Russian Federal Service for Hydrometeorology and Monitoring of the Natural Environment
State Research Center of the Russian Federation
The Arctic and Antarctic Research Institute

 

 

TECHNOLOGICAL HANDBOOK
OF THE CLIMATE OF RUSSIA
(Arctic Region)

SOLAR RADIATION

 

Edited by
V. F. Radionov

 

 

St. Petersburg
Hydrometeorological Publishers
1997


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Table of Contents

Foreword
Introduction
Standard Designations and Abbreviations
The Radiation Regime
General Description and Environmental Considerations
Direct Solar Radiation
Diffuse Radiation
Global Radiation
Albedo
Net Radiation
Table Captions and Explanation of the Tables
References

Foreword

This Handbook is a continuation of the publications in the series entitled "Handbook of Technology on the Climate of the USSR," which was prepared in departments and research institutes of the Russian Federal Service for Hydrometeorology and Monitoring of the Environment. A uniform method has been used which was developed by Voeikov Main Geophysical Observatory (MGO) and approved by the editorial board of Hydrometeorological Service of the USSR.

Included in this handbook are the results of climatological processing of actinometric observations obtained from the network of Russian polar stations. The data consist of continuous and uniform series of observations.

The goal of this handbook is to provide climate information for use in research and for promoting the objectives of the national economy. Basic data included in the handbook and results based on these data can be used for:

In the handbook, the data are presented in tables of statistical parameters of various temporal distributions - monthly, daily, and for specific times.

Parameters related to monthly distributions were calculated for the period 1939-1980. For tables including data on extreme values, the data series were extended to 1992. Parameters related to daily distributions and observations at particular times were calculated for the period 1935-1980.

The Handbook was prepared using direct observational data and results from initial processing obtained from the climate departments of the Regional Centers of the Russian Hydrometeorological Service (Roshydromet) at Amderma, Dixon, Tiksi and Pevek.

At the Amderma Regional Center the data reduction and processing were performed by the following specialists: engineer-climatologist - L. N. Molchanova (local director); actinometric engineers N. G. Antonova, V. Yu. Shvareva, N. I. Chuprakova; engineer-climatologist V. A. Ashmyantseva, and senior technician I. L. Kalabina. S. G. Bazilevskaya, L.N. Nikolenko, V. V. Tikhanov also participated in this work. The computer programming needed to calculate the data and construct the tables was developed under the direction of the head of the Department of Mechanized Data Processing of the Hydrometeorological Center V. I. Molochnikov, engineer-programmers E. N. Voloshina and A. Ya. Korshun.

At the Dixon Regional Center, the work was performed by the following specialists: head of the Department of Climate of the Hydrometeorological Center N. G. Kanunnikova, senior engineer N. B. Grigorieva, engineers T. N. Adamovich, V. V. Gorbenko, N. L. Eliseeva, O. L. Savva.

At the Tiksi Regional Center, the work was performed by the following specialists: head of the Department of Climate of the Hydrometeorological Center M. G. Artamonov, engineer-meteorologists O. N. Pavlov, N. V. Sigalaeva, senior technicians S. B. Fedyukovich, V. V. Chernyavskaya and T. K. Yakovleva.

At the Pevek Regional Center, the work was performed by the following specialists: senior engineer-climatologist A. I. Lobanov, engineer-climatologist L. P. Shapovalova and technician V. N. Nekrasova.

Preparation of the present Handbook was carried out in 1996 at the Department of Meteorology of AARI under the general scientific direction of the Head of the Department of Meteorology, Dr. nbsp;F. Radionov, senior scientist Dr. M. S. Marshunova, research assistant Yu. E. Pimanova, research associates A. A. Mishin, N. I. Lukianchikova, senior engineer V. V. Dubovtseva, engineers E. O. Vanyushina, Z. P. Grobovikova, V. A. Shirokova.

Scientific examination of the data was performed at the Arctic and Antarctic Research Institute by Dr. M. S. Marshunova and at the Voeikov Main Geophysical Observatory by the senior engineer N. N. Plokhinskaya.

INTRODUCTION

This Handbook of the radiation regime of the Russian Arctic contains long-term data of direct (S, S'), diffuse (D) and global (Q) solar radiation, albedo (A), net radiation (B) at the earth's surface. The Russian radiation monitoring network in the Arctic, which in some cases began observations before the Second World War, made it possible to collect a great volume of observational data. Observational data from 15 Arctic stations (see Table I) are included in the Handbook. The observation period at some of these stations is more than 50 years (Tables II and III).

