Mesoscale convective processes and how they affect and interact with mid-latitude cyclones were studied. The ageostrophic and associated vertical motion field was calculated using a highly accurate iterative method of solving the semigeostrophic omega equation. The tendencies for convective destabilization in the 850-750 mb layer due to differential geostrophic and ageostrophic advection and differential moist adiabatic ascent, were found. The spectral models of the index oscillation, one barotropic and the other baroclinic, were developed. Theoretical and observational studies of cloud streets were conducted

Clark, J. H. E.

Dutton, J. A.

Shirer, H. N.

English

NASA Technical Reports Server

The Use of Satellite Data in Understanding and 
Predicting Convective and Large-Scale Dynamical Processes 
John A. Dutton, Professor of Meteorology (814-865-1534) 
John H. E. Clark, Associate Professor of Meteorology (814-863-1581) 
Hampton N. Shirer, Assistant Professor of Meteorology (814-863-1992) 
Department of Meteorology 
The Pennsylvania State University 
University Park, PA 16802 
Accomplishments in M-84: 
1. Observational Studies of the Index Oscillation 
Mr. Robert Schlaak has completed his M.S. Thesis in which he has combined, 
in a unique way, conventional and NOAA-111 and NOAA-IV Earth Radiation Budget 
(ERB) data to study the pronounced index oscillation of the 1974-75 winter. 
has determined that the principal driving mechanism for the oscillation is 
barotropic wave-mean flow energy exchanges stimulated by the mean westerlies 
becoming periodically unstable. 
radiative processes are phased with the oscillation such as to reinforce it. 
Variations in mid and high latitutde cloud cover resulting from intrusions of 
warm air into high latitude regions modulate the net radiative cooling in such 
a way as to reinforce strong mid-latitude westerlies because of thermal wind 
balance and thus intensify the oscillation. 
2. 
He 
He has also determined that polar cap 
Theoretical Studies of the Index Cycle and Blocking Phenomena 
A two-layer truncated baroclinic spectral model was developed to study 
the long-term evolution of disturbances to a baroclinically unstable mean 
flow. Topography and crudely-parameterized radiative processes were accounted 
41 
https://ntrs.nasa.gov/search.jsp?R=19840026771 2020-03-22T11:02:07+00:00Z
f o r .  A s  a r e s u l t  of M r .  Schlaak 's  discovery of t h e  underlying ba ro t rop ic  
na tu re  of t he  index o s c i l l a t i o n  as w e l l  as reviewers sugges t ions  about the 
o r i g i n a l  manuscript ,  t h e  model has been r ev i sed  t o  a l low f o r  ba ro t rop ic  as 
w e l l  as b a r o c l i n i c  wave-mean flow i n t e r a c t i o n s .  The form-drag exer ted  by t h e  
topography on the  ba ro t rop ic  p a r t  of the mean flow is l a r g e r  than on t h e  
b a r o c l i n i c  p a r t  and thus  we a n t i c i p a t e  s i g n i f i c a n t  changes from t h e  o r i g i n a l  
c a l c u l a t i o n s  on the  index o s c i l l a t i o n  when it is s t r o n g l y  modulated by 
topography. 
3 .  Numerical Modeling of Index Cycle Var i a t ions  
We be l i eve  t h a t  s i n c e  the  index o s c i l l a t i o n  accounts  f o r  a s i g n i f i c a n t  
po r t ion  of atmospheric temporal var iance ,  t he  long t e r m  p r e d i c t a b i l i t y  could 
be improved i f  r e l i a b l e  f o r e c a s t s  of t h e  index o s c i l l a t i o n  were ava i l ab le .  
Two s p e c t r a l  models of t he  index o s c i l l a t i o n ,  one ba ro t rop ic  and t h e  o the r  
b a r o c l i n i c ,  have been developed. The la t te r  al lows f o r  moisture ,  r a d i a t i o n ,  
