Microphysical Processes in Weather and Climate Models III Posters
Presiding: M K Dubey, Los Alamos National Laboratory; V T Phillips, Atmospheric and Oceanic Sciences, Princeton University
A43A-01 1330h
A simplified Explicit Scheme of Phase-mixed Cloud Used in WRF model and precipitation experimentation
Based on WRF model (Version 1.3) system introduced in National Meteorological Center /CMA, a simplified explicit scheme of phase-mixed cloud (HL3) was introduced in the model successfully. The case study of precipitation prediction, with the initial fields and boundary conditions provided by the medium-range prediction system T213 run in the National Meteorological Center, were made for the scheme (HL3) and compared with the original simple ice explicit scheme (Ncloud3) in the model, and the diagnosis analysis on the horizontal and vertical distributions of cloud physical parameter such as cloud water and rain water were made for the two schemes, also. HL3 is a simplified version of explicit moisture scheme of phase-mixed cloud developed by Z. Hu and Q. Liu in CAMS/CMA, in which the moisture, cloud water, cloud ice, rain water, snow and graupel are considered as prognostic variables. Compared with Ncloud3 scheme, the main differences included: (1) the cloud was divided into cloud water and ice crystal according to the atmospheric temperature in Ncloud3; but in HL3, the supercooled cloud water is the only form when temperature is lower than 0C, no cloud ice existed. (2) two processes, the nucleation and multiplication of ice crystal, are taken into account in HL3. In these two processes, the cloud water was transformed into snow crystal directly, and falling toward to the ground with terminal speed. The precipitation prediction experiment was made with initial fields at 0000UTC 10 October 2003. This is a heavy rainfall case occurred in east part of China. Fig.1 (a) is the observed accumulated precipitation amount (mm) from 0000 UTC 10, October 2003 to 0000 UTC 11 October 2003. The blue shaded area showed the rain area over 10 mm. Fig.1 (b) and (c) are the corresponding 24-h prediction by HL3 and Ncloud3 respectively. From Fig.1 we can see that the rainfall area predicted by two schemes is the same completely, almost, but the distribution of heavy rain belt is different. Compare the rain belt over 50mm with Fig.1 (a), (b) and (c), we can see that although the heavy rain belt predicted by two schemes was deviated to the east from the observation, the prediction for the sub-heavy rain belt near the Yangtse River is different obviously. Since the prediction of the precipitation intensity made by HL3 is stronger than that by Ncloud3 scheme, the prediction of this rain belt made by Ncloud3 scheme was pass over, but it was predicted correctly by HL3 scheme. Fig.1 Comparison of precipitation prediction with two schemes (a) Observed accumulated precipitation amount from 0000UTC 10 October 2003 to 0000UTC 11 October 2003 (b) 24-h accumulated precipitation amount prediction made by HL3 (c) 24-h accumulated precipitation amount prediction made by Ncloud3 The preliminary results was shown that the precipitation forecast made by the simplified explicit scheme of phase-mixed cloud is correspond to that by simple ice explicit scheme, and has a improvement on the precipitation intensity, slightly. The predictions to the spatial and temporal distributions of cloud water and rainwater as well as the vertical distribution of mean rainwater over main precipitation area are improvement somewhat, also.
A43A-02 1330h
The Sensitivity of Simulations of the North American Monsoon to Convective Parameterization in CCM3
Two nine-year runs of the NCAR Community Climate Model (Ver. 3) are compared in their simulations of the North American summer monsoon. The two simulations differ by their closures of the parameterization for deep convection: for the control run, closure is based on CAPE, while for the experimental run, it is based on the large-scale forcing of temperature and humidity. The sensitivity to the choice of closure in simulating the North American monsoon is measured. Model validation relies on hourly precipitation rates from surface gauges over the U.S., those derived from the combination of microwave and radar measurements from NASA's TRMM (Tropical Rainfall Measuring Mission) satellite over Mexico, and tropospheric horizontal wind, specific humidity, and CAPE values from NCEP-NCAR reanalysis. Results show that the experimental run improves the timing of monsoon onset and peak in the regions of core monsoon influence considered here, though it increases a negative bias in the peak monsoon intensity in at least one region. While deficiencies in the concentration of upper-tropospheric specific humidity are reduced by the experimental run, the upper and lower-tropospheric simulated horizontal circulations are largely insensitive to the change in the convective scheme and, aside from some biases in the simulation of the U.S. Great Plains low-level jet, agree well with the reanalysis-based circulation. Sensitivity of the diurnal cycle of precipitation to the convective scheme closure is highly geographically-dependent. The experimental run greatly improves the diurnal cycle of precipitation over the U.S. Great Plains and Upper Midwest, but in the monsoon region, the quality of the simulation over northern Mexico is degraded. The same degradation is seen in the southeastern and northeastern U.S. In these latter regions, the diurnal cycles of precipitation are better simulated when they are more in phase with the diurnal cycles of CAPE.
