Weather
Phil Chadwick introduces his home country Canada and talks about the challenges a forecasters has to face in this large coutry. He puts most emphasis on satellite images and water vapour patterns.
Length: 50 min
Author: Phil Chadwick
Trained at Queen's University as a nuclear physicist, "Phil the Forecaster" has been a professional meteorologist since 1976. Officially retired in 2011 Phil still continues to advance his research efforts with COMET and the Meteorological Service of Canada (MSC). Satellite and radar meteorology are his forte. Much of this research has been published by COMET under the Satellite Palette banner. Phil has also completed original and extensive research on performance measurement. This large body of work resides in the Case Studies section of Northern Latitude Meteorology (NorLatMet/COMET). Aside from the above Phil has been painting en plein air forever - Philtheforecaster.blogspot.com - art and science are indeed similar endeavours. A sense of humour bundles all of this together and makes learning and teaching fun.
Cb Clusters consist of a cluster of thicker and larger cloud cells within the usual cold air cloudiness behind fronts. It differs from ECs by a looser structure and different cell sizes.
This chapter contains information about Cb and Mesoscale Convective System at small and mesoscale size. Additionally there exist another chapter (CONVECTIVE CLOUD FEATURES IN TYPICAL SYNOPTIC ENVIRONMENTS) which addresses larger scale features. Cbs and Mesoscale Convective Systems form in strong convective processes. The life time and intensity of a Cb and Mesoscale Convective System depend upon the vertical wind shear. Most important is the shear in the lowest layer reaching from the surface up to 2-3 km. Cells developing within strong vertical shear have long lifetime and produce severe weather.
Small bright cloud cells and cell complexes, accompanying convection and unstable processes.
Cluster of Cumulonimbi can be found in an unstable environment where dynamical forcing in the atmosphere plays a role as an additional triggering effect. Cumulonimbus cluster can occur in any unstable air mass: in a cold air mass behind a polar Cold Front, in the frontal zone of a polar front and in warm air of a thermal ridge. Cb Cluster in Warm Air, which are the subject of this investigation, are mesoscale cloud phenomena with an average diameter of 200 km. Over land they start to be generated when the surface temperature enhanced by insolation becomes sufficient to trigger convection. They dissolve during night, and this is one of the main characteristics to differentiate them from Mesoscale Convective System which can exist during the night. Cb Cluster are often embedded in cellular low cloudiness of other types.
A Cold Air Development describes the increase of a Comma to a synoptic scale cloud spiral having similarities with an Occlusion stage.
A Cold Air Development is represented by a cloud spiral at the rear side of a frontal system. As the name already indicatees it is bound to cold air advection. Cold Air Developments often result of enlargening comma systems. Like the comma system they are linked to a PVA maximum. The intensive moving PVA maxima is regarded as the reason for cyclogenesis taking place within the cold air mass.
A Baroclinic Boundary is accompanied by a stationary front-like cloud band situated at synoptic positions which are not typical for classical fronts.
Baroclinicity means that in the atmosphere surfaces of constant pressure intersect surfaces of constant temperature (or density), implying that on a surface of constant pressure there exists a temperature gradient. Consequently a horizontal stream on a pressure surface causes a change in temperature. In general the atmosphere is in a baroclinic state. But there are self contained areas with stronger baroclinicity like i.e. fronts. A Baroclinic Boundary has no significant propagation. The Baroclinic Boundary to the rear of a synoptic scale trough is the most frequent type and will therefore serve as an example.
A Back-Bent Occlusion is that part of an Occlusion cloud spiral which reforms into a Cold Front band with some cyclonic curvature with the approach of a cold air mass.
The concept Back Bent Occlusion refers to a part of a warm occluded front that changes its direction of motion and turns into a Cold Front. This back bending is due to remarkable cold air advection at the rear side. The bending back of an occluded front can be seen from the curvature of TFP field around the Occlusion.The surface pressure gradient is relatively weak near the centre of the low, and often elongated in the direction of the occluded front.
