Assimilation of GPS Radio Occultation Profiles in the HARMONIE model.

Radio Occultation (RO) measurements utilising the Global Positioning System (GPS) is an emerging technique which probes the atmosphere horizontally, as opposed to conventional satellites that views the atmosphere from above. GPS RO measurements complement conventional satellite retrievals have proven very valuable for initializing global numerical weather prediction (NWP) models. The assimilation of GPS-RO data in NWP can be done without bias correction as opposed to basically all other assimilated data, and therefore they serve as a unique tool for anchoring the models.

At the DMI we wish to investigate the possible benefits from assimilation of GPS-RO in the non-hydrostatic local area model, HARMONIE. The assimilation algorithm for this purpose has been implemented. We propose a pilot study, to be performed by a master student, which investigates the effect of including GPS-RO in HARMONIE. One problem is the currently sparse spatial coverage of GPS-RO that may dampen the effect of assimilating the data. In meteorology such obstacles are overcome by producing artificial realistic data and investigate the effect of assimilation of such data in the model. On that background it may be possible to assess the feasibility of GPS-RO assimilation in local area models in a future scenario with better RO satellite coverage. 
Johannes K. Nielsen jkn@dmi.dk
Mats Dahlbom mda@dmi.dk
          

Validation of GPS-RO retrieved temperature and humidity profiles against radiosondes.

At the DMI we produce atmospheric profiles of temperature and humidity (and surface pressure) based on  Global Positioning System (GPS) Radio Occultations (RO) in a "Satellite Application Facility" under EUMETSAT. The processed data are disseminated in near real time at operational basis and they are also used for climate studies. We wish to assess the quality of these retrievals and one  way of doing this is to validate them against other measurements. 

In this project we would like to compare the retrievals to co-located radiosonde measurements.  Radiosondes are balloon-borne instruments launched a few times per day in order to assist numerical weather forecasting, but occasionally research missions are carried out with dedicated finer instrumentation. We can access  data of both kinds and would like carry out a comparison project in collaboration with either a master or bachelor student. A bachelor student  would focus on  the comparison, describing biases and variances and discuss their origin. A master student might in addition take an interest in looking closer on the retrieval algorithm and the mathematics behind it.

Johannes K. Nielsen jkn@dmi.dk