Technical papers in hydrology 9

(1)

(2)

Technical papers in hydrology 9

(3)

In this series:

1 Perennial Ice and S n o w Masses. A Guide for Compilation and Assemblage of Data for a World Inventory.

2 Seasonal S n o w Cover. A Guide for Measurement, Compilation and Assemblage of Data.

3 Variations of Existing Glaciers. A Guide to International Practices for their Measurement.

4 Antarctic Glaciology in the International Hydrological Decade.

5 Combined Heat, Ice and Water Balances at Selected Glacier Basins. A Guide for Compilation and Assemblage of Data for Glacier Mass Balance Measurements.

6 Textbooks on Hydrology. Analyses and Synoptic Tables of Contents of Selected Textbooks.

7 Scientific Framework of World Water Balance.

8 Flood Studies. A n International Guide for Collection and Processing of Data.

9 Guide to World Inventory of Sea, Lake and River Ice.

(4)

A contribution to the International Hydrological Decade

Guide to world inventory of sea, lake and river ice

Unesco/IAHS Paris 1972

(5)

T h e selection and presentation of material and the opinions expressed in this publication are the responsibility of the authors concerned, and do not necessarily reflect the views of Unesco. N o r d o the designations employed or the presentation of the material imply the expression of any opinion whatsoever on the part of Unesco concerning the legal status of any country or territory, or of its authorities, or concerning the frontiers of any country or territory.

1972 International Book Year

Published in 1972 by the United Nations Educational, Scientific and Cultural Organization,

Place de Fontenoy, 75 Paris-?«

Printed by Imprimerie-Reliure Marne, Tours

© U n e s c o / I A H S 1972 Printed in France S C . 7 1 / X X I . 9 / A

(6)

Preface

The International Hydrological Decade ( I H D ) 1965-74 was launched by the General Conference of Unesco at its thirteenth session to promote inter- national co-operation in research and studies and the training of specialists and technicians in scien- tific hydrology. Its purpose is to enable all countries to m a k e a fuller assessment of their water resources and a more rational use of them as m a n ' s demands for water constantly increase in face of develop- ments in population, industry and agriculture. In

1970 National Committees for the Decade had been formed in 107 of Unesco's 125 M e m b e r States to carry out national activities and to contri- bute to regional and international activities within the programme of the Decade. T h e implementa- tion of the programme is supervised by a C o - ordinating Council, composed of twenty-one M e m b e r States selected by the General Confer- ence of Unesco, which studies proposals for devel- opments of the programme, recommends projects of interest to all or a large number of countries, assists in the development of national and regional projects and co-ordinates international co-operation.

Promotion of collaboration in developing hydro- logical research techniques, diffusing hydrologi- cal data and planning hydrological installations is a major feature of the programme of the I H D which encompasses all aspects of hydrological studies and research. Hydrological investigations are encouraged at the national, regional and interna- tional level to strengthen and to improve the use of natural resources from a local and a global per- spective. T h e programme provides a means for countries well advanced in hydrological research to exchange scientific views and for developing coun- tries to benefit from this exchange of information

in elaborating research projects and in implement- ing recent developments in the planning of hydro- logical installations.

A s part of Unesco's contribution to the achieve- ment of the objectives of the I H D the General Conference authorized the Director-General to collect, exchange and disseminate information concerning research on scientific hydrology and to facilitate contacts between research workers in this field. T o this end Unesco has initiated t w o collections of publications: 'Studies and Reports in Hydrology' and 'Technical Papers in Hydrology'.

The collection 'Technical Papers in Hydrology' is intended to provide a means for the exchange of information on hydrological techniques and for the co-ordination of research and data collection.

The acquisition, transmission and processing of data in a manner permitting the intercomparison of results is a prerequisite to efforts to co-ordinate scientific projects within the framework of the I H D . The exchange of information on data collected throughout the world requires standard instru- ments, techniques, units of measure and termino- logy in order that data from all areas will be comparable. M u c h work has been done already towards international standardization, but m u c h remains to be done even for simple measurements of basic factors such as precipitation, snow cover, soil moisture, streamflow, sediment transport and ground-water phenomena.

It is hoped that the guides on data collection and compilation in specific areas of hydrology to be published in this collection will provide means whereby hydrologists m a y standardize their records of observations and thus facilitate the study of hydrology on a world-wide basis.

(7)

Foreword

T h e Co-ordinating Council of the International H y - drological Decade in its resolution 1-12 considered the world inventory of perennial and annual ice and snow masses to be one of the long-terra ob- jectives of the Decade and invited the International

Commission of S n o w and Ice (ICSI) of the Inter- national Association of Hydrological Sciences (IAHS) to act as scientific adviser in this activity.

ICSI undertook to stimulate, guide and co-ordinate measurements of floating ice which could contribute to the establishment of an over-all picture of the world-wide distribution of floating ice and its va- riations.

