1. THE MIDDLE ATMOSPHERE AND SSW

2. CONTENT ATMOSPHERE AND ITS LAYER HOW STRATOSPHERE AFFECT THE WEATHER
COUPLING BETWEEN TROPOSPHERE AND STRATOSPHERE.
SUDDEN STRATOSPHERIC WARMING.
STRATOSPHERIC JET STREAMS.
IONOSPHERE

3. ATMOSPHERE AND ITS LAYER
1. TROPOSPHERE 2. STRATOSPHERE 3. MESOSPHERE 4. THERMOSPHERE 5. EXOSPHERE

4. STRATOSPHERE 1. IT IS THE SECOND MAJOR LAYER OF EARTH’S ATMOSPHERE.
2. JUST ABOVE THE TROPOSPHERE AND BELOW THE MESOPHERE.
3. WARMER LAYER HIGHER UP AND COOLER LAYER FATHER DOWN.
4. TROPOPAUSE IS WHERE INVERSION BEGINS WHICH IN TERMS OF ATMOSPHERIC THERMODYNAMICS IS IN THE EQUILIBRIUM .

5. STRATOSPHERE
5. IT IS SITUATED BETWEEN AT ABOUT TO 50Km ABOVE THE SURFACE WHILE AT POLES IT STARTS AT ABOUT 8KM AND NEAR THE EQATOR IT STARTS AT ALTITUDE AS HIGH AS 18Km.

6. MESOSPHERE
1. IT IS THE LAYER OF EARTH’S ATMOSPHERE WHICH IS DIRECTLY ABOVE THE STRATOPAUSE AND BELOW THE MESOPAUSE.
2. IN MESOSPHERE TEMPERATURE DECREASES WITH INCREASING IN HEIGHT.
3. THE UPPER BOUNDARY OF THE MESOSPHERE IS THE MESOPAUSE WHICH CAN BE THE COLDEST NATURALLY OCCURING PLACE ON EARTH WITH TEMPERATURE BELOW 143° C.

7. MESOSPHERE
4. MESOPAUSE AT AN ALTITUDE OF 80-90Km SEPARATES THE MESOSPHERE FROM THE THERMOSPHERE.

8. IONOSPHERE
1. THE IONOSPHERE IS THE REGION OF UPPER ATMOSPHERE FROM ABOUT 85Km TO 600Km ALTITUDE. 2. IT IS DISTINGUISHED BECAUSE IT IS IONIZED BY SOLAR RADIATION. 3. IT PLAY AN IMPORTANT PART IN ATMOSPHERIC ELECTRICITY AND FORMS THE INNER EDGE OF MAGNETOSPHERE.

9. The atmospheric layers- vertical temperature structure
O2 absorption
0.01mb
0.1mb
Atmospheric “heat sources”
Ozone layer
1mb
10mb
surface
100mb

10. HOW STRATOSPHERE AFFECT THE WEATHER

11. 1. EVERY WINTER THE STRATOSPHERE OVER THE NORTH POLE COOLS WHEN THE SUNLIGHT CAN NO LONGER PROVIDE THE ENERGY TO HEAT THE OZONE. WITHOUT THIS THE STRATOSPHERE COOL RAPIDLY CREATING A THERMAL IMBALANCE WITH THE WARMER STRATOSPHERE FURTHER SOUTH. 2. THIS IMBALANCE CREATES A LARGE PRESSURE DIFFERENCE AND COMBINE WITH THE CORROLIS EFFECT CREAT A LARGE STRONG JET STREAM .

