Journal o/Clacio/ug)'. Vol. 7.
~o .
49, 1968
CORRESPONDENCE
The Editor,
Journal of Glaciology
SIR,
Glacier variation alld weather: comments
Oil
Professor Hoinkes' !Ja!Jer
Professo r Hoinkes' paper ( 1968) will give a useful impetus to th e study of this subject, in particular
to th e search for simple relationships b etween th e large-scale atmosph eri c circulation and the behaviour
of glac iers in th e various main g lacier reg ions of th e Earth.
The late Professor Wagner p erform ed a very useful service in drawing attention to the plOgressivc
intensification of th e main zonal circul a tion of th e atmosphere from the la tter part of the last century
to th e earli er decades of th e present century. H e may however have been mistaken in thinking that th e
relatio nships between an increase of th e m ean pressure gradien ts associated with th e prevailing westerlies
and vari a tions of "contin entality" (i. e. summer- winter tempera ture differ ence) and glacier growth and
retreat would b e simpler than is in fa ct the case. To understand this and th e problems in volved, it is
necessary to distinguish between th e scales of various phenom ena. Wagner found eviden ce of an
incr ease of th e strength of th e general circulation from th e 1880'S up to som e tim e about th e ' 92o's,
whi ch many other workers hav e since found represented in the courses followed by various indices of th e
zonal wes terli es of middl e latitudes in th e Northern H emisphere. From my own work, it appears a lso to
have affected th e trade winds and the Southern-Hemisph ere wes terli es. This is clearly a large-scale
phenom enon , apparently of global dimensions. Changes in the strength of th e main zonal wind streams
are, however, accompanied by changes in th e prevailing positions occupied by th e great warm ridges
and cold trough s in the upper westerli es, apart from those which are most closely anchored by th e
effec ts of th e m eridional mountain barriers (e.g. th e Rocky Mo un tains) upon th e flow of the upper
westerli es. Longitude shifts of th e warm ridges a nd cold trough s, corresponding to changes of wavelength
downstream from the anchored disturbances, result in some areas experi encing for some time, in th e
course of a climatic change, temperature changes whi ch are out of phase with the more general experien ce
of th e rem a inder of the latitude zone, or of the world, at th e same time.
The relevance of both these points to recent climatic changes and th eir effec ts on glaciers is explained
in th e following paragraphs.
The frequen cy of westerly weather type (which implies gen eral surface wes terl y and south-wes terl y
winds) over th e British Isles since 1873 has varied in the way shown by Professor Hoinkes- a gradua l rise
from 1873 to a n epoch aro und th e 1920'S, when the frequency was 50 per cen t greater than in th e 1870's,
and a subsequent fall to values in th e 1960's that are similar to those ruling in th e 1870's or earli er. T he
upward a nd then downward trend of th e frequency of westerly situations in Britain applies to nearly
every month of th e year and closely parallels changes of the pressure grad ient indices for the prevailing
zonal westerlies in the middle latitud es over th e same period . The sam e trend is shown by the fr equ en cy
of G irs' westerly type, affecting the whole north ern hemisphere, from 1890 to 1958. Very much th e sa m e
trend h as also been d erived by Dr. H. Trenkle of th e Deutsch er W etterdi enst for th e 500 mbar geostrophi c wind lats. 50- 60 ° N., longs. 60° W.- 60 0 E. in winter from 1880 to 1963. Dr. Trenkl e d erived
his values of th e 500 mbar zonal index between lats. 50 ° and 60 ° N . from study of th e varying fr equen cy
of th e differ ent Grosswetterlagen of H ess and Brezowsky. Trenkl e found that th e 500 mbar zonal index
incr eased from low values around 1890 to high values betwee n 1900 and 1925, after which the values
fell once more, apart from a brief r ecovery around 1950 : by the 1960's th e values were much lower than
in 1890. Stud y of the behaviour of a ll th ese different indicators- of th e frequ ency of westerl y situations
over th e British Isles, of south- north differences of m ean pressure assoc iated with th e prevailing westerli es
over th e sector between longs . 60° W. a nd 60 ° E. and of the frequ ency of genera ll y zona l wes terl y flow
a round the who le Northern H emisphere- thus produces the same result: a rise and th en a recent fall of
the strength of the main zonal wind circulation, a trend which is seen as a ffec ting th e whol e North ern
H emisphere and apparently the whole Earth.
