Thomas Hauf | Leibniz Universität Hannover (original) (raw)

Papers by Thomas Hauf

Research paper thumbnail of Convective Waves and Cumulus Growth

Technical Soaring, 1988

Numerical simulations and aircraft measurements show that thermal waves are gravity waves develop... more Numerical simulations and aircraft measurements show that thermal waves are gravity waves developing under the presence of shear in the stable troposphere above a heated boundary layer. The waves are launched when thermals rise from the ground and impinge into the stable layer where they act as obstacles to the mean flow, thus forcing the air to flow over them. This paper reviews some basic aspects of thermal waves based on the papers of Clark, Hauf and Kuettner, Clark and Hauf, and Kuettner, Hildebrand and Clark.

Research paper thumbnail of The In-flight icing warning system ADWICE for European airspace – Current structure, recent improvements and verification results

Meteorologische Zeitschrift, 2017

The Advanced Diagnosis and Warning System for Aircraft Icing Environments (ADWICE) has been in de... more The Advanced Diagnosis and Warning System for Aircraft Icing Environments (ADWICE) has been in development since 1998 in a collaboration between the German Aerospace Centre (DLR), Deutscher Wetterdienst (German Weather Service, DWD) and the Institute of Meteorology and Climatology of the Leibniz Universität Hannover (IMuK). ADWICE identifies atmospheric regions containing supercooled liquid water where aircraft icing can occur. Running operationally at DWD since 2002, ADWICE is used at the German Advisory Centres for Aviation (Luftfahrtberatungszentrale) to support pilots in route planning by warning of hazardous in-flight icing conditions. The model domain covers Europe and the Mediterranean coast of North Africa with a horizontal grid spacing of about 7 km and 30 vertical hybrid levels. The warning system consists of two algorithms. Based on output data of the operational numerical weather prediction model COSMO-EU (Consortium of Small-Scale Modelling-Europe), the Prognostic Icing Algorithm (PIA) allows the forecast of areas with an icing hazard. The Diagnostic Icing Algorithm (DIA) realises a fusion of forecast, observational and remote sensing data such as satellite data to describe the current icing hazard. Both algorithms create a three-dimensional icing product containing information about the likely icing scenario and its associated icing intensity. This paper describes the current structure of ADWICE, its output, as well as its diagnosis and forecast skill. For verification, the output of the two algorithms was compared with pilot observations over Europe. The results show satisfactory values for the probability of detection and the volume efficiency.

Research paper thumbnail of Aviation and Weather - a New Initiative in Germany

Research paper thumbnail of Case Study of Adverse Weather Avoidance Modelling

Adverse weather conditions like thunderstorms cause about 50 % of all aircraft delays. Avoiding t... more Adverse weather conditions like thunderstorms cause about 50 % of all aircraft delays. Avoiding the hazards generally results in additional workload for air traffic controllers. The project MET4ATM deals with a case study for the 17 July 2010, when several flights in the Austrian and the Czech airspace had to be diverted due to several thunderstorms. One aim of MET4ATM is to estimate the benefit of ground-based weather information for ATM in such a case with regard to sector occupancies. This paper deals with an application of the weather avoidance model DIVMET coupled to the air traffic model NAVSIM. Aircraft are simulated based on the flight plan route and diverted around the storms keeping a safety margin. The analysis of the simulated trajectories compared with actually flown routes provides promising results in terms of optimized trajectories.

Research paper thumbnail of Universal Functions for Post-Frontal Showers-Geometrical Characteristics and Rain Rate Development

The study deals with the well-known convective cloud and precipitation patterns in the rear of co... more The study deals with the well-known convective cloud and precipitation patterns in the rear of cold-fronts passing Central Europe, typically in south-easterly directions. The structure and temporal development of those postfrontal shower fields were analysed aiming for a quantitative analytical description of that precipitation field as displayed in Figure 1. In this paper, we present a summary of ongoing work, comprising analyses of the geometrical structure and investigations on the temporal development of individual rain areas. The geometrical structure was analysed following the procedure of THEUSNER (2007) (in the following referred to as THEU) and MESNARD AND SAUVAGEOT (2003) (in the following referred to as MESN). We refined those studies by using a higher resolution radar product to calculate the diurnal cycle of the whole precipitation area and evaluate the individual rain areas within the precipitation field, e.g. with respect to area size. In addition, the temporal develo...

