Characterization of Gravity Waves in the Lee of the Southern Andes - My time as a PhD student
- robertreichert
- 23. Aug. 2023
- 8 Min. Lesezeit
Aktualisiert: 16. Sept.
2016
I am studying for a Master's degree in Physics at the Ludwig-Maximilians-University (LMU) in Munich and this semester I am persuaded by my fellow student Felix Gödde to attend a Meteorology lecture, specifically the lecture by Prof. Markus Rapp on the "middle atmosphere". In this course, I come into contact with the theory and observation of atmospheric gravity waves (GW) for the first time. Prof. Rapp mentions that they have just returned from a scientific campaign (GW-LCYCLE-II) in Finland and need someone to help with the analysis of lidar data. Since I am looking for a Master's thesis topic at the end of the semester (and unfortunately have not found one in the field of plasma physics), I decide to do my Master's thesis with him at the Institute of Atmospheric Physics at the German Aerospace Center (DLR) in Oberpfaffenhofen. It is not an easy decision since I still live in Rosenheim at that time, and it takes me 4 hours a day to commute to DLR. During my Master's thesis, I get to know the programming language IDL and delve into the data analysis of temperature measurements from CORAL and the AMTM. Both instruments measured mesospheric temperatures over Sodankylä during GW-LCYCLE-II, with CORAL capturing the temperature structure vertically and the AMTM horizontally. Specifically, I try, among other things, to determine with the help of wavelet analysis whether both instruments detected the same GWs. The title of my thesis is: "Detection of propagating and stationary GWs in the middle atmosphere in lidar and airglow measurements."
2017
Since I enjoy data analysis very much, I decide to pursue a PhD in the field of atmospheric physics. Fortunately, there are still financial resources available from the DFG project "Multi-Scale Dynamics of Gravity Waves" (MS-GWaves), and Prof. Rapp will be my doctoral advisor, with Dr. Bernd Kaifler as my technical supervisor. At the beginning of my PhD, I travel with Bernd to Tierra del Fuego, at the southern tip of the South American continent, to install CORAL in Río Grande and conduct temperature measurements in the middle atmosphere. I have never been so far away, and it is a small adventure since both Bernd and I speak very little Spanish. Fortunately, Jose Luis Hormaechea speaks very good English. He is the operator of the Estación Astronómica Río Grande (EARG), an old observatory on the outskirts of Río Grande, just a 5-minute walk from the airport. At that time, in late November, we are also accompanied by Dominique Pautet, the PI of the AMTM, as the instrument is installed in the same container as CORAL. As in Sodankylä, both instruments will jointly detect GWs in the mesosphere. I also get to know Alejandro de la Torre and Jacobo Salvador. Both are atmospheric physicists from the University of Buenos Aires and operate an ozone lidar in Rio Gallegos, a few hundred kilometers further north.
From left to right: Alejandro de la Torre, Jose Luis Hormaechea, Dominique Pautet, Jacobo Salvador, Bernd Kaifler, and myself in front of the CORAL container.
Business Trips / Campaigns / Conferences / Workshops:
CORAL installation, Río Grande, Argentina
2018
The observation and characterization of GWs in the mesosphere is anything but trivial. Until now, only the combination of observations from various instruments allows for the precise determination of the wave field at around 87 km altitude. As previously mentioned, CORAL and the AMTM measured temperatures vertically and horizontally over Sodankylä. Additionally, the Meteor Radar (MR) "SLICE" in Sodankylä provided wind measurements in the mesosphere. To derive mesospheric wave parameters, I develop a methodology that combines the three datasets and present this in my first publication. Still in October this year, I submit my manuscript to the journal AMT (Atmospheric Measurement Techniques).