land-sea temperature c o n t r a s t s ,  and energy exchanges wi th  t h e  underlying 
su r face ,  They a r e  c u r r e n t l y  being t e s t e d  f o r  conservat ion of energy and 
v o r t f c i t y o  
4,  Theore t i ca l  and Observat ional  S tudies  of Cloud Streets 
Two manuscripts,  S h i r e r  (1984) and S h i r e r  et  al. (1984), have been 
completed recent ly ;  t h e s e  d i scuss  r e s u l t s  obtained from a three-dimensional 
t runca ted  s p e c t r a l  model of moist convection i n  a shea r ing  environment. I n  
S h i r e r  (19841, two poss ib l e  cloud street modes a r i s i n g  from a combined 
Ray le igh /pa ra l l e l  i n s t a b i l i t y  were found t o  be possible--one having 
o r i e n t a t i o n s  f o r  which the  Four ie r  c o e f f i c i e n t  of t h e  wind shea r  perpendicular  
t o  the  r o l l  w a s  near ly  zero and t h e  o t h e r  f o r  which t h e  Four i e r  c o e f f i c i e n t  of 
t h e  shear  p a r a l l e l  t o  t h e  roll was nea r ly  equal  t o  that perpendicular  t o  the  
r o l l .  These two modes have d i f f e r e n t  h o r i z o n t a l  c h a r a c t e r i s t i c  wavelengths 
i 
42 
t h a t  vary wi th  wind speed a t  t h e  top of t h e  domain, which is usua l ly  taken t o  
be the  base of t h e  inversion.  I n  S h i r e r  et  al. (1984), a n a l y s i s  of a i r c r a f t  
d a t a  taken during 4 cloud street cases from KonTur revealed t h a t  i n  each case 
t h e  mode f o r  which both shear  c o e f f i c i e n t s  were nea r ly  equal  corresponded t o  
t h e  observed one, 
Work has begun on a three-dimensional spectral model ab le  t o  represent  
t h e  convective modes developing as a r e s u l t  of t h e  i n f l e c t i o n  poin t  
i n s t a b i l i t y .  I n  add i t ion ,  sa te l l i t e  p i c t u r e s  and r e l evan t  upper a i r  da ta  have 
been archived f o r  30 cloud street days during t h e  1983-84 win ter  season; t hese  
w i l l  be used t o  assess the  r e s u l t s  obtained from t h e  above Ray le igh /pa ra l l e l  
and i n f l e c t i o n  poin t  i n s t a b i l i t y  models. 
Plans f o r  FY-85 
1. Observat ional  and Theore t i ca l  S tudies  of t h e  Index O s c i l l a t i o n  
We plan  t o  concent ra te  on the  a n a l y s i s  of our s ix -coe f f i c i en t  
baroc l in ic -baro t ropic  s p e c t r a l  model of t he  index o s c i l l a t i o n .  I n  add i t ion ,  
t h e  blocking phenomenon w i l l  be analyzed by seeking low and high index 
e q u i l i b r i a  and examining t h e i r  s t a b i l i t y .  Fur ther  observa t iona l  s t u d i e s  are 
planned which w i l l  concent ra te  on e s t a b l i s h i n g  t h e  condi t ions lead ing  t o  t h e  
establ ishment  of atmospheric blocking p a t t e r n s  and t h e i r  subsequent 
maintenance. A mix of conventional and sa te l l i t e  da ta  is a n t i c i p a t e d  j u s t  as 
i n  our s tudy of t h e  index o s c i l l a t i o n .  
2, Modeling of t he  Index Cycle 
It is proposed t h a t  t h e  two s p e c t r a l  models be used t o  produce f o r e c a s t s  
from observed f i e l d s .  The des i r ed  p red ic t ion  q u a n t i t i e r s  are t h e  index 
va lues ,  and t h e  poin ts  of regime changes. The index values  are, of course,  
ca l cu la t ed  d i r e c t l y  from the  f o r e c a s t  he ight  f i e l d .  The regime changes may be 
43 
found by c a l c u l a t i n g  t h e  a t t r a c t o r  a s soc ia t ed  wi th  t h e  fo recas t  f i e l d s  a t  
c e r t a i n  po in t s  i n  t h e  f o r e c a s t  cycle.  I f ,  f o r  example, t he  assoc ia ted  
a t t r a c t o r  were ca l cu la t ed  every 6 hours and changed a f t e r  36 hours,  t h i s  would 