Table I

List of the stations with their coordinates

Station Coordinates, degrees Elevation
Above Sea Level, m
N. Lat. E. Long.
Bely Nos 69.60 60.20 6
Vankarem 67.50 184.10 5
Vize Island 79.30 76.59 11
Wrangel Island 70.58 181.31 2
Golomyanny Island 79.33 90.37 9
Dixon Island 73.30 80.14 42
Cape Zhelaniya 76.57 63.34 9
Kotelnyy Island 76.00 137.54 11
Muostakh Island 71.33 130.01 3
E. T. Krenkel Observatory 80.37 58.03 21
E. K. Fedorov Observatory 77.43 104.17 12
Preobrazheniya Island 74.40 112.56 24
Uedineniya Island 77.30 82.14 22
Uelen 66.10 190.10 6
Chetiryokhstolbovoy Island 70.38 162.24 32

The standard set of radiation observations includes measurements at fixed intervals of the fluxes of direct, diffuse and global radiation, albedo, reflected radiation and net radiation at the surface. All measurements of radiation fluxes were accompanied by a measured value of the solar elevation and detailed meteorological characteristics. Radiation fluxes were measured at 4 to 8 discrete times a day. Observations were made at noon and midnight local solar time, and the remaining observations were distributed evenly between them. The hourly, daily, monthly and annual totals of the radiation regime parameters were obtained at all stations. In cases where the record was interrupted, the daily totals of the corresponding radiation elements were calculated based on the existing observations by linear interpolation between observation times.

Table II: Observation periods for solar radiation and net radiation

Table III: Statistical characteristics of monthly totals of solar radiation and net radiation

Note: S - direct solar radiation on a surface which is normal to the direction of the incident radiation; S' - direct solar radiation flux incident on the horizontal surface; D - diffuse radiation; Q - global radiation; A - surface albedo; B - net radiation; P2-transmission coefficient (index of atmospheric transparency for global solar radiation in the 0.4 to 4 mm band)

This Handbook contains transmission coefficients values (P2) calculated on the basis of direct solar radiation values using the standard techniques as specified in the Manual on Radiation Observations for Hydrometeorological Stations, 1971. Average standard deviations and extremes of monthly radiation totals are also included. Besides the radiation values for average cloud conditions, tables for clear skies (cloud cover 2 tenths or less) have been developed.

In 1970, significant modifications were made in the process for producing the standard radiation results as follows: a method was introduced for continuous determination of all elements of the radiation balance (except direct radiation) to avoid the need to carry out discrete observations at specified intervals. To check the values of the data, corresponding observations using reference instruments were performed. Because of the absence of follow-up systems, direct solar radiation continued to be observed 4 times a day. As a result, in this Handbook the monthly totals S' have been calculated as the difference between the global and diffuse radiation (S' = Q - D).

Standard sets of instruments [Yanishevskiy, 1957] were used as radiation sensors: AT-50 actinometers, M-80 pyranometers, and M-10 net radiation meters. The GSM-1 galvanometer was the main measuring device used for discrete time observations. Until 1965 the data recording was carried out by disk galvanometers or recording millivoltmeters. From 1965 the EPP-09 multichannel electronic potentiometer was used starting. All thermoelectric sensors were calibrated at the Central Calibration Bureau and were calibrated periodically during the work by comparison with standard actinometers (during the day) or net radiation meters (during the night). This system of calibration ensures the reliability of the values of all elements of the shortwave radiation (S', D, Q, A). The net radiation values have somewhat lower quality due to systematic errors of up to 30 percent for observations taken with net radiation meters.

All types of observations as well as the associated processing and checking were carried out as specified in the Handbook on Radiation Observations for Hydrometeorological Stations [1971] and according to the instructions of AARI.

Standard Designations and Abbreviations

S - direct incident solar radiation flux on a surface normal to the direction of the radiation.

S' - direct incident solar radiation flux incident on a horizontal surface.

D - diffuse radiation

Q - global radiation

A - surface albedo

B - net radiation

Bs - net shortwave radiation

Bl - net longwave radiation

Rs - upwelling (reflected) shortwave radiation

P2 - atmospheric transmission coefficient for global solar radiation in the 0.4 to 4.0 m m band.

h¤ - angular elevation of sun above the horizon

p.d. - polar day

p.n. - polar night

 

THE RADIATION REGIME

General Description and Environmental Considerations

The radiation data accumulated up to the present time make it possible to evaluate the role of various factors which make up the radiation regime of the surface, to make more precise the average values of the values obtained earlier, and to study spatial and temporal variability of the individual radiation elements.

It is well known that the radiation regime of the Arctic is characterized by a series of particular features compared with the other regions of the earth. These features depend on the geographic location of the Arctic, the structure of the atmosphere and the cloud cover, and the properties of underlying surface [Atlas of the Energy Balance of the North Polar Regions, 1992; Marshunova and Radionov, 1988; Handbook of the climate of the USSR, 1966-67; Chernigovskiy and Marshunova, 1965].