Research paper thumbnail of Universal Functions for Post-Frontal Showers-Geometrical Characteristics and Rain Rate Development

The study deals with the well-known convective cloud and precipitation patterns in the rear of co... more The study deals with the well-known convective cloud and precipitation patterns in the rear of cold-fronts passing Central Europe, typically in south-easterly directions. The structure and temporal development of those postfrontal shower fields were analysed aiming for a quantitative analytical description of that precipitation field as displayed in Figure 1. In this paper, we present a summary of ongoing work, comprising analyses of the geometrical structure and investigations on the temporal development of individual rain areas. The geometrical structure was analysed following the procedure of THEUSNER (2007) (in the following referred to as THEU) and MESNARD AND SAUVAGEOT (2003) (in the following referred to as MESN). We refined those studies by using a higher resolution radar product to calculate the diurnal cycle of the whole precipitation area and evaluate the individual rain areas within the precipitation field, e.g. with respect to area size. In addition, the temporal develo...

Research paper thumbnail of Uncertainty Analysis of Thunderstorm Nowcasts for Utilization in Aircraft Routing

Weather related uncertainty is a major disturbing factor in accurate aviation route planning. Adv... more Weather related uncertainty is a major disturbing factor in accurate aviation route planning. Adverse weather itself impacts the planning process but that might be mitigated if weather forecasts or nowcasts are used. Knowing that no forecast is perfect, the forecast for a certain time will always differ from the real weather at that time. Assuming that the forecast represents the best knowledge about the future development, deviations from it can be interpreted as the current inherent uncertainty of the forecast. We focus on thunderstorm nowcasts for the next hour using the DLR Rad-TRAM nowcast system. We analyse the nowcast error, respectively the increasing uncertainty with nowcast time by determining the spatial deviations of nowcast and observed thunderstorm extension. An intuitively expected increase of uncertainty with nowcast time is confirmed and quantified by the study results. A potential application of the uncertainty will be presented.

Research paper thumbnail of Adverse weather diversion model DIVMET

Journal of Aerospace Operations

Research paper thumbnail of Aircraft route forecasting under adverse weather conditions

Meteorologische Zeitschrift

In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Ai... more In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Airport are used to forecast deviation routes through a field of storms for arriving and departing aircraft. Storms were observed and nowcast by the nowcast system SWIRLS from the Hong Kong Observatory. Storms were considered as no-go zones for aircraft and deviation routes were determined with the DIVSIM software package. Two days (21 and 22 May 2011) with 22 actual flown routes were investigated. Flights were simulated with a nowcast issued at the time an aircraft entered the TMA or departed from the airport. These flights were compared with a posteriori simulations, in which all storm fields were known and circumnavigated. Both types of simulated routes were then compared with the actual flown routes. The qualitative comparison of the various routes revealed generally good agreement. Larger differences were found in more complex situations with many active storms in the TMA. Route differences resulted primarily from air traffic control measures imposed such as holdings, slowdowns and shortcuts, causing the largest differences between the estimated and actual landing time. Route differences could be enhanced as aircraft might be forced to circumnavigate a storm ahead in a different sense. The use of route forecasts to assist controllers coordinating flights in a complex moving storm field is discussed. The study emphasises the important application of storm nowcasts in aviation meteorology.

Research paper thumbnail of Aircraft route forecasting under adverse weather conditions

Meteorologische Zeitschrift

In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Ai... more In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Airport are used to forecast deviation routes through a field of storms for arriving and departing aircraft. Storms were observed and nowcast by the nowcast system SWIRLS from the Hong Kong Observatory. Storms were considered as no-go zones for aircraft and deviation routes were determined with the DIVSIM software package. Two days (21 and 22 May 2011) with 22 actual flown routes were investigated. Flights were simulated with a nowcast issued at the time an aircraft entered the TMA or departed from the airport. These flights were compared with a posteriori simulations, in which all storm fields were known and circumnavigated. Both types of simulated routes were then compared with the actual flown routes. The qualitative comparison of the various routes revealed generally good agreement. Larger differences were found in more complex situations with many active storms in the TMA. Route differences resulted primarily from air traffic control measures imposed such as holdings, slowdowns and shortcuts, causing the largest differences between the estimated and actual landing time. Route differences could be enhanced as aircraft might be forced to circumnavigate a storm ahead in a different sense. The use of route forecasts to assist controllers coordinating flights in a complex moving storm field is discussed. The study emphasises the important application of storm nowcasts in aviation meteorology.

