1. Chapter 7: convective initiation
squall line development in Illinois
a visible satellite image loop of CI in the eastern US
35°N
103°W
Fig. 7.2

2. 35°N
103°W
97.5°W
92°W
Fig. 7.10

3. diurnal cycle of convective precip
Afternoon convection in the Rockies and Southeast
Nocturnal convection is prevalent over the Gulf & Gulf Stream, and in a broad swath of the Great Plains.
time UTC
108.8°W
JJA
40°N
35°N
average rainfall frequency (June-August )
source:
David Ahijevych

4. annual cycle of lower-tropospheric stability & BL moisture across N America at 35°N
Fig. 7. 1: numbers refer to months (1 … 12)

5. 7.1 CI requisites understanding destabilization: lapse rate tendency equation
First law of thermodynamics

6. Fig. 7. 4: term I: shown is the 700-500 mb T difference
Fig. 7.4: term I: shown is the mb T difference. Larger differences are advected from the NW into Texas.
Fig. 7.5: term II: effect of vertical lapse rate advection plotted on a skew T.
Fig. 7.6: term I + III: effect of differential horizontal temp. advection
Fig. 7.7: term IV: effect of stretching
Fig. 7.8: term V: effect of latent heat release.

7. severe benign no convection equilibrium level LFC
convective inhibition

9. sensitivity of CAPE / CIN to choice of “parcel”
surface-based CAPE / CIN
mixed-layer CAPE / CIN

10. how to derive the MU CAPE
(most unstable CAPE)
shaded area: MU CAPE
WLR: wet-bulb lapse rate
deep convection
source layer

11. 7.4 elevated convection

12. destabilization without lapse rate changes: the effect of LL moisture & heating, and the lifting of a potentially-unstable layer
three ways to remove CIN:
LL convergence, CBL deepening
adding water vapor to the CBL
CBL heating (sfc sensible heat flux)
note that LL moistening & warming not only reduce CIN, but also increase CAPE
Fig. 7. 9

13. potential instability, layer lifting, and convective initiation
Lifting a potentially
unstable layer yields CAPE
potential instability: or

14. qe* Typical wet-season tropical sounding d < 0 dz
Conditional instability:
< 0 dz

15. 7.2 Mesoscale circulations and boundaries affecting CI
Fig. 7.11: Sea breeze, HCR’s,
and convective initiation (CI)
Atkins et al. 1995
CI may occur along single boundaries, or at intersections between boundaries, or between boundaries and HCRs
Fig. 7.16: Horizontal convective rolls & CI (Weckwerth et al 1996)

16. 3D structure of boundaries: core/gap, cleft & lobe, misocyclones, and CI
Fig and 13 (based on the paper by Marquis, Richardson, Markowski 2007)

17. another example of BL variability due to mesoscale circulations and boundaries
gravity wave ridges
old outflow boundary
dryline

18. predicting CI from a sounding
real parcel? Tw
The key reason why the parcel may follow the dashed black curve is entrainment, mainly as soon as a shallow Cu cloud forms. Note the very dry air above the BL. The shallow Cu will be diluted by the dry air, and the Cu temperature will cool towards the wet-bulb T (Tw) of the mixed air.

19. CI failure
Fig. 7.15: CI failure. The Forth Worth sounding suggest no CIN, plenty of CAPE. CI did occur further north.
Misocyclones
(Marquis et al 2007)

20. destruction of embryonic convection by shear
wind profile
wind profile
wind profile
wind profile
tick marks every 2 km on x axis every 1 km on z axis
Fig and 21

21. 7.3 Moisture convergence & CI
changes in mixing ratio by moisture convergence in flux form:
Most model Cu parameterization schemes use resolved moisture convergence & stability changes as arguments. They may not capture the fine-scale structure of mesoscale boundaries.