航海英语(20)

在远离海岸，没有浅水的广阔水域，太阳照射或夜间辐射对海水表层温度的影响很小。

0.5

摄氏度 。

It

is

possible

to

estimate

the

likelihood

of

the

formation

of

fog

from

observations of air temperatures, wind direction and other weather signs, plus a

knowledge of sea temperatures to be expected on the course ahead. Admiralty Ocean

Routeing Charts give information, for each month of the year on.

通过对空气温度，

风向及其他天气信号的观察再加上预期到达水域海面无额度 的了解，

就有可能估算到形成海雾的可能性大小。英版海洋航行图给出了每月有关以下各 项的信息：

Mean sea temperatures

Mean dew-point temperatures

Percentage frequency of fog (visibility

–

less than half a mile )

Percentage frequency of low visibility (less than 5 miles )

Mean air temperatures

Mean barometric pressures

平均海面温度

平均露点温度

海雾发生概率（能见度 小于

1

英里）

能见度不良发生概率（小于

5

英里）

平均空气温度

平均气压

2 Frontal or missing fog

锋前雾或混合雾

This may occur along the boundary when two widely differing air masses meet.

Usually associated with either a warm front or a warm occlusion when cold air meet

warm moist air hence it is normally experienced in temperate or high latitudes.

It is caused by the evaporation of relatively warm rain or drizzle which in turn

cools the air through which it falls. < /p>

这种情形可能在两个性质迥异的气团相遇的交界处发生。

当冷空气 团遇到暖空气团往

往会与冷锋或锢囚锋联系在一起。因此，

这种 情况一般发生在中高纬度。相对较暖的雨，毛

毛雨的蒸发导致它的发生，反过来降雨也冷 却了空气。

3 Radiation fog

辐射雾

This forms over land, most frequently during autumn and winter over low-lying

land,

especially

if

it

is

damp

and

marshy

and

in

valleys

on

quiet

nights

with

clear

skies. Under these conditions the land loses heat by radiation and cools the air

close to the ground, possibly to below its dew-point. If there is a gentle breeze

bowing,

(

up

to

5

knots)

this

will

cause

turbulent

mixing

but

only

close

to

the

surface

and

condensation

in

the

form

of

fog

will

take

place.

A

stronger

wind

will

cause

the

cooling to be diffused through a greater depth of air and dew-point will not be

reached.

这种雾形成与陆地，

多发于秋冬季节的低地。

尤其是晴夜，潮湿泥泞的河谷流域。

具备

这些条件的陆地因辐射而失去热量，

使空气冷却，

接近地面，

可能会低于其露点温度。

如果

再有一阵微风的吹拂，

（达到

5

节）

，

就会在地表形成气流的混合，

形成雾的冷凝现象也会发

生。更强的风则会使降温作用扩散到更大的气团，将不 会达到露点温度。

Since cold air is heaver than warm air ,it will tend to drain down in valleys.

Although

it

never

actually

forms

over

the

sea,

it

may

drift

from

the

land

for

several

miles

but

seldom

extends

for

more

than

10

miles

off-shore.

Cloudy

skies

over-night

will

reduce

the

effect

of

the

radiation

from

the

land,

or

even

re-radiate

heat

back

to the surface and radiation fog will not occur under these conditions.

由于冷气团重于暖气团，

他将倾向于流向河谷。

虽然他并不形成于海上，

但它可能从陆

地漂移数英里。很少伸展到离岸

10

英 里以外。夜晚多云的天空可以减缓陆地的辐射作用，

或者说热量又被反射回地表。这种情 况下辐射雾便不会形成。

Radiation fog will be most dense around sunrise and normally disperses fairly

rapidly as the land warms.

辐射雾在黎明时候最为严重，当地表变暖时迅速消失。

4 Arctic sea smoke

北冰洋烟雾

This is a type of fog occurring close to the sea surface when the air is dry

and

cold-probably

at

least

9c

below

the

sea

surface

temperature.

Rapid

evaporation

takes

place

from

the

relatively

warm

sea

surface

into

the

colder

air

and

condensation

tales place, giving the effect of steam or smoke risking from the sea.

这是一种发生于近海面的雾，

当空气干燥且温度低于海面至少

摄氏度时有可能发生。

快速蒸发发生，

从相对较暖的海洋表面蒸发至较冷的空气中，

其间冷凝也会发生，

造成海绵

蒸汽，烟雾的效果。

It is most common in Arctic and Arctic and Antarctic waters and the Baltic

but it can also occur off the eastern coasts of continents in winter e.g. off

Newfoundland

and

over

inland

seas

and

lakes.

This

is

one

type

of

fog

which

may

also

be associated with strong winds since it requires a continual supply of cold air.

这种现象多发于南北 极海域和白令海，但在新大陆的东海岸，内陆的湖海也有发生。

这种无可能会与强风联系 在一起，因为该雾形成需要冷空气的持续供应。

, dust and haze

薄雾，灰尘，烟雾

As stated above, visibility which is impaired but is more then 1000 metres

is

described as mist-when caused by water droplets and when the relative humidity is

more than 95%. When caused by smoke or dust particles it is described as haze.

如前所述， 能见度受水滴影响，相对湿度大于

95%

，但能见度仍大于

1000

米，称为

mist- when

。当影响因素为灰尘时称其为

haze.

