The VAS soundings derived by NOAA personnel and NASA personnel and rawinsonde soundings are compared: (1) directly by plotting on Skew t-log p diagrams; (2) by pairing rawinsonde soundings with the closest satellite soundings and calculating the mean and standard deviations of differences between the two data sets; and (3) by constructing synoptic and subsynoptic scale analyses with rawinsonde and satellite data. Differences for various parameters are discussed

Scoggins, J. R.

English

NASA Technical Reports Server

Prepared for 
May 2 and 3 ,  1984 
FY-84 Atmospheric Processes Research Program Review 
Title: VAS Sounding Data Evaluation 
Principal Investigator: Dr. James R. Scoggins 
Department of Meteorology 
Texas A&M University 
College Station, TX 77843 
409 f 845-7671 
Significant Accomplishments to Date in FY-84: 
between the VAS sound'ingsderived by N O M  personnel at the University of 
Wisconsin (UW) and NASA personnel at the Goddard Space Flight Center (GSFC), 
and rawinsonde soundings. 
Three different types of comparisons between VAS and rawinsonde sound- 
ings were made. The first was a direct comparison between satellite and 
rawinsonde soundings plotted on Skew T-log p diagrams. 
sounding represents a highly smoothed version of the rawinsonde sounding; 
the satellite smoothing is both in the vertical and horizontal, but the 
vertical smoothing seems to be the more dominant feature. 
and the mean and standard deviations of differences between the two data 
sets were calculated. 
differences of about 1.5QC and 3.0°C, respectively, with the standard devi- 
ations roughly constant with height. The differences are related to atmo- 
spheric structure and are dependent on synoptic and subsynoptic scale features 
that affect the variability of the rawinsonde (ground truth) profiles of 
temperature and moisture. 
dependence on the satellite profiles of temperature and moisture and can be 
explained by satellite vertical smoothing. The temperature differences show 
similar characteristics for both the UW and GSFC soundings, but statistical 
tests showed the two retrieval methods are producing statistically signifi- 
cantly different temperature profiles. The dewpoint differences between GSFC 
and UW show greater differences than the temperature profiles although the 
GSFC profiles were found to give a better representation of the ground truth. 
Statistical tests between satellite-rawinsonde differences show that at times 
corresponding to the greatest number of pairs, there is a statistically 
significant difference between the two data sets. 
Synoptic and subsynoptic scale analyses were constructed with both 
rawinsonde and satellite data. Large scale systems are represented reason- 
ably well by the satellite data with best analyses at higher levels. Small 
scale systems were poorly represented by the satellite data. The constant 
pressure charts show height and temperature fields that are highly smoothed 
compared to the rawinsonde. All but large scale features are lost in meso- 
scale vertical cross sections. 
An analysis of temperature and height gradients showed that they would 
A contract report has just been finalized which presents a comparison 
The satellite 
Rawinsonde soundings were paired with the closest satellite soundings 
The profiles of temperature and dewpoint show mean 
Satellite-rawinsonde differences for other parameters showed a strong 
be poorly represented by the satellite data at low levels, but would improve 
with height and for this case it was not possible to accurately measure 
gradients over small distances (<200 km) with the satellite data. 
217 
https://ntrs.nasa.gov/search.jsp?R=19840026822 2020-03-22T10:40:44+00:00Z
The r e s u l t s  given here  pe r t a in  t o  one synopt ic  s i t u a t i o n  i n  which the re  
w a s  a high degree of vertical  s t r u c t u r e  i n  t h e  temperature p r o f i l e .  