Incident solar radiation is non-uniform over the course of a year primarily due to the phenomena of polar day and polar night. The data on the duration period of polar day and polar night for the stations are included in this handbook in Table 1. Calculations take into account atmospheric refraction. As a result of refraction, the duration of polar day is somewhat longer than that of polar night. During the polar day the noontime solar elevation decreases with increasing latitude, and the solar elevation at midnight increases. Thus, the average solar elevation at various latitudes over the Arctic during the polar day remains constant (Table 2). This circumstance significantly influences the geographical distribution of monthly radiation totals.

Table IV

Characteristics of the surface at the actinometric station sites

Station Period of stable snow cover Surface characteristics during the snow-free period
Krenkel Observatory 7 Sep-29 Jun Tundra, lichen, stones
Cape Zhelania 29 Sep-3 Jul Alluvial sandstone deposits
Golomyanny Island 12 Sep-28 Jun Small stones, clay
Vize Island 12 Sep-23 Jun Silt-sandy soil, moss
Fedorov Observatory 16 Sep-4 Jul Stony tundra
Uedinenia Island 20 Sep-20 Jun Silty tundra, moss, lichen
Dixon Island 1 Oct-14 Jun Moss, exposed soil, stones
Kotelnyy Island 16 Sep-16 Jun Tundra covered by grass
Preobrazhenia Island 12 Sep-11 Jun Sandstone covered by grass
Muostakh Island 2 Oct-6 Jun Tundra, peaty hillocks
Chetyryokhstolbovoy Island 25 Sep-30 May Tundra covered by moss or grass
Wrangel Island 27Sep-4 Jun Pebbles, gravel, sand
Vankarem 9 Oct-2 Jun Pebbles, sand
Uelen 18 Oct-9 Jun Pebbles, sand

Stable snow cover is observed at all stations from October through May (see Table IV). In June the snow cover melts away, and in September it is reestablished. The formation and melting in different years can occur 2 to 3 weeks earlier or later than the average dates. This results in large variations in the albedo during these seasons.

The character of radiation processes depends to a considerable extent on the cloud-cover conditions and the atmospheric transparency, variations of which are largely specified by the atmosphere circulation. For the Arctic as a whole, cloudiness increases from winter to summer followed by a decrease in early autumn, but some differences are observed in certain areas.

The parameters of cloud cover differ in specific Arctic areas, particularly in winter, due to the influence of atmospheric circulation, which is most intense during that season. The anticyclone weather regime becomes stronger from west to east. In summer, inhomogeneities in climatic conditions smooth out in certain parts of the Arctic. Cloudiness is large everywhere, and low level stratus clouds are predominant.

Three climatic regions can be specified in the Russian Arctic according to the characteristics of circulation and the distribution of the basic meteorological elements.

The following stations are included in the western region: E. T. Krenkel Observatory, Cape Zhelania, Vize Island, Uedinenia Island, and Dixon Island. The maximum frequency of cyclones originating in the North Atlantic is observed in this region in winter. As a result, there is an increase in cloudiness and atmospheric aerosol pollution in comparison with the other regions.

The Siberian (or central region) includes the following stations: E. K. Fedorov Observatory, Preobrazhenia, Kotelnyy, and Muostakh and Chetyryokhstolbovoy islands. During the cold part of the year, the meteorological conditions of this region are determined by the influence of the Siberian anticyclone. The air temperature is lower there, the cloudiness is less, and the precipitation occurs less often and in smaller amounts than in the other regions. In summer the amount of cloudiness is large.

The eastern region includes the following stations: Wrangel Island, Vankarem, and Uelen. In winter, the Pacific cyclones exert a significant influence on this region, but their frequency and intensity are significantly less than those in the western region.

The atmospheric transparency in the Arctic is high as a result of the low humidity and relatively low levels of aerosol pollution.

Direct Solar Radiation

One of the basic parameter sets defining the radiation regime for any part of the earth are the monthly totals of solar radiation.

Solar elevation changes and cloudiness determine the annual variability of direct radiation. The maximum possible monthly totals have been calculated assuming clear skies the entire time (Tables 6, 7).

The annual variability of maximum possible direct radiation is specified primarily by changes in the solar elevation and the duration of daylight and, to a lesser extent, by changes in atmosphere transparency. During the polar day, monthly totals of direct radiation incident on a horizontal surface in the Arctic do not depend on latitude because the increase of solar elevation at midnight compensates for the decrease of noontime solar elevation. In spring and autumn, solar radiation decreases with increasing latitude.