Research paper thumbnail of Method for determining the size of airborne water droplets

Research paper thumbnail of Wolken, Klima und Umwelt

Physik in unserer Zeit, 1991

ABSTRACT Die Welt ist so groß und breit, Der Himmel auch so hehr und weit, Ich muß das alles mit ... more ABSTRACT Die Welt ist so groß und breit, Der Himmel auch so hehr und weit, Ich muß das alles mit Augen fassen, Will sich aber nicht recht denken lassen.Dich im Unendlichen zu finden, Mußt unterscheiden und dann verbinden; Drum danket mein beflügelt Lied Dem Manne der Wolken unterschied.

Research paper thumbnail of The Provision of In-Flight Icing Information in the Cockpit - The Flysafe Concept

SAE Technical Paper Series, 2007

... Background ACARE (Advisory Council for Aeronautics Research in Europe) Vision 2020ACARE'... more ... Background ACARE (Advisory Council for Aeronautics Research in Europe) Vision 2020ACARE's Safety Challenge: ““The ambition of Vision 2020 is that increased traffic (tripling in 20 years) will not be accompanied by increased accidents.” ...

Research paper thumbnail of Three-dimensional numerical experiments on convectively forced internal gravity waves

Quarterly Journal of the Royal Meteorological Society, 1989

Results are presented of thermally forced dry and moist convection and the associated gravity wav... more Results are presented of thermally forced dry and moist convection and the associated gravity wave fields from three-dimensional numerical simulations using a non-hydrostatic anelastic model. This paper extends earlier two-dimensional simulations to include effects of the third spatial dimension employing a very similar environmental speed-shear case for the study. The present simulations produce scattered fair weather cumuli in agreement with observations. In many important respects, the physical response is quite similar to that obtained in the earlier two-dimensional calculations. The near-uniform surface sensible heat flux results in Rayleigh modes filling the convective boundary layer (CBL) to begin with, whereas later, after convective motions start interacting with the overlying stable layer, larger horizontal scale deep modes become evident and in some cases dominant. The eigenfunction structure of these dominant forced normal modes consists of boundary layer eddies in the lower levels and gravity waves above. They are important organizers of the cumulus convection. As in the earlier two-dimensional simulations, the efficiency of gravity wave excitation was found to be very sensitive to the mean wind shear in the region spanning the CBL and the overlying stable layer. The dominant horizontal wavelength in the shear direction ranges between 10 and 15 km in the free atmosphere whereas it peaks at about 6 km in the CBL.

Research paper thumbnail of Aircraft Observation of Convection Waves over Southern Germany—A Case Study

Monthly Weather Review, 1993

Research paper thumbnail of Aircraft icing research flights in embedded convection

Meteorology and Atmospheric Physics, 2006

Results from in-cloud measurements with an instrumented aircraft from an icing research campaign ... more Results from in-cloud measurements with an instrumented aircraft from an icing research campaign in Southern Germany in March 1997 are presented. Measurements with conventional optical cloud probes and of the ice accretion on a cylinder exposed to the flow show the existence of supercooled large drops (SLD) in the size range up to 300 µm simultaneously with severe icing with ice-accretion rates of up to 3.5 mm min-1. Nearly all periods with icing, including the ones with severe icing, occurred in mixed-phase convective cells embedded in surrounding stratus clouds. The spatial scales of SLD occurrence, respectively severe icing, ranged between several hundred meters and some kilometers and correspond to the length of the transects through the embedded cells. SLD formed through the coalescence process and were found through the whole cloud depth pointing to a source region near cloud top, in line with the arguments of Rauber and Tokay (1991). No indication of ice-multiplication by the Hallet-Mossop process was found, despite of the favorable temperatures for that process. Comparisons of the measured amount of accreted ice with the observed cloud-particle size distributions quite surprisingly indicate that ice accretion is mostly caused by 10-30 µm sized drops rather than by SLD. The latter, therefore, appear to be a by-product of a hypothesized liquid water accumulation zone near cloud top which is also the primary cause of the observed severe ice accretion. The results confirm the importance of embedded convection and of mixed phase clouds with high amounts of liquid water and simultaneously occurring SLD.