T o achieve the compilation of a world inventory of sea, lake and river ice it is first necessary to collect information on the methods of measuring and mapping floating ice cover and to propose a programme simple enough to be carried out without elaborate means.

The present guide has been prepared by ICSI in

a form similar to the publications Perennial Ice and Snow Masses (a Guide for Compilation and Assem- blage of Dala for a World Inventory) and Seasonal Snow Cover (a Guide for Measurement, Compilation and Assemblage of Data) which were the first to appear in this Unesco collection of 'Technical Papers in Hydrology'. Together, these three guides propose methods for international standardization of data collection concerning perennial and annual ice and snow masses both on land and afloat.

It is hoped that the above-mentioned technical papers will aid in establishing methods for an inter- national exchange of information and lead to a world inventory of snow and ice.

Unesco wishes to express its appreciation of the work carried out under the direction of D r . E . R . Pounder, Chairman of the Division of Sea, Lake and River Ice of ICSI of I A H S and of the contributions by individual experts from m a n y countries.

9

(9)

1 Introduction

The ice on seas, lakes, and rivers is important for a number of practical reasons, including navigation, transportation and flood problems. These are local problems which have prompted most northern coun- tries to maintain some records of freeze-up and break-up dates and of ice thicknesses. Little atten- tion has been paid to estimating the volume of ice present, but the synoptic data accumulated can be put to use for this purpose. Such data are very important. It seems that a m i n i m u m of about five years of observation at a site is needed before meaningful averages can be obtained. The cost and effort in making ice-thickness observations are such as to limit the number of observation points severe- ly, and full use must be m a d e of existing observa- tions, even if not taken completely in accord with the recommendations which follow later. It must also be recognized that any inventory that is prepar- ed is bound to be inaccurate, even rather crude for the sea-ice aspects, but greater accuracy could only be achieved at very great cost and is hardly warranted.

Responsibility for the I H D Inventory of Floating Ice

It seems appropriate that the I H D national c o m - mittee of each country should take responsibility for the inventory of lake and river ice within its boun-

daries, and for sea ice in its coastal waters. T h e great masses of sea ice are found in the Arctic Ocean and in the seas bordering Antarctica. Data on the areal extent of this sea ice will have to be derived largely from satellite photography, and in- ternational organizations will be needed to oversee the data compilations and calculations. For Antarc- tica the Scientific Committee on Antarctic Research ( S C A R ) is the obvious agency. A similar inter- national committee is recommended to co-ordinate a study of the extent and volume of Arctic sea ice. It should include representatives from Canada, D e n - mark, Japan, N o r w a y , U . S . S . R . and United States and possibly from other northern countries as well.

Data centres

It is proposed that each national and international committee transmit data for the world inventory of sea, lake, and river ice to the U n e s c o / I H D Secreta- riat and to the three I G Y world data centres for glaciology: A , T a c o m a ; B , M o s c o w ; and C , C a m - bridge.

11

(10)

2 Measurement of ice thickness

Non-destructive sounding

It has been a goal for some time to develop methods of measuring ice thickness continuously from a moving vehicle. Radio altimeter methods have been applied successfully to glacier thickness investiga- tions (Evans and Robin, 1966) but the present limit of resolution is of the order of 10 metres. Pulse (Cook, 1960) and variable frequency electromag- netic methods (Bogorodskii and Rudakov, 1962) have been used experimentally with s o m e success to measure the thickness of lake and river ice, but they appear of little value for sea ice because of the smooth impedance change across a sea ice/sea water interface. Acoustic pulse methods (echo-soun- der techniques) are unsuitable for similar reasons;

the difference in the acoustic impedance of ice and water is too small. T h e use of air-coupled flexural waves was suggested by Press et al. (1951), Press and Ewing (1951a) and investigated with some success (Pounder, 1962) but m o r e development work is needed to produce operational devices and methods.

All of the above indirect techniques are thus in the experimental stage at present and not available for routine surveys. The only technique recommend- ed in this guide is direct thickness measurement through a hole in the ice cover. O n e possible excep- tion is a probe developed by the Defence Research Board of C a n a d a (Houle, 1961). It consists of a long plastic tube through the wall of which are sealed bare wire electrodes spaced 1 c m apart.

Each electrode has a separate lead to the top end of the tube. T h e tube is filled with a resin whose thermal conductivity more or less matches that of ice. T h e tube is frozen into the ice cover at the beginning of the season, in a vertical position with the top projecting. A measurement consists of ob- serving the resistance between successive pairs of

electrodes until a significant change in resistance occurs. T h e ice/water interface is thus located within an accuracy of about 1 c m . This device works well in fresh water, but has proved unsuitable in sea water. The resistance change from solid sea ice to sea water is too small and too gradual for the necessary accuracy.