12. 3. THE STRATOSPHERE IN AN EASTWARD DIRECTION THIS SYSTEM IS KNOWN AS THE POLAR NIGHT JET AND CONTAINED WITHIN IT IS A STRONG VORTEX KNOWN AS THE POLAR VORTEX. 4. THE POLAR VORTEX INCREASES AND DECREASES IN STRENGTH DEPENDING UPON HOW COLD THE POLAR STRATOSPHERIC ATMOSPHERE BECOMES DURING THE COLD. 5. THE POLAR STRATOSPHERE BECOMES STRONGER AND STRENGTH OF THE STRATOSPHERE POLAR VORTEX INFLUENCE THE ATMOSPHERE BELOW IT IN THE TROPOSPHERE.

13. COUPLING BETWEEN TROPOSPHERE AND STRATOSPHERE

14. INTRODUCTION
1. WE SHALL LOOK AT THE COUPLING BETWEEN THE TROPOSPHERE AND THE STRATOSPHERE IN THREE ASPECTS:
(a) MASS EXCHANGE
(b) RADIATIVE INTERACTION
(c) DYNAMICAL INTERACTION

15. MASS EXCHANGE 1. FIVE PROCESS FOR THE MASS BUDGET.
(a) SEASONAL CHANGE OF THE TROPOPAUSE HEIGHT.
(b) VETICAL MASS TRANSPORT BY MEAN MERIDIONAL CIRULATION CELL ACROSS THE TROPOPAUSE.
(c) ETC AND ANTI-CYCLONE EXCHANGING MASS BETWEEN THE TROPOPAUSE AND STRATOSPHERE ACROSS THE TROPOPAUSE.

16. (d) SMALL SCALE AND MESO-SCALE DIFFUSION PROCESS AT TROPOPAUSE LEVEL.
MASS EXCHANGE
(d) SMALL SCALE AND MESO-SCALE DIFFUSION PROCESS AT TROPOPAUSE LEVEL.
(e) INTER-HEMISPHERE EXCHANGES.
EDDIES HC
Northern Hemishere
Souththern Hemishere
STRATOSPHERE
TROPOSPHERE
15%
20%
38%

17. RADIATIVE INTERACTIONS
1. OZONE ABSORBS SOLAR ULTRAVIOLET RADIATION WITH HEATING . 2. THE HEATING RATES ARE LARGER IN THE SUMMER HEMISPHERE AND ALSO INCREASES TOWARDS THE POLE. 3. EXCHANGE OF AEROSOL, OZONE AND WATER VAPOUR BETWEEN THE STRATOSPHERE AND THE TROPOSPHERE INFLUENCE THE PENETRATION OF SOLAR RADIATION TO THE GROUND AND THUS AFFECT THE HEAT BUDGET OF THE STRATOSPHERE AND TROPOSPHERE.

18. DYNAMICAL INTERACTION
1. DURING SUMMER , THE STRATOPHERIC FLOW IS NEARLY ZONAL WITH WARM ANTICYCLONE CENTERED NEAR THE POLE AND EASTERLIES OVER MOST OF THE SUMMER HEMISPHERE. 2. DURING WINTER, THERE IS COLD CYCLONIC CENTRED NEAR THE WINTER POLE AND WESTERLIES OVER MOST OF THE WINTER HEMISPHERE.

19. DYNAMICAL INTERACTION
3. SUBSEASONAL VARIATION IN THE FLOW PATTERN IN THE STRATOSPHERE LEADS TO SSW AND THE BREAKDOWN OF WINTER POLAR JET STREAM IN THE STRATOSPHERE. 4. INTER-ANNUAL VARIABILITY OF THE LOWER STRATOSPHERIC CIRCULATION IS SIGNIFICANTLY CORRELATED WITH THE INTER-ANNUL VARIABILITY OF THE MONSOON RAINS OVER INDIA .

20. TEMPERATURE CHANGES IN ASSOCIATION WITH CIRCULATION IN WINTER
1. THE MIDWINTER TEMPERATURE CHANGES OF THE MESOSPHERE AND STRATOSPHERE ARE DESCRIBED BY MEANS OF SATELLITE IR SPECTROMETER AND ROKET SONDE DATA WHICH SHOWS THAT STRATOSPHERIC MIDWINTER EXTEND AT LEAST INTO THE UPPER MESO-SPHERE. 2. THE EVENT BEINGS AROUND A VERY HIGH STRATOSPHERE ~60Km WHICH DESCEND 20Km WITHIN SEVERAL DAYS WHILE THE WARMING INTENSIFIES.