The spatial distribution of monthly totals of direct solar radiation incident on a horizontal surface (Table 10) in spring and autumn is defined by astronomical factors (by variations in the duration of sunlight). Radiation decreases with increasing latitude. The influence of cloudiness throughout these seasons modulates the pure variation with latitude that would otherwise exist. During the polar day when the influence of astronomical factors is smoothed out, the radiation distribution is specified by the cloudiness regime.

A maximum in the average monthly totals of direct solar radiation over the course of the year is observed not only in June, when the length of the day and the solar elevation are greatest, but also in other months (April to July), when cloudiness is less than in June.

Variability of average monthly and annual radiation totals is evaluated quantitatively by the values of standard deviations, s, which indicate the stability of the radiation regime. Direct solar radiation shows the greatest fluctuations. Its coefficient of variation changes from 30 percent in March and April to 40 to 50 percent in August and September.

Fluxes of direct solar radiation (S') measured for clear skies (Table 4) are used to specify the atmospheric transparency. The following index defined for an atmosphere air mass of m = 2 is used to characterize the atmospheric transparency:

Image6.gif

where S(rho,30) is the flux of direct solar radiation, which is reduced to the average distance between the Earth and the Sun and to a solar elevation of 30 degrees (or an air mass of 2). So is the flux of solar radiation at the top of the atmosphere, or the solar constant, which is equal to 1.38 kW/m2 according to the International Pyrheliometric Scale (IPS-1956).

Both the mean values of the transparency index (P2) and their annual variability are significantly different in various parts of the Arctic. An increase in P2 is observed in summer over the most of the Arctic at the northernmost stations in contrast with the other parts of the Earth. On the other hand, the atmosphere transparency decreases during the summer in the southernmost Arctic regions (the Sea of Okhotsk). This peculiarity is especially distinct evident in the extreme values of P2. Such features of the annual variability in P2 are determined by the different correlations between the radiation decrease and the atmospheric water vapor and aerosol contents (Marshunova and Mishin, 1988).

In certain periods, there have been significant transparency decreases in comparison with the average long-term values. Three global decreases of atmosphere transparency have been observed in the Arctic during the time that direct solar radiation has been monitored there [Marshunova and Radionov, 1988; Radionov, 1993; Radionov, 1994]. These decreases were caused by the clouds from the volcanic explosions of Mt. Agung in March 1963 (8.2 degrees south latitude), El Chichon in April 1982 (17.3 degrees north latitude) and Mt. Pinatubo in June 1991 (15 degrees north latitude). The atmospheric transparency decreased by 8 to 12 percent. During these years, the portion of the decrease in the direct solar radiation due to aerosol was 50 percent of the total compared to 38 percent over the long-term average.

Diffuse Radiation

Values of diffuse radiation fluxes depend on the solar elevation, cloud amount and type, and reflectivity of the underlying surface. When mid- and low-level clouds are present, the maximum values of diffuse radiation are observed, which are equal to the global incident radiation. Because of the high degree of cloudiness, characteristic of the entire Arctic during the summer, almost all of the global radiation is accounted for by diffuse radiation.

The maximum monthly totals of diffuse radiation are always observed in June when the solar elevation is highest. A characteristic property of the spatial distribution of diffuse radiation is small regional variability. Only in March and October does the distribution of monthly diffuse radiation totals have a weak latitude dependence (Table 11).

Over the year, the diffuse radiation contributes 20 to 25 percent of the global incident solar radiative flux for clear skies and 60 to 70 percent of the total for mid-level cloudiness. The fraction of diffuse radiation changes over the year: its minimum is observed in March and April (55 to 60 percent), and a secondary small minimum is observed in July (60 to 70 percent), while a value of 70 to 80 percent is observed for the remaining months.

Global Radiation

The global radiation is regulated by the atmospheric transparency, the amount and type of clouds, and to some extent by the properties of the underlying surface.

Monthly totals of the maximum possible global radiation decrease with increasing latitude from September through April. From May through July during polar day, the maximum possible radiation increases as latitude increases by 5 to 8 percent. In addition to the latitude dependence of the radiation, which is determined by astronomical factors, a dependence on the properties of the underlying surface is also observed producing variations of 10 to 15 percent. During this period the value of maximum possible global radiation for a given latitude differs between the regions free from snow and ice, and the regions with drifting ice and glaciers.

Due to the large amount of cloudiness characteristic of the Arctic during the summer, the incident direct solar radiation decreases by 70 to 80 percent and at the same time the diffuse radiation increases. As a result, the global radiation decreases by only 20 to 50 percent throughout the year (Table V).

Table V

Monthly values of the direct and global solar radiation as a percentage of the maximum possible values.

