Final Report Summary - CONSYDER (CONvective SYstems DEtection and analysis using Radio occultations)
The general objective of this project was to use Global Positioning System (GPS) Radio Occultation (RO) observations validated with independent measurements, to detect convective systems and to determine and analyse their structure in tropical and extra-tropical areas.. In particular the aims were: (1) to get a good understanding of the role of convection in climate change and in determining the thermal structure and composition of the Upper Troposphere Lower Stratosphere (UTLS), both in the tropics and in the extra-tropics, (2) to link the GPS RO signal to the intensity of the storm, (3) to characterize the deep convective cloud top and (4) to assess the capabilities of GPS RO in other extreme cases such as overshooting or volcanic eruptions. We used GPS RO observations together with in situ and remote sensing measurements in order to define a solid algorithm for detecting the storm cloud top and the storm thermal structure with high accuracy. The algorithm is based on the so-called bending angle anomaly technique exploiting the information of bending angle anomalies near cloud tops with respect to the bending angle climatology. High quality GPS RO records of Wegener Center (WEGC) Global Climate Observing System (GCOS) essential climate variables of the atmosphere (such as temperature and water vapour, geopotential height of pressure levels, refractivity and bending angle) have been used for the analysis providing a strong background for our studies.
The availability of GPS RO profiles allows getting information regarding the same storm at different stages and this is really useful to link the bending angle signal to the intensity of the convection. Using this new technique we are able to monitor the convective systems (tropical cyclones or thunderstorms) and to follow their development providing fundamental information for modelling and forecasting these processes. The bending angle and the temperature profiles at different stages of the storm also allow understanding the microphysics of the clouds and their impact on the climate. The bending angle anomaly technique developed during the project can be applied to different fields since the determination of cloud tops is not dependent on the cause of the perturbation, but it depends on the variation of the actual bending angle with respect to the climatology. In this way we are able to detect overshootings contributing to the troposphere-stratosphere transport, and to detect for example the cloud top of volcanic clouds. It is evident the interdisciplinarity of the project, different fields of Earth sciences are interested like remote sensing, climate, and meteorology and this project will contribute to the development of all of them.
We have established a standard atmosphere based on GPS RO profiles including refractivity, pressure, temperature and water vapour, from the Earth´s surface to 80 km of altitude. We have created a monthly-mean reference atmosphere based on multi-annual RO observations in the period 2001-2012 from multi-satellites. Climatologies based on RO observations from single satellites only were also computed. With the GPS RO standard atmosphere we can now provide 3D maps of refractivity, pressure, temperature, and water vapour together with uncertainty information such as frequency of measurements at each location and altitude level, the standard deviation.
We have mainly worked in two different macro-areas: Tropical Cyclones (TCs) characterization and Volcanic Clouds (VCs) characterization. The TC best tracks were collected together with other co-located satellite data and ground based data from the ARM Convective Radio Occultation Campaign (CROC). With this project we have clearly demonstrated that the GPS RO technique is very well suited for monitoring and understanding the TCs thermal structure and its contribution to the atmospheric circulation through possible overshootings into the stratosphere, and for monitoring the VCs and understanding their impact on climate variability.
The thermal structure of TCs in different ocean basins and the conditions for possible overshooting of cloud tops into the stratosphere, were investigated based on GPS RO measurements. The results indicate that the effects of TCs on the UTLS should be studied in connection to the ocean basin where they develop, since their thermal structure is clearly connected to the basin. In particular, basins in the northern and southern hemisphere show a different thermal structure: In the southern hemisphere, storms reach higher altitudes and the cloud top is colder than in the northern hemisphere. The temperature anomaly above the cloud top becomes positive over northern hemisphere ocean basins while it stays negative up to about 25 km of altitude over the southern hemisphere ocean basins. The reason of this warming above the storm cloud top in the northern hemisphere is not clear yet and is a topic of further investigations.
