14 research outputs found
4DVAR assimilation of GNSS zenith path delays and precipitable water into a numerical weather prediction model WRF
The GNSS data assimilation is currently widely discussed
in the literature with respect to the various applications for meteorology
and numerical weather models. Data assimilation combines atmospheric
measurements with knowledge of atmospheric behavior as codified in computer
models. With this approach, the “best” estimate of current conditions
consistent with both information sources is produced. Some approaches also allow
assimilating the non-prognostic variables, including remote sensing
data from radar or GNSS (global navigation satellite system). These
techniques are named variational data assimilation schemes and are based on
a minimization of the cost function, which contains the differences between
the model state (background) and the observations. The variational
assimilation is the first choice for data assimilation in the weather forecast
centers, however, current research is consequently looking into use of an
iterative, filtering approach such as an extended Kalman filter (EKF).
This paper shows the results of assimilation of the GNSS data into numerical
weather prediction (NWP) model WRF (Weather Research and Forecasting). The
WRF model offers two different variational approaches: 3DVAR and 4DVAR, both
available through the WRF data assimilation (WRFDA) package. The WRFDA
assimilation procedure was modified to correct for bias and observation
errors. We assimilated the zenith total delay (ZTD), precipitable water
(PW), radiosonde (RS) and surface synoptic observations (SYNOP) using a 4DVAR
assimilation scheme. Three experiments have been performed: (1) assimilation
of PW and ZTD for May and June 2013, (2) assimilation of PW alone; PW,
with RS and SYNOP; ZTD alone; and finally ZTD, with RS and SYNOP for 5–23 May 2013, and (3) assimilation of PW or ZTD during severe weather events in
June 2013. Once the initial conditions were established, the forecast was
run for 24 h.
The major conclusion of this study is that for all analyzed cases, there are
two parameters significantly changed once GNSS data are assimilated in the
WRF model using GPSPW operator and these are moisture fields and rain. The
GNSS observations improves forecast in the first 24 h, with the strongest
impact starting from a 9 h lead time. The relative humidity forecast in a
vertical profile after assimilation of ZTD shows an over 20 % decrease of
mean error starting from 2.5 km upward. Assimilation of PW alone does not
bring such a spectacular improvement. However, combination of PW, SYNOP and
radiosonde improves distribution of humidity in the vertical profile by
maximum of 12 %. In the three analyzed severe weather cases PW always
improved the
rain forecast and ZTD always reduced the humidity field bias. Binary rain
analysis shows that GNSS parameters have significant impact on the rain forecast
in the class above 1 mm h−1.</p
Are Estimates of Wind Characteristics Based on Measurements with Pitot Tubes and GNSS Receivers Mounted on Consumer-grade Unmanned Aerial Vehicles Applicable in Meteorological Studies?
The objective of this paper is to empirically show that estimates of wind speed and wind direction based on measurements carried out using the Pitot tubes and GNSS receivers, mounted on consumer-grade unmanned aerial vehicles (UAVs), may accurately approximate true wind parameters. The motivation for the study is that a growing number of commercial and scientific UAV operations may soon become a new source of data on wind speed and wind direction, with unprecedented spatial and temporal resolution. The feasibility study was carried out within an isolated mountain meadow of Polana Izerska located in the Izera Mountains (SW Poland) during an experiment which aimed to compare wind characteristics measured by several instruments: three UAVs (swinglet CAM, eBee, Maja) equipped with the Pitot tubes and GNSS receivers, wind speed and direction meters mounted at 2.5 m and 10 m (mast), conventional weather station and vertical sodar. The three UAVs performed seven missions along spiral-like trajectories, most reaching 130 m above take-off location. The estimates of wind speed and wind direction were found to agree between UAVs. The time series of wind speed measured at 10 m were extrapolated to flight altitudes recorded at a given time so that a comparison was made feasible. It was found that the wind speed estimates provided by the UAVs on a basis of the Pitot tube/GNSS data are in agreement with measurements carried out using dedicated meteorological instruments. The discrepancies were recorded in the first and last phases of UAV flights
A Tissue-Mapped Axolotl De Novo Transcriptome Enables Identification of Limb Regeneration Factors
Mammals have extremely limited regenerative capabilities; however, axolotls are profoundly regenerative and can replace entire limbs. The mechanisms underlying limb regeneration remain poorly understood, partly because the enormous and incompletely sequenced genomes of axolotls have hindered the study of genes facilitating regeneration. We assembled and annotated a de novo transcriptome using RNA-sequencing profiles for a broad spectrum of tissues that is estimated to have near-complete sequence information for 88% of axolotl genes. We devised expression analyses that identified the axolotl orthologs of cirbp and kazald1 as highly expressed and enriched in blastemas. Using morpholino anti-sense oligonucleotides, we find evidence that cirbp plays a cytoprotective role during limb regeneration whereas manipulation of kazald1 expression disrupts regeneration. Our transcriptome and annotation resources greatly complement previous transcriptomic studies and will be a valuable resource for future research in regenerative biology
Comparative virtual screening and novelty detection for NMDA-Glycine B antagonists
10.1007/s10822-009-9304-1Journal of Computer-Aided Molecular Design2312869-881JCAD