Research paper thumbnail of Aircraft observation of a small-scale solitary wave near the tropopause

Contributions to Atmospheric Physics in Honor of Dr Manfred Reinhardt on His 65th Birthday, Sep 1, 1991

Aircraft observations at 10,100 m height provide evidence for a small scale solitary wave with 13... more Aircraft observations at 10,100 m height provide evidence for a small scale solitary wave with 130 m half amplitude width. The instant snapshot taken with the aircraft is consistent with what is known from solitary waves. The measurements are discussed and the structures of the solitary wave are analyzed.

Research paper thumbnail of Inversion and shear layer detection using AMDAR and wind profiler soundings

The terminal area of Frankfurt airport (EDDF) offers as unique opportunity to campare vertical so... more The terminal area of Frankfurt airport (EDDF) offers as unique opportunity to campare vertical soundings of the planetary boundary layer (PBL) by two independent sources. One of these sources is a wind and temperature radar profiler (WTR/RASS) located at the western end of the main pair of runways. This wind temperature radar (WTR) is a Scintec "AP1000" radar wind profiler with RASS (radioacoustic sounding system) extension "WT RASS". The WTR/RASS at Frankfurt is the first wind profiler for operational purposes, which uses RASS also for wind measurements. The second source are AMDAR (aircraft meteorological data relay) data collected by commercial passenger aircraft. They contain at least time, position, temperature, wind speed and direction. German weather service (Deutscher Wetterdienst, DWD) collects hourly profiles at the Central European airports. Since Frankfurt is not completely closed at night, this setup leads to a roughly continuous coverage with hourly vertical profiles. Together, both offer a rare opportunity to compare the ability of both systems to identify inversion and wind-shear layers in the terminal area. To asses the degree of consent between layers detected by both systems, we use probability of detection (POD). The mutual inversion POD is in the range 40 to 60%, except at night below 250 m. With the weak shear criteria used to gain sufficient statistics, consenting shear detection is limited to low-level jets and similar structures. Only the lower edges of detected layers agree well. The vertical extent and top heights of layers detected are frequently underestimated by WTR/RASS in general. AMDAR data seem to be more suitable for the detection of elevated inversions (and probably shear layers). In Contrast, WTR/RASS data are more suitable for detecting low and shallow as well as short-lived structures. In turn, data fusion of both systems seems to be advantageous for monitoring of hazardous atmospheric structures in the terminal area.

Research paper thumbnail of A study of thunderstorm-induced delays at Frankfurt Airport, Germany

Meteorological Applications, 2003

Research paper thumbnail of The life cycle of convective‐shower cells under post‐frontal conditions

Quarterly Journal of the Royal Meteorological Society, 2008

Seventeen days with post-frontal shower precipitation are analysed by means of radar data obtaine... more Seventeen days with post-frontal shower precipitation are analysed by means of radar data obtained from the German Weather Service's C-band radar network. The life cycle of clusters -defined here as contiguous rain areas including one or more radar-reflectivity peaks (i.e. convection cells) -is investigated. To allow for the continuous tracking of clusters, sometimes over a time period of more than an hour, a new, specially adapted tracking algorithm has been developed. The life cycle of convective clusters comprises five different stages: genesis; growth (including merging); stagnation; decay (including splitting); and dissolving. The transition likelihoods from a cluster with n maxima to one with m maxima are determined (the case m > n corresponding to growth and m < n to decay). It is found that, predominantly, clusters grow or decay by one cell. Results relating to the temporal evolution of post-frontal showers are presented, and a conceptual growth model is proposed. Although single cells are the most frequent cluster type, the spatial structure of the post-frontal precipitation field is dominated by multi-celled clusters. Their life cycle is essentially affected by cell merging and splitting. Although the transitions of all (about one million) identified clusters have been analysed and quantified, more research is necessary in order to understand the underlying principles of cluster growth.