21. TEMPERATURE CHANGES IN ASSOCIATION WITH CIRCULATION IN WINTER
3. AT THE SAME TIME THE UPPER MESOSPHERE AND LOWER STRATOSPHERE COOLS. 4. WHEN THE POLAR VORTEX BREAK DOWN THE WARMING REACHES THE LOWER STRATOSPHERE AND THE WARM STRATOPAUSE REGION IS DESTROYED THROUGH COOLING OF THE LAYER BETWEEN 30Km AND 60Km AND UPPER MESOSPHERE WARM. 5. THE MEAN VERTICAL TEMPERATURE PROFILE SUGGEST THE UPPER MESOSPHERE IS COLD AT HIGH LATITUDE IN EARLY WINTER AND AGAIN IN LATE WINTER AND THE WARM UPPER MESOSPHERE OBSERVED IN LATE JANUARY AND EARLY FEBRUARY IS THE STRATOSPHERIC POLAR VORTEX.

22. SUDDEN STRATOSPHERIC WARMING

23. DEFINITION
1. THE FIRST OBSERVATION OF SUDDEN STRATOSPHERIC WARMING (SSW) WAS REPORTED BY SCHERHAG (1952) AND THE FIRST THEORETICAL EXPLANATION PROPOSED BY MATSUNO (1971).
2. SUDDEN STRATOSPHERIC WARMING (SSW) IS AN EVENT WHERE THE POLAR VORTEX OF WESTERLY WINDS IN THE NORTHERN WINTER HEMISPHERE ABRUPTLY (I.E., IN A FEW DAYS’ TIME) SLOWS DOWN OR EVEN REVERSES DIRECTION, ACCOMPANIED BY A RISE OF STRATOSPHERIC TEMPERATURE BY SEVERAL TENS OF DEGREES CELSIUS.

24. CLASSES OF WARMINGS
1. CLASSES OF WARMINGS. QUIROZ ETAL (1975) HAVE CLASSIFIED STRATOPHERIC WARMINGS AS MAJOR WARMINGS AND MINOR WARNING. (a) MAJOR WARMINGS. THOSE EVENT IN WHICH WESTERLIES ARE REPLACED BY EASTERLIES AT 10HPA. (b) MINOR WARMINGS. EVENT IN WHICH WARMING TAKES PLACE BUT IS INSUFFICIENT TO CHANGE THE WESTERLIY FLOW TO EASTERLY FLOW.

25. FEATURES OF SSW
1. JANUARY AND FEBRUARY ARE THE PRIME MONTHS FOR OCCURRENCE OF BOTH MAJOR AND MINOR WARMING EVENT. 2. EACH YEAR SHOWS EITHER A SINGLE MAJOR WARMING OR A SINGLE MINOR WARMING OR A SERIES OF MINOR WARMINGS. 3. ON THE AVERAGE , MAJOR WARMING OCCURS EVERY OTHER YEAR (QBO), THE LONGEST INTERVAL BETWEEN MAJOR WARMING BEING FOUR YEARS. 4. MAJOR AND MINOR WARMING TEND TO EXCLUDE EACH OTHER.