Region Feb Mar Apr May Jun Jul Aug Sep Oct Nov Year
Direct
Western 33 47 47 27 18 24 15 11 15 -- 24
Central 30 53 58 33 25 27 18 15 20 67 29
Eastern 49 58 58 30 34 36 24 21 16 37 34
Global
Western 63 75 82 78 63 56 46 42 53 47 63
Central 67 83 88 78 66 58 48 43 62 48 66
Eastern 84 85 89 78 69 64 53 50 55 74 69

The ratio of direct to diffuse radiation, and hence the relative contributions to the incident global radiation, changes significantly over the year and the regional dependence varies significantly. Over most of the Arctic, diffuse radiation is much greater than direct radiation throughout the entire year. In spring, this is due to the low solar elevation, and in summer and autumn it is due to high degree of cloudiness. Only at the southernmost polar stations, where the maximum amount of sunny days occurs, does the percentage of direct solar radiation reach 40 to 50 percent of the total. This occurs primarily during the spring months (March and April).

The main features of the intra-annual and spatial variability of the radiation characteristics are related to the fact that in spring and fall months the magnitudes of the direct and global radiation are determined primarily by astronomical factors: when the latitude increases the radiation decreases. During the polar day, the radiation field is determined by the cloudiness regime while the influence of the astronomic factors is reduced. The global radiation also depends on the properties of the underlying surface.

During the arctic polar night, from November through January, there is no incident short-wave radiation flux. The radiation is less than 20 MJ/m2 at the latitude of the Arctic Circle.

The distribution of radiation values is almost exclusively latitude dependent from February through March and from September though October. There is, however, a small decrease in the values over the open water surface of the Barents Sea where the greatest cloudiness is observed.

The radiation distribution does not have a pronounced latitude dependence from April through August. The formation of areas with increased or decreased radiation income is determined by the cloud conditions and the albedo of the underlying surface, which depends on the presence or absence of ice. The radiation minimum is observed over the open water surface of the Barents Sea. Over the pack ice of the Arctic basin, the global radiation increases, in spite of a cloud cover of more than 9 tenths, due to multiple reflections between ice and the base of cloud layer.

Albedo

The values of the surface albedo, presented in the tables of this handbook, have been obtained from observation data at selected sites and represent the integral parameters of surface reflectivity for the meteorological site. In summer, the albedo of the natural surfaces encountered at the actinometric observation sites of the polar stations is 10 to 18 percent. During the period with snow cover, albedo is stable at 78 to 85 percent, and varies weakly over the region. Albedo is 30 to 40 percent during the decay and formation of the snow cover period.

In some years, significant deviations of albedo from the average values have been observed, especially in June and September depending on dates of formation and decay of the snow cover.

Table 18 shows the extreme monthly albedo values obtained during the observation period for each station together with the standard deviations that characterize the interannual variability.

Presented in Table VI are the albedos of different land and sea surfaces according to the airborne and surface-traverse observation data obtained in the region of the polar stations.

Table VI

Albedo of the natural surface types

Surface Albedo (A), percent
Fresh dry snow 85-90
Compact dry clean snow 70-80
Melting clean snow 50-75
Dense wind packed snow 60
Melting loose snow 40-45
Fast ice 40-50
Ponds on fast ice 16-26
Frozen tundra 19-26
Brown/red-brown tundra 12-24
Forest/tundra 14-20
Sand 18-20
Pebbles 11-18
Basalt 9-10
Water 5-10

The surface albedo in the Arctic experiences significant seasonal variations. For most of the year, the surface is snow-covered. The longest period with a snow cover, up to 300 days per year, is observed in the western sector, and the shortest one in the eastern sector. Stable snow cover in the Arctic forms, on average, in late September or early October and can remain through the middle of June.

The duration of the snow cover defines the value of albedo and net radiation at the stations considered here. Snow cover has a very high reflectivity: its albedo is equal to 80 to 85 percent. The albedo of the tundra surface after the snow cover has melted away is 15 to 20 percent.

From year to year, the albedo changes little both during the period with stable snow cover (October-April) and during the snow-free period (July-August). The difference between the maximum and minimum monthly albedo values is 5 to 10 percent, and the coefficient of variation for albedo does not exceed 10 percent. The maximum interannual albedo variability is observed in June and September. The coefficient of variation during these months is 30 to 40 percent, and the difference between the maximum and minimum values of albedo reaches 40 to 50 percent.

Net Radiation

Net radiation (B) is the difference between the values of incident radiation, and the expenditure of radiation absorbed and emitted by the earth's surface. It is a function of many physical and geographical and hydrometeorological factors. In different seasons these factors influence the value to varying degrees.

From November through February (the period of polar night and small influx of global radiation), net radiation is determined only by thermal radiation. During these months the average value of net radiation is negative in all Arctic regions. The lowest values were observed over the water surface in the marginal ice zones, where the contrast between the surface (water) and air temperatures is greatest. Areas of the Arctic Ocean without ice cover in winter lose heat in the form of thermal radiation 2 to 3 times more rapidly than the snow-covered ground surface.

