The document discusses travelling waves and bores in the lower atmosphere, focusing on the "Morning Glory" phenomenon. It provides: 1) An overview of the Morning Glory, describing it as a spectacular low roll cloud associated with solitary wave disturbances at the leading edge of an undular bore that propagates on a low-level stable layer. 2) Details on the structure and preferred directions of travel of Morning Glory disturbances in northern Australia, as well as their genesis, demise, and relation to nocturnal solitary wave disturbances. 3) An explanation of the theoretical background involving equations like Korteweg-de Vries and Benjamin-Ono-Burgers that can model these types of atmospheric

1. Travelling Waves and Bores in the Lower Atmosphere:
The ‘Morning Glory’ and Related Phenomena
Roger K. Smith

2. Presented by:
Andi Syahid Muttaqin
Riza Adriat
Terencio Fernandes Moniz
Krismianto

3. Outline
o Introduction
o The Morning Glory
o Theoretical Background
o Laboratory and Numerical Experiments
o Related Phenomena
o Conclusion

4. Introduction
(Section 1)

6. o The last ten years have seen a burgeoning interest in large amplitude
waves and bores generated on a stably-stratified layer in the lower
atmosphere.
o The ‘morning glory’ is the name given to a spectacular low roll cloud
or succession of roll clouds that occur early in the morning.
o It is now known that they are associated with solitary wave
disturbances at the leading edge of an undular bore that propagates
on a low-level stable layer.
o Solitary wave disturbances in the low atmosphere, including the
morning glory, may give rise to significant low-altitude wind shear
which make them a particular hazard to low-flying aircraft.

7. Schematic of the simplest solitary wave
o When waves travel at
different speeds, the
disturbance must
spread over time
unless some other
mechanism
intervenes.
o In a solitary wave,
dispersion and
nonlinear steepening
exactly balance 
create a wave which
propagates without
change of shape.

8. The Morning Glory
(Section 2)

9. Brief description
o Not all morning-glory bore waves are
accompanied by cloud.
o For that reason, morning-glory
phenomenon refer to:
 wind squall,
 wind surge.
o The origin and structure of these
phenomenon have been determined
mainly on the basis of observational
experiments in the years 1978-1984.
o Morning-glory disturbances have two preferred directions of travel
(in northern Australia):
 Northeasterly morning glory (most common type)
 Southerly morning glory (less frequent type)
o While the structure of northeasterly and southerly morning glories is
similar, the mechanism of generation must differ considerably.

10. o Northeasterly morning glories:
 Moved from sector about 60 deg. and 67 deg.
 Mean speed about 10.2 ms-1 and 10.6 ms-1
o Southerly morning glories:
 Moved from sector 140-220 deg. (mean dir. 180 deg)
 The speed in the range 6-17 ms-1 (mean speed 11.6 m)

11. Structure

14. Genesis of northeasterly glories

16. Demise of disturbances
o A few hours after sunrise,
the low-level stable layer is
destroyed over the land by
convective mixing.
o But, disturbances can
continue to propagate
inland in some form for
considerable distances
during the day.
o Indeed, it has been suggested that some of the nocturnal solitary-
wave-dominated disturbances are the remnants of northeasterly
morning glories generated on the previous night:
 if this is the case, the disturbances would have to propagate on an
upper level wave-guide,
 perhaps the capping inversion at the top of the mixed layer,
 and there would have to be an effective mechanism for
suppressing the vertical radiation of wave energy.
o At this stage, the precise mechanisms associated with the daytime
transformation and decay of disturbances are unknown.

17. Southerly morning glories
o On the day after 1979 morning-glory experiment had ended it was
considerable surprise to observe a significant-amplitude morning glory,
oriented east-west and moving from the south.
o Mechanism possibilities, include:
 The northeastwards movement of a front or frontal trough over central
Australia into the developing nocturnal inversion ahead of it,
 The interaction between the inland nocturnal low-level jet and the deeply
penetrating sea breeze from the southern gulf coast,
 Katabatic drainage from the Barkly Tablelands northwards to this coast.

18. o However, the data are inadequate
to assess the relative importance of
katabatic drainage.
o There is circumstantial evidence that a few surges are generated by the
motion of a front, but this does not appear to be the most usual
mechanism.
o Precursor to a southerly surge at
Burketown is a marked increase
in the southerly component of
the low-level wind at Mount Isa
during the late evening and early
morning, following some hours
later by an increase in the
easterly component, a feature
indicative of a nocturnal low-
level jet (Mount Isa wind
signature).