26. THEORY
1. DURING NORTHERN WINTER, OCCASIONALLY THE CIRCULATION BECOMES HIGHLY DISTURBED, ACCOMPANIED BY A MARKED AMPLIFICATION OF PLANETARY WAVES.
2. THE DISTURBED MOTION IS CHARACTERIZED BY MARKED DECELERATION OF ZONAL MEAN WESTERLIES OR EVEN A REVERSAL INTO ZONAL MEAN EASTERLIES.
3. AT THE SAME TIME, TEMPERATURE OVER THE POLAR CAP INCREASES SHARPLY BY AS MUCH AS 50 K, SO THE DARK WINTER POLE ACTUALLY BECOMES WARMER THAN THE TROPICS. THIS DRAMATIC SEQUENCE OF EVENTS TAKES PLACE IN JUST A FEW DAYS AND IS HENCE KNOWN AS A SUDDEN STRATOSPHERIC WARMING.

27. SUDDEN STRATOSPHERIC WARMING

30. WEATHER EFFECTS
Although sudden stratospheric warmings are mainly forced by planetary scale waves which propagate up from the lower atmosphere, there is also a subsequent return effect of sudden stratospheric warmings on surface weather.
Following a sudden stratospheric warming, the high altitude winds reverse to flow westward instead of their usual eastward.
The westward (Ely) winds progress down through the atmosphere and weaken the jet stream, often giving westward winds near the surface and resulting in dramatic reductions in temperature in the Eastern U.S. and Europe.

31. CONCLUSION
Planetary Rossby waves propagate upwards on the stratospheric winter polar vortex, occasionally leading to a sudden warming.
Sudden warmings propagate downwards to the lower stratosphere, where they nudge the tropospheric jet stream and weather systems to a more equatorwards postion.

32. BASIC SSW CHARACTERISTICS
January and february are the prime months for occurrence of both major and minor warming events.
Each year shows either a single major warming or a single minor warming or a series of minor warming.
On the average, major warmings occur every year, the longest interval between major and minor warming is of 4 years.
Average temperature difference in both the warmings at 10 hPa is 30 deg.

33. DYNAMICS
In a usual northern-hemisphere winter, several minor warming events occur, with a major event occurring roughly every two years.
One reason for major stratospheric warming to occur in the Northern hemisphere is because orography and land-sea temperature contrasts are responsible for the generation of long  Rossby waves in the troposphere.
These waves travel upward to the stratosphere and are dissipated there, decelerating the winds and warming the Arctic.
This is the reason that major warmings are only observed in the northern-hemisphere.

34. DYNAMICS
At an initial time a blocking type circulation pattern establishes in the troposphere.
This blocking pattern causes Rossby waves with zonal  to grow to unusually large amplitudes.
The growing wave propagates into the stratosphere and decelerates the mean zonal winds.
Thus the polar night jet weakens and simultaneously becomes distorted by the growing planetary waves.

35. DYNAMICS
If the waves are sufficiently strong the mean zonal flow may decelerate sufficiently so that the winter westerlies turn easterly.
At this point planetary waves may no longer penetrate into the stratosphere.
Hence further upward transfer of energy is completely blocked and a very rapid easterly deceleration and the polar warming occur at this critical level, which must then move downward until eventually the warming and zonal wind reversal affect the entire polar stratosphere.

36. STRATOSPHERIC JET STREAMS
1. FOUND AT LEVELS ABOVE 20Km IN THE ARTIC AND ANTARTIC REGIONS. 2. WESTERLIES IN WINTER AND EASTERLIES IN SUMMER. 3. TWO TYPES OF JET STREAMS ARE AVAILABLE IN STRATOSPHERE. (a) POLAR NIGHT STRATOSPHERIC WESTERLY JET STREAM OR ARTIC STRATOSPHERIC JET. (b) BERSON WESTERLIES OR QBO JET IN LOWER EQUATORIAL STRATOSPHERE.

37. THE ARCTIC STRATOSPHERE JET STREAM DURING THE WINTER
1. THE EXISTENCE OF AN ARCTIC STRATOSPHERIC JET STREAM IN WINTER HITHERTO LARGELY INFERRED FROM MEAN GEO-STROPIC WIND SECTION IS CONSIDERED ON THE BASIS OF ACTUAL WIND OF THE CANADIAN.
2. ARCTIC AREA DURING THE WINTER OF TEMPERATURE AT THE 100hPa LEVEL AT A NUMBER OF STATION OVER THE CANADIAN ARCTIC WERE EXAMINED TO THROW LIGHT ON THE INTENSELY BAROCLINIC ZONE BELOW THE JET STREAM.