Net radiation is close to zero in April and September (in March and October for the southernmost areas of the Arctic). B is always positive from May through August. During this time, its distribution is determined by changes in the surface albedo (from 10 to 80 percent): minimum values are observed on glaciers, maximum values in snow- and ice-free regions.

The annual net radiation in the Arctic varies over a wide range: from 500 to 1000 MJ/m2 over open water surfaces that remain ice free over the whole year; to -100 to -200 MJ/m2 on glaciers and the pack ice of the Arctic basin. The zero isoline coincides with the pack-ice boundary. Thus, the annual negative net radiation is determined by the properties of the surface. According to the observations, the net radiation is always negative where the annual average value of the albedo is more than 70 percent, regardless of how great the global incident radiation flux may be. Results of long-term observational data obtained from the soviet drifting stations show that the albedo decreases to as little as 50 percent in July and August when the snow melt is particularly intense. The annual net radiation can then be close to zero or slightly higher; however, it is always negative on glaciers.

Of the multitude of factors that influence the net radiation variability, the following are the most important: cloudiness, the properties of the surface, and the atmosphere stratification. In different seasons these factors play various roles in determining the mean value of net radiation and its variability. During the dark part of the year, the magnitude of the net radiation depends primarily on cloud conditions and atmosphere stratification, and the coefficient of variation for the monthly values is 15 to 20 percent. During the light part of the year when the net radiation becomes positive, the influence of the absorbed solar radiation increases, and its variability determines the variability of the net radiation. The value of absorbed radiation is, in turn, determined primarily by the surface albedo as well as by the global radiation values.

For most of year, ice and snow are the prevalent surface types in the Arctic. Thus, the duration of stable snow cover has the most significant influence on the mean values of monthly and annual net radiation. Formation and decay of snow cover that occurs 1 to 2 weeks earlier or later than the mean dates can change the albedo by 15 to 20 percent. As a result, during the period of formation and decay of the snow cover, the variability of the net radiation is determined primarily by the variability in the surface albedo.

Fluctuations in the annual values of net radiation depend on all factors which influence the net radiation variability throughout the year. Analysis of the extreme values (Table 19) shows that the maximum annual values of net radiation in half of all cases are observed for increasing cloudiness during the 4 to 5 winter months, when the thermal radiation plays the dominant role. For the remaining half, the annual maximum occurred in years when decreasing cloudiness was observed in the summer months when the snow had melted, giving rise to an increase in the absorbed solar radiation.

 

Table Captions and Explanation of the Tables

Table 1 Times of sunrise ( R ) and sunset ( S ) on the 15th day of each month (mean solar time, hr/min).

Included in the table are the times of sunrise and sunset for each station on the 15th day of each month (the 14th day of February) in mean solar time.

The time of sunrise(sunset) is defined in meteorology as the instant when the upper limb of the sun appears on (disappears below) the horizon.

Using the time of sunrise and sunset, given in table 1, one may calculate the duration of the day on the middle day of the month.

The true solar time of sunrise and sunset for a given day of the month can be obtained from the table, included, for example, in "The Manual on Radiation Observations for Hydrometeorological stations, 1971" with the introduction of the correction from the equation of time or from an astronomical ephemeris.

Table 2 Solar elevation on the 15th day of each month, degrees.

Included in the table is the elevation of the sun above the horizon at the times of the basic actinometric measurements (mean solar time) on the 15th day of the month (the 14th day of February). The values are determined using the following formula:

sin h¤ = sin j sin d + cos j cos d cos t

where j is the latitude of the station, d is the declination of the sun on the 15th day of the month, and t is the local solar time.

Table 3 Dates of the beginning and end of polar day and the polar night.

Included in the table are data on the beginning and end of polar day and polar night, calculated for the upper limb of the sun taking into account its angular extent as well as refraction (h¤ = -50').

Table 4 Solar radiation fluxes (kW/m2) and atmospheric transmission coefficient for clear skies.

Included in the table are mean values of the fluxes of direct radiation (S, S'), diffuse radiation (D), global radiation(Q), net radiation(B), and the atmospheric transmission coefficient(P2) for the conditions of cloudiness and state of the solar disk recorded at the times of the actinometric observations.

The conditions are as follows: for diffuse radiation, global radiation and net radiation - total cloudiness less than or equal to 2 tenths, solar disk and circumsolar zone free of clouds or traces of clouds out to an angular radius of 5°; for direct radiation and atmospheric transmission coefficient - independent of the amount of clouds, but measured for the solar disk and a circumsolar zone of angular radius 5° free of clouds or traces of clouds. For the conditions described above, the solar disk is indicated by the symbol ¤2.

