Tephigrams for Dummies

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Tephigrams for Dummies. An introduction. NEXT. Introduction to Tephigrams. Te phi gram “T” is the symbol used for Temperature “Phi” φ is the symbol used for pressure “gram” means graph (Invented by Napier Shaw in 1915) . NEXT. NEXT. NEXT. NEXT. NEXT. NEXT.

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### Tephigrams for Dummies

An introduction

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Introduction to Tephigrams

Te phi gram

“T” is the symbol used for Temperature

“Phi” φis the symbol used for pressure

“gram” means graph

(Invented by Napier Shaw in 1915)

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Introduction to Tephigrams

Temperature normally reduces with height.

But not always

Pressure

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Temperature

Introduction to Tephigrams

Air Pressure

REDUCES

with altitude

Lower pressure

Pressure

Higher Pressure

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Temperature

Introduction to Tephigrams

Lower pressure

Pressure

ALTITUDE

Higher pressure

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Temperature

Introduction to Tephigrams

Bronze C question

The surface temperature is 20°C, The

Environmental Lapse Rate (ELR) is

2°C/1000ft. Trigger temperature is 24°C.

The Dry Adiabatic Lapse Rate (DALR) is

3°/1000ft. How High will the thermals go?

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Introduction to Tephigrams

ENVIRONMENTAL LAPSE RATE 2°C/1000ft

7000ft

But this is idealised---In reality the ELR is never a steady reduction like this

6000ft

5000ft

4000ft

ALTITUDE

3000ft

2000ft

TEMPERATURE

1000ft

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10°C

20°C

Introduction to Tephigrams

ACTUAL or FORECAST SOUNDING

7000ft

It is far more usual to see it like this.

6000ft

5000ft

4000ft

OR THIS

3000ft

2000ft

1000ft

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10°C

20°C

Introduction to Tephigrams

Adiabatic Heating and Cooling of a parcel of air

As air is compressed it gets warmer

As air expands it also cools

Warmer

cooler

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Introduction to Tephigrams

Air pressure decreases with Altitude

If a parcel rises, it expands in the lower pressure above

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Introduction to Tephigrams
• In this context, if air has not cooled to its Dew point, it is considered to be dry.
• The Dry Adiabatic Lapse Rate (DALR) is 3°C/1000ft
• Air below its Dew Point temperature is saturated.
• The Saturated Adiabatic Lapse rate (SALR) is approximately 1.5°C/1000ft.

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Introduction to Tephigrams

When shown on our graph these lines look like this

7000ft

6000ft

DALR≈ 3°/1000ft

SALR≈ 1.5°C/1000ft

5000ft

4000ft

3000ft

2000ft

1000ft

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10°C

20°C

Introduction to Tephigrams

Remember our question?

The surface temperature is 20°C, The Environmental Lapse Rate (ELR) is 2°C/1000ft. Trigger temperature is 24°C. The Dry Adiabatic Lapse Rate (DALR) is 3°/1000ft. How High will the thermals go?

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24°C

Introduction to Tephigrams

Environmental air temp

The Sun heats the ground

Surface temperature is

20°C

7000ft

6°C

The environmental Lapse rate is 2°C/1000ft

6000ft

8°C

5000ft

10°C

4000ft

12°C

14°C

3000ft

Local Hotspot Warms to Trigger Temp

The local surface warms the air

18°C

2000ft

16°C

1000ft

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Introduction to Tephigrams

Environmental air temp

BUT What if the dew point happened to be 15°C ?

7000ft

6°C

Well Cloud would form from 3000ft

6000ft

8°C

The packet of air stopped rising because it is the same temperature as the environment.

5000ft

10°C

4000ft

12°C

12°C

The answer to the Bronze C question is 4000ft

3000ft

14°C

15°C

2000ft

16°C

18°C

The parcel of air is cooling at the DALR, 3°C/1000ft

18C

21°C

1000ft

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20°C

24°C

Introduction to Tephigrams

Environmental air temp

7000ft

6°C

Well Cloud would form from 3000ft

6000ft

8°C

Dewpoint Temp

5000ft

10°C

Cloudbase

4000ft

12°C

12°C

3000ft

14°C

15°C

If it does, Cloud will form

2000ft

16°C

18°C

As it rises and cools, it might reach its dewpoint

18C

21°C

1000ft

The dewpoint of the air near the surface is (say)15°C

20°C

24°C

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Introduction to Tephigrams

Environmental air temp

SO if the dew point happened to be 15°C

7000ft

6°C

9°C

6000ft

8°C

10.5°C

Once saturated, the parcel cools at the SALR

5000ft

10°C

12°C

4000ft

12°C

13.5°C

The air has now become unstable

3000ft

14°C

15°C

2000ft

16°C

18°C

The parcel of air is cooling at the DALR, 3°C/1000ft

18C

21°C

1000ft

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20°C

24°C

Introduction to Tephigrams

SALR≈ 1.5°C/1000ft

Remember this?

7000ft

If the slope of the ELR falls here

DALR≈ 3°/1000ft

6000ft

Conditionally Unstable

The airmass is

Unstable

Stable

5000ft

4000ft

3000ft

2000ft

1000ft

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10°C

20°C

Introduction to Tephigrams

UDCSS

=Urban District Council Shovels Snow

7000ft

6000ft

Conditionally Unstable

SALR≈ 1.5°C/1000ft

Stable

5000ft

DALR≈ 3°/1000ft

4000ft

3000ft

2000ft

Unstable

1000ft

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10°C

20°C

Introduction to Tephigrams

Location, N 52.00° W 2.00°

The minus figure indicates West of the prime meridian

Valid for Date

30th January 2008

Valid time

12.00hrs Zulu

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Introduction to Tephigrams

A forecast tephigram. TheNational

Pressures not Altitudes

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Introduction to Tephigrams

Temperatures, lines skewed at 45°

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Introduction to Tephigrams

2°C temperature divisions

An aid to working out the temperature

-6°C

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Introduction to Tephigrams

Wind strength and direction

Northwest 60 knots

Northwest 35 knots

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Introduction to Tephigrams

Approx 3°C/1000ft

Approx 1.6°C/ 1000ft

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Introduction to Tephigrams

Moisture content lines

The amount water the air can hold at that temperature in grammes per Kg

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Introduction to Tephigrams

So far we have only described the graph paper

The two traces on it are

Red line is the predicted temperature as we climb through the atmosphere.

The Green line is the dew point

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