AMOSSG/3-SN No. 12

15/1/02

AERODROME METEOROLOGICAL OBSERVING SYSTEMS STUDY GROUP (AMOSSG)

THIRD MEETING

Miami, 22 to 25 January 2002

Agenda Item	5 :	Review of the requirements for meteorological observations and reports at aerodromes contained in Chapter 4 of Annex 3

PRESENT WEATHER REPORTING CONSIDERATIONS

(Presented by E. Robinson)

(Inputs by E. Robinson, Wil Van Dijk, Byran Boase, Walter Woveris)

1.	INTRODUCTION

1.1	Present weather reporting was reviewed at the second AMOSSG meeting and three perspectives were presented which included: a) operational aviation; b) forecasting; and c) emerging technologies. Although there were discussions on these perspectives, there were no significant recommendations. It was also recognized that operational aviation should be the primary focus for Annex 3. This paper presents some further views on these issues for discussion and consideration.

2.	THE NEED FOR PRESENT WEATHER DATA

2.1	Further discussions, reviews and opinions have been gathered on the possible grouping and reduction of present weather types to minimize the large list of possible reportable types. For example, a grouping such as: a) liquid; b) freezing; c) frozen; and d) hazards, as an example, could simplify the present weather reporting process without restricting the value of the data. It would also help to integrate the current technological capabilities of automatic weather stations into a compatible reporting structure while reducing the possibilities of misinterpretation.

2.2	Although there are practical reasons why this could or should occur, the general consensus from the aviation community is to not change what is the current practice. In fact, Australia states that "any depletion in quantity and quality would not be welcome."

2.3	The challenge is to ensure the pilot's understanding of what they are receiving, how they interpret it and how it relates to a particular forecast product. This opens the need for better display systems and the impact of the evolution of new graphical methods into the distribution technologies, an area of significant change and importance.

2.4	In Australia, and many other countries, the increase in automatic weather stations and the staff losses have significantly reduced or changed the available present weather data so the need for "ground truthing data" is at an absolute premium. In Australia's case, these automatic weather stations do not have present weather capability. It is clear that the use of either ad hoc human observers or reduced capacity automatic stations is insufficient for the collection of adequate present weather information. In some countries, such as Canada, a significant effort has been made to develop advanced present weather sensors and algorithms for automatic stations and these operational systems have been nationally approved and accepted for aviation use. The level of adequacy is the subject of great discussion, debate and diversity of views. There is no doubt that the continued development and evolution of improved present weather technologies is desirable.

2.5	The measurement of present weather data is not the only issue. Dissemination is a critical factor, particularly where the present weather information is limited or sparse. If the frequency of reporting is increased, the benefit is also increased due to the timeliness of the data. Since METAR data are collected hourly, or SPECI data are triggered by event, the actual present weather on site is partially "stale" when the pilot receives them. Current conditions may be much more important to the pilot under some conditions. This issue will evolve with the continued development of telecommunications methods, digital networks, wireless communications, WEB's and other technologies. It would be useful to have some discussion on the needs and implications of real time data since this is the trend.

3.	LIGHTNING DATA

3.1	One of the most critical Occupational Health & Safety issues for the aviation industry is alerting ground staff to the presence or anticipated arrival of lightning. The majority of airlines have fairly comprehensive "ramp instructions" for actions to be taken when lightning is imminent. To meet this requirement a combination of radar, visual and audible observations are used to identify CB cells and the presence of thunderstorms. This information is then used to disseminate lightning alerts at the major aerodromes.

3.2	With the increased use of automatic weather stations it is important to find better technologies for the detection and integration of lightning information into these reports. Technologies currently exist which have adequate performance that can be selected and integrated into new systems. In Europe, for example, the Vaisala SAFIR "Total Lightning Localization and Thunderstorm System" is increasing in use. North American networks, which use wavefront detectors and time-of-arrival central post processing from Global Atmospherics Inc. (GAI), provide very timely, and accurate data in a standalone lightning detection network. Various options also exist to integrate these data into METAR reports which would be of immense benefit to many sectors of the aviation industry, including pilots, airport owners, refuellers and other ground operators.