Besides that, I travel a lot this year. I present parts of my methodology at the MS-GWaves Workshop in March in Kassel, where I meet the German community (including Ulrich Achatz, Franz-Josef Lübken, Gunter Stober, Peter Preusse) for the first time. Two weeks later, I am at the EGU (European Geophysical Union) in Vienna and meet Dave Fritts and Mike Taylor, also two authorities in the field. It quickly becomes clear to me that the community is very friendly. There seems to be little competition. At Dominique's request, I plan a business trip to São José Dos Campos in Brazil to attend the ANGWIN Workshop. Since I am already traveling, Bernd suggests I also stop by CORAL and clean the telescope mirror again. Shortly after, I travel once more to Río Grande to clean the aforementioned telescope mirror. There I meet Diego Janches, a very likable, somewhat eccentric American with Argentine roots who has a shared history with Markus Rapp. Diego operates the MR "SAAMER" in Río Grande and makes important wind measurements in the mesosphere, similar to "SLICE" in Sodankylä. One evening we visit Jose Luis and his wife at their cabin near the Chilean border. We drink mate and take a magical walk through an autumn forest in Tierra del Fuego. We are curiously but shyly observed by guanacos. Shortly after, I travel on to Brazil and participate in the ANGWIN Workshop, which this year is held at the Instituto Nacional de Pesquisas Espaciais (INPE). There I meet Dominique Pautet and Mike Taylor again. The group photo shows all participants of the workshop. Since São José Dos Campos is not far, I decide to take a week's vacation and visit Rio de Janeiro.
Group photo from the ANGWIN workshop in April 2018 at INPE, São José Dos Campos, Brazil.
Since the late 1980s, the Columbia Scientific Balloon Facility (CSBF) has been launching long-duration balloons that can fly at an altitude of 35 km for several weeks. These balloons are considered a kind of low-cost satellite since at this altitude, more than 99% of the atmosphere is below them. In the gondola of such a balloon, Bernd installed a Rayleigh Lidar to observe not only temperatures but also Polar Mesospheric Clouds (PMCs). In parallel, PhDs from Dave Fritts' group have installed high-resolution cameras in the gondola to take high-resolution pictures of PMCs. In July, the time has come, and the CSBF is preparing everything to launch the balloon with its payload from Kiruna in northern Sweden. As the balloon slowly but surely drifts from northern Sweden to Canada, the instruments will take measurements 24 hours a day. Since we need to work in shifts, I also travel to Kiruna to support the campaign on site.
At the beginning of the year, Tiziana Bräuer and I are elected as PhD representatives. In addition to organizing joint activities such as lunches and evening outings to Munich's nightlife, we dedicate ourselves to the task of increasing the salary of PhD students at DLR - successfully! From now on, PhD students receive a recruitment allowance of 15% in addition to the 50% of the TVÖD.
Business Trips / Campaigns / Conferences / Workshops:
CORAL maintenance, Río Grande, Argentina
MS-GWaves workshop, Kassel, Germany, 19.-21. March
European Geophysical Union (EGU) conference, Vienna, Austria, 8.-13- April
Antarctic Gravity Wave Instrument Network (ANGWIN) workshop, São José Dos Campos, Brazil, 24.-26. April
Polar Mesospheric Clouds (PMC)-Turbo campaign, Kiruna, Sweden, July
2019
The Polar Night Jet is a band of wind speeds sometimes exceeding 100 m/s (360 km/h). It is located in the stratosphere and extends over the entire high and mid-latitudes. It results from the temperature gradient that builds up over the winter pole during winter due to the lack of solar radiation. Planetary waves, which are excited in the troposphere, can propagate into the Polar Night Jet and slow it down significantly through momentum deposition, causing it to reverse or leading to a vortex split. This also results in a sudden descent of air masses and thus adiabatic heating. The entire event is also referred to as Sudden Stratospheric Warming (SSW). While such an event occurs regularly once or twice a year in the northern hemisphere, there has only been one observed event in the southern hemisphere, which was in 2002.
In the late southern hemisphere winter, we plan a large-scale measurement campaign called SouthTRAC together with colleagues from KIT (Karlsruhe Institute of Technology) and FZJ (Forschungszentrum Jülich). The aim is to investigate dynamic processes such as the propagation of GWs, as well as mixing processes and chemical components of the atmosphere. Río Grande is selected as the base for our research aircraft HALO. However, since we also intend to fly over Chilean territory, a preliminary diplomatic meeting is held in Santiago de Chile, which I attend on behalf of DLR. There I meet Martin Riese, Björn-Martin Sinnhuber, and Jörn Ungermann.