Ice drilling

Making a hole in the ice by chiselling, sawing or blasting is possible but m u c h less efficient than drill- ing a small hole. T h e S I P R E1 ice-thickness kit has become more or less standard in North America while a corer developed by the Ice Research L a b o - ratory of the Arctic and Antarctic Institute is widely used in the U . S . S . R . The S I P R E kit consists of a long, 1-inch (2.54 c m ) diameter auger bit, usually operated by hand with a brace. Extension rods can be used if necessary. It is not difficult to drill through 2 metres of ice in 15 minutes. The measurement of thickness is m a d e by lowering a tape measure through the hole. The tape is attached to the middle of a weight in the form of a short rod (about 10 c m long).

After the weight is lowered below the ice it swings into a horizontal position, and the tape can be pulled up until the rod is seated on the lower side of the ice cover. The thickness of the ice is then read off the tape. It should be noted to the nearest half- inch or nearest centimetre. Recovery of the weight and tape is effected with an auxiliary wire attached to one end of the rod.

A n alternative to drilling a hole for each obser- vation is to drill a single hole and lower through it a resistance wire with a suitable weight on the end.

1. Snow Ice and Permafrost Research Establishment: sub- sequently renamed Cold Regions Research and Engineering

Laboratory ( C R R E L ) .

12

(11)

Measurement of ice thickness

The wire is allowed to freeze in and w h e n a thickness observation is to be m a d e an electric current is sent through the wire until it heats up enough to melt free of the ice. It is then pulled u p until the bottom weight seats against the lower face of the ice cover and the ice thickness is then read off the wire. This technique has the advantage that the series of ice- thickness measurements are taken at an identical location in the ice cover. This method appears to have been proposed first in 1933 by Syrinkov (1963).

A description in English of such apparatus is found in Untersteiner and Badgley (1958) and an automatic version has just been described by Schwerdtfeger (1968).

Test site

It is important that the site chosen for measuring ice thickness be as representative as possible of the general ice cover of the lake or river or sea. T h e site should be at least 50 metres from the shore-line to avoid abnormal ice thickness resulting from heat conduction in a horizontal direction to or from land and also to avoid an abnormal thickness of snow cover because of the wind-break action of trees. T h e snow cover is a major factor in controlling ice thickness and test areas where wind scouring or excessive snow accumulation are likely should be avoided. It is hard to be specific, but areas near sharply curving shore-lines (points of land or nar- row bays), or near marked gradients in the height of the land (such as cliffs) are unlikely to be repre- sentative sites. Test areas should not be chosen near the m o u t h of tributary streams. O n river ice, areas of exceptionally rapid current (such as rapids or eddies) should be avoided. T h e depth of water at the test site should if possible be 2 metres or more and in any event at least twice the expected m a x i m u m thickness of ice.

Test programme

The ice thickness at the test site should be measured at least once a week throughout the winter season and preferably twice a week during the first m o n t h after freeze-up (or to be more accurate, after the ice is safe to walk on) w h e n growth is most rapid.

(It is important to protect the safety of the obser-

ver; recommended m i n i m u m ice thicknesses, safe for a m a n carrying light equipment, are: 8 c m for fresh-water ice and 13 c m for sea ice.)

In making measurements care must be taken to disturb the snow cover as little as possible. T h e thickness of the snow cover must always be recorded w h e n the ice thickness is measured. If possible the density of the snow cover should also be determined.

A n ice cover is rarely of completely uniform thickness at any time. It is obvious that a represen- tative thickness will not be obtained by measuring through a ridge or h u m m o c k of ice, but even w h e n the upper surface is level it does not necessarily follow that the bottom surface is also smooth, with a uniform thickness of ice. Sometimes the lower surface of an ice cover has a wavy character. F o r this reason it is recommended that the weekly measurement of ice thickness be m a d e by drilling at least three holes at the test site, within an area of radius 1 or 2 metres. A n average and standard deviation should then be computed so that an estimate of the variability is available.

For a representative test site it is desirable to have the standard deviation small compared to the m e a n , although reliable estimates of the m e a n ice thickness can always be obtained by increasing the number of measurements. A simple empirical test of representativeness is also quite valuable. It is recom- m e n d e d that once during the winter season a n extended series of measurements be m a d e , prefer- ably after the cover has reached two-thirds or m o r e of its m a x i m u m thickness. Figure 1 shows the m e a - surements proposed. T h e regular test site is at A . T h e points G form a cross with each a r m 100 m long and with the distance between adjacent points of measurement being 20 m . If the average thickness measured at A agrees within 10 per cent with the average of 21 measurements at points G on the same date this can be accepted as reasonable evid- ence for the representativeness of site A . If the discrepancy is greater than 10 per cent, a different test site should be chosen for the next season.

