Weather

Commas are meso-scale structures developing within cold air, that can cause severe weather on the ground, often behind frontal cloud bands. They occur mainly during the cold season and are a common feature for Northern and Western Europe - nevertheless commas can also be found in the south. In this lecture life cycles and the appearance of commas in satellite imagery will be demonstrated. Different types of development exist - Within the cold air commas can grow out of EC starting as a small feature which is growing in to the typical meso-scale cloud spiral. On the other hand commas can be found in connection with occlusion when they split off the cloud spiral and become a separate feature on their own. Typical weather events are storms and heavy precipitation (in form of showers and thunderstorms). Examples of real cases will be shown and they shall illustrate the typical synoptic situations.

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Precipitation within extratropical cyclones often organizes into mesoscale substructures known as precipitation bands. The purpose of this presentation is to better understand how precipitation organizes into bands. We will discuss about Shapiro-Keyser and the Norwegian models of cyclones, why do they form, the differences between them, also where in cyclones precipitation bands form, their structures and evolutions, what controls their locations and intensities, and techniques to diagnose precipitation bands. In the end we will discuss about occlusion bands and how do they actually form considering latest researches.

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In this second part of the Cyclogenesis and Occlusion Cloud Bands lecture, a special form of cyclogenesis is treated in detail: the “rapid cyclogenesis” which is connected with very severe and often catastrophic weather events.

All processes and weather systems are presented from the aspect of “Conceptual Model thinking”; that means the typical appearance in satellite images is connected to the physical background which is responsible for the cloud configurations; then these results are connected to relevant numerical parameters in horizontal and vertical presentation. And all of the presented CMs are connected to the typical connected weather events. This combination of different meteorological material is especially important in forecasting and nowcasting.

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Cyclogenesis and occlusion cloud bands are common meteorological phenomena which are tightly connected. While “cyclogenesis” is a process, describing the development of a low centre, which can last from few hours to several days, the occlusion cloud bands are the result of this cyclogenesis process. Occlusion cloud bands differ from cold and warm front bands because of their history as well as their physical status.

The two lectures start from the classical cyclogenesis (occlusion) processes which are related to the classical polar front theory and introduce then the conveyor belt view of these processes culminating in the warm and cold conveyor belt occlusion types.

The occlusion cloud band types are described and compared to cold and warm front types in their horizontal as well as vertical depiction.

Also special subtypes of occlusion processes like “instant occlusion” and “cold air development” are mentioned.

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When observing the development of frontal zones in satellite imagery, forecasters should always keep an eye on frontal sub-structures like upper waves, front intensifications or rapid cyclogenesis. It is important to look for frontal substructures, because they often show new developments. NWP models sometimes catch the situation, sometimes not. Especially for rapid or small scale developments, model performance may leave a lot to be desired.

Here we focus on comparison of model outputs and satellite data regarding frontal substructures. Because the data are easily compared and show great results, satellite images are a good tool for model output verification.

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Fronts as described in the “Bergen school” by Vilhelm Bjerknes are early conceptual models. Parameters typical for the changing of air masses were named and used by forecasters to recognize transition zones (fronts) between air masses. Satellite information expressed how right Bjerknes was in his CM thinking, but this information showed also that fronts can have much more complicated structure and life cycle Bjerknes could imagine.

In SatManu there are 5 different types of cold- and 3 different types of warm fronts that are recognized and described.

In this lecture we concentrate on warm- and cold fronts and show how we can analyze them with help of CM thinking.

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Getting a good, actual weather picture within short time is essential for a forecaster who has to react quickly and adequately on weather changing’s.

The huge amount of weather data which are available makes it almost impossible for a human being to handle. Thinking in conceptual models is the only way to deal with this problem

Meteorological satellites opened a whole new field in the conceptual model thinking in operational meteorology. Now there was an opportunity to recognize weather systems by detecting cloud patterns and verify this first guesses with observations and numerical parameters.