Causes

of

the

latter

range

from

forest

fires,

smoke

from

industrial

areas,

to

dust or sand storms which may be experienced to seaward of desert regions such as

off the West African

Coast or off the Arabian coast when seasonal winds blow off the land.

后者的起因可能包括森林火灾，工业区的烟尘，沙尘暴等。可能发生在向海的沙漠地

区，例如非洲西海岸，季风盛行的阿拉伯海岸。

Sand storms may extend up to 100 miles out to sea and constitute a serious

problem for the mariner.

沙尘暴可能会延伸上百里直至海洋，从而对航海者造成很大的影响。

Description

Scale

Visibility

Dense fog

0.

<50m/0.25 cable

Thick fog

1.

50-200m/1.0 cable

Fog

2.

200-500m/2.5cable

Moderate fog

3.

500-1km/0.5n.m

Thin fog or mist

4.

1-2km/1.0n.m.

Visibility poor

5.

2-4km/2n.m.

Visibility moderate

6.

10-20km/10n.m

Visibility good

7.

20-50km/30n.m.

Visibility very good

8.

20-50km/30n.m.

Visibility exceptional

9.

>50km/30n.m.

Atmospheric pressure and wind

大气压力和风

Relationship between wind direction and isobar

风向和等压线的关系

The

horizontal

pressure

gradient

force

acts

at

right

angles

to

isobars,

but

it

not

the

only

forces

upon

the

air.

The

earth

is

rotating

upon

its

axis

and

this

produces

an

effort

upon

the

motion

the

air

which

is

seen

by

an

observer

at

the

earth’s

surface.

The

path

of

the

air

appears

to

be

deflected

to

the

right

in

the

northern

hemisphere

and

to

the

left

in

the

southern

hemisphere

.

Calculation

of

this

effect

is

simplified

by using an imaginary force , the Coriolis Force, to represent the effect of the

earth’s

rotation.

水平气压横向力作用于等压线的右侧，

但它并非唯一作用于空气的力，

观测者从地球表

面来看，地球 绕地轴转动，它将对空气运动产生影响，空气运动的路径在北半球向右偏，南

半球向右偏 。这一附加效应被简化做一种假想力，科氏力，替代地球偏转的影响作用。

At heights of 600m or more above the earth’s surface the effects of surface

friction can be ignored. If the isobars are straight and parallel, the pressure

gradient force is balanced by the Coriolis Force and the Geostrophic Wind blows

parallel to the isobars.

地表< /p>

600

米及以上的高空，

地表摩擦力可以 被忽略不计。

如果等压线平行且密集，

气压

梯度力会科氏力相平衡，地转风沿着等压线吹拂。

The

pressure

gradient

is

the

change

in

pressure

with

distance,

where

the

distance

is measured perpendicular to the isobars. The greater the pressure gradient the

closer

the

isobars

and

the

stronger

the

wind.

Pressure

gradient

is

described

as

steep

when the isobars are close together and slack when they are widely spaced.

气压梯度力是气压随距离的变化量，

距离是指 垂直于等压线的长度。

气压梯度越大，

等

压线越密集，风力越强。等压线较密时，气压梯度较大，等压线分布较稀疏时。气压梯度较

小。

Gradient Wind

梯度风

This

wind

flows

parallel

to

curved

isobars.

A

resultant

force

is

needed

to

allow

the

air

to

travel

on

a

curved

path

,so

that

now

Pressure

Gradient

Force

and

Coriolis

Force

are

not

exactly

equal.

This

results

in

the

gradient

wind

speed

being

less

than

the geostrophic wind speed when circulating around low pressure and more then

geostraphic when circulating around high pressure.

该风向与等压线相平行，

合力应该让空气按曲线路径吹拂。

所以，

此时气压梯 度力与科

氏力并不相等。这导致地转风速在其绕低压吹时低于地转风。绕高压吹时风速高 于地转风。

At

the

surface

the

angle

between

the

wind

and

the

isobars

varies

with

the

nature

of the surface over which the wind blows;it may generally be taken ad about 10 to

15

over

the

sea.

风向和等压线间的夹 角随风下垫面的作用产生变化。在海面上吹时一般用

10

到

15 °计算。

Diurnal variation of wind speed at the surface is caused by diurnal variation

in

convection

currents.

During

the

day,

when

convection

currents

are

strongest

,the

retarding

effect

of

surface

friction

is

diffused

through

a

greater

depth

of

turbulence.

Thus

the

reduction

in

surface

wind

force

is

less

by

day.

At

night

,when

the

depth

of

turbulence

is

shallow,

the

retarding

effect

is

greater

and

therefore,

the wind force is less . The diurnal variation of wind speed over sea areas is

negligible.

一日内空 气对流的变化导致地转风的日变化，在白天，当对流最强时地面摩擦

力的加大而变缓慢，

夜间，气流改变小，

减速作用变小因而风力更大。

海上风速的日变化量

可以忽掉。

The prevailing Winds of the Oceans

海洋的盛行风

The prevailing winds of the oceans conform to the main flow of isobars for the

season

and

follow

Buys

Ballot’s

Law.

The

w

inds,

especially

in

the

southern

hemisphere, show a similarity to those described for the uniform globe. They are,

however, only mean winds and considerable variations can be expected locally from