Identify and interpret fields and derived products
Thomas Krennert (ZAMG) talks about the importance of moisture gradients in analysing the possibility of development of deep moist convection.
The exact predictability of convection in the Alpine region in the absence of fronts in weak-surface-pressure-gradient-situations during the warm season remains challenging for forecasters. The development into single-cell deep moist convection SC-DMC under these conditions depends on the availability of well-known ingredients like low level moisture, steep tropospheric lapse rates and sufficient lift. Satellite studies have shown that favourable locations for the first onset of SC-DMC resulting from widespread shallow convection over mountainous terrain are water vapour gradients in the middle or upper troposphere UTMG (upper tropospheric moisture gradients, Krennert, et al., 2003, https://doi.org/10.1016/S0169-8095(03)00067-X). The contributions of the respective ingredients related to UTMG supporting the initiation of DMC are discussed. A focus is set on moist symmetric instability MSI as a possible mechanism for favouring the transition from shallow to deep moist convection.
Ralph Petersen (University of Wisconsin) talks about forecasting satellite-derived moisture using all available observation data on moisture and Lagrangian methods to give forecasters more information on the possibility of storm formation.
The CIMSS Lagrangian NearCasts system 1) expands the utility of clear-air sounding and products related to the pre-convective environment (from MTG-IRS Sounder and MTG-Imager) into the 1-9 hours period before storm formation and 2) now combines Geostationary Infrared Products with less frequent microwave products from multiple Polar Orbiting systems to fill information gaps in cloudy areas. For a heavy precipitation event, quantitative measures of both retrieval and short-range forecast accuracy are provided, including a new, non-uniform bias correction approach, and explorations of predictive clear-sky RGBs.
Including “all-weather”, real-time MiRS retrievals not only provide a more visually pleasing product (improving coverage by 30-40%), but also exposes forecasters to here-to-fore underutilized POES observations over land.
Validation against hourly surface-based GPS-TPW observations testify to the ability of the Satellite-based products to capture observed small-scale moisture features properly. Results show error growth rates < 1%/hour (without initial shocks) and support applying non-uniform bias corrections derived over 5mm bands to assure realistic TPW distributions.
Because RGB presentations are more popular than quantitative retrieval product displays the parcel-based Lagrangian NearCast approach was also used to “predict” clear-air RGBs based on the projection of radiance, with quantitative values overlaid. Examples of initial tests will be shown.
Christo Georgiev (NIMH) discusses the effect of vorticity on tropical cyclones and development of severe thunderstorms, through the scope of water vapour imagery.
Water vapour (WV) images provide useful information to anticipate the effects of upper-level dynamic environment on the intensity of a tropical cyclone (TC) as well as on its extratropical transition (ET), a gradual process in which a TC loses tropical characteristics and becomes more extratropical in nature. Analyses of WV imagery shows that during ET stage over subtropical areas, advection of potential vorticty anomaly can influence the ET and control the process.
Large amounts of water vapour, originated by TCs may be involved in transfer of moisture by planetary waves, associated with ET developments and give rise to a narrow regions of strong meridional water vapour flux. The presentation shows WV imagery synoptic-scale analysis, which shows supply with additional large amount of moisture of an existing already favourable convective environment. The
combination lead into an environment with very high CAPE and potential to accelerate upward, acquiring kinetic energy and forming strong vertical motions in a deep tropospheric layer. The process is illustrated by a case of catastrophic hailstorm over Bulgaria, Eastern Mediterranean.
Christian Herold (DWD) investigates the usefulness of IASI L2 products in nowcasting, detecting and analyzing sting jets in rapid cyclogenesis.
Strong winds southwest of the center of a Shapiro-Keyser-Cyclone are often associated with a cold conveyor jet or a sting jet. The sting jet is a strong mesoscale flow with a very high damage potential. It is a massive challenge for NWP and forecasters to correctly predict a sting jet. The question is, can IASI profiles help forecasters for a better prediction of such mesoscale severe wind events connected with sting jets? In this specific context, some case studies will be presented.
Zsofia Kocsis (OMSZ) talked about the reasons behind the experiment of merging SYNOP data with the IASI L2 profiles.
Using IASI L2 profiles, different instability indices (e.g. Lifted Index, CAPE) and water vapour content in different layers can be determined, which provides information on the convective environment. These indices were studied in several convective cases which led us to try to merge the IASI profiles and Synop measurements. In this presentation we present the reasons why we choose to combine these different measurements and we also present some of our experiences with the blended IASI product.
Phil Watts and Loredana Spezzi (EUMETSAT) give an overview of the possibilities of water-vapour retrieval of the future EPS-SG satellites.
The METimage instrument on board of the future EPS-SG satellite series opens a new era for the retrieval of water wapour imaging products at EUMETSAT. Equipped with 20 channels covering the spectral range 0.4-13μm and including both Near infrared and thermal infrared water vapour absorption bands (0.9, 6.7 and 7.3μm), METimage will allow the retrieval of operational water vapour imagery products with unprecendented resolution (down to 500m) from a low-Eart orbit. These products are expected to greatly enhance the EUMETSAT service in support of numerical weather prediction, nowcasting and climate monitoring.
In this contribution, we report the retrieval approach chosen for METimage water vapour imagery products and demonstrate it using MODIS measurements. We focus in particular on the uncertainty and quality assessment planned for these products. We aim at gathering the fundamental user feedback to achieve the state-of-the-art retrieval and validation approach, and to foster cooperation and exchange for the analysis and characterization of these products once they become available. In particular, we would like to discuss key points that have an impact on the use of our products in forecasting applications (such as the use of prior forecast information in the retrieval, the product spatial resolution and content (e.g., uncertainties, quality indicators, diagnostic parameters, etc., and the advantage of combining NIR/IR measurements, not available from previous EUMETSAT missions).