38. THE ARCTIC STRATOSPHERE JET STREAM DURING THE WINTER
3. MERIDIONAL MOVEMENT AND INTENSITY CHANGES OF THE JET STREAM DURING THIS WINTER AS INFERRED FROM A STATISTICAL STUDY OF THE 100hPa TEMPERATURE FIELD ARE IN ACCORD WITH THE CONVENTONAL VIEW THAT THE JET STREAM IS MAINTAINED BY DIFFERENT RADIATIONAL HEATING AND COOLING OF THE OZONE LAYERED ACROSSN THE BOUNDARY OF POLAR NIGHT

39. POLAR NIGHT STRATOSPHERIC WESTERLY JET STREAM
1. LOCATION 35 KM ABOVE 65 ˚ LATITUDE
2. IN GENERAL IT IS STRONGER OVER SOUTHERN HEMISPHERE THAT ITS COUNTERPART IN NORTHERN HEMISPHERE.
3. SPEEDS EXCEEDING 250KT HAVE ALSO BEEN OBSERVED ON INDIVIDUAL DAYS
4. DURING THE PHENOMENON KNOWN AS ‘ SUDDEN STRATOSPHERIC WARMING’ THIS JET STREAM WEAKENS CONSIDERABLY AND MAY BE REPLACED BY WEAK EASTERLY CURRENT.

40. FORMATION
1. ONLY DURING WINTER MONTHS, I.E., POLAR NIGHTS (WHERE NIGHT LASTS MORE THAN 24 HOURS), WHICH OCCURS ONLY INSIDE THE POLAR CIRCLES , AND AT A GREATER HEIGHT THAN POLAR JETS. 2. DURING POLAR NIGHTS , THE AIR OVER POLES BECOMES COLDER THAN THE AIR OVER EQUATOR. 3. TEMPERATURE DIFFERENCE GIVES RISE TO EXTREME AIR PRESSURE DIFFERENCES IN THE STRATOSPHERE, WHICH WHEN COMBINED WITH CORIOLIS EFFECT.

41. IONOSPHERE
1. THE IONOSPHERE IS THE REGION OF THE EARTH’S ATMOSPHERE IN WHICH THE NUMBER OF IONS , OR ELECTRICALLY CHARGED PARTICLES, IS LARGE ENOUGH TO AFFECT THE PROPAGATION OF RADIOWAVES . 2. THE IONOSPHERE BEGINS AT AN ALTITUDE OF ABOUT 50 KM BUT IS MOST DISTINCT ABOVE ABOUT 80 KM. THE IONIZATION IS CAUSED MAINLY BY SOLAR RADIATION AT X-RAY AND ULTRAVIOLET WAVELENGTHS. 3. THE IONOSPHERE IS RESPONSIBLE FOR THE LONG-DISTANCE PROPAGATION BY REFLECTION, OF RADIO SIGNALS IN THE SHORTWAVE AND BROADCAST BANDS.

42. STRUCTURE OF IONOSPHERE
1. IONOSPHERE IS HIGHLY STRUCTURED IN THE VERTICAL DIRECTION. IT WAS FIRST THOUGHT THAT DISCRETE LAYERS WERE INVOLVED, REFERRED TO AS THE D, E, F1, AND F2 LAYERS. 2. HOWEVER, THE LAYERS ACTUALLY MERGE WITH ONE ANOTHER TO SUCH AN EXTENT THAT THEY ARE NOW REFERRED TO AS REGIONS RATHER THAN LAYERS. 3. THE VERY HIGH TEMPERATURES IN THE EARTH’S UPPER ATMOSPHERE ARE CO LOCATED WITH THE UPPER IONOSPHERE SINCE BOTH ARE RELATED TO THE EFFECT OF X-RAYS FROM THE SUN. 4. THAT IS, THE X-RAYS BOTH IONIZE AND HEAT THE UPPERMOST PORTION OF THE EARTH’S ATMOSPHERE.

