Short-term forecasting (nowcasting) of rainfall is widely used in providing early warning, and therefore, has very practical application. The CASA demonstration network deployed in the Dallas-Fort ...Worth (DFW) area consists of high-resolution X-band radars deployed around the National Weather Service Radar WSR-88D, and nowcasting of precipitation is an important product of this network. The current nowcasting technique DARTS was developed in frequency domain using fast Fourier transforms in order to provide nowcasts in a computationally efficient manner. Building on the earlier work on the CASA Project and the STEPS methodology, a stochastic nowcasting method is developed and tested for the first time in a small-scale urban environment using high-resolution radar data. The key idea is to decompose the reflectivity field into multiple spatial scales and generate stochastic perturbations in each scale to account for uncertainties in the nowcasts. It is shown that the proposed method can produce reliable nowcasts and uncertainty estimates up to 45 min and performs as well or better than DARTS in terms of the standard critical success index and mean error verification scores. Using the scale decomposition of STEPS, a power-law relationship is derived between the spatial scale and Lagrangian lifetime of precipitation on scales between 500 m and 50 km.
The Radiation Assessment Detector onboard the Mars Science Laboratory rover Curiosity is detecting the energetic particle radiation at the surface of Mars. Data collected over the first 350 Martian ...days of the nominal surface mission show a pronounced diurnal cycle in both the total dose rate and the neutral particle count rate. The diurnal variations detected by the Radiation Assessment Detector were neither anticipated nor previously considered in the literature. These cyclic variations in dose rate and count rate are shown to be the result of changes in atmospheric column mass driven by the atmospheric thermal tide that is characterized through pressure measurements obtained by the Rover Environmental Monitoring Station, also onboard the rover. In addition to bulk changes in the radiation environment, changes in atmospheric shielding forced by the thermal tide are shown to disproportionately affect heavy ions compared to H and He nuclei.
Key Points
Dose rate is inversely related to variations in atmospheric column mass
Neutral count rate is proportional to variations in atmospheric mass
Heavy ions are disproportionately affected by atmospheric shielding
•Curiosity hourly humidity and temperature data for sols 15–17 and 80–82 is considered.•Data suggests adsorption to soil in the evening, desorption in the morning.•A column atmosphere–regolith model ...with adsorption can simulate the observed diurnal cycles reasonably well.•Suggested porosity of the regolith is 35–40% and thermal inertia 300tiu.
Hourly temperatures T, relative humidities RH and mass mixing ratios of moisture q at 1.6m derived from the Mars Science Laboratory REMS-H and REMS-P measurements are shown for MSL sols 15–17 (Curiosity at Bradbury) and 80–82 (Curiosity at Rocknest). They are compared to column model simulations with and without adsorption to porous regolith. The observed mixing ratio is small at night (10–30ppmm). It increases rapidly to 50–80ppmm after sunrise and decreases slowly during the evening. The model gives a good account of the observed T and, with adsorption and realistic precipitable water content (PWC), reproduces the diurnal cycles of both RH and q relatively well. The suggested regolith thermal inertia is 300tiu and porosity 35–40% for both sites. According to the simulations moisture is adsorbed and diffused to the cooling regolith in the evening from the lowest very stable air layer. It is then desorbed in the morning from the rapidly warming regolith and mixed throughout the growing convective boundary layer. Estimates of PWC based on night-time near-surface moistures (assuming an even distribution with height) might therefore be on the low side in areas of porous adsorbing regolith.
Currently, there are several spaceborne microwave instruments suitable for the detection and quantitative estimation of snowfall. To test and improve retrieval snowfall algorithms, ground validation ...datasets that combine detailed characterization of snowfall microphysics and spatial precipitation measurements are required. To this endpoint, measurements of snow microphysics are combined with large-scale weather radar observations to generate such a dataset. The quantitative snowfall estimates are computed by applying event-specific relations between the equivalent reflectivity factor and snowfall rate to weather radar observations. The relations are derived using retrieved ice particle microphysical properties from observations that were carried out at the University of Helsinki research station in Hyytiälä, Finland, which is about 64 km east of the radar. For each event, the uncertainties of the estimate are also determined. The feasibility of using this type of data to validate spaceborne snowfall measurements and algorithms is demonstrated with the NASA GPM Microwave Imager (GMI) snowfall product. The detection skill and retrieved surface snowfall precipitation of the GPROF detection algorithm, versions V04A and V05A, are assessed over southern Finland. On the basis of the 26 studied overpasses, probability of detection (POD) is 0.90 for version V04A and 0.84 for version V05A, and corresponding false-alarm rates are 0.09 and 0.10, respectively. A clear dependence of detection skill on cloud echo top height is shown: POD increased from 0.8 to 0.99 (V04A) and from 0.61 to 0.94 (V05A) as the cloud echo top altitude increased from 2 to 5 km. Both versions underestimate the snowfall rate by factors of 6 (V04A) and 3 (V05A).