Research paper thumbnail of Convective Waves and Cumulus Growth

Technical Soaring, 1988

Numerical simulations and aircraft measurements show that thermal waves are gravity waves develop... more Numerical simulations and aircraft measurements show that thermal waves are gravity waves developing under the presence of shear in the stable troposphere above a heated boundary layer. The waves are launched when thermals rise from the ground and impinge into the stable layer where they act as obstacles to the mean flow, thus forcing the air to flow over them. This paper reviews some basic aspects of thermal waves based on the papers of Clark, Hauf and Kuettner, Clark and Hauf, and Kuettner, Hildebrand and Clark.

Research paper thumbnail of The In-flight icing warning system ADWICE for European airspace – Current structure, recent improvements and verification results

Meteorologische Zeitschrift, 2017

The Advanced Diagnosis and Warning System for Aircraft Icing Environments (ADWICE) has been in de... more The Advanced Diagnosis and Warning System for Aircraft Icing Environments (ADWICE) has been in development since 1998 in a collaboration between the German Aerospace Centre (DLR), Deutscher Wetterdienst (German Weather Service, DWD) and the Institute of Meteorology and Climatology of the Leibniz Universität Hannover (IMuK). ADWICE identifies atmospheric regions containing supercooled liquid water where aircraft icing can occur. Running operationally at DWD since 2002, ADWICE is used at the German Advisory Centres for Aviation (Luftfahrtberatungszentrale) to support pilots in route planning by warning of hazardous in-flight icing conditions. The model domain covers Europe and the Mediterranean coast of North Africa with a horizontal grid spacing of about 7 km and 30 vertical hybrid levels. The warning system consists of two algorithms. Based on output data of the operational numerical weather prediction model COSMO-EU (Consortium of Small-Scale Modelling-Europe), the Prognostic Icing Algorithm (PIA) allows the forecast of areas with an icing hazard. The Diagnostic Icing Algorithm (DIA) realises a fusion of forecast, observational and remote sensing data such as satellite data to describe the current icing hazard. Both algorithms create a three-dimensional icing product containing information about the likely icing scenario and its associated icing intensity. This paper describes the current structure of ADWICE, its output, as well as its diagnosis and forecast skill. For verification, the output of the two algorithms was compared with pilot observations over Europe. The results show satisfactory values for the probability of detection and the volume efficiency.

Research paper thumbnail of Aviation and Weather - a New Initiative in Germany

Research paper thumbnail of Case Study of Adverse Weather Avoidance Modelling

Adverse weather conditions like thunderstorms cause about 50 % of all aircraft delays. Avoiding t... more Adverse weather conditions like thunderstorms cause about 50 % of all aircraft delays. Avoiding the hazards generally results in additional workload for air traffic controllers. The project MET4ATM deals with a case study for the 17 July 2010, when several flights in the Austrian and the Czech airspace had to be diverted due to several thunderstorms. One aim of MET4ATM is to estimate the benefit of ground-based weather information for ATM in such a case with regard to sector occupancies. This paper deals with an application of the weather avoidance model DIVMET coupled to the air traffic model NAVSIM. Aircraft are simulated based on the flight plan route and diverted around the storms keeping a safety margin. The analysis of the simulated trajectories compared with actually flown routes provides promising results in terms of optimized trajectories.

Research paper thumbnail of Universal Functions for Post-Frontal Showers-Geometrical Characteristics and Rain Rate Development

The study deals with the well-known convective cloud and precipitation patterns in the rear of co... more The study deals with the well-known convective cloud and precipitation patterns in the rear of cold-fronts passing Central Europe, typically in south-easterly directions. The structure and temporal development of those postfrontal shower fields were analysed aiming for a quantitative analytical description of that precipitation field as displayed in Figure 1. In this paper, we present a summary of ongoing work, comprising analyses of the geometrical structure and investigations on the temporal development of individual rain areas. The geometrical structure was analysed following the procedure of THEUSNER (2007) (in the following referred to as THEU) and MESNARD AND SAUVAGEOT (2003) (in the following referred to as MESN). We refined those studies by using a higher resolution radar product to calculate the diurnal cycle of the whole precipitation area and evaluate the individual rain areas within the precipitation field, e.g. with respect to area size. In addition, the temporal develo...