19. Theoretical Background
(Section 3)

20. o For disturbance on a water surface the theories fall into
two classes: those relating to steady bores; and those
relating to transient, but in some sense, long lived bores
which evolve from rather general initial disturbance
o Numerical solutions of the initial-value problem for the
Korteweg-de Vries (KdV) equation, the equatin appropriate
to transient finite amplitude disturbance, indicate that an
initial surge with an abrupt rise in water level propagating
on water of uniform depth at rest will subsequently
develop wave-type undulations at its leading edge.

21. Korteweg de Vries (KdV) Equation
Where :
= horizintal coordinate in the direction of propagation
= linear long wave phase speed
= the coeffisient of the nonlinier
= dispersive terms
= relatively shallow stable layer
03
3
0 











x
A
x
A
A
x
A
c
t
A

x
0c

A


22. o In the deep fluid case where a relatively shallow stable layer
of depth h underlies a much deeper layer of neutrally stable
fluid, finite amplitudo disturbance with amplitudo a are
governed to a fisrt approximation in a/h by the so called
Benjamin-Davis-Ono (BDO) equation rather than the Kdv
equation.

23. Benjamin Davis Ono (BDO) Equation
Where :
: Shear distribution
: depth
: Hilbert Transform
0)(2
2
0 











A
xx
A
A
x
A
c
t
A

h
uc )(2 10 

)(])12[(
)(4
10
2
2
0
ucn
uch


 






 dx
xx
xA
xA
'
)'(1
))((


u
h


25. o Even if the well mixed layer extends to 4 km, the
atmosphere is stably stratified above this level and the
vertical radiation of wave energy there becomes a
possibilty
o Atmosphere bore waves range of solutions for the
evolution of solitary wave trains from a variety of initial
disturbances, mostly in the form of long waves of elevation,
including step like bores of infinite extent. The solution are
based on integrations of the time-dependent forms of the
BDO-equation and its frictional counterpart, the so-called
BDO-Burgers equation

26. BDO – Burgers Equation
Where :
= Amplitude of the leading soliton
= Eddy diffusivity coefficient
02
2
2
2












X
U
X
U
X
U
U
T
U

)(
1
0tcx
h
X  t
h
T 2


),(),( txA
h
TXU





 
U


27. o Fig shown an example of the amplitude evolution of a long wave
of elevation of finite extent as governed by BDO-Burgers
equation for relatively smaal dissipation

28. Laboratory and Numerical Experiments
(Section 4)

29. o A number of laboratory experiments have been carried out with
obvious relevance to the morning glory and related phenomena.
o Of particular importance is a series of experiments by Maxworthy
(1980) which concerns the production of non linear internal solitary
wave from the gravitational collapse of mixid regions of fluid into a
stably stratified wave-guide.
o The basic configuration has features in common with the envisaged
collapse of negatively buoyant air generated by the collision of the east
and west coast sea breezes over Cape York Peninsula (as indicated in
the numerical simulations of Noonan and smith (1986,1987).
o Maxworthy found that the collapse creates a sequence of amplitude
ordered solitary waves in line with the theoretical predictions.
o Quite general and uncontrolled mixing events created solitary wave
train and lead us suspect that they should be exited under many
circumstances in natural system.

30. o Tepper (1950) argues that a cold front acceleration into a
low-level stable layer would, in certain circumstances,
lead to a propagating wave type disturbance on the layer
which runs ahead of the front, eventually steepening to
form a near discontinuity, a type of internal hydraulic
jumps or bore.
o Baines(1984), along rectangular channel was filled
through most of its depth with fresh water and then
topped up with a much shallower layer of paraffin,
forming a two layer system.
o Smith e al. (1982), describe an experiment of this type
and snow a photograph of a wave like disturbance
running ahead of the gravity current on the stable layer.

31. o A key feature of such flow is that the maximum phase
speed Cw, for wave propagation on the stable layer is
faster than the speed at which the gravity current
advance, Cgr.
o However the supercritical case Cgr>Cw, is of interest also
in relation to bore formation as demonstrated in
laboratory experiments by wood and Simpson (1984).
o Conclude, undular bores can be generated, either in the
subcritical regime as a disturbance moving ahead of a
gravity current on stable layer, or supercritical regime as
gravity current that has been modified by its interaction
with the stable layer, or by the collapse of a mixed region
of fluid into a table wave guide as occurs for example
when two gravity current collide.