43. STRUCTURE OF IONOSPHERE
1. TREMENDOUS VARIATIONSOCCUR IN THE IONOSPHERE AT HIGH LATITUDES BECAUSE OF THE DYNAMICAL EFFECTS OFELECTRICAL FORCES AND BECAUSE OF THE ADDITIONAL SOURCES OF PLASMA PRODUCTION. 2. THE MOST NOTABLE IS THE VISUAL AURORA, ONE OF THE MOST SPECTACULAR NATURAL SIGHTS. 3. THE AURORA HAS A POLEWARD AND EQUATORWARD LIMIT DURING TIMES OF MAGNETIC STORMS. RESIDENTS OF THE ARCTIC REGIONS OF THE NORTHERN HEMISPHERE SEE THE NORTHERN LIGHTS IN THEIR SOUTHERN SKY. 4. THE AURORA FORMS TWO RINGS AROUND THE POLES OF THE EARTH. THE SIZE OF THE RINGS WAXES AND WANES WHILE WAVELIKE DISTURBANCES PROPAGATE ALONG ITS EXTENT.

44. Zonal MeanWinds in the Equatorial Stratosphere
1. THE ZONAL MEAN WINDS IN THE MIDLATITUDE WINTER HEMISPHERE ARE WESTERLY, WITH A MAXIMUM VELOCITY OF 80 MS−1 AT 65 KM ALTITUDE AND 40◦ LATITUDE. IN SUMMER HEMISPHERE IT BECOMES EASTERLY, WITH A MAXIMUM VELOCITY OF ABOUT 50 M/S.
2. IN THE NORTHERN HEMISPHERE, ZONAL MEAN WINDS CHANGE FROM WESTERLY TO EASTERLY IN MAY, STARTING AT THE HIGHEST LATITUDES AND ALTITUDES AND MOVING DOWNWARD TOWARDS THE TROPICS. WINDS CHANGE FROM EASTERLY TO WESTERLY IN SEPTEMBER, ONCE AGAIN STARTING FROM HIGH LATITUDES AND ALTITUDES.MS−1 AT 65 KM ALTITUDE AND 40◦ LATITUDE.

45. ZONAL MEANWINDS IN THE MIDLATITUDE STRATOSPHERE
1. THE ZONAL MEAN WINDS IN THE MIDLATITUDE WINTER HEMISPHERE ARE WESTERLY, WITH A MAXIMUM VELOCITY OF 80 MS−1 AT 65 KM ALTITUDE AND 40◦ LATITUDE. 2. IN SUMMER HEMISPHERE IT BECOMES EASTERLY, WITH A MAXIMUM VELOCITY OF ABOUT 50 MS−1 AT 65 KM ALTITUDE AND 40◦ LATITUDE. 3. IN THE NORTHERN HEMISPHERE, ZONAL MEAN WINDS CHANGE FROM WESTERLY TO EASTERLY IN MAY, STARTING AT THE HIGHEST LATITUDES AND ALTITUDES AND MOVING DOWNWARD TOWARDS THE TROPICS.

46. ZONAL MEANWINDS IN THE MIDLATITUDE STRATOSPHERE
4. WINDS CHANGE FROM EASTERLY TO WESTERLY IN SEPTEMBER, ONCE AGAIN STARTING FROM HIGH LATITUDES AND ALTITUDES. 5. AS IN THE TROPOSPHERE, THE ACTUAL WINDS IN THE STRATOSPHERE HAVE SIGNIFICANT MERIDIONAL COMPONENTS.

47. THANK YOU