A double tropopause characterizes a storm, which is evident in all the ocean basins for all storm intensities and can be definitely defined as a feature reflecting the high-altitude convection dynamics. Comparisons between the monthly mean tropopause altitude and the storm cloud top altitude indicate a significant fraction of possible overshootings. Results show that the possible overshootings will overpass the climatological tropopause more deeply at extra-tropical latitudes, where the tropopause is lower, but there is no clear tendency connected to specific basins. While the co-locations between GPS ROs and TC tracks for all the intensities are well distributed in all the ocean basins, conditions for overshooting occur more frequently in the southern hemisphere and over the North Indian ocean basin. However, the number of possible overshootings for high intensities (i.e. TC categories 1 to 5) is higher over the West Pacific ocean basin. In this area, conditions for overshooting are found for a percentage of 30% to 50% of the cyclones, especially within tropical latitudes.
Cloud structure and cloud top height are key parameters also for the monitoring of VC movement and for characterizing eruptive processes and understanding the impact on short-term climate variability. We demonstrated that the anomaly technique developed for detecting cloud tops of convective systems and TCs can also be used for detecting and monitoring VC tops. Volcanic ash clouds and SO2 clouds have a different impact on the atmospheric thermal structure. Our results revealed a cooling of about 2.5 K near the cloud top for ash clouds, confirming previous findings. In contrast, we found a clear warming signature from SO2 (and hydrated sulfate) clouds after the eruption of Nabro, with mean amplitudes of about 4 K to 6 K just after the eruption and persisting for a few months. From this encouraging evidence we conclude that, due to their independence from weather conditions and due to their high vertical resolution, RO observations can valuably contribute to improve detection and monitoring of VCs and to support warning systems. The high accuracy and vertical resolution of RO observations for detecting the tropopause with global coverage will also help to understand whether eruptions overshoot into the stratosphere and contribute to short-term climate variability.
Several new RO missions are planned for the near future, like the COSMIC-2 constellation and further RO receivers in the European MetOp and Chinese FY3 meteorological satellite series. These, together with a much higher number of GNSS signals from the U.S. GPS, the Russian Globalnaya navigatsionnaya sputnikovaya sistema (GLONASS), the European Galileo system, and the Chinese Bei-Dou system will provide RO profiles with unprecedented coverage in space and time for monitoring the thermal structure impacts of volcanic eruptions and their cloud dispersions at any stage.
The results of this project will be relevant for:
- forecasters, helping them to improve the models for understanding the TCs and VCs development
- climatologists, contributing to understand the contribution of TCs and VCs to the tropospheric and stratospheric thermal variability
- volcanologists, having a new tool for detecting and monitoring the volcanic clouds and for analysing the impact of the eruptions on the climate variability
- space agencies, having new input to understand the capabilities of GPS ROs
- teachers, having a reference survey and tools for explaining the geosciences to the school students
http://www.biondiriccardo.it/CONSYDER/indexconsyder.htm
Riccardo@biondiriccardo.it
The availability of GPS RO profiles allows getting information regarding the same storm at different stages and this is really useful to link the bending angle signal to the intensity of the convection. Using this new technique we are able to monitor the convective systems (tropical cyclones or thunderstorms) and to follow their development providing fundamental information for modelling and forecasting these processes. The bending angle and the temperature profiles at different stages of the storm also allow understanding the microphysics of the clouds and their impact on the climate. The bending angle anomaly technique developed during the project can be applied to different fields since the determination of cloud tops is not dependent on the cause of the perturbation, but it depends on the variation of the actual bending angle with respect to the climatology. In this way we are able to detect overshootings contributing to the troposphere-stratosphere transport, and to detect for example the cloud top of volcanic clouds. It is evident the interdisciplinarity of the project, different fields of Earth sciences are interested like remote sensing, climate, and meteorology and this project will contribute to the development of all of them.
We have established a standard atmosphere based on GPS RO profiles including refractivity, pressure, temperature and water vapour, from the Earth´s surface to 80 km of altitude. We have created a monthly-mean reference atmosphere based on multi-annual RO observations in the period 2001-2012 from multi-satellites. Climatologies based on RO observations from single satellites only were also computed. With the GPS RO standard atmosphere we can now provide 3D maps of refractivity, pressure, temperature, and water vapour together with uncertainty information such as frequency of measurements at each location and altitude level, the standard deviation.