Robert Joyce presents the second generation CMORPH product.
Length: 30 min
Author: Robert Joyce (NOAA)
As reported at the AMS annual meeting of 2015, a prototype system was developed for the second generation CMORPH to produce global analyses of 30-min precipitation on a 0.05° lat/lon grid over the entire globe from pole to pole through integration of information from satellite observations as well as numerical model simulations. The second generation CMORPH is built upon the Kalman Filter based CMORPH algorithm of Joyce and Xie (2011). Inputs to the system include rainfall and snowfall rate retrievals from passive microwave (PMW) measurements aboard all available low earth orbit (LEO) satellites, precipitation estimates derived from infrared (IR) observations of geostationary (GEO) as well as LEO platforms, and precipitation simulations from numerical global models. Key to the success of the 2nd generation CMORPH, among a couple of other elements, are the development of a LEO-IR based precipitation estimation to fill in the polar gaps and objectively analyzed cloud motion vectors to capture the cloud movements of various spatial scales over the entire globe. In this presentation, we report our recent work on the LEO-IR based precipitation estimation.
The prototype algorithm for the LEO IR precipitation estimation is refined to achieve improved quantitative accuracy and consistency with PMW retrievals. AVHRR IR TBB data from all LEO satellites are first remapped to a 0.05olat/lon grid over the entire globe and in a 30-min interval. Temporally and spatially co-located data pairs of the LEO TBB and inter-calibrated combined satellite PMW retrievals (MWCOMB) over the tropics and mid latitudes and CloudSat radar precipitation over high latitudes and polar regions are then collected to construct tables. Precipitation at a grid box is derived from the TBB through matching the PDF tables for the TBB and the MWCOMB/Cloudsat-precipitation. This procedure is implemented for different season, latitude band and underlying surface types to account for the variations in the cloud – precipitation relationship.
Quantitative experiments are conducted to optimize the LEO IR based precipitation estimation technique using MWCOMB/CloudSat.
Arctic Fronts are accompanied by mostly low and some mid-level clouds.
Arctic Fronts form in the Arctic region, and move southwards in southerly flows. When they reach Northern Europe, they have usually travelled over an open sea, and convective cloudiness has developed. The appearance of an Arctic Cold Fronts is then, essentially, that of a shallow Cold Front. Arctic Cold Fronts are usually so far north that Meteosat images alone are inadequate to recognize them. The final check is best made using a loop of AVHRR images with the help of numerical model parameter fields.
Tristan L'Ecuyer presents satellite precipitation products based on radar technology.
Length: 30 min
Author: Tristan L´Ecuyer (University of Wisconsin-Madison)
Radars provide the most direct means of remotely measuring precipitation over large areas. The value of ground-based radars for indicating the location and intensity of rainfall was recognized shortly after the first surveillance radars were developed during World War II. Since then radar networks have been widely used to estimate precipitation accumulations, track storms, and provide valuable information to the public. However, vast areas of the Earth including oceanic, mountainous, and densely forested regions are largely inaccessible to ground-based instruments. As a result, much of our knowledge of precipitation in such areas derives from passive satellite measurements that can suffer from uncertainties owing to the indirect relationship between radiation measured at the satellite and rainfall at the surface. Satellite precipitation radars offer some of the benefits of their ground-based counterparts with the enhanced coverage afforded by orbiting the Earth. To date three such radars have been launched providing a new perspective of global precipitation from tropical rainfall to polar snows that complements the longer-term record provided by passive instruments. This lecture will describe the physical principles used to relate the reflectivities measured by these radars to precipitation intensity. We will examine the main features of the associated precipitation retrieval algorithms and some of the important factors that need to be considered will be highlighted through illustrative examples. We will conclude by contrasting the strengths and limitations of satellite radars against passive satellite sensors and ground-based radar systems.
