  the Antarctic (Hlscvicr) (1984)S Kobayashi and N Ishikawa Proc Fifth Symp Polar Meteor dt Glacial (N I Polar Research, 37-49, Tokyo) (19 8 3)

Acoustic Remote Sensing of LPBI Over Antarctic Environment

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Acoustic Remote Sensing of LPBI Over Antarctic Environment

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