Research paper thumbnail of Universal Functions for Post-Frontal Showers-Geometrical Characteristics and Rain Rate Development

The study deals with the well-known convective cloud and precipitation patterns in the rear of co... more The study deals with the well-known convective cloud and precipitation patterns in the rear of cold-fronts passing Central Europe, typically in south-easterly directions. The structure and temporal development of those postfrontal shower fields were analysed aiming for a quantitative analytical description of that precipitation field as displayed in Figure 1. In this paper, we present a summary of ongoing work, comprising analyses of the geometrical structure and investigations on the temporal development of individual rain areas. The geometrical structure was analysed following the procedure of THEUSNER (2007) (in the following referred to as THEU) and MESNARD AND SAUVAGEOT (2003) (in the following referred to as MESN). We refined those studies by using a higher resolution radar product to calculate the diurnal cycle of the whole precipitation area and evaluate the individual rain areas within the precipitation field, e.g. with respect to area size. In addition, the temporal develo...

Research paper thumbnail of Uncertainty Analysis of Thunderstorm Nowcasts for Utilization in Aircraft Routing

Weather related uncertainty is a major disturbing factor in accurate aviation route planning. Adv... more Weather related uncertainty is a major disturbing factor in accurate aviation route planning. Adverse weather itself impacts the planning process but that might be mitigated if weather forecasts or nowcasts are used. Knowing that no forecast is perfect, the forecast for a certain time will always differ from the real weather at that time. Assuming that the forecast represents the best knowledge about the future development, deviations from it can be interpreted as the current inherent uncertainty of the forecast. We focus on thunderstorm nowcasts for the next hour using the DLR Rad-TRAM nowcast system. We analyse the nowcast error, respectively the increasing uncertainty with nowcast time by determining the spatial deviations of nowcast and observed thunderstorm extension. An intuitively expected increase of uncertainty with nowcast time is confirmed and quantified by the study results. A potential application of the uncertainty will be presented.

Research paper thumbnail of Adverse weather diversion model DIVMET

Journal of Aerospace Operations

Research paper thumbnail of Aircraft route forecasting under adverse weather conditions

Meteorologische Zeitschrift

In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Ai... more In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Airport are used to forecast deviation routes through a field of storms for arriving and departing aircraft. Storms were observed and nowcast by the nowcast system SWIRLS from the Hong Kong Observatory. Storms were considered as no-go zones for aircraft and deviation routes were determined with the DIVSIM software package. Two days (21 and 22 May 2011) with 22 actual flown routes were investigated. Flights were simulated with a nowcast issued at the time an aircraft entered the TMA or departed from the airport. These flights were compared with a posteriori simulations, in which all storm fields were known and circumnavigated. Both types of simulated routes were then compared with the actual flown routes. The qualitative comparison of the various routes revealed generally good agreement. Larger differences were found in more complex situations with many active storms in the TMA. Route differences resulted primarily from air traffic control measures imposed such as holdings, slowdowns and shortcuts, causing the largest differences between the estimated and actual landing time. Route differences could be enhanced as aircraft might be forced to circumnavigate a storm ahead in a different sense. The use of route forecasts to assist controllers coordinating flights in a complex moving storm field is discussed. The study emphasises the important application of storm nowcasts in aviation meteorology.

Research paper thumbnail of Aircraft route forecasting under adverse weather conditions

Meteorologische Zeitschrift

In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Ai... more In this paper storm nowcasts in the terminal manoeuvring area (TMA) of Hong Kong International Airport are used to forecast deviation routes through a field of storms for arriving and departing aircraft. Storms were observed and nowcast by the nowcast system SWIRLS from the Hong Kong Observatory. Storms were considered as no-go zones for aircraft and deviation routes were determined with the DIVSIM software package. Two days (21 and 22 May 2011) with 22 actual flown routes were investigated. Flights were simulated with a nowcast issued at the time an aircraft entered the TMA or departed from the airport. These flights were compared with a posteriori simulations, in which all storm fields were known and circumnavigated. Both types of simulated routes were then compared with the actual flown routes. The qualitative comparison of the various routes revealed generally good agreement. Larger differences were found in more complex situations with many active storms in the TMA. Route differences resulted primarily from air traffic control measures imposed such as holdings, slowdowns and shortcuts, causing the largest differences between the estimated and actual landing time. Route differences could be enhanced as aircraft might be forced to circumnavigate a storm ahead in a different sense. The use of route forecasts to assist controllers coordinating flights in a complex moving storm field is discussed. The study emphasises the important application of storm nowcasts in aviation meteorology.

