Refer to figure.

NOTE – we are being asked for a situation in the SOUTHERN HEMISPHERE.

• Polar Front Jet Core altitude approx. 30 000 – 35 000ft, we are therefore flying above the core (FL400)

• North of front – warm air mass => wider isobar spacing (tropical airmass).
• South of front – cold air mass => closer isobar spacing (Polar airmass).

Tropical air mass tropopause – situated at a higher altitude and its temperature is lower, compared to the polar air tropopause.
Polar air mass tropopause – situated at a lower altitude and its temperature is higher, compared to the tropical air tropopause.

=> Above the cold sector tropopause the temperature remains constant. But on the warm sector, temperatures will continue to decrease until the tropopause is reached. Which means that above the jet core, temperatures are colder in the warm sector. Therefore, we can say that flying from the south to the north (Cold sector to Warm sector SH) above the core, the temperature will decrease.

Note: Core of the jet stream is located in the warm air – above the level of cold air tropopause and below the warm air tropopause.