Chanda, Amitabha

Deb, N C

IACS Institutional Repository

Indian J. Phys. 75B (3), 251-253 (2001)U P  1— an international joiimalOn the structure of horizontal wind flow in the surface layer of Maitri,AntarcticaN  C D eb *  an d  A m itab h a  C h an d aElectronics & Communication Sciences Unit, Indian Stalislical Institute, 203, B T Road. Kolkala (Calcutta)-700 035, IndiaE-mail narayan^J'iisical.ac in andH P M azu m d arPhysics and Applied Mathematics Unit, Indian Statistical Institute, 203, B T Road, Kolkata (Calculla)-700 035, Indiaan dH N D u ttaRadio and Atmospheric Sciences Division, National Physical Laboratory, K S Knsnan Marg, New Delhi-110 011 , IndiaAbstract ' Wind field in Antarctica has been studied with the help of data, collected during XV-lh Indian Scientific Expedition to Antarctica 1995-97 Based on the data of wind velocity measured at the surface layer of Indian Antarctic station Maitri (70 76°S, 11 73“E), a simple model on wind direction pattern is presented Analysis of the daily/monthly/seasonal (3 month/scason) and yearly variation of such wind velocity is made from the statistical point of view Various aspects of the model, presented here are discussedKeywords Wind velocity, log-normal distribution, Antarctica,PACS Nos. 92 70 Cp, 93 30 Ca, 92.60.Gn1. I n t r o d u c t io nThe c lim a to lo g ic a l s tu d y  o f  w in d  is im p o rta n t as it p ro v id e s  in fo rm ation  a b o u t v a r io u s  p a ra m e te rs , re g a rd in g  c h a n g e s  in w eather [ I ] .  T h e  s ta tis tic a l a n a ly s is  o f  d a ta  o n  w in d  sp e e d  and its d ire c tio n , m e a s u re d  a t th e  m e te o ro lo g ic a l s ta tio n  is considered  im p o rta n t in  th is  re sp e c t. T h e  sy n o p tic  sy s tem  around A n ta rc t ic a  a re  ty p ic a lly  in h o sp ita b le  an d  d re a d fu l, unlike e ls e w h e re . M a n y  u n iq u e  fe a tu re s  lik e  th e  p re se n c e  o f  ice-sheet, lo n g  w in te r  n ig h t, a v e ra g e  s lo p e  o f  th e  co n tin e n t, p resence o f  c o n tin e n ta l sca le  in v e rs io n , o c c u rre n c e  o f  b lizza rd  and a s so c ia te d  o th e r  p h e n o m e n a  e x p e c te d ly  in f lu en ce  th e  m eteo ro log ical v a r ia b le s  s ig n ifican tly . M o re o v e r, it is b e liev ed  that the  A n ta rc t ic  c lim a te  d ire c tly  in f lu e n c e s  th e  g lo b a l clim ate in  v a r io u s  w a y s  [2 ]. T h e  p re s e n t s tu d y  is c o n c e rn e d  with th e  d a ta , m a in ly  o n  w in d  v e lo c ity , m e a s u re d  in th e  surface la y e r  o f  th e  In d ia n  A n ta rc t ic  s ta tio n  M a itri. V a rio u s  statistical fe a tu re s , su c h  a s  m o n th ly , s e a so n a l an d  y ea rly  variation  o f  w in d  s p e e d  a n d  its  d ire c tio n a l c o m p o n e n ts  a re  analysed  [ 3 ,4 ]  th ro u g h  c a lc u la tio n s  o f  m e a n , s ta n d a rd  dev ia tion , f r e q u e n c y  d is tr ib u tio n  c o rre s p o n d in g  to  tim eseries  d a ta  c o lle c te d  a t the  M aitri s ta tio n . In th is  p a p e r, it is ex am in ed  i f  it is p o ss ib le  to  b u ild  m o d e ls  o f  w in d  fie ld s  fo r th e  A n ta rc tic  c lim a te .2 . M e a s u r e m e n t  a n d  d a ta  c o lle c tio nE x ten siv e  m ea su re m e n t w as ca rr ied  o u t to  c o lle c t d a ta  on w in d  sp eed  an d  d irec tio n . In s tru m en ts  u sed  in th is  ex p e rim en t a re  a  cu p -a n e m o m e te r and  sen s itiv e  ro ta tin g  arm  w in d  van e  to  