Research paper thumbnail of Method for determining the size of airborne water droplets

Research paper thumbnail of Wolken, Klima und Umwelt

Physik in unserer Zeit, 1991

ABSTRACT Die Welt ist so groß und breit, Der Himmel auch so hehr und weit, Ich muß das alles mit ... more ABSTRACT Die Welt ist so groß und breit, Der Himmel auch so hehr und weit, Ich muß das alles mit Augen fassen, Will sich aber nicht recht denken lassen.Dich im Unendlichen zu finden, Mußt unterscheiden und dann verbinden; Drum danket mein beflügelt Lied Dem Manne der Wolken unterschied.

Research paper thumbnail of The Provision of In-Flight Icing Information in the Cockpit - The Flysafe Concept

SAE Technical Paper Series, 2007

... Background ACARE (Advisory Council for Aeronautics Research in Europe) Vision 2020ACARE'... more ... Background ACARE (Advisory Council for Aeronautics Research in Europe) Vision 2020ACARE's Safety Challenge: ““The ambition of Vision 2020 is that increased traffic (tripling in 20 years) will not be accompanied by increased accidents.” ...

Research paper thumbnail of Three-dimensional numerical experiments on convectively forced internal gravity waves

Quarterly Journal of the Royal Meteorological Society, 1989

Results are presented of thermally forced dry and moist convection and the associated gravity wav... more Results are presented of thermally forced dry and moist convection and the associated gravity wave fields from three-dimensional numerical simulations using a non-hydrostatic anelastic model. This paper extends earlier two-dimensional simulations to include effects of the third spatial dimension employing a very similar environmental speed-shear case for the study. The present simulations produce scattered fair weather cumuli in agreement with observations. In many important respects, the physical response is quite similar to that obtained in the earlier two-dimensional calculations. The near-uniform surface sensible heat flux results in Rayleigh modes filling the convective boundary layer (CBL) to begin with, whereas later, after convective motions start interacting with the overlying stable layer, larger horizontal scale deep modes become evident and in some cases dominant. The eigenfunction structure of these dominant forced normal modes consists of boundary layer eddies in the lower levels and gravity waves above. They are important organizers of the cumulus convection. As in the earlier two-dimensional simulations, the efficiency of gravity wave excitation was found to be very sensitive to the mean wind shear in the region spanning the CBL and the overlying stable layer. The dominant horizontal wavelength in the shear direction ranges between 10 and 15 km in the free atmosphere whereas it peaks at about 6 km in the CBL.

Research paper thumbnail of Aircraft Observation of Convection Waves over Southern Germany—A Case Study

Monthly Weather Review, 1993

Research paper thumbnail of Aircraft icing research flights in embedded convection

Meteorology and Atmospheric Physics, 2006

Results from in-cloud measurements with an instrumented aircraft from an icing research campaign ... more Results from in-cloud measurements with an instrumented aircraft from an icing research campaign in Southern Germany in March 1997 are presented. Measurements with conventional optical cloud probes and of the ice accretion on a cylinder exposed to the flow show the existence of supercooled large drops (SLD) in the size range up to 300 µm simultaneously with severe icing with ice-accretion rates of up to 3.5 mm min-1. Nearly all periods with icing, including the ones with severe icing, occurred in mixed-phase convective cells embedded in surrounding stratus clouds. The spatial scales of SLD occurrence, respectively severe icing, ranged between several hundred meters and some kilometers and correspond to the length of the transects through the embedded cells. SLD formed through the coalescence process and were found through the whole cloud depth pointing to a source region near cloud top, in line with the arguments of Rauber and Tokay (1991). No indication of ice-multiplication by the Hallet-Mossop process was found, despite of the favorable temperatures for that process. Comparisons of the measured amount of accreted ice with the observed cloud-particle size distributions quite surprisingly indicate that ice accretion is mostly caused by 10-30 µm sized drops rather than by SLD. The latter, therefore, appear to be a by-product of a hypothesized liquid water accumulation zone near cloud top which is also the primary cause of the observed severe ice accretion. The results confirm the importance of embedded convection and of mixed phase clouds with high amounts of liquid water and simultaneously occurring SLD.