Sheldon J. Kusselson (CIRA) shows us the Advected Layered Precipitable Water (ALPW) and Total Precipitable Water (TPW) products and how to apply them for forecasting hazardous events.
Water vapor availability is a key factor in forecasting heavy precipitation. Passive microwave instruments onboard several polar orbiting spacecraft measure emission from water vapor and provide a capability to sense layers of and total water vapor in the atmosphere. Via fusion of passive microwave retrievals from five or more polar orbiting spacecraft and model wind fields, the Advected Layered Precipitable Water (ALPW) and Total Precipitable Water (TPW) products are created hourly. The new ALPW product and upgraded Total Precipitable Water products, including a percent of normal TPW product, will become operational for forecasters in 2023. In the meantime, CIRA already produces the products hourly on the internet. During the past decade applications for the ALPW and TPW products have been developed for many different types of weather events, with a focus on heavy precipitation. This presentation will highlight applications for various weather hazards such as heavy rain causing flooding and heavy snow. Case studies using applications for the ALPW and TPW products in different parts of the world, including Europe, will be presented.
Xavier Calbet (AEMET) presents his work on water vapour variability in the atmosphere and the effect of the variability on the water vapour fields in its vicinity.
Water vapor at small scales (< 6 km) behaves, on average, in an stochastic way. This behavior can be described by simple stochastic models (Gaussian Random Fields). Knowing the variability (or turbulence) of water vapor in a location, mainly via measurements, we can infer the statistical characteristics of water vapor fields in its vicinity. This model will help us in: determining whether water vapor measurements from satellites can be more or less biased, integrate different water vapor measurements coming from differing spatial scales together in a coherent way, estimate the turbulence that is potentially present in the atmosphere. Direct consequences of this concept regarding Nowcasting still need to be explored in the future.
Jan El-Kassar and Cintia Carbajal Henkel (Free University of Berlin) talk about their efforts to develop an optimal estimation algorithm for the 0.865 and 0.914 micrometer bands to retrieve a total column water product.
MTG-FCI will feature a band configuration in the rho-sigma-tau absorption band of water vapour (0.865 and 0.914 microns). We are developing an optimal estimation algorithm for these two bands to retrieve a total column water vapour product, which will be highly sensitive to boundary layer moisture.
We show preliminary results from a first prototype based on COWa (Copernicus Sentinel-3 OLCI Water Vapour) applied to spatially high-resolved data (~300m) from the Ocean and Land Colour Imager (OLCI) onboard the polar-orbiting satellites Sentinel-3.
In a next step we analyse the relationship between spatial variability metrics in the water vapour field and convective initiation over Germany, exploiting the advanced observation capabilities of current and future satellite-based imagers.
Thomas August (EUMETSAT) presents the current polar satellite sounders and makes a comparison with the capabilities of the future MTG infrared sounder
Satellite infrared sounders like IASI allow retrieving the vertical structure of the atmospheric humidity. Their measurements are exploited in synergy with the microwave (MW) sounders, when such companions are present on the same platforms as is the case in the operational EUMETSAT Polar System (EPS) programme and in the EPS-Second Generation (SG). This synergy increases the yield and quality of sounding in cloudy pixels. The future infrared sounder (IRS) onboard Meteosat Third Generation (MTG) will operate without MW companions. It will however provide unprecedented spatio-temporal sounding, with a typical ground-resolution of 7km and observations every 30 minutes over Europe.
The extensive utilisation of machine learning guarantees the provision of reliable atmospheric temperature and humidity profiles and uncertainty estimated within less than 30 minutes from sensing. We present here the characteristics of satellite thermodynamic profiles from the current and future missions and the experience made in studies with meteorological services to contribute to nowcasting severe weather events, and prepare to the future sounder missions.
Hans Peter Roesli showcases the usefulness and characteristics of the 0.9 micrometer band channels, one of which will be available with MTG satellites.
At the time of refining the FCI requirements for nowcasting applications, numerical forecasts had much difficulty in handling low-level humidity (low-level forecasts rapidly dried with increasing forecast time). This was one of the reasons why the expert team for nowcasting proposed to add in MTG’s FCI.a solar water-vapour-absorbing in the 0.9-micron region (now NIR 0.914 micron) alongside the clear NIR 0.865 micron band. Although nowadays operational numerical models have overcome the moisture problem, NIR 0.914 might still find valuable applications, in particular when accounting for the frequent imaging of the same scene in daylight.
MODIS includes a clear NIR 0.8585 band and 3 bands in the 0.9-micron region: 0.936, 0.940 and 0.905 micron, with decreasing water vapour absorption. Selecting NIR 0.8585 and the weakest absorbing NIR0.905 as proxy bands for FCI some meteorological situations were investigated, where low-level humidity monitoring could have been beneficial to nowcasts. MODIS flying on Terra and Aqua usually deliver two daylight overflights of the same scene, which allows for a rough appreciation of evolution in time.
Gao&Kaufman (2003) discussed the MODIS bands in view of the MOD05/MYD05 products for Total Precipitable Water Vapour. Based on their paper MODIS imagery of the reflectivity ratio 0.905/0.8585 was produced as a proxy for FCI. Taking the ratio is simple and damps further the (minor) differences in background reflectivity between the two bands. It was found that the ratio generally varies between 0.6 (humid boundary layer) and (dry boundary layer), as already given by Gao&Kaufman.
Examples under clear European skies will show situations of old frontal zones, convergence lines or north foehn. A more complex situation of low-level moisture advection under cloudy skies over the Po Valley affords the frequent FCI imaging, in order to get the full picture of the moist-air advection.
The purpose of the lecture is to provide a necessarily brief overview of the basic physical principles underlying satellite precipitation estimation methods.
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.