Mean values of the radiation fluxesS, D, Q, and B have been evaluated from measurements selected to have the indicated conditions for each period of actinometric observations at the stations. The calculations assume the highest values of direct radiation, global radiation, and net radiation for a solar elevation greater than 15° as well as the lowest values of diffuse radiation.

Direct radiation, S', referred to a horizontal surface, was obtained as the difference between the selected values of global and diffuse radiation:

S' = Q - D

The values of P2 characterize the transparency of the atmosphere for integrated direct radiation flux. It is determined using selected measurements of direct radiation, S, by noting the solar disk, ¤2, and reducing the results to a solar elevation of 30° (an air mass of 2).

Indicated in the column "time" are the initial observations in mean solar time.

For the time of year when the sun is below the horizon all or part of the time, the value of the radiation given in the table is not a mean monthly value but refers only to the part of the month when the sun is above the horizon. These cases are indicated by the symbol (*).

The data in the table give a representation of the changes in the solar radiation for mean conditions of atmospheric transparency from measurement to measurement (on average). They can be used for producing curves of the diurnal variation of radiation for clear skies. The data can also be used to evaluate the flux of direct illumination for clear skies on an inclined or sloped surface, Sc using the formula Sc = S cos i, where i is the inclination angle for the surface.

Table 5 Solar radiation fluxes for mean cloud conditions, kW/m2.

Presented in the table are mean monthly values of direct radiation fluxes (S, S'), diffuse radiation flux (D), global radiation (Q) and net radiation (B) from measurements at the times specified by the actinometric program. They have been obtained by direct calculation of long term mean magnitudes from series of monthly averages from different years. Indicated in the column "time", as in Table 4, are the initial observations in mean solar time.

The values of the radiation fluxes given in Table 5 are characteristic of the mean cloud conditions in the vicinity of the stations. In certain years the mean monthly time value may differ from the value shown in the table. The upper limit of the direct and global radiation fluxes and net radiation under average conditions of atmospheric transparency are the values presented in Table 4, that is, for clear sky conditions.

Direct radiation, incident on a horizontal surface, is determined as the difference between the global and diffuse radiation: S' = Q - D.

Table 6 Totals of direct solar radiation (MJ/m2 ) incident on a surface normal to the incident beam for clear skies and atmosphere transmission coefficient.

Table 7 Totals of the direct solar radiation incident on a horizontal surface for clear skies, MJ/m2.

Table 8 Totals of the global solar radiation for clear skies, MJ/m2.

Presented in tables 6, 7, and 8 are the magnitudes of total direct solar radiation S and S', and global radiation per hour, day (24 hour period), month and year for clear skies, and also mean values of atmospheric transmission coefficient by month. The indicated values of radiation characterize the maximum possible influx of solar radiation for mean atmospheric transparency in the region of the given station.

Hourly and daily values of the radiation sums are obtained using graphical displays of the daily variation, constructed using the data from table 4 (observations at the actinometric observing times). From the graphs, values of radiation flux at half-hour intervals were read, from which the hourly and daily sums were determined. Monthly magnitudes were calculated as the product of daily values and the number of days in each month. Yearly totals are similar sums of the monthly values. For months in which there was a transition from polar night to alternating light and dark each 24-hour period (and vice versa), the hourly and daily radiation sums were determined at the middle of the sunlit period, monthly sums were calculated as the product of the obtained daily totals and the number of days with sunlight in the month. The number of sunlit days for each station was determined from the dates of beginning and end of polar night and polar day presented in Table 3.

Mean monthly atmospheric transmission coefficients were calculated from mean daily values of P2.

Taking the difference of the sums of global and direct radiation one can obtain totals of diffuse radiation, D = Q - S'. For most months of the year this gives a minimum value of the flux compared to the flux of diffuse radiation for average cloud conditions.

Mean monthly totals of radiation determined from the discrete observations for clear skies, taking into account the diurnal variation, agree well with sums over extended time intervals for cloudless days using data obtained from chart recorders (deviations are about 1-2 percent). The value 0.00 in Tables 6 through 8 indicates that the observed magnitude of the radiation is less than 0.005 MJ/m2.

Table 9 Totals of direct solar radiation on a surface normal to the incident beam for mean cloud conditions, MJ/m2.

Table 10 Totals of direct solar radiation incident on a horizontal surface for mean cloud conditions, MJ/m2.

Table 11 Totals of diffuse radiation for mean cloud conditions, MJ/m2.

Table 12 Totals of global solar radiation (MJ/m2) and surface albedo (percent) for mean cloud conditions.

Table 13 Net radiation at the surface for mean cloud conditions, MJ/m2.

