A PROCEDURE OF SHORT-RANGE WEATHER FORECASTING 
isosteric-isobaric solenoids.) The foregoing, rather well- 
known observation, which dates from 1938, has prob- 
ably been considered of questionable value for some 
time, but it serves historically to introduce Sutcliffe’s 
much more recent (1947) and reliable considerations 
in also applying the relative hypsography® for estimat- 
ing sea-level cyclogenesis. 
The development of sea-level systems can also be 
inferred from the relative hypsography. Using certain 
assumptions based on the vorticity equation, Sut- 
773 
velopment term. It is on the basis of this term that we 
apply the relative hypsography for estimating sea-level 
cyclogenesis and anticyclogenesis. During the initial pe- 
riod of a quasi-stationary and developing sea-level 
system, term (a7) makes its maximum contribution, 
as shown empirically by Sawyer [69]. Positive cen- 
ters of the computed field of term (77) lie to the 
right, or east of the cold trough in the relative hypsog- 
raphy; negative centers, to the left. The pretrough 
areas on the surface map are cyclogenetic, the post- 
TABLE I. CoNsTANT-PRESSURE TERMINOLOGY* 
(1) : (2) (3) (4) (5) 
: Adjectives modifying entries in columns 
ren columns (3); @), and (5) Quantity Tsopleth Configuration 
General Specific 
bsolut 500-mb —_| height isohypse hypsography 
ae es ee a ue baric topography 
contour contour map 
dat fi tial 500/7%00-mb+ | height isoh hypsography 
mandatory surface | partia mu eg tsohypse inate (opnartorane) 
4 contour contour map 
relative ee oe ee 
total 500/1000-mb | height, change in the§ | zsallohypse allohypsography 
contour change-line 
; layer-isotherm 
partial 700-500-mbt | layer-temperature p 
layer-isentrope 
thickness thickness “thick-thin’’? map 
mean-temperature 
mandatory layer nap a 
total 1000-500-mb_ | layer temperature, layer-isallotherm layer-isallotherms 
change in the layer-isallentrope layer-isallentropes 
thickness, change in | thickness change- thickness change-line 
the line map 
* Sets of consistent expressions are given in succeeding columns. Italicized expressions are those used in text. 
t 500/700-mb—read as ‘‘the ———— 
is read as ‘“‘the hypsography, 500 mb above 700 mb.” 
t 700-500-mb—read as ‘‘the ————— 
§ Written also as 500/700-mb height change, etc. 
cliffe [76, p. 204] has arrived at the following expression 
for the divergence of the thermal wind: 
(2) (it) (22) (wv) 
oon = VO WO AV 
CB 7 3 WP Gs i @8” (1) 
where V’ is the thermal wind vector defined by 0V«/dp, 
f is the Coriolis parameter 29., ¢’ and { are the ver- 
tical components of the vorticities of the thermal wind 
and the geostrophic wind at 1000 mb, respectively, and 
0/ds represents differentiation along the relative 
isohypse. Term (7) may also be thought of as, for in- 
stance, the geostrophic divergence at 500 mb relative 
to that at 1000 mb. In other words, it is the divergence 
at 500 mb in excess of that at 1000 mb. It is thus di- 
rectly connected with vertical motion. 
Term (wz) is the so-called thermal vorticity or de- 
of the 500-mb surface above (relativeto) the 700-mb surface”’; cf, 500/700-mb hypsography 
from 700 mb to 500 mb’’; cf, 700-500-mb layer is read as ‘‘the layer from 700 mb to 500 mb.” 
trough areas anticyclogenetic. A low will readily pass 
through a trough and intensify. On the other hand, a 
“self-developing” system is one with a low in the right 
half of the thermal trough and a high in the left half. 
Analogous considerations apply to highs and thermal 
ridges. 
Next, let us apply term (27) to a pattern of con- 
centrated relative isohypses,® such as is found in a 
frontal strip, the so-called “thermal jet.’’ The thermal 
jet has an “entrance” region and an “exit”? region. An 
example of such a difluent-confluent jet is found in 
Fig. 3. According to term (77), there is sea-level cy- 
clogenesis in the colder half of the difluent thermal jet 
and also in the warmer half of the confluent thermal jet. 
(Similar considerations can be formulated for anti- 
cyclogenesis.) The genetic regions of the thermal jet 
thus favor the existence of lows in the confluent 
warmer half of the thermal jet and in the difluent 