i n d i c a t e  a t r a n s i t i o n  t o  another  flow pa t t e rn .  It is  an t i c ipa t ed  tha t  s eve ra l  
f o r e c a s t s  with s l i g h t l y  d i f f e r e n t  i n i t i a l  condi t ions  w i l l  be needed t o  
e s t a b l i s h  the  p r o b a b i l i t y  of a regime change. The form of the  p robab i l i t y  
d i s t r i b u t i o n  f o r  t h e  change might t ake  t h e  form of a log-normal d i s t r i b u t i o n .  
This  sample s t o c h a s t i c  approach a l s o  takes i n t o  account t h e  p o s s i b i l i t y  of no 
regime change -- something t h e  s i n g l e  f o r e c a s t  cannot handle. 
The c a l c u l a t i o n  of t he  a t t r a c t o r  restricts t h e  number of spectral 
components t o  about 60 ( o r  l e s s )  f o r  p r a c t i c a l  reasons of computer t i m e  and 
core.  Thus, t he  i n i t i a l  f i e l d s  must be r e s t r i c t e d  t o  j u s t  t h e  l a r g e r  observed 
f e a t u r e s .  Since cur ren t  sa te l l i t e  observing systems are a b l e  t o  reso lve  these  
s c a l e s ,  analyses  der ived s o l e l y  from sa te l l i t e  observat ions should serve  as 
s a t i s f a c t o r y  i n i t i a l  data.  
3.  Cloud S t r e e t s  
The new i n f l e c t i o n  po in t  i n s t a b i l i t y  model w i l l  be developed s u f f i c i e n t l y  
t h a t  o r i e n t a t i o n  angles  and ho r i zon ta l  wavelengths can be predic ted  f o r  t h e  
r o l l s  and these  r e s u l t s  compared t o  both t h e  KonTur da t a  and the  l o c a l l y  
archived data. Development of approximate formulas r e l a t i n g  f o r  each poss ib le  
mode t h e  o r i e n t a t i o n  angles  t o  components of t h e  mean wind shear  is one goal  
of t he  ana lys i s .  
Prel iminary work is planned on gene ra l i z ing  t h e  present  three-dimensional 
Ray le igh /pa ra l l e l  i n s t a b i l i t y  model t o  one a b l e  t o  represent  t h e  t r a n i s i t i o n s  
from r o l l s  having one wavelength t o  ones having o t h e r ,  l a r g e r  ones, 
broadening is observed i n  l abora to ry  models of Rayleigh-Benard convection and 
i n  s a t e l l i t e  p i c t u r e s  of cloud streets over t h e  ocean, and is  modeled w e l l  
Such cell  
44 J 
in 
Chang and Shirer (1984). 
role in determining the details of this cell broadening, and will be an 
important factor in any usable boundary layer wind-measuring scheme. 
a new simple spectral model of two-dimensional shallow convection given by 
The background wind field will likely play a crucial 
Publications 
Shirer, H.N. and R. Wells, 1983: Mathematical Sturcture of the Singularities 
at the Transitions Between Steady States in Hydrodynamic Systems. 
Lecture Note in Physics, - 185, 276 pp. 
In review or to appear: 
Feldstein, S.B., J.H.E. Clark, 1984: The Hadley and Rossby Regimes on a 
Sphere, Monthly Weather Review. 
Chang, H-R and NH.M Shirer, 1984: Transitions in Shallow Convection: An 
explanation for cell broadening. Journal of the Atmospheric Sciences. 
Shirer, H.N., 1984: On Cloud Street Development in Three Dimensions: 
Parallel and Rayleight Instabilities. Contributions to Atmospheric 
Physics. 
Shirer, H.K., B. Brummer and A. Grant, 1984: Cloud Streets During KonTur and 
the Parallel/Rayleigh Instabiltty. Contributions to Atmospheric Physics. 
Thesis comp1.e ted: 
Schlaak, R.A., 1984: An Observational Study of the Winter 1974/75 Index 
Oscillation with Conventional and Satellite ERB Data (in preparation for 
submission to Monthly Weather Review). 
45 
J 


The use of satellite data in understanding and predicting convective and large-scale dynamical processes

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