32. o In recent papers, Crook (1986, 1987) has considered the
effects of ambient shear, continuous vertical
stratification and moisture on the motion of atmospheric
undular bores.
o The first of these paper shows that presence of the
continuous stratification throughout the atmosphere
significantly reduce the disturbance amplitudes at low
levels by allowing wave energy to propagate upwards.
o The second paper, explores the relative importance of
three mechanisms that may inhibit the leakage of energy
from the bore wave into the upper atmosphere; these
are opposing winds in the middle and upper troposphere;
the presence of an opposing jet in the lower atmosphere.

33. Related Phenomena
(Section 5)

34. • From laboratory experiments (Maxworthy)
concluded that:
If a physical system is capable of supporting solitary
wave motions then such motions will invariably arise
from quite general excitations.
Frequent occurrences of Morning glories from varies
directions in the southern gulf region of northern
Australia and Nocturnal solitary wave disturbances in
central Australia.
CONCUR

35. What is so special about Australia ?
Do such disturbances occur frequently elsewhere?
While….
• The Gulf of Carpentaria region may be
exceptional for the variety of mechanisms
that operate to produce undular-type bores.

36. • Schreffler and
Binkowsky (1981)
describe two
pressure jump lines
(PJL) that were
observed on
consecutive nights in
the St. Louis area.
• PJL a line along
which an
atmospheric
pressure wave
produces a sudden
increase of pressure
that often results in
storms.

37. o Haase and Smith (1984). Morning Glory was
observed shortly after sunrise in central
Oklahoma and appeared also to have been
generated late on the previous evening by
thunderstorms some 500 km away.

38. o In all these cases, the most plausible
generation mechanism for the bore waves is
that they were produced by thunderstorm
outflows moving subcritically into the wave-
guide provided by the nocturnal low-level
stable layer underlying a much deeper well-
mixed layer.

39. o Doviak and Ge (1984) investigated the
characteristics of a nocturnal solitary-wave
disturbance that was observed also in
central Oklahoma.
From a synthesis of Doppler radar
concluded that the wave was initiated by a
thunderstorm outflow moving into an
inversion layer formed by the passage of an
earlier storm. The wave was followed by at
least one weaker wave.

40. o A bore-like disturbance accompanied by two
spectacular low roll-clouds, was apparently
generated by the interaction of a sea-breeze
front with a thunderstorm outflow near the
northern coast of Western Australia (Smith,
1986).

41. Conclusion
(Section 6)

42. Concluding Remarks (1)
o The morning glory is a line wind squall,
accompanied by a pressure jump, and often
by a long roll-cloud or series of such clouds.
o The morning glory frequently occurs in the
early morning.

43. Concluding Remarks (2)
o Disturbances are sometimes accompanied by
spectacular low-level roll cloud lines and
frequently by low-level wind shears and up-and-
down currents that are hazardous to low flying
aircraft.
o Observations support the results of laboratory
experiments which show that whenever a
suitable wave-guide exists, solitary waves and
bores evolve from quite general excitation
mechanisms.

44. Concluding Remarks (3)
o Southerly morning glories are structurally similar to
their northeasterly counterparts, but their
mechanism of generation remains uncertain and
there may be more than one mechanism.
o Laboratory and numerical simulations show that:
1. solitary waves and bores may be generated ahead
of a gravity current on a stable layer.
2. The gravity current itself is modified in structure
by the stable layer
3. in the aftermath of the collision of two gravity
currents.

45. Morning Glory Roll Clouds (videos)

46. References
Clarke RH, Smith RK, Reid DG. 1981. The morning glory
of the Gulf of Carpentaria: an atmospheric undular
bore. Mon Wether Rev. 109:1726-1750
Christie DR. 1988. Long linear waves in the lower
atmosphere. J Atm Sci.
Smith RK. 1988. Travelling waves and bores in the lower
atmosphere: The ‘morning glory’ and related
phenomena. Earth Sci Rev 25:267-290
Smith RK. 2002. Advanced lectures on dynamical
meteorology. Munich.