Emmanouil Anagnostou reviews a comprehensive error analysis of the currently available global-scale HPE products based on a number of major flash flood-inducing storms.
Length: 30 min
Author: Emmanouil Anagnostou (University of Connecticut)
The advancements in satellite rainfall observations over the past decade have opened new horizons in hydrological applications at global scale. Specifically, newly available high resolution (8-25 km, 1-3 hourly) satellite precipitation estimates (HPE) have allowed researchers to consider their potential integration with hydrologic models for flood modelling applications. However, performance evaluation of HPEs in cases of major flash flood-inducing storms is needed to assess their ability to represent the high rainfall variability associated with these storms. Furthermore, derivation of error metrics are usually based on long time records (years) thus results are bulked and cannot provide clear evidence for the efficiency of high resolution satellite precipitation products in quantifying heavy precipitation events that are usually responsible for the occurrence of flash floods. In this talk we will review a comprehensive error analysis of the currently available global-scale HPE products based on a number of major flash flood-inducing storms that occurred in Southern Europe and Western Mediterranean basins over the past 12 years. Quality controlled rainfall datasets derived from high-resolution radar-rainfall estimates and/or dense rain gauge network observations are used for reference. The ability of satellite-rainfall to represent the magnitude and spatiotemporal patterns of each storm is examined. Strengths and limitations of each product are highlighted and general findings are anticipated to serve as a valuable reference to both hydrologists and satellite product developers. Finally, the error propagation from rainfall to flood simulation is examined, and error correction techniques based on a newly developed NWP-based correction technique are evaluated in terms of their impact on flood prediction efficiency.
Sheldon Kusselson talks about microwave sensors aboard operational polar orbiters.
Length: 30 min
Author: Sheldon Kusselson (former NOAA/NESDIS)
Polar-orbiting microwave sensor generated rain rate estimates are the most accurate satellite-derived estimates of rainfall because of their direct relationship between liquid and ice hydrometeors and surface precipitation. People may find that surprising because the timeliness, latency and spatial resolution are inferior to geostationary satellite rain estimates. But the primary advantage that microwave sensors aboard operational polar orbiters have over geostationary satellites is the ability to see through the clouds and capture what is below the cloud tops. The current operational polar-orbiting satellite sensors aboard the DMSP (SSMI/S sensor) and NOAA/METOP/S-NPP satellites (AMSU/MHS and ATMS sensors) that generate instantaneous areal average microwave rain rates will be presented and explained, along with the recent development of combining these measurements into a Blended Rain Rate Product and an additional blended product called QMORPH. In the future polar-orbiting microwave rain rates will be used as a calibration of the next generation of geostationary satellite-derived rain estimates. A few recent case studies of the best use of operational microwave rain rates will also be shown, as well as those from more research oriented missions, such as GCOM (AMSR-2 sensor) and GPM (GPI sensors) that are also used in operations.
Vincenzo Levizzani provides a brief overview of the basic physical principles underlying satellite precipitation estimation methods.
Length: 46 min
Author: Vincenzo Levizzani (CNR - ISAC)
The estimation of precipitation from space was attempted almost at the beginning of the satellite meteorology era by establishing a somewhat loose link between visible and infrared imagery of cloud tops and precipitation intensity at the ground. Since the early days estimation methods have qualitatively and quantitatively evolved with the advent of passive microwave sensors first and precipitation and cloud radars more recently. The purpose of the lecture is to provide a necessarily brief overview of the basic physical principles underlying satellite precipitation estimation methods trying to make the audience aware of what the sensors actually “measure” (radiation properties) and how these measurements are converted into precipitation intensity. All the methods, either based on “passive” or “active” sensing, are necessarily indirect and thus a clear understanding of the physics of radiation and of cloud hydrometeors is needed for the correct use of the products. In fact, such understanding helps in identifying the limitations of the existing precipitation products, which are too often used improperly or taken for granted. The lecture will try to pave the way to the in depth lectures of the other instructors on more specific topics of the discipline.