•Moist summer column simulations are presented for the Viking lander sites.•Observed diurnal winds and temperatures are adequately reproduced.•Adsorption in the evening and frost from midnight ...deplete near-surface water vapor.•Fog is formed at night, increasing optical depth as observed.•Porosity of 22% conserves PWC from sol to sol at both sites.
Boundary layer simulations are shown for the first sols of the two Viking landers (VL1, VL2) on Mars. The column model (with cloud/radiation interaction and Prandtl slope wind terms), used successfully for Phoenix and Curiosity, is equipped here with an adsorption-diffusion scheme for water vapor transport in porous regolith. The model's 1.6 m temperatures and winds are quite close to those observed by the two landers; in particular the weak summer slope winds of VL2 are excellently reproduced.
The model predicts for both sites diffusion and adsorption of water into regolith in the evening, very thin ground frost deposition from about midnight, and an early morning fog with an inflection in T1.6 m slightly weaker than observed. At the moister VL2 site fog increases optical depth as observed. Fogs and frosts sublimate away after sunrise, allowing desorption and diffusion of water off the sun-heated regolith. For porosity of 22% column water is approximately conserved from sol to sol at both sites with only little diurnal variation, as the depleted layer of air moisture is quite shallow.
In simulations without adsorption frost forms early and it grows thick. At VL2 fog now forms earlier and the jump in optical depth is larger than observed. At the drier VL1 fog still forms nearly as with adsorption, so observations could also be explained without adsorption. On the other hand VL1 certainly landed onto porous regolith and frost was not observed. Hence it is suggested that adsorption is likely at both VL sites in summer.
In situ
measurements by an atmospheric entry probe allow for sounding and investigating atmospheric composition, structure and dynamics deep into the atmosphere of a Giant planet. In this paper, we ...describe an Atmospheric Structure Instrument (ASI) for an entry probe at Uranus and/or Neptune. The scientific objectives, the measurements and the expected results are discussed in the framework of a future opportunity for an NASA-ESA joint mission to the Ice Giant planets.
Dose rate measurements from Mars Science Laboratory‐radiation assessment detector (MSL‐RAD) for 300 sols on Mars are compared to simulation results using the Badhwar‐O'Neill 2011 galactic cosmic ray ...(GCR) environment model and the high‐charge and energy transport (HZETRN) code. For the nuclear interactions of primary GCR through Mars atmosphere and Curiosity rover, the quantum multiple scattering theory of nuclear fragmentation is used. Daily atmospheric pressure is measured at Gale Crater by the MSL Rover Environmental Monitoring Station. Particles impinging on top of the Martian atmosphere reach RAD after traversing varying depths of atmosphere that depend on the slant angles, and the model accounts for shielding of the RAD “E” detector (used for dosimetry) by the rest of the instrument. Simulation of average dose rate is in good agreement with RAD measurements for the first 200 sols and reproduces the observed variation of surface dose rate with changing heliospheric conditions and atmospheric pressure. Model results agree less well between sols 200 and 300 due to subtleties in the changing heliospheric conditions. It also suggests that the average contributions of albedo particles (charge number Z < 3) from Martian regolith comprise about 10% and 42% of the average daily point dose and dose equivalent, respectively. Neutron contributions to tissue‐averaged effective doses will be reduced compared to point dose equivalent estimates because a large portion of the neutron point dose is due to low‐energy neutrons with energies <1 MeV, which do not penetrate efficiently to deep‐seated tissues. However the exposures from neutrons to humans on Mars should become an important consideration in radiobiology research and risk assessment.
Key Points
Model simulation agrees with RAD measurements on Mars surface
Dose rate varies with heliospheric condition and atmospheric pressure
Neutron flux on Mars to be considered for radiobiology and risk assessments
Diurnal solar radiation causes global oscillations in pressure, temperature, and wind fields, known as atmospheric tides, which are further modified by topography, surface properties, and atmospheric ...dust loading. Hence, the tides are a combination of sun‐synchronous and non sun‐synchronous tides that propagate around the planet both eastward and westward. In the Martian tropics, atmospheric tides dominate daily pressure variations on the surface. Therefore, surface observing platforms are extremely useful for detailed analysis of atmospheric tides. In this investigation, we analyze diurnal and semi‐diurnal components of atmospheric surface pressure measured by the simultaneously operating InSight and Mars Science Laboratory (MSL) payloads. We utilize observations of the time period from Martian year (MY) 34 solar longitude 296° to MY 36 solar longitude 53°. The diurnal tide average amplitude is 17 Pa with an average phase of 03:39 local true solar time (LTST), while the semi‐diurnal tide average amplitude and phase are 7 Pa and 09:34 LTST for the InSight. The corresponding values for the MSL are 33 Pa with 04:25 LTST for the diurnal and 10 Pa with 09:36 LTST for the semi‐diurnal component. Thermo‐topographic lateral hydrostatic adjustment flow generated by topography causes the higher diurnal amplitude observed by MSL. Both platforms observe a similar response between these harmonic components and dust loading. Furthermore, amplitudes obtained from a Mars Climate Database mimic the observations well. Our study provides for the first time a comparison of atmospheric tides at two simultaneously observing tropical surface platforms for more than 1 MY.