l imi t a t ions  of t h e  satell i te soundings f o r  prescr ibing s m a l l  scale hor izonta l  
f ea tu re s  are d i r e c t l y  r e l a t ed  t o  the  l imi ted  v e r t i c a l  reso lu t ion  of t h e  sat- 
e l l i t e  sensor.  
sounder with higher  v e r t i c a l  reso lu t ion .  
The 
This study demonstrates t he  need f o r  a geostat ionary satell i te 
Focus of Current Research Ac t iv i t i e s :  
Now t h a t  we have achieved a reasonable understanding of t he  accuracy and 
representat iveness  of t h e  VAS da ta ,  we  have turned our a t t e n t i o n  t o  the  u t i l i -  
za t ion  of the  data.  Our approach is  t o  develop a method f o r  combining t h e  VAS 
and rawinsonde soundings i n t o  a un i f i ed  da t a  set t h a t  w i l l  preserve t h e  large- 
scale f ea tu res  of t he  rawinsonde da ta  and u t i l i z e  the  VAS da ta  t o  add hor izonta l  
reso lu t ion .  W e  hope t h i s  can be done f o r  areas with and without rawinsonde 
soundings. I f  rawinsonde soundings do not ex i s t  as over t he  ocean, constant 
pressure cha r t s  w i l l  be  u t i l i z e d  t o  determine c h a r a c t e r i s t i c s  large-scale  
f ea tu res  of t h e  rawinsonde soundings. Once the  uni f ied  da t a  set is derived, 
geopotent ia l  he ights  w i l l  be recomputed, a method developed f o r  der iving wind 
from the  geopotent ia l  heights ,  and analyses conducted t o  determine the  u t i l i t y  
of the  new da ta  set i n  d iagnos t ic  ana lys i s ,  spec i f i ca t ion  of i n i t i a l  condi t ions,  
and i n  forecast ing.  
begun before t h e  present  cont rac t  expires  a t  the end of May 1984, is t o  combine 
the  zeroth and f i r s t  harmonics from rawinsonde da ta  with the  second and t h i r d  
harmonics from sa t e l l i t e  data .  Gridding procedures are used t o  match the  two 
f i e lds .  Over t h e  VAS regional  net- 
work, t h e  one case analyzed s o  f a r  shows improved hor izonta l  reso lu t ion  compared 
with rawinsonde da ta  alone, and the  measured winds appear  t o  agree b e t t e r  with 
the  height  f i e l d s  computed from the  uni f ied  da ta  than with the  rawinsonde height  
f i e l d s .  These are very preliminary r e s u l t s ;  much addi tonal  research is required 
before conclusions are reached. 
The i n i t i a l  approach i n  developing a uni f ied  da t a  set, although barely 
I n i t i a l  r e s u l t s  are extremely promising. 
Plans f o r  FY-85: 
A proposal has been submitted t o  NASA f o r  the  cont inuat ion of t h i s  research. 
Our hope is t o  continue the  research on the  u t i l i z a t i o n  of t he  VAS soundings. I f  
funded, t h e  research w i l l  concentrate  on the  development of a uni f ied  da t a  set 
and i ts  va l ida t ion ,  and on u t i l i z a t i o n  of t he  data.  
Recommendations f o r  New Research: 
Our research on t h e  accuracy and representat iveness  of t he  VAS soundings 
shows t h a t  addi t iona l  v e r t i c a l  reso lu t ion  i n  the  VAS da ta  is  des i rab le .  
is  needed t o  determine whether o r  not  addi t iona l  v e r t i c a l  reso lu t ion  can be 
achieved by increasing the  number of channels i n  the  radiometer. 
a l  research i s  needed on the  u t i l i z a t i o n  of the  VAS soundings. 
subjec t  has barely begun. 
A study 
Also, addition- 
Research on t h i s  
Publ icat ions Prepared Since June 1983: 
Townsend, Tamara L. and James R. Scoggins, 1983: The Inf luence of Convective 
Act iv i ty  on the  Vor t i c i ty  Budget. NASA CR 3752, 105 pp. 
Rhodes, Robert C. and James R. Scoggins, 1984: An Analysis of t h e  Proper t ies  of 
VAS Satel l i te  Soundings. NASA Contractor Report ( I n  Publ ica t ion) ,  104 pp. 
218 


VAS sounding data evaluation

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