On August 14, 2019, temperatures below 0°C and a failed heater in the CORAL container led to the freezing of CORAL's laser cooling circuit. Bernd immediately sends a replacement laser to Río Grande, which we plan to install at the beginning of the SouthTRAC campaign so that CORAL can continue detecting GWs in parallel with the campaign. And then the models show a reversal of the 10 hPa zonal wind at 60°S: a SSW! The second ever observed. And CORAL is out of action and cannot measure temperatures. What bad luck! But it's not just bad luck for our CORAL measurements, it's also bad luck for the entire SouthTRAC campaign. Only under suitable propagation conditions can the mountain waves generated by the Andes propagate into the mesosphere, a scenario we are targeting with our instruments.
On September 3, 2019, a few days before HALO arrives in Río Grande, I travel to Río Grande with our DLR electronics technician to replace the defective laser and make CORAL operational again. However, on site, we find out that the laser is still stuck in customs in Buenos Aires. We have to be patient. Meanwhile, the first measurement flights with ALIMA, the airborne lidar system, begin. Unlike CORAL, ALIMA can make "cross sections" through the atmosphere and measure GWs in space. As one measurement flight after another takes place, I am told every day, "The laser will come out of customs tomorrow." "Maybe after the weekend." Only on my last day, just before my departure, can we get the laser out of customs and install it in CORAL. Unfortunately, it was not possible during this campaign to observe GWs simultaneously with CORAL and ALIMA.
However, one great message arrives during my stay in Río Grande: my first paper is accepted for publication!
Business Trips / Campaigns / Conferences / Workshops:
MS-GWaves workshop, Kühlungsborn, Germany, 26.-28. March
AMTM maintenance, Río Grande, Argentina, April
SouthTRAC cooperation workshop, Santiago de Chile, Chile, May
SouthTRAC campaign, Río Grande, Argentina, September
2020
Linear theory suggests that stronger airflow over mountains leads to increased GW potential energy. To explore this relationship, I correlate near-surface wind speeds (taken from the ECMWF reanalysis product ERA5) with the measured potential energy over Río Grande. Since the correlation is always too low, I include more and more parameters, such as wind direction, thermal stability, and even horizontal wind shears. Eventually, I program my own simplified ray tracer to better analyze the conditions under which GWs propagate over Río Grande. In a final step, I turn to colleagues at FZJ to use their ray tracer "GROGRAT" to calculate the paths along which GWs propagate as accurately as possible. Once again, linear theory is confirmed: short-scale (<100 km) waves propagate quickly upwards and originate from orography in the immediate vicinity of Río Grande. Large-scale (>100 km) waves propagate upwards more slowly and can spread more laterally, meaning their region of origin is far away. This makes it possible to observe quasi-stationary mountain waves at a location where the forcing itself is not sufficient to generate waves.
Business Trips / Campaigns / Conferences / Workshops
MS-GWaves workshop, online participation, 23.-27. November
American Geophysical Union (AGU) conference, online participation, December
2021
On 29th of January I submit my second manuscript presenting the temperature measurements which CORAL has obtained in its first 3 years of operation in Río Grande. Now, I have time to focus on my PhD thesis. Conceptually, I start with describing temperature variations on large scales. With large scales I mean temporal variations of one year and half a year which arise due to Earth's rotation around the sun. After that I'm dealing with planetary waves which have periods longer than 2days and vertical scales larger than 50km. Subsequently, I present my results on the extraction of the migrating diurnal tide which is not easy given a night time only data set but with some limitations possible. With this thermal background defined, I investigate GWs.
My second paper "High-Cadence Lidar Observations of Middle Atmospheric Temperature and Gravity Waves at the Southern Andes Hot Spot" gets published in the Journal JGR (Journal of Geophysical Research).
Submission of my PhD thesis in December! There couldn't be a better Christmas present.
2022
Defense of my PhD thesis in March!
From left to right: Andreas Marsing, Bernd Kaifler, Markus Rapp, Andreas Dörnbrack, Franz-Josef Lübken, Lukas Steinbauer, Sebastian Wolff, Olivia Reichert, Ira Reichert, Christopher Geach, Michael Reichert, Robert Reichert, Sarah Fischbacher, Benedikt Urbanek, Eleni Marinou, Benedikt Mailänder, Anna Nickl, Stefanie Knobloch, Isabel Krisch, and Sonja Gisinger.
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