North of Darwin this massive storm complex forms each season and heralds the coming storms for our own region.  Hector truly is something to view from the coast!

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'HECTOR'

 

DEEP CONVECTION TO THE EXTREME
The storms over Bathurst and Melville Islands (11.5°S, 131°E)




(Magnificent high level photograph of the imense proportions of Darwin's hector storm courtesy http://ufam.nerc.ac.uk/)



convective storm Darwin

(Fabulous Hector photo above credited to Rob Goler from www.meteo.physik.uni-muenchen.de/~robert/

 


This page I'll give some details of a massive storm affectionately called 'Hector' by the Darwin's Bureau of Meteorology that forms between Darwin and the Tiwi Islands to our north. .  I've previously posted a photo and a little on this in the storm types page, but in essence there's significantly more to this storm system as you'll find out. 

Hector convection is not a 'unique event' or 'system' in the global essence of storm systems, it is unique in the northern parts of Australia due to the right conditions with sea breeze wind patterns and the topography of the islands and the surrounding ocean for its formation during the  pre-wet season build up period.

 



HURRICANE HECTOR 2006  (no relation!)

 

 


What makes this convective process special is that it's part of what's called a mesoscale convective system or MCS.  Mesoscale Convective Systems are groups of thunderstorms organized by the underlying terrain, synoptic-scale weather systems, or their interaction with each other. Scales range from half a dozen thunderstorm cells in a line less than 50 km long to scores of cells along synoptic-scale fronts or in some tropical super-clusters. Strong updrafts and downdrafts on both the mesoscale and within individual thunderstorm cells lead to heavy rain, high winds, lightning, and other forms of severe weather.  Our very own deep convective hector storm can reach heights of 20 kilometres or more and is truly an amazing sight when he's in full maturity.

 

 


MCS storms are very broad and our convection is similar to other tropical areas in the mid lat zone, South Africa, Mexico, parts of the US coast and South America also have these hector convective systems.  Although one must be careful in characterising those severe MCS storms of the US inland regions - there are many things associated with these systems and I'm giving a brief overview and leaving the rest to the experts!

Below are  GOES sat images from 2 December 2003 of hector in a two hour maturity stage. You can see by the last three frames the anvil spreading to the west due to strong easterlie winds high up.  There are other large thunderstorms inland
below Darwin also shown.





The above radar images and article excerpt credited to the following link which is an article on the relationship between precipitation and lightning in tropical island convection.

 


Excerpt from the article is below discussing lightning and Hector:

One of the primary scientific objectives of the Maritime Continent Thunderstorm Experiment (MCTEX) was to study cloud electrification processes in tropical island convection, in particular, the coupling between ice phase precipitation and lightning production.

 

To accomplish this goal, a C-band polarimetric radar (BMRC C-pol) was deployed in the tropics (11.6° S, 130.8° E) for the first time, accompanied by a suite of lightning measurements.

 

Using observations of the propagation corrected horizontal reflectivity and differential reflectivity, along with specific differential phase, rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex (known locally as Hector) over the Tiwi Islands on 28 November 1995. Hector's precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field, cloud-to-ground (CG) and total lightning flash rates, and ground strike locations.

 

During Hector's developing stage, precipitating convective cells along island sea-breezes were dominated by warm rain processes.No significant electric fields or lightning were associated with this stage of Hector, despite substantial rainfall rates.Aided by gust front forcing, a cumulus merger process resulted in larger, taller, and more intense convective complexes which were dominated by mixed phase precipitation processes.

 

 

During the mature phase of Hector, lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall.Merged convective complexes produced 97% of the rainfall and mixed phase ice mass and 100% of the CG lightning.As Hector dissipated, lightning activity rapidly ceased.

 

   

As evidenced from the multiparameter radar observations, the multicell nature of Hector resulted in the continuous lofting of supercooled drops to temperatures between -10° C and -20 ° C in discrete updraft cores during both the early and mature phases. The freezing of these drops provided instantaneous precipitation-sized ice particles which may have subsequently rimed and participated in thunderstorm electrification via the non-inductive charging mechanism.

 

 

 


 
 

 

The following excerpt courtesy from

Robert Cifelli *, Steven A. Rutledge's article from the Colorado State University titled    'USA Vertical motion, diabatic heating, and rainfall characteristics in north Australia convective systems.'

 


Very-high-frequency wind-profiler data are used to study the vertical draught structure within 13 tropical Mesoscale Convective Systems (MCSs) near Darwin, Australia during the 1989-90 and 1990-91 wet seasons. These studies are supported by single-Doppler radar, soundings, and surface rainfall data to correlate radar reflectivity, thermal buoyancy, and surface rainfall patterns with vertical air-motion structures.

Because of Darwin's unique location at the southern tip of the Maritime Continent, vertical draughts in both the monsoon (maritime) and monsoon break (continental) convective regimes can be observed. The break-regime MCSs (six in total) were all squall lines, characterized by a leading line of convection with heavy precipitation and trailing stratiform rainfall containing a characteristic radar bright band. These MCSs exhibited a pronounced life-cycle pattern and were all sampled by the profiler in the mature to dissipating stages. In contrast, the monsoon systems (seven in total) were composed of regions of stratiform cloud with embedded convective bands which moved on-shore in the monsoonal flow. Results from the Darwin rain-gauge network indicated that the majority of the total rainfall in each MCS (break and monsoon) was associated with the convective portion of the system.

The break-regime MCSs were all characterized by a low-level (4 km) updraught peak associated with convective cells on the leading edge of each squall line, trailed by deeper convective updraughts in the middle and upper troposphere. For the monsoon cases, the lower-troposphere convective updraughts were typically less than those in the squall lines, yet were stronger in the upper troposphere.

The low-level differences in the convective updraughts were consistent with the smaller virtual-temperature excess in the monsoon soundings, as well as the larger vertical radar-reflectivity gradients observed in monsoon convection. Consistent with the differences in vertical air-motion patterns, diabatic heating and moistening profiles for the monsoon MCSs were characterized by a higher-level heating and drying peak compared with the break MCSs.
 

The results have important implications for cumulus parametrizations in numerical models since the large-scale circulation is sensitive to the vertical distribution of diabatic heating in tropical MCSs.   

What supports a mesoscale system is

STRONG SPEED SHEAR, WEAK DIRECTIONAL

SHEAR.


Also known as 'unidirectional shear'.  Speed shear allows the storm to move. The movement ensures the storm will last longer than an airmass or 'a' typical pulse thunderstorm. Unidirectional shear often produces storms that form into lines (Mesoscale Convective Systems  or MCS's). Since the storm moves, outflow wind produces lift that enables new storms to grow within the storms periphery.  Over a period of hours a new line a storms are born as a result. These storms produce small hail, heavy rain when they are associated with severe weather.  Hector has produced strong winds gusts and heavy rain during most of his appearances.




Above is the flight plan of the SCOUT-03 aircraft used by visiting scientists to probe and collect data through Darwin's Hector storm at various levels over a four hour period.  You can see the height of this storm as indicated by the 16km marker at the LH top and the times along the bottom 



Cross section above of a deep convective storm. The intense updraft region is marked by the arrows in the reflectivity and vertical velocity frames.  Outflow cold pooling indicated by the cold front markers are shown during the storms dying stage.  The image below is a radar signature showing height, anvil and core information.

cross section of Hector storm

 

The aircraft that does all the work - NASA's Falcon!  Photographs used with kind permission from

Michael J Mahoney PhD, NASA Jet Propulsion Laboratory at http://mtp.jpl.nasa.gov/