Presented in tables 9 through 13 are long term values of total direct radiation (S and S'), diffuse radiation (D), global radiation (Q), and net radiation (B) for various time intervals - hourly, daily, monthly, yearly. Also included are mean monthly and mean annual surface albedos (A).

For cases where continuous (chart recorder) data are not available for a certain type of radiation and for stations where chart recorders were generally unavailable, the tables essentially consist of curves of long term diurnal variations which have been constructed from data from discrete observations (Table 5).

From the graph of long-term diurnal variation of radiation, the value of radiation flux has been taken from the middle of each time interval and used to evaluate the hourly totals of radiation. The daily and monthly totals have been calculated from these values.

Mean long term monthly sums of radiation, determined from the discrete observations by the graphical method agree satisfactorily with the data from the continuously recording instruments (± 1 to 3percent in the warm part of the year and ± 1 to 6percent during the cold part).

From the hourly totals, expressed in MJ/m2, one may obtain the hourly mean radiation flux in kW/m2 by dividing by 3.6.

The monthly total is obtained by multiplying the daily sums by the number of days per month with sunlight. Upon comparing the data in tables 9 to 11 with the values in tables 6 to 8, which characterize the incident radiation fluxes for clear skies, one can obtain an estimate of the level of attenuation of the radiation by clouds in the vicinity of the stations.

From the monthly totals of global radiation, net radiation and monthly mean albedos one can obtain:

1. The reflected solar radiation from the surface(Rs) from the equation

Rs = Q A/100

2. The net shortwave radiation(Bs) from

Bs = Q (1 - A/100) or Bs = Q - Rs

3. The net longwave radiation Bl from the expression

Bl = B - Q + Rs or Bl = B - Bs

Yearly totals are obtained by summing the monthly totals. Mean annual albedo is calculated as the ratio (in percent) of the annual total of reflected radiation to the annual total of global radiation. The annual values of net shortwave and longwave radiation can be expressed using to the formulae given above.

Table 14 Statistical characteristics for the atmospheric transmission coefficient (P2).

Table 15 Statistical characteristics for direct solar radiation incident on a horizontal surface, MJ/m2.

Table 16 Statistical characteristics for diffuse radiation, MJ/m2.

Table 17 Statistical characteristics for global radiation, MJ/m2.

Table 18 Statistical characteristics for the surface albedo, percent.

Table 19 Statistical characteristics for net radiation at the surface, MJ/m2.

Presented in tables 14 through 19 are long term mean (up to 1992) minimum and maximum values, and standard deviations of (i) the atmospheric transmission coefficient (P2), (ii) monthly totals of direct radiation on a horizontal surface (S'), (iii) monthly totals of diffuse radiation (D), (iv) monthly totals of global radiation (Q), (v) albedo (A), and (vi) net radiation at the surface (B).

For each station, the number of years over which statistical data have been obtained is indicated.

For station Bely Nos, statistical characteristics are not presented because the time series was not considered to be long enough.

 

References

Atlas of the Energy Balance of the Northern Polar Region. St.Petersburg, Gidrometeoizdat (Hydrometeorological Publishing House), 1992, 72 pp.

Chernigovsky, N. T. and M. S. Marshunova, Climate of the Soviet Arctic (the radiation regime). Leningrad, Gidrometeoizdat, 1965, 198 pp.

Handbook of Climate of the USSR. Solar radiation and net radiation. Leningrad, Gidrometeoizdat, Issues. 21, 24, 33, 1966-1967.

Manual on Radiation Observations for Hydrometeorological Stations. Leningrad, Gidrometeoizdat, 1971, 220 pp.

Marshunova, M. S. and A. A. Mishin, Monitoring of the atmosphere transparency in the polar regions. Monitoring of the Arctic climate. Leningrad, Gidrometeoizdat, 1988, pp. 132-140.

Marshunova, M. S. and V. F. Radionov, Changes of the integral atmosphere transparency in the polar regions. Meteorologia i Gidrologia, No. 11, 1988, pp. 71-80.

Radionov, V. F. and M. S. Marshunova, Decrease in the atmosphere transparency in the polar regions (Effect of the eruptions of the Pinatubo and Hudson volcanoes). Izv. RAN, series Fizika Atmosfery i Okeana, Vol. 29, No. 4,1993, pp. 570-571.

Radionov, V. F., M. S. Marshunova, E. N. Rusina, K. E. Lubo-Lesnitchenko and Yu. E. Pimanova, Aerosol atmosphere turbidity in the polar regions. Izv. RAN, series Fizika atmosfery i okeana, Vol. 30, N 6, 1994, pp. 797-801.

Yanishevsky, Yu. D., Actinometric instruments and observation methods. Leningrad, Gidrometeoizdat, 1957, 415 pp.