We have mainly worked in two different macro-areas: Tropical Cyclones (TCs) characterization and Volcanic Clouds (VCs) characterization. The TC best tracks were collected together with other co-located satellite data and ground based data from the ARM Convective Radio Occultation Campaign (CROC). With this project we have clearly demonstrated that the GPS RO technique is very well suited for monitoring and understanding the TCs thermal structure and its contribution to the atmospheric circulation through possible overshootings into the stratosphere, and for monitoring the VCs and understanding their impact on climate variability.
The thermal structure of TCs in different ocean basins and the conditions for possible overshooting of cloud tops into the stratosphere, were investigated based on GPS RO measurements. The results indicate that the effects of TCs on the UTLS should be studied in connection to the ocean basin where they develop, since their thermal structure is clearly connected to the basin. In particular, basins in the northern and southern hemisphere show a different thermal structure: In the southern hemisphere, storms reach higher altitudes and the cloud top is colder than in the northern hemisphere. The temperature anomaly above the cloud top becomes positive over northern hemisphere ocean basins while it stays negative up to about 25 km of altitude over the southern hemisphere ocean basins. The reason of this warming above the storm cloud top in the northern hemisphere is not clear yet and is a topic of further investigations.
A double tropopause characterizes a storm, which is evident in all the ocean basins for all storm intensities and can be definitely defined as a feature reflecting the high-altitude convection dynamics. Comparisons between the monthly mean tropopause altitude and the storm cloud top altitude indicate a significant fraction of possible overshootings. Results show that the possible overshootings will overpass the climatological tropopause more deeply at extra-tropical latitudes, where the tropopause is lower, but there is no clear tendency connected to specific basins. While the co-locations between GPS ROs and TC tracks for all the intensities are well distributed in all the ocean basins, conditions for overshooting occur more frequently in the southern hemisphere and over the North Indian ocean basin. However, the number of possible overshootings for high intensities (i.e. TC categories 1 to 5) is higher over the West Pacific ocean basin. In this area, conditions for overshooting are found for a percentage of 30% to 50% of the cyclones, especially within tropical latitudes.
Cloud structure and cloud top height are key parameters also for the monitoring of VC movement and for characterizing eruptive processes and understanding the impact on short-term climate variability. We demonstrated that the anomaly technique developed for detecting cloud tops of convective systems and TCs can also be used for detecting and monitoring VC tops. Volcanic ash clouds and SO2 clouds have a different impact on the atmospheric thermal structure. Our results revealed a cooling of about 2.5 K near the cloud top for ash clouds, confirming previous findings. In contrast, we found a clear warming signature from SO2 (and hydrated sulfate) clouds after the eruption of Nabro, with mean amplitudes of about 4 K to 6 K just after the eruption and persisting for a few months. From this encouraging evidence we conclude that, due to their independence from weather conditions and due to their high vertical resolution, RO observations can valuably contribute to improve detection and monitoring of VCs and to support warning systems. The high accuracy and vertical resolution of RO observations for detecting the tropopause with global coverage will also help to understand whether eruptions overshoot into the stratosphere and contribute to short-term climate variability.
Several new RO missions are planned for the near future, like the COSMIC-2 constellation and further RO receivers in the European MetOp and Chinese FY3 meteorological satellite series. These, together with a much higher number of GNSS signals from the U.S. GPS, the Russian Globalnaya navigatsionnaya sputnikovaya sistema (GLONASS), the European Galileo system, and the Chinese Bei-Dou system will provide RO profiles with unprecedented coverage in space and time for monitoring the thermal structure impacts of volcanic eruptions and their cloud dispersions at any stage.
The results of this project will be relevant for:
- forecasters, helping them to improve the models for understanding the TCs and VCs development
- climatologists, contributing to understand the contribution of TCs and VCs to the tropospheric and stratospheric thermal variability
- volcanologists, having a new tool for detecting and monitoring the volcanic clouds and for analysing the impact of the eruptions on the climate variability
- space agencies, having new input to understand the capabilities of GPS ROs
- teachers, having a reference survey and tools for explaining the geosciences to the school students
http://www.biondiriccardo.it/CONSYDER/indexconsyder.htm
Riccardo@biondiriccardo.it