Rule 2.
Cumulus Cloud Rule:
Rule 2(d) Do not launch if the flight path will carry the vehicle through any cumulus cloud with its cloud top between the +5 deg C and -5 deg C levels unless:
(1) The cloud is not producing precipitation; and
(2) The horizontal distance from the center of the cloud top to at least one working field mill is less than 2 NM; and
(3) All
electric field measurements at the surface within 5 NM of the flight path and
at the mill(s) specified in (2) above have been between -100 V/m and
+500 V/m for 15 minutes. If mill 33 or
25 is exhibiting a negative offset that (1) is characteristic of powerlines and
(2) preceded the occurrence of any clouds that might produce electric fields at
the surface, the field at these sites must have been between – 500 V/m and +
500 V/m for 15 minutes.
1. For
clarification, why is the precipitation exemption in Rule 2d1 different than
the exemptions in 3b3c (Anvil Clouds) and 4b3 (Debris Cloud)? It is not clearly
understood why the exemption in Rule 2d1 is different than the ‘radar return’
exemptions in 3b3c and 4b3. Is
the rationale different?
Reference: Exemptions 3b3c and 4b3: “The maximum radar return from any part of the (detached anvil or debris) cloud within 5nm of the flight path has been less than 10dBZ for 15 minutes
2. Definition of
‘Precipitation’; Does moisture on the Windscreen of the Weather Aircraft
constitute ‘detectable rain’ in the Precipitation definition? If so, is there any threshold that can be
used between suspended cloud particles and suspended ‘precipitation’ in the
cloud? There have been cases when the Wx aircraft detected
moisture on the windscreen of the aircraft in clouds where there was no virga,
visible rain below the cloud base or radar reflectivity greater than 18 dBZ (or
any radar reflectivity). In these
cases, it is believed the moisture on the windscreen is caused by suspended
cloud particles and not ‘precipitation’ intended in this rule.
Reference: Precipitation: Detectable rain, snow, sleet, etc. at the ground, or virga, or a radar reflectivity greater than 18 dBZ.
Rule 3. Anvil
Clouds:
Case 1. If a
convective cumulus cloud or a dissipating cumulus cloud with a cloud top
entirely below the –20 C (that has never produced lightning of any type)
produces a mid-level horizontal “blow-off” at the top of the cloud due to
strong mid-level winds and remains attached to what’s left of the cumulus cloud
or this mid-level blow-off detaches from the dissipating cumulus or
the cumulus cloud beneath dissipates entirely and leaves only this horizontal
remnant cloud, what do we consider this remnant “blow-off”?
3. Do we treat
this cloud remnant as Detached Anvil, Debris Cloud or do we consider it the
cloud edge in the Cumulus Cloud Rule, or something else?
While the mid-level ’blow-off’
cloud remains attached to the vertically developed cumulus cloud, we would
consider it the cloud edge of the Cumulus Cloud. If it detaches or the cumulus cloud below it dissipates, since
it’s a horizontally stratified layer, we would no longer consider it a Cumulus
Cloud edge. Since the parent cloud
never got to the –20 C, it is not a Debris cloud by definitio,, see Debris
cloud definition. Since it never got
above the –20 C and never produced lightning, the parent cloud was never
considered a cumulonimbus cloud or a thunderstorm by our definitions. Since the official definition of ‘anvil’ is
‘cumulonimbus capillatus’ (Glossary of Meteorology), it cannot be considered
Anvil, since it was always a mid-level ‘Alto’ type cloud and there was never a
cumulonimbus cloud (cloud top > -20 C by our definitions). In this case, we would treat it only as a
cloud layer that may be a Thick Cloud Rule concern if it’s > 4,500 ft
thick and if it stays between the 0 C and –20 C.
Recommendation:
Modify the definition
of ‘Anvil’
FROM:
Anvil: Stratiform or fibrous cloud produced by the upper level outflow or blow-off from thunderstorms or convective clouds.
TO:
Anvil: Stratiform or fibrous cloud produced by the upper level outflow or blow-off from thunderstorms or cumulonimbus clouds.
This would also improve
consistency between the ‘Anvil’ and ‘Debris Cloud’ definitions. The ‘Debris Cloud’ definition uses ‘cumulonimbus
cloud or thunderstorm’ where the ‘Anvil’
definition currently uses ‘thunderstorms or convective clouds’.
Reference: Debris Cloud: Any cloud, except an anvil cloud, that has become
detached from a parent cumulonimbus cloud or thunderstorm, or that results from
the decay of a parent cumulonimbus cloud or thunderstorm.
Rule 3. Anvil Clouds (Continued):
Case 2. There is a
pre-existing layer of cirriform clouds that extends from the Gulf of Mexico to
over the launch site (that has never been associated with convective clouds
with cloud bases above the –20 C).
Thunderstorms begin to develop and penetrate this non-convective cirrus
layer in the eastern Gulf of Mexico and the Florida peninsula well west of the
launch site.
4. How do we evaluate this cirrus layer that
extends over the launch site but has never been associated with convective
clouds prior to the thunderstorms penetrating the layer? Do we treat this layer as ‘Attached Anvil’
even though it is clearly a mixture of the pre-existing non-convective cirrus
and the new thunderstorm cells?
Rule 6. Thick
Cloud Rule:
5. Does this rule
apply to convective Cumulus Clouds?