m easu re  w in d  sp eed  an d  d irec tio n . T h e  acc u ra c y  in m e asu rin g  w in d  sp eed  jin d  d irec tio n  are  0 1 m /s  an d  + 2°, re sp ec tiv e ly . E ach  sen so r w as c a lib ra te d  as p e r th e  s ta n d a rd s  m a in ta in ed  b y  th e  In d ian  M e te o ro lo g ic a l D e p a rtm e n t (IM D ), G o v e rn m en t o f  In d ia . S en so rs  w e re  m o u n ted  a t 4 leve ls (1 .8  m , 4 .5  m , 11.3 m an d  28  in ) o f  a  to w e r 28  m e te r  h igh . T h e  d a ta  w ere  re c o rd e d  by  a m ic ro p ro c e sso r  b a se d  d a ta  lo g g in g  sy s tem  c o n n ec ted  w ith  th e  sen so rs . T h e  d a ta  w ere  c o lle c te d  ro u n d  th e  c lo ck  w ith  10 m in u te  av e ra g e  basis . F o r th e  p re se n t an a ly s is , w e are  c o n s id e r in g  o n ly  4 ,5  m e te r  level d a ta  w h ich  is a v a ila b le  as a  co n tin u o u s  tim e  se ries . T h e  raw  d a ta  h av e  b een  p re p ro c e sse d  fo r th e  p re s e n t s tu d y  in th e  fo llo w in g  m an n er. D a ta  se t is firs t d iv id e d  sea so n  w ise  th en* Corresponding Author 2001 lACS252 N C Deb et ald a ta  a t a  p a r t ic u la r  tim e  o f  th e  d a y  h av e  b een  av e ra g e d  o v e r  th e  fiill se a so n .3. Observation and analysisD a ily  w in d  v a r ia tio n  is c le a r , it can  b e  seen  fro m  th e  F ig u re  I th a t w in d  sp e e d  in  W in te r  an d  S p rin g  rem a in s  h ig h e r  th a n  in A u tu m n  an d  S u m m er. W in d  sp e e d  s ta rte d  d e c re a s in g  a f te r  7 :0 0  h loca l tim e  (L T ). It d e c re a se s  to  re a c hth e  m in im u m  a t 1 8 :00  h  (L T )  an d  th e n  in c re a se s  to  re a c h  th e  m a x im u m  a t 7 :0 0  h (L T ) e sp e c ia ly  in  A u tu m n  an d  S u m m er se a so n s . In  F ig u re  2 , w e  p re s e n t th e  p lo t o f  w in d  d ire c tio n  fo r th e  fo u r  se a so n s . It c a n  b e  se e n  fro m  F ig u re  2  th a t th e  m a in  w in d  d ire c tio n s  a re  in th e  se c o n d  q u a d ra n t (1 1 0 °  to  1 6 0 °) th ro u g h o u t th e  y e a r  a t th e  s ite  o f  e x p e rim e n t. S o , m a in160°), w h e re a s  d u rin g  S u m m e r p e r io d  w in d  d irec tio n  ntay re d u c e  to  E S E  (1 1 0 ° )  in  th e  s e c o n d  q u a d ra n t a t 1 1 :00 h (LT) A fte r  sc ru tin iz in g  re c o rd e d  o b se rv a tio n s  th o ro u g h ly  it fo u n d  th a t la rg e  f lu c tu a tio n s  in  w in d  d ire c tio n  occurred  in S u m m e r (1 1 0 °  to  147°). T h e se  tw o  d ire c tio n s  c o m p rise  92% o f  th e  o b se rv a tio n s . W in d  sp e e d  v a lu e s  <  1 m s '*  a re  below th e  a n e m o m e te r  th re sh o ld , a n d  a re  c o n s id e re d  to  be calm T h e y  re p re se n t 3 3 %  o f  th e  w h o le  a v a ila b le  d a ta . From  the o b se rv a tio n  it w as  re v e a le d  th a t  f re q u e n c y  o f  w in d  direction h a v e  tw o  d o m in a n t p a r ts , o n e  in  th e  E a s t d ire c tio n  and  other in th e  S o u th  d ire c tio n  fo r  a ll th e  fo u r  se a so n s . W e have re so lv e d  w in d  v e lo c ity  in  tw o  c o m p o n e n ts  a s  fo llow s :E a s t c o m p o n e n t o f  w in d  v e lo c ity  Fe =  w sin  ^ a n d  South c o m p o n e n t o f  w in d  v e lo c ity  F , =  i/ c o s  0  (w h e re  'w' is wind sp e e d  in  m e te r  p e r  se c o n d  a n d  6  is th e  a n g le  sub tended  by w in d  w ith  th e  N o rth ) .O u t o f  th e  e ig h t d is