Within 20 years of the project fifty-three different conceptual models were described in a manual: Sat Manu. Also for the southern hemisphere, we have already fifteen CM’s described.

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Pyroconvection is not a new concept. However, the idea that pyroconvection can be explosive enough to inject a smoke plume into the stratosphere that pollutes hemispherically, goes against the grain of textbook atmospheric physics. Since the discovery of forest fire smoke in the stratosphere, skepticism has given way to acceptance, understanding, excitement, and wonder. That is because pyrocumulonimbus (pyroCb for short) research continues to make more discoveries, involve growing collaborations, and invite new questions.
This presentation will be an overview of pyroCb research. It will focus on observations from satellite sensors. Emphasis will be on platforms such as MODIS, AVHRR, GOES, TOMS, OMI, GOME 2, and CALIPSO. Also to be explored will be the curious historic connection between pyroCb and volcanic eruptions.

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In the frame of the 2020 SEEMET course, Andreas Wirth gave an overview talk on the conveyor belts theory. The three main conveyor belt types are explained and application examples are shown.

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In the frame of the 2020 SEEMET course, Andreas Wirth gave an overview talk on the two main mid-latitude low pressure systems: the classical Norwegian cyclone and the more recent Shapiro-Keyser cyclone. Both models were shown side by side and the main differences were pointed out. A real case example of both cyclone types illustrated the stages of the cyclones' life cycle. Finally, a quick overview was given on Sting Jets, a phenomenon that often accompanies Shapiro-Keyser cyclones.

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Passive microwave (PMW) radiometry is recognized as the most suitable for global precipitation monitoring and quantification. The H SAF precipitation products portfolio is being extended to provide Level 3 (gridded) PMW-based precipitation products to facilitate and promote the use of MW-based products for several applications. One of these products (labelled as P-IN-PWM, or H68) provides instantaneous precipitation rate estimates, based on calibrated and merged PMW Level 2 instantaneous precipitation rate products. H68 provides precipitation rate estimates every half hour, on a regular grid at 0.25°x0.25° resolution over the extended H SAF area (LAT 60°S – 75°N, LON 60°W – 60°E). The calibration is based on the precipitation estimates provided by the NASA Global Precipitation Measurement (GPM) DPR-GMI (Dual-frequency Radar and GPM Microwave Imager) combined product (2B-CMB). The H68 algorithm mainly consists of three modules (i.e. remapping module, adjustment module and merging module) that will be described. The other Level 3 PMW-based product that will be presented is P-DM-PMW (or H67), which provides as main output a 24 h mean precipitation rate based on the H68 product outputs. H67 provides data at the same spatial resolution as H68 at 00, 06, 12 and 18 UTC of each day for the previous 24 hours. Examples of H68 and H67 product outputs and applications will be provided.

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The goal of this seminar is to provide an overview of the state-of-the-art of remote sensing techniques for precipitation retrieval exploiting Low Earth Orbit (LEO) microwave (MW) and/or geostationary (GEO) visible/infrared (VIS/IR) observations, analyzing their potentials and limitations, and perspectives in view of future satellite missions. The first part will focus on the description of the main space borne observing systems with focus on passive MW sensors on board LEO satellites, and on the basic principles of precipitation retrieval from space. Particular emphasis has been given to the NASA/JAXA Global Precipitation Measurement (GPM) mission, and to its Core Observatory launched on February 27, 2014, equipped with the most advanced space borne microwave imager (the GMI) and the first space borne dual-frequency (Ku and Ka-band) precipitation radar, providing semi-global (between 65°S and 65°N) 3-D view and retrieval of the precipitation (solid and liquid). The second part will focus on the main precipitation retrieval techniques and in particular on those used in the EUMETSAT Hydrology Satellite Application Facility (H SAF) precipitation products. Finally, in the third part a few applications of satellite precipitation products will be shown to highlight scientific challenges and future perspectives to improve precipitation quantitative estimation from space.

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