Tables 1 and 2 are simple forms suggested for recording ice-thickness measurements. These tables are particularly useful in arctic areas with little snow. T h e remarks entry is for recording any spe- cial circumstances observed, such as cracks, s n o w drifts, ridges in vicinity, etc. Table 1 is for the weekly (or repeated) measurements, Table 2 for the grid survey. In some sub-arctic areas, the presence

13

(12)

Guide to world inventory of sea, lake and river ice

T A B L E 1. Ice-thickness report form T A B L E 2. Ice-thickness grid survey

S T A T I O N : 1. Measureme

2. Date

17 17 17 Average

24

3. Remarks:1

nt site:1

Ice thickness2

(nearest cm)

34 34 36 35 37 etc.

Snow depth¹ (nearest

cm) 21 26 22 23 34

M o n t h : . . .

Type of ice surface*

Smooth

19

Cracks (nil, few, numerous)

Few

S T A T I O N : . _ 1. Grid point

Test site Gl G2 etc.

G21 Average of grid points 2. R e m a r k s :

Instructions for us 1. D r a w a sketch

and distances f

D a t e : . .. ._. 19...

\

Ice S n o w Remarks thickness thickness

(nearest cm) (nearest cm)

e of form

on the back of this form showing locations rom each other of grid points and test site Instructions for use of form

1. For 'Measurement Site' note bearing and distance from a prominent landmark and report any significant change of the site. The ice thickness should be measured near the same spot throughout the ice season.

2. Each thickness observation is to be entered o n a separate line with average values shown as in the example.

3. Type of ice surface should be reported in terms of the per- centage of the surface covered by ridges together with es- timates of the average ridge height.

4. In Remarks list any particularly significant data such as date of first ice formation, date when ice first extends from shore to shore or to horizon, date of first ice movement or visible break-up; also, location, length and width of near-by ridges or snow drifts or leads.

in relation to shore-line. (See text and Figure 1 for recom- mended layout of grid.)

Give recommendation as to whether test site is satisfactory, and if not where a better site might be chosen for next winter.

of abundant snow and pronounced temperature fluctuations m a k e more elaborate forms such as used by the Swedish Meteorological and H y d r o - logical Institute desirable. Such forms facilitate the description of complex interlayered snow-water-ice systems. It also m a y be desirable to note the relative volume and shape of the air inclusions in the differ- ent ice layers.

_o-i-

Analysis of ice thickness data — isolines

Assuming that a p r o g r a m m e of ice-thickness measu- rements as discussed above has been carried out at a n u m b e r of stations or test sites in a country for a

o E

in

A\

F I G . 1. Test site for ice-thickness measurements.

14

(13)

Measurement of ice thickness

F I G . 2. Greatest ice thickness observed at the time of m a x i m u m thickness for the years of record (in c m ) . winter season, the best display of the data is prob-

ably in m a p form. Three different m a p displays are recommended; plots of the date of freeze-up, of the m a x i m u m ice thickness recorded and of the date of break-up. O n each of these m a p s isolines of equal date or equal thickness should be drawn.

Unless the network of observation points is dense (which is improbable), some artistic licence will be inevitable in drawing these isolines. Also, if complex interlayered snow-water-ice systems are observed, some convention should be established to convert such results to a 'single' equivalent or effective ice thickness. Variations in climatic régime from coun- try to country (and even from area to area in the larger countries) preclude a single such convention.

Examples which have been employed are given in Gold (1960), Rose and Silversides (1958) and Röthlisberger (1968).

A network of such ice-observations sites has been in operation in Canada for more than a decade, both on the mainland and in the Canadian arctic archipelago. In the latter case, most of the observa- tions have been m a d e near joint United States/Cana- dian weather stations. These data are taken in accordance with a manual (Department of Trans- port (Canada), 1959), and published annually by the Department of Transport (e.g. 1964). For several years an analysis of the Canadian and other North American data on ice has been carried out by C R R E L (Bilello, 1961, 1964; Bilello and Bates, 1966). Figure 2 (taken from Bilello and Bates, 1966), is an example of an isoline m a p of m a x i m u m ice thickness. This particular chart shows the extreme ice thicknesses recorded over several years, but for the purpose of ice inventories the m a p should be prepared in terms of average m a x i m u m ice thickness.

15

(14)

3 Areal extent

Lakes and rivers

T h e other variable, beside ice thickness, needed to compute ice volumes is the superficial area occupied by ice. Basically this is a mapping problem, which is equally vital for all hydrological studies and not pecu- liar to the inventory of ice. T h e starting-point is a complete set of large-scale topographic m a p s , pre- pared either from ground surveys or more usually from photographic surveys from the air. T h e areas of lakes can be measured from the topographic m a p of each region using a planimeter. This method is rarely applicable to rivers because the m a p scale is not large enough, and the information has to be derived from the original survey data or air photographs.

The lengths and widths of each river and stream in a drainage basin should be computed in this way.

For practical reasons some limit must be placed on the size of tributary streams to be considered, and it is recommended that streams whose m a x i m u m width is less than 5 m be ignored, as well as the areas of larger streams above the point where the width of each stream decreases to 5 m . T h e resulting inventory of river ice will give a slightly lower volume than actually exists but, since the total volume of river ice is a minor factor in the total of water stored in solid form, this inaccuracy is negli- gible compared to the uncertainties in the over-all inventory.