Plain Language Summary
The Curiosity rover landed on Mars in August 2012 and has been observing meteorological variables ever since. The next surface observing station, the InSight lander, landed in the equatorial region of Mars in November 2018, relatively close to Curiosity. Unfortunately, InSight reached end of its mission on 15 December 2022, but fortunately they observed Martian atmosphere simultaneously for more than one Martian year. Atmospheric pressure is a very important meteorological variable, since many weather phenomena are associated with changes in surface pressure. Here, we use pressure observations from these two weather stations to determine Martian equatorial atmospheric tides and compare them with model simulations. They are forced by solar radiation and additionally modified by topography, surface properties, and atmospheric dust. They propagate around the planet in periods that are integer fractions of a Martian day. The two strongest components, diurnal and semi‐diurnal, with periods of 24 and 12 hr, are studied here. The results show the effect of atmospheric dust loading and the location on these components. We find a similar response between these components and atmospheric dust loading on both platforms and a higher amplitude of the diurnal tide at the Curiosity location due to differences in topography.
Key Points
We analyze diurnal and semi‐diurnal atmospheric tidal components from simultaneous InSight and Mars Science Laboratory (MSL) observations
We find higher amplitude of the diurnal harmonic component at MSL location due to differences in topography
We find a similar response between the harmonic components and atmospheric dust loading on both platforms
•A statistical modeling scheme for biases and uncertainties in radar-based rainfall estimation.•The model incorporates auxiliary information such as distance from radar and fine-structure of ...precipitation.•Multivariate techniques and spatiotemporal Kriging are used.•For a radar-measured rainfall field, the model gives probability distributions for the corresponding ground rainfall.•Validation is done by using the Finnish C-band dual-polarization radars with rain gauges as the ground reference.
The quality of quantitative precipitation estimation (QPE) is degraded by considerable discrepancies between radar and ground measurements, which are common due to inherent uncertainties between these two kinds of sensor systems. The causes include measurement errors and differences in sampling schemes. Nevertheless, the remaining discrepancies can be statistically modeled. A model describing detection probabilities of ground rainfall, systematic biases as well as the variance of residual discrepancies between radar and rain gauges is developed. These are modeled by means of multiple explanatory variables such as rain rate and distance from radar. The model is implemented by using nonparametric kernel methods and spatiotemporal Kriging interpolation. A key feature of the model is that for a given radar-derived rainfall field and explanatory variables, it determines probability distributions for the corresponding ground rainfall. Unbiased estimates for ground rainfall can be obtained from the expected values of the distributions. From such distributions, one can also obtain uncertainty estimates and exceedance probabilities that are important for hydrological applications. Performance of the model is assessed by cross-validation using hourly rainfall accumulations measured by the Finnish rain gauges and C-band dual polarization radars.
•The signature of equator crossing frontal systems on Mars has been detected by the Curiosity Rover's pressure sensor.•These systems occasionally trigger regional dust storms in the Southern ...Hemisphere and are thus important the planet's dust cycle.•The periods and seasonal variations of these equator crossing eddies suggest a complex dynamical response to seasonal changes and dust storms.•This work opens up a new line of research for Mars atmospheric dynamics.
The Rover Environmental Monitoring Station (REMS) on the Curiosity Rover is operating in the Southern Hemisphere of Mars and is detecting synoptic period oscillations in the pressure data that we attribute to Northern Hemisphere transient eddies. We base this interpretation on the similarity in the periods of the eddies and their seasonal variations with those observed in northern midlatitudes by Viking Lander 2 (VL-2) 18 Mars years earlier. Further support for this interpretation comes from global circulation modeling which shows similar behavior in the transient eddies at the grid points closest to Curiosity and VL-2. These observations provide the first in situ evidence that the frontal systems often associated with “Flushing Dust Storms” do cross the equator and extend into the Southern Hemisphere.
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