3.3	There is a strong argument to see reference to lightning observed by AWS sensors and/or integrated networks to be included as a recommendation in Annex 3. For example, under 4.12 Observing and reporting of supplementary information within paragraph 4.12.1. Although cumulonimbus and thunderstorms are mentioned, lightning is not but it should be identified within the context of this recommendation.

4.	THE NEED FOR AWS STANDARDS

4.1	As the trend toward AUTO METAR reporting increases, it is important to try to enhance the ability of automatic systems to better detect and report present weather in as compatible a manner as possible with the currently accepted human generated present weather reporting methods. With this AWS trend, it is imperative to formulate the minimum specifications, guidelines and perhaps even detailed algorithms that should be common to these AWS applications. Without these "standards" there will be differences in AWS reports under the same meteorological conditions, some perhaps which are critical to operational aviation. Therefore harmonization of reporting must be a goal for both ICAO and for WMO. It may be prudent for ICAO to initiate such a request with WMO in this regard.

5.

5.1	AUTO METAR reporting should also sustain the descriptive present weather interpretations that the aviation community currently uses and understands. Although new and emerging technologies have the ability to provide different information, such as rates in mm/hour or drop size distribution statistics, Mr. Paul Johnson, the UK AWOS representative for the International Federation of Air traffic Controllers Associations (IFATCA) states that it is more important to ensure that definitions, such as "light, medium and heavy", remain descriptive, clear and are properly defined to ensure international compatibility. Note: these are not his personal views as he represents AWG/PT/LVP as the rapporteur of the METG/PT/METAOP.

5.2	IFATCA has also stated: "Visibility reduction due to haze has a different interpretation to mist, where a reduction to fog is likely if the temperature drops. The descriptive phrases for present weather have implications for the controller. Blowing snow may obscure visual aids. Shallow fog may result in sudden unpredictable changes in the RVR".

5.3	IFATCA's views on weather information include: "The controller is responsible for passing the most complete information possible regarding the conditions on the aerodrome and in the surrounding airspace. In order to do this, the controller will additionally provide other information available to him such as wind and RVR and will pass these frequently in rapidly changing conditions. The report of the present weather is a fundamental to this and the controller should be able to pass the best possible description. The person best qualified to assess the weather is the qualified MET observer (except in cases where the controller is suitably qualified)".

5.4	It is clear from the last comment that the future conversion to AUTO METAR capabilities must overcome these limitations and perceptions to establish operational credibility and must continue to enhance the technological capability for better present weather representativeness from automatic weather stations.

5.5	IFATCA further expressed: "The reaction to these proposals is that a reduction in the descriptive nature of the MET reports will result in a lack of awareness for both pilots and controllers of the conditions at and around the airport. When considering these changes, the operational affect of any proposal should be taken into account. A review of the reporting of present weather must ensure that this information continues to provide controllers with the fullest description of weather so that they can make sound operational decisions."

5.6	Recent weather conditions appear to be of less interest to the operational aviation community than present weather conditions. Present weather information provides more useful information on the state of the runway (dry vs. wet) or aircraft icing probabilities. Instrumentation improvements are required specifically for better differentiation between different types and intensities of freezing or frozen precipitation.

6.

6.1	The group is invited to consider and discuss the issues in this report; in particular:

a)	the implications and possibilities of changes to reportable present weather types;

b)	the implications of merging AWS methods with currently accepted present weather practices;

c)	the need to formalize AWS "standards" and WMO's role on behalf of ICAO;

d)	the need for more timely access to real time data and the impacts on the collection, distribution, display and use of METAR data;

e)	the need to encourage the development of advanced present weather sensors and algorithms for use on AWS equipment;

f)	the adding of lightning to paragraph 4.12 of Annex 3; and

g)	the implications of "descriptive" data in AWS equipment;

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