This p r o g r a m m e of measuring the area of lakes and rivers which are ice-covered at some season will be a tedious and costly operation and each national I H D committee should ensure that there is no duplication in effort at this point by the various groups working on Decade programmes.

Sea ice

S o m e countries such as Canada and the United States carry out regular air reconnaissance patrols of sea ice and prepare charts of ice concentration and estimated thicknesses as an aid to ship naviga- tion. Methods are described in a Department of Transport (Canada) manual (1959). In some areas, such as the Gulf of St. Lawrence, data from these ice charts will be sufficient to compute the volume of sea ice at different seasons. T h e air surveys, however, are not frequent enough or sufficiently extended in coverage to delimit accurately the extent and concentration of the great areas of sea ice in the arctic and antarctic regions. There is also, at present, no adequate w a y to estimate accurately either the thickness of undisturbed ice or the volume of ice occurring in ridges and h u m m o c k s . The boundaries of this pack ice can best be observed by satellites and it is recommended that the two countries, U . S . S . R . and United States, using weather-observation satel- lites undertake to supply this information. Such data are limited at present because the few satellites in polar orbits have usually been programmed to stop observing w h e n above 60° N . There is the problem of observing the boundary of the pack during the dark season but it appears that the technology of infra-red sensors has n o w improved to the point where it is possible to distinguish with reasonable accuracy between open water and ice- covered areas.

16

(15)

4 Volume of lake ice

Recommended method

W h e r e the network of ground stations reporting ice thickness is sufficient to permit preparation of iso- line m a p s of m a x i m u m ice thickness (preferably representing data averaged over a five-year period) such as Figure 2 , this method of obtaining ice volumes is recommended. T h e area of the country should be divided up into a small number of regions which the isoline m a p shows to have essentially uniform m a x i m u m ice thickness. With the area data of Section 3, 'Lakes and Rivers', the calculation of the m a x i m u m volume of lake ice is then straight- forward.

Climatological approach

If the data on representative ice thickness used in the above-recommended method are not available, a less accurate estimate can be obtained from clima- tological data which are usually accessible. This method is ultimately based on the original theoreti- cal calculation of Stefan (see e.g. Pounder, 1965, p. 133). His equation is that

where h is the ice thickness at time /, 0 is the tem- perature difference between the surface of the ice (usually, air temperature must be used) and the freezing point of the water (fresh or salt), t0 is the time of first freeze-up, and k, L, p are the thermal conductivity, latent heat and density of ice respect- ively. The quantity ist) called the freezing exposure, is usually measured in degree-days or degree-months.

The basic Stefan equation does not apply w h e n there are changes in the heat content of the ice either by absorbed radiation, advection of heat by water cur- rents or other effects (a fact clearly recognized by

Stefan himself). Nevertheless this equation has been used with considerable success in the modified form

h = aEfi (2 where a is an empirical coefficient dependent

on the area in question and the a m o u n t of snow cover, and ß is another empirical coefficient c^ 0.5.

N u m e r o u s authors have suggested various values of the coefficients under different conditions. It is recommended that the following values be taken as representative of conditions with a snow cover of thickness 20 c m ; fresh ice, a = 2.7, ß = 0.5; sea ice, a. = 2.4, ß = 0.5.

If Et is the freezing exposure in degree-days (Celsius scale) and these values of a, ß are used, h will be in c m . Equation (2) can be applied equally well to lake ice or sea ice, but with different values of a as noted. The values of « can be reduced somewhat if it is k n o w n that the average snow cover in an area is considerably greater than 20 c m . It is recommended that the reduction be 10 per cent if the average snow cover is 30 c m or more. This seems a small reduction considering the large ther- mal insulation of a snow cover, but a compensating factor comes into play. Over any long time period ice flows plastically, so that a thick snow cover deposi- ted on an ice cover depresses the ice, causing cracks to appear and water to flow to the ice surface and thus restore the hydrostatic balance. T h e lower, water-saturated snow layers freeze to form so-called snow ice or white ice, thus increasing the thickness of the ice cover.

T o apply this method, the area of the country should be divided into regions of more-or-Iess constant winter régime, that is, duration of the season of below-freezing air temperatures, snow fall and date of first ice formation. For each such region the m a x i m u m value of Et should be calculated

• (from the date of freeze-up to the date at which the

17

(16)

Volume of lake ice

m e a n air temperature goes above freezing) and then the value of A , ^ using Equation (2) and the tabu- lated values of the coefficients. T h e volume of ice can then be found as in the above-recommended method. For a more rigorous solution of the

problems of ice growth the methods suggested by Schwerdtfeger (1963,1964) should be applied. These papers clearly show h o w the thermal properties of sea ice vary with density, salinity and temperature and differ from those of fresh-water ice.