The recent d ecline of the westerl ies has b ee n accompanied by an evid ent shorten in g of wavelength
in the upp er wes terlies such that the upper cold trough in th e European sec tor has in the 1960'S te nd ed
to occupy more western positions than in th e earlier part of thi s cen tury a nd h as often lain over Central
Europe in winter and over north ern or north-western Europe in summ er. (Thus, th e yea rs of reduced
wes terlies in the 1960's have tend ed to have cold summers and cold win ters in north-west Europe- not
12 9
JO U R N AL OF GL A C10LOGY
th e usua l expectatio n wh en continenta lity increases !) The amount of m eridional (north- south ) d evelopm ent of this troug h is important a nd differs in different years. Its position was over north-western
Europ e, with th e ax is lying between lo ngs. 00 a nd 10 0 E. in the summers of both 1962 a nd 196y in
1962 th e troug h was la rgely confined to la titud es north of 50 0 N. , a nd onl y th e Scandinavian g laciers
wer e d irec tl y a ffec ted , wh ereas C entra l Europe h ad a rather warm summ er ; but in 1965 th e trough axis
was well marked as far south as Spa in, so that C entra l Europe not only experi enced some of th e cold
a ir but a lso th e r epea ted cyclogen esis ch a racteristic of th e forward side of a n upper cold troug h . Thus th e
Alpine glaciers wer e well nourish ed in the summ er of 1965 but not in 1962.
Computa tions by ]. M . Mitch ell, U.S . W eath er Bureau, of changes in world tempera ture since 1880
show very much the sam e trend as th e vi gour of th e wes terli es. World tempera tures a tta ined a maximum
in the earl y 1940'S of t he order of 0 .5 d eg above th e tem peratures genera ll y prevailing a round 1880 a nd
subsequently fell aga in . The cooling since th e earl y 1940'S has been sharpest in the Arctic, wher e the
sea ice h as increased aga in, but by the 1950'S th e area of cooling showed long extensions into middl e
latitudes in certain sec tors- presuma bl y th e sectors a ffec ted most by the cha nged positions of th e upper
cold tro ughs. In th e 1960's so far , average tempera tures over th e Arcti c a nd in Brita in a nd Scandinavia,
especia ll y in the summ ers, are believed to be lower th a n a t any time sin ce well back in th e last century.
In th e 1950's C entra l E urope, like th e eas tern U .S.A., European Russia and parts of Cen tral Asia, was
experien cing higher temperatures than before, i. e. a ch an ge of tempera ture out of ph ase with that going
on ove r most of the world and nota bly out of phase with that going on over neighbouring sectors of th e
n orthern h emisph ere. This presuma bl y m eans that C entral Europe, European Russia a nd Central Asia
were m ore affec ted tha n formerly by upper warm r id ges owing to th e lo ngi tud e shift of th e waves in th e
upper wes terlies. In view of the cooling tend ency of recent years in n eig hbouring secto rs of that sam e
la titude zone, a nd over most other pa rts of the world, it may be prem ature to conclude th a t th e prosp ects
for the A lpine glaciers a t the presen t time are fa r from favouring fr esh growth- tho ugh a n y g rowth
would probably come o nly after an a ppropriate lapse of years for increased a ccumul a tion a t the gl ac ier
h eads to a ffect the lower r eaches .
In studying the effects of th e a tmos pheri c circul a tion it will be essenti al to study d eta ils of th e position
a nd n o rth- south a mplitude of th e upper cold trou ghs a nd ridges, as well a s the layout of regio ns of
cha nge of vorticity in the flow of th e upper wes terli es favouring cyclogen esis. These item s are no t
n ecessaril y reveal ed by such m easures as the zon a l index however d efin ed .
A pa rt from relati onships b etween gl ac ier ch a nges a nd th e genera l wind circul a ti o n, I believe it is
n ecessary to consider th e effec ts of occasional volca nic dust veils such as the great one whi ch cover ed
most of the world in 1963- 65 after the eruption of Mount Agung in Bali early in 1963. There is unmista ka ble evid ence of a (doubtless temporary) a dditi o na l redu ction of world tempera ture for those
years amounting to a bout 0. 5 d eg a t its strongest. It m ay a lso b e d esira ble to keep a continuous r ecord
of va ri a tions of the albedo of glaciers, from month to m o nth a nd from year to year, in case pollution of
the glacier surface by industri a l smoke or wind-blown dust should have importa nt consequ ences in th e
a blati on season.
H . H.
M eteorological Office,
London Road,
Bracknell, Berkshire, England
1 August 1967
L AMB
REFERE N CE
H oinkes, H . C. 1968. Glacier va riation and weather. J ournal of Glaciology, Vo\. 7, No. 49, p. 3- 19.
SIR,
Primary and secondary polygons
During a visit to I celand in the summer of 1966 a species of patterned ground, possibly hith erto
und escribed , was observed . It was discover ed on th e small summit pla teau of the 998 m p eak on th e
Thingeyri peninsula, V es tfirthir, no rth-west Iceland. A la rge area of thi s plateau was covered with la rge
sorted polygons inside ea ch of which several small er sorted polygons were situa ted . The primary
polygons measured 5- 6 ft ( 1.5- 1.8 m ) and the secondary polygons 1- 2 ft (0. 3- 0 .6 m ), r especti vely,
across th eir internal diam eters (Figs. I and 2).