Research paper thumbnail of Aircraft observation of a small-scale solitary wave near the tropopause

Contributions to Atmospheric Physics in Honor of Dr Manfred Reinhardt on His 65th Birthday, Sep 1, 1991

Aircraft observations at 10,100 m height provide evidence for a small scale solitary wave with 13... more Aircraft observations at 10,100 m height provide evidence for a small scale solitary wave with 130 m half amplitude width. The instant snapshot taken with the aircraft is consistent with what is known from solitary waves. The measurements are discussed and the structures of the solitary wave are analyzed.

Research paper thumbnail of Inversion and shear layer detection using AMDAR and wind profiler soundings

The terminal area of Frankfurt airport (EDDF) offers as unique opportunity to campare vertical so... more The terminal area of Frankfurt airport (EDDF) offers as unique opportunity to campare vertical soundings of the planetary boundary layer (PBL) by two independent sources. One of these sources is a wind and temperature radar profiler (WTR/RASS) located at the western end of the main pair of runways. This wind temperature radar (WTR) is a Scintec "AP1000" radar wind profiler with RASS (radioacoustic sounding system) extension "WT RASS". The WTR/RASS at Frankfurt is the first wind profiler for operational purposes, which uses RASS also for wind measurements. The second source are AMDAR (aircraft meteorological data relay) data collected by commercial passenger aircraft. They contain at least time, position, temperature, wind speed and direction. German weather service (Deutscher Wetterdienst, DWD) collects hourly profiles at the Central European airports. Since Frankfurt is not completely closed at night, this setup leads to a roughly continuous coverage with hourly vertical profiles. Together, both offer a rare opportunity to compare the ability of both systems to identify inversion and wind-shear layers in the terminal area. To asses the degree of consent between layers detected by both systems, we use probability of detection (POD). The mutual inversion POD is in the range 40 to 60%, except at night below 250 m. With the weak shear criteria used to gain sufficient statistics, consenting shear detection is limited to low-level jets and similar structures. Only the lower edges of detected layers agree well. The vertical extent and top heights of layers detected are frequently underestimated by WTR/RASS in general. AMDAR data seem to be more suitable for the detection of elevated inversions (and probably shear layers). In Contrast, WTR/RASS data are more suitable for detecting low and shallow as well as short-lived structures. In turn, data fusion of both systems seems to be advantageous for monitoring of hazardous atmospheric structures in the terminal area.

Research paper thumbnail of A study of thunderstorm-induced delays at Frankfurt Airport, Germany

Meteorological Applications, 2003

Research paper thumbnail of The life cycle of convective‐shower cells under post‐frontal conditions

Quarterly Journal of the Royal Meteorological Society, 2008

Seventeen days with post-frontal shower precipitation are analysed by means of radar data obtaine... more Seventeen days with post-frontal shower precipitation are analysed by means of radar data obtained from the German Weather Service's C-band radar network. The life cycle of clusters -defined here as contiguous rain areas including one or more radar-reflectivity peaks (i.e. convection cells) -is investigated. To allow for the continuous tracking of clusters, sometimes over a time period of more than an hour, a new, specially adapted tracking algorithm has been developed. The life cycle of convective clusters comprises five different stages: genesis; growth (including merging); stagnation; decay (including splitting); and dissolving. The transition likelihoods from a cluster with n maxima to one with m maxima are determined (the case m > n corresponding to growth and m < n to decay). It is found that, predominantly, clusters grow or decay by one cell. Results relating to the temporal evolution of post-frontal showers are presented, and a conceptual growth model is proposed. Although single cells are the most frequent cluster type, the spatial structure of the post-frontal precipitation field is dominated by multi-celled clusters. Their life cycle is essentially affected by cell merging and splitting. Although the transitions of all (about one million) identified clusters have been analysed and quantified, more research is necessary in order to understand the underlying principles of cluster growth.