18

(17)

5 Volume of river ice

Ideally the amount of river ice should be found by the same method as in Section 4 ( ' R e c o m m e n d e d Method'). However, the difficulty of finding suit- able test sites o n rivers w a s suggested in Section 2 ('Test Site'), and sufficiently extensive networks of thickness measurement will rarely exist. Because of heat generated by hydraulic drag, river ice in a n area is usually less thick than lake ice. Butiagin

(1966, C h a p . II) quotes U . S . S . R . experience that river ice is usually 15 to 20 per cent thinner than lake ice. It is recommended that the volume of river ice in each region be calculated by taking the maxi- m u m thickness of river ice to be 15 per cent less than the comparable figure for lake ice in that region (whether calculated by the recommended method or the climatological approach, given in Section 4).

19

(18)

6 Volume of sea ice

Annual or one-year ice

Extensive areas in the Northern Hemisphere are covered with sea ice for a limited part of each year.

In general, this ice is fairly uniform, and the average thickness and ice boundaries in each area are rea- sonably well k n o w n , although additional satellite data on the location of the ice boundaries in the open ocean are still needed. At the height of the ice season the cover is essentially complete. That is, the amount of open water within the ice boundaries is usually negligible. T h e calculation of the volume of annual sea ice in the north is thus a relatively straightforward matter if a correction for the amount of ice involved in ridging can be m a d e . It is recommended that the I H D Co-ordinating Council assign this task to various countries as follows:

1. Canada. Gulf of St. Lawrence, Hudson Bay, Canadian Arctic Archipelago, Labrador Sea, Davis Strait and Baffin Bay.

2. Denmark. East and south Greenland waters from Svalbard to Cape Farewell and Godthaab.

3. Finland. Baltic Sea and surrounding waters.

4. Japan. Sea of Okhotsk and all waters west of the Kamchatka Peninsula to the Asian mainland.

5. Norway. Polar seas to the north of Europe from Svalbard to Novaya Zemlya.

6. United States. Beaufort Sea, Chukchi Sea, Bering Sea and west to Kamchatka.

7. U.S.S.R. Polar seas to the north of Europe and Asia from Novaya Zemlya to the East Siberian Sea.

The areas of annual ice surrounding Antarctica have not been studied as extensively as the northern areas. Neither do they lend themselves to the sort of subdivision listed above. This problem will have to be studied by S C A R in conjunction with that of perennial sea ice in the south.

20

Arctic sea ice

Almost the only certainty is that any inventory m a d e of Arctic sea ice in the near future will be highly inaccurate. T h e boundaries with the sur- rounding zone of first-year ice are k n o w n roughly, although here again additional satellite data are needed. The basic problem is lack of knowledge of the m e a n thickness of the 'smooth' parts of the pack, the extent of ridging and the amount of open water or thin ice. Present knowledge was reviewed at the symposium on the arctic heat budget and atmospheric circulation held at Lake Arrowhead, California, in 1966. Particularly valuable is the paper of Wittman and Schule (1966). It summarizes in- formation on the problem topics listed above which has been obtained from Soviet and American drift- ing stations, Birdseye and other air reconnaissance flights, and under-ice submarine cruises. Yet the Glaciology Panel, Committee on Polar Research (1967) points out that Wittman and Schule's data appear to be irreconcilable with other observations and with heat and mass balance studies. The impor- tance of the problem of arctic sea ice from m a n y points of view ensures that further research will continue. Present estimates of the volume of this ice are available. T h e international committee which was recommended in Section 1 ('Responsibility for the I H D Inventory of Floating Ice') should decide whether they are worth including in a world inven- tory of ice and snow.

Antarctic sea ice

Everything which has been said in the previous sec- tion applies to the antarctic region as well, but even more strongly. Boundaries are k n o w n with less accuracy and there is m u c h less information on thickness. A n inventory at present could give only an order of magnitude and further data are needed from satellite and other types of reconnaissance.

Valuable new techniques for processing satellite observations are given in Booth and Taylor (1969).

(19)

7 Seasonal variations

For inventory purposes the important information is the m a x i m u m amount of ice during the cold season and this guide has stressed methods of obtaining this information. However the seasonal variation is often important for other reasons and comes as part of programmes of ice-thickness m e a - surement such as described in Section 2. Figure 3 shows the measurements on the growth of the ice cover taken one winter at Resolute Bay, N . W . T . , Canada. This is a cover of first-year sea ice. It started to form on 29 September (1958), reached a m a x i m u m thickness of about 1.8 m by m i d - M a y , remained constant in thickness until mid-June, and then melted completely in the next six weeks. T h e reduction in growth rate with increasing ice thick- ness is evident in the figure. Butiagin (1966) reports that in Siberia 'on the average, toward the middle of January the thickness of the ice cover has already reached 70=75 percent of its greatest value'.