Although not stated directly in the rule, we
do not believe this applies to Cumulus Clouds based on rationale of the old Layered
Cloud Rule below (now the Thick Cloud Rule) and discussions during the 1998
rewrite. Also, the rule describes a
‘Cloud Layer’ and not an individual cloud element, and the definition of ‘Cloud
Layer’ in the LCCs does not describe individual Cumulus Clouds. Also, if this rule does apply to Cumulus
Clouds, there is a discrepancy between the two rules (there is a case where one
rule can be GREEN and the other rule RED, see Case 1 below).
Reference: Rationale of Layered Cloud Rule (precursor
to Thick Cloud Rule):
“Based on the Imyanitov, et al,
airborne electric field measurements of non-thunderstorm clouds,
Imyanitov found that it is possible for significant charging to occur, for cloud
layers 5,900 ft and greater, in altitude region between 0 degrees Celsius
and minus 10 degrees and when clouds contain supercooled water and ice. Present electrification theories require
supercooled water, ice, precipitation (within cloud) and convection”.
6. If this rule does NOT apply to Cumulus Clouds, can there be a Note added to the Thick Cloud Rule stating that this rule does not apply to convective Cumulus clouds covered in Criterion 2 (Cumulus Cloud Rule)?
If convective Cumulus clouds are covered in this rule, there is a case where we can be GREEN for one rule (Cumulus Rule) and RED for the other (Thick Cloud rule).
Case 1. A Cumulus cloud in the flight path with a cloud top at the –1.0 C level, that contains no precip, and all field mills within 5nm of the cloud and flight path are benign. The Cumulus Cloud is greater than 4,500 feet thick. We would be GREEN for the Cumulus Cloud Rule and RED for the Thick Cloud Rule.
Recommended NOTE to be added to the ‘Thick Cloud Layers’ Rule:
Note: Thick Cloud Layers in Criterion 6 do not include Cumulus
clouds.
Definitions:
Transparency: From actual occurrences during launch countdowns (eg. Delta XTE ’95, and Delta Contour ‘02), it is noted that there may be a delay as long as 5-10 minutes between the time the Weather Aircraft visually observes a dissipating cloud becoming Transparent to the time the Weather Radar no longer observes a radar reflectivity of 10 dBZ or greater. The Weather Aircraft has also reported times when they are ‘Clear and Convinced’ a certain Cloud is transparent, however the weather radar still shows a 10 dBZ or greater radar return from that area due to unknown reasons. This can be critical in launch operations with very short launch windows.
In the definition of ‘Transparent’, the Note states that ‘Visible Transparency is required’. However, in the ‘Nontransparent’ definition, it states that ‘Clouds with a radar reflectivity of 10 dBZ or greater are also considered nontransparent. In the cases described above, we had both, confirmed visible observations of transparency however the weather radar was still showing a reflectivity greater than 10 dBZ. In these cases, can we use the visible observations to conclude the cloud is ‘transparent’?
7. Can the Weather Aircraft visual observation in day or night be used to conclude the cloud is or has become Transparent while the Weather Radar still shows a 10 dBZ radar return if we are Clear and Convinced that Weather Aircraft is providing an accurate observation? Can we use the visible observations from the wx aircraft as a higher ‘priority’ than the weather radar observations in these cases? Can a note be added to the definitions of Transparent and Nontransparent to clarify this?
8. Other
Proposed Definitions Changes:
Cloud Edge: The visible nontransparent
cloud edge is preferred. If this is not possible, then the 10 dBZ radar
reflectivity cloud edge is acceptable.
Cloud Top: The visible nontransparent cloud top is preferred. If this is
not possible, then the 10 dBZ radar reflectivity cloud top is acceptable.
Anvil: Stratiform or fibrous cloud produced by
the upper level outflow or blow-off from thunderstorms or cumulonimbus clouds.
Add a New Definition:
Cloud Base: The visible nontransparent cloud base is preferred. If this is not possible, then the 10 dBZ radar reflectivity cloud base is acceptable.
9. Proposed
Changes to Thick Cloud Layers Rule:
FROM
6. Thick
Cloud Layers
Do not launch if the flight path will carry the vehicle through nontransparent parts of a cloud layer that is
(1) Greater than 4,500 ft thick and any part of the cloud layer along the flight path is located between the 0 deg C and the -20 deg C levels;
or
(2) Connected to a cloud layer that, within 5 NM of the flight path, is greater than 4,500 ft thick and has any part located between the 0 deg C and the -20 deg C levels;
unless the cloud layer is a cirriform cloud that has never been associated with convective clouds, is located entirely at temperatures of -15 deg C or colder, and shows no evidence of containing liquid water (e.g. aircraft icing).
Definitions: Associated, Cloud Layer, Flight Path, Nontransparent
TO
6. Thick
Cloud Layers
Do not launch if the flight path will carry the vehicle through nontransparent parts of a cloud layer that is
(1) Greater than 4,500 ft thick and any part of the nontransparent cloud layer along the flight path is located between the 0 deg C and the -20 deg C levels;
or
(2) Connected to a nontransparent cloud layer that, within 5 NM of the flight path, is greater than 4,500 ft thick and has any part located between the 0 deg C and the -20 deg C levels;
unless the cloud layer is a cirriform cloud that has never been associated with convective clouds, is located entirely at temperatures of -15 deg C or colder, and shows no evidence of containing liquid water (e.g. aircraft icing).
Definitions: Associated,
Cloud Layer, Flight Path, Nontransparent
NOTE: Thick Cloud Layers in Criterion 6 do not
include Cumulus clouds.