tr ib u tio n s  (sh o w n  in  F ig u re  3a to 3h), fiv e  a re  u n im o d a l a n d  th e  o th e r  th re e  a re  m ultim odalI I  18 IT 18 21 n  28 IT 1 8  8 13 IT 2l 28 28 33 37 V(C)II3 8  48  6 1  87  a i  8 8  T6 81  i t  8 3(e) (0n y* V lOD j(g)8 8  1 *  83  8 8 8  108(h)Figure 2. Season averaged diurnal wind direction for four seasonsw in d s  b lo w  fro m  th e  fo u r th  q u a d ra n ts  th o u g h o u t th e  y ea r. T h is  m e a n s  th a t  th e  p re v a ilin g  w in d  d ire c tio n s  a rc  S E , E S E  d u e  to  th e  c h a n n e lin g  in d u c e d  b y  th e  p o la r  c a p  ice  an d  th e  d o m e  lik e  sh a p e  o f  th e  c o n tin e n t. D u rin g  A u tu m n , W in te r  a n d  S p r in g  s e a s o n  w in d  d ire c tio n  re m a in s  w ith in  (1 3 0 °  toFigure 3. (a) Vg for Summer, (b) F, for Summer, (c) V, for Autumn, (d) Vs for Autumn, (e) F, for Winter, (0 F, for Winter, (g) F^  tor Spring and (h) Fj for Spring.W e  c o n c e n tr a te  to  f i t  th r e e  p a ra m e tr ic  log-normal d is tr ib u tio n  o n  f re q u e n c y  c u rv e  o b ta in e d  fro m  the wind v e lo c ity  fo r  u n im o d a l c a se s  o n ly . In  v ie w  o f  th e  observe sk e w n e ss  w e  h a v e  tr ie d  to  fit th re e -p a ra m e tr ic  log-norma d is tr ib u tio n  in th e se  c a se s  in s te a d  o f  th e  n o rm a l distributionOn (he structure o f horizontal wind flow in the surface etc 253There a rc  tw o  ty p es  o f  th ree -p aram etric  log-norm al distribution. In  ty p e  1, th e  th re sh o ld  v a lu e  ^  >  m ax  [xj and in tvpe II. ^  w h ere  x is th e  in stan taneous valuesof wind speed  co m p o n en t. T y p e  I and 11 m ay be g iven as■ , |ioe({-A)-/ip ^ 2(7?Type I : P=where ft\ -  £ [ l o g ( ^  ~  s tan d ard  d ev ia tio n  o f( [iog(j-o-/iTI ' ia\I(2)lo g ( if - Jf)-^ = ( x - ^ ) c r , V 2 ^where / / 2 "" £ f lo g (Jc  -  and <T2 is s tan d ard  d ev ia tion  o floti ( V ^)- R esu lts  w h ich  w e have o b ta in ed  using  above equations are g iv en  in T ab le  1. -Fahlf 1 . Rciulls obtained using cqs. ( 1 ) and (2)Wind vector fT r(or Autumn 0 0 1 1 544 0 2037 42 44 28(^  (or Winter 12 5 1 664 0 186 35 09 301, (or Winter 18.0 1 9733 0 0931 24 22 24(, (or Spring 0 01 1.9733 0 1455 56.5 301, lor Spring 129 0.8997 0 3909 56 48 294. C o n c lu s io n sIt m ay be observed  from  the resu lts in T ab le  1 and  chart [5] that w in ter velocity  com ponen ts p ass  test w ith 5% . fo r A utum n and V^. and fo r S pring  are m arginally  unsuccessfu l in p ass in g  the test w ith 2% . So, it m ay be concluded  th a t w ind in w in ter and spring  possesses som e sort o f  sta tistica l pattern . Sam e is true for the eastern  com ponen t o f  w ind in A utum n. A s against this the o ther three cases, stud ied  here  have show n grea ter variability  and no sim ple d is tribu tion  pattern  can n o t be fit to  them .KffcrenccsHI M Martin, L V Cremndcs and J M Santaharbara Int J Climatol 19 197 (1999)[2] A C Brcll and S V Taller J Appl Met 30 823 (1991)13] H Islnda Houndary-Layer Met 52 335 (1990)[4] J Gavalda, J Massons J Camps and V Dia/ Theor Appl Clim 46(2-3) 143 (1992)[5] John K Freund Modern Elementary Statistia (New York Frenticc Hall) (1952)

On the Structure of Horizontal Wind Flow in the Surface Layer of Maitri, Antarctica

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On the Structure of Horizontal Wind Flow in the Surface Layer of Maitri, Antarctica

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