F r o m Figure 3, this proportion was not reached until mid-February. This illustrates the variability in climate in different parts of the hemisphere. T h e curve of Figure 3 can be fitted quite accurately by the exponential growth equation

It = 1.35 //max(l-e - - - u s , , IT) (3) where t is the time in days since freeze-up, T is the duration of the^ total growth season, Am a x is the m a x i m u m ice thickness and h is the thickness at time r. The equality of the numerical coefficients in Equation (3) is purely coincidental.

Prediction of ice thickness at a certain location on a given date can be done in various ways. T h e best depends on the ice-thickness survey of Section 2.

The first step is to determine in which climatic zone (zone of equal m a x i m u m ice thickness) the location lies. Then one can assume that the growth curve for this location is the same as for the nearest test site in this zone. A n alternative (likely to be less accur- ate) is to determine (possibly from an isoline chart

of freeze-up dates) the probable date of first ice formation. Climatological data from the nearest weather station can then be used to calculate Et

and hence h from Equation (2). If the tedious cal- culation of Et is to be avoided, Equation (3) will probably give equally accurate results.

200 n

FIG. 3. The growth of a cover of annual sea ice, Resolute Bay, N . W . T . , Canada, October 1958 to M a y 1959.

21

(20)

8 Ice nomenclature

T h e attention of I H D National Committees is drawn to problems relating to nomenclature of sea, lake and river ice which need to be solved if data transmitted to I G Y World Data Centres for Glacio- logy are to be of m a x i m u m usefulness. In this con- nexion attention is also drawn to International Hydrological Decade resolution 65, concerning the need for an international glossary of hydrology, and to the approval by the president of the World Meteorological Organization on 15 M a r c h 1968 of an international sea ice nomenclature prepared by the W M O Commission of Maritime Meteorology (Recommendation 35 C M M - 6 8 ) Working G r o u p on Sea Ice. T h e Illustrated Glossary of Snow and Ice (Armstrong et ai, 1966) will also be of great use.

Sea ice

The need for an internationally agreed sea ice nomenclature has been widely recognized for m a n y years and resulted in the preparation of the WMO Abridged International Ice Nomenclature (1956). A s a result of the rapid progress of sea-ice studies, the above nomenclature was comprehensively revised by the Working G r o u p on Sea Ice of the W M O Commission of Maritime Meteorology in Sep- tember 1967. At present (July 1970) the WMO Sea Ice Nomenclature (1968 edition) is available in English and Russian. Translations into French and Spanish are in preparation. So that data on sea ice transmitted internationally are understandable to all w h o m a y wish to use them subsequently I H D National Committees are urged to use this n o m e n - clature. A publication entitled WMO Sea Ice Nomenclature containing both the Sea Ice Glossary and Illustrated Sea Ice Glossary is being printed by W M O .

River ice and lake ice

There is no internationally agreed nomenclature covering river ice. Since there has been no c o m - monly acknowledged requirement for the exchange of data on river ice, national nomenclatures have grown up in isolation. The concepts which it m a y be necessary to describe are the same for all rivers seasonally frozen over but the terms used and the definitions applied to those terms m a y differ widely between the various language and national n o m e n - clatures. This situation is an example of the prob- lems foreseen by the Co-ordinating Council for the I H D at their first session and which resulted in resolution 65. T o ensure that data transmitted inter- nationally shall be understandable, it is necessary that national river ice glossaries should be available at the I G Y data centres. In this connexion National Committees are invited to consider means of ful- filling the second operative paragraph of resolu- tion 65 for river ice.

With regard to lake ice the situation is similar but with one important difference. M a n y river-ice phenomena are due to the fact of water flowing beneath it consistently in one direction but with volumes and rates differing from time to time and from place to place along the river. Apart from the differences in physical properties of fresh-water ice and sea-water ice, the only other difference between lake ice and sea ice relates to the differences in the scale of phenomena. Ice on the Great Lakes of North America, which only very rarely freeze over completely, m a y be described in essentially the same terms as sea ice as regards its development, arrangement and deformation processes, etc., are concerned. For m u c h smaller lakes, which normally freeze over, the processes remain the same as for large lakes but the range of phenomena observed will be less. In view of the highly developed sea-ice terminology which is already internationally avail- able and because of the obvious practical advan- tage to be gained by referring to the same ice phe- n o m e n a by the same term, independent of the shape or size of the body of water on which it is observed, the sea-ice terminology should, as far as possible, be used for describing lake ice.

22

(21)

Bibliography

AMERICAN GEOPHYSICAL UNION. GLACIOLOGY PANEL. 1967.

Glaciology in the arctic. Trans. Amer. Geophys. Un., vol. 48, p. 759-67.

ARMSTRONG, T. E.; ROBERTS, B. B.; SWITHINBANK, C. W . M . 1966. Illustrated glossary of snow and ice. Cambridge, Scott Polar Research Institute. 66 p. (Special publ.

no. 4.)

B I L E L L O , M . A . 1961. Ice thickness observations in the North American arctic and subarctic for 1958-59,1959-60. H a n o - ver, N . H . , United States A r m y , Corps of Engineers.

( C R R E L Special Report 43, pt. I.)

. 1964. Ice thickness observations in the North American arctic and subarctic for 1960-61, 1961-62. Hanover, N . H . , United States A r m y , Corps of Engineers, 113 p. ( C R R E L Special Report 43, pt. II.)

B I L E L L O , M . A . ; B A T E S , R . E . 1966. Ice thickness observa- tions in the North American arctic and subarctic for 1962-63, 1963-64. Hanover, N . H . , United States A r m y , Corps of Engineers. 103 p. ( C R R E L Special Report 43, pt. III.) B O G O R O D S K I I , V . V . ; R U D A K O V , V . N . 1962. Electromagnetic

methods of determining the thickness of floating ice. Zh.

tekh. Fiz., vol. 32, no. 7, p. 874-82.

B O O T H , A . L . ; T A Y L O R , V . R . 1969. Meso-scale archive and computer products of digitized video data from E S S A satellites. Bull. A m . Met. Soc, vol. 50, p. 431-8.

B U T I A G I N , I. P . 1966. Prochnosti I'da i ledianogo pokrova [Strength of ice and ice cover]. Novosibirsk, Izdatel'stvo 'Nauka', Sibirskoe Otdelenie.

CANADA. DEPARTMENT OF TRANSPORT. 1959. MANICE, Ma- nual of standard procedures and practices for ice reconnais- sance. Meteorological Branch. (CIR-3188, Ice 3.)

. 1964. Ice thickness data for Canadian selected stations, freeze-up 1963 to break-up, 1964. Meteorological Branch.

(CIR-4153,Icel9.)

C O O K , J. S. 1960. Proposed monocycle-pulse V H F radar for airborne ice and snow measurements. Trans. Am. Inst.

Elect. Engrs, vol. I, no. 79, p. 588.

E V A N S , S . ; R O B I N , G . d e Q . 1966. Glacier depth-sounding from the air. Nature, vol. 210, p. 883-5.

G O L D , L . W . 1960. Field study on the load bearing capacity of ice covers. Pulp and paper magazine of Canada, Wood- lands section, M a y 1960, 9 p.

H O U L E , J. L . 1961. Two instruments for the measurement of ice thickness. Ottawa, Canada, Defence Research Board. 7 p.

( D R N L Technical note no. 5/61.)

P O U N D E R , E . R . 1962. Ice research project, p. 6-10. Montreal, Canada, McGill University. (Report G - 8 . )

. 1965. The physics of ice. Oxford, Pergamon. 151 p.

P R E S S , F . ; C R A R Y , A . P . ; O L I V E R , J.; K A T Z , S. 1951. Air coupled fiexural waves in floating ice. Trans. Am. Geophys.

Un., vol. 32, p. 166-72.

PRESS, F . ; E W I N G , M . 1951a. Theory of air coupled fiexural waves. / . appl. Phys., vol. 22, p. 892-9.

R O S E , L . B . ; SILVERSIDES, C . R . 1958. T h e preparation of ice landings by pulp and paper companies in Eastern Canada.

Trans. Engng. Inst. Can. vol. 2, no. 3, p. 101-7.

R Ö T H L I S B E R G E R , H . 1968. D a s Problem der Tragfähigkeit der Eisdecke anlässlich der Zürcher Seegfrörni 1963. Schweiz.

Bauztg, vol. 86, no. 31, 1 August 1968, p. 565-9.

S C H W E R D T F E G E R , P . 1963. The thermal properties of sea ice.

/ . Glacial., vol. 4, no. 36, p. 789.

. 1964. The effect of finite heat content and thermal dif- fusion on the growth of a sea ice cover. J. Glaciol., vol. 5, no. 39, p. 315.

. 1968. A n automatic gauge for measuring sea ice thick- ness. J. Glaciol. vol. 7, no. 49, p. 109.

S Y R I N K O V , P . I. 1963. Means of measuring the thickness of ice without making holes in the ice. Sbornik za ratsionali- zatsiyu v gidrologii. Leningrad.

U N T E R S T E I N E R , N . ; B A D G L E Y , F . I. 1958. Preliminary results of thermal budget studies on arctic pack ice during s u m m e r and autumn. In: Arctic sea ice, p. 85-92. Washington, National A c a d e m y of Sciences, National Research Council.

(Publ. n o . 598.)

W I T T M A N , W . I.; S C H U L E , Jr. J. J. 1966. C o m m e n t s o n the mass budget of arctic pack ice. Proc. Symp. Arctic Heat Budget and Atmos. Circ, p. 215-46. Santa Monica, Calif., Rand Corporation.

23

(22)

1972

International Book Year

[A. 2964]

U . S . S2.50; 75p (stg.); 10 F Plus taxes, if applicable