A43A-03 1330h
A Comparison of Observed and Modeled Brightness Temperatures for Hurricane Erin (2001)
The Advanced Microwave Precipitation Radiometer (AMPR) is a four-frequency passive microwave radiometer with high spatial resolution. On the mission to Hurricane Erin (2001) during the Fourth Convection and Moisture Experiment (CAMEX-4), the AMPR onboard the ER-2 high-altitude aircraft measured brightness temperatures (Tb) at 10.7, 19.35, 37.1 and 85.5 GHz channels. The observed Tb are compared against those calculated from a microwave Radiative Transfer Model (RTM) that uses hydrometeor fields obtained from high-resolution simulations of Erin conducted using the Fifth-Generation PSU/NCAR Mesoscale Model (MM5). The 10.7 and 19.35 GHz channels are most sensitive to the thermal emission from rain. At 10.7 GHz, the simulation overestimates the frequency of Tb greater than 235 K, but underestimates that between 150 and 235 K. This shows that the simulation overpredicts the frequency of heavy rain and underestimates that of light rain. The comparison of simulated radar reflectivity factor (Z) with that observed by the NASA ER-2 Doppler Radar (EDOP) further verifies this point. At 37.1 GHz, the simulation overestimates the frequency of Tb between 190 K and 255 K, and underestimates that between 255 K and 285 K. By artificially removing the graupel from the modeled hydrometeor fields, the frequency distribution of Tb at 37.1 GHz and at 85.5 GHz more closely resembles the AMPR observations.
A43A-04 1330h
The use of WRF model to Investigate Rainshowers and Flooding in Taiwan during the Monsoon Break Period
A rainfall minimum is normally observed in Taiwan between the end of the Mei-Yu season and the end of June, a part of the monsoon break. Nevertheless,rainshowers still occurred ocasionally during that period. On 20 June 2000, more than 100 mm/day rainfall were observed at several stations on the lower slops in northern Taiwan. Flooding is unusual in most of Taiwan during the monsoon break period. However, flash floodd occurred in central and southern Taiwan on 2-4 July 2004 during the climatological minimum rainfall period. This event was initialized by typhoon Mindulle and by mesoscale convective systems embedded in the southwesterly flow that followed the passage of the typhoon over Taiwan.The maximun daily rainfall was more than 500 mm over Taiwan during that period. In this paper we use the WRF model to investigate rainshowers and flash flooding cases during the monsoon break in Taiwan. The simulation results suggest that a convergence zone formed over the leeward side of northern Taiwan due to a split in the prevailing flow from south. This convergence was enhanced by the onshore and upslope wind. When an updraft forms on the downwind side of heated mountain sloped, and moveds in to the convergence area heavy rainshower occurs. The preliminary results, forecasting the heavy rainfall associated with typhoon and the MCSs, show great promising. The heavy rainfall pattern and its evolution can be captured well by the WRF model. The confluene of the northwesterly flow associated with Mindulle and the wide-spread southwesterly flow, initiated the formation of MCSs. These MCSs moved into the costal area and the dynamic effect of the mountain range resulted in continuous heavy rainfall in the central and southern Taiwan. The microphysical process and the dynamical effects play by the central mountain range will be discussed in this study.
A43A-05 1330h
The impact of the global warming climate on rainfall-systems during the Baiu season around the East Asia by a cloud-resolving non-hydrostatic regional model
The impact of the global warming climate on rainfall-systems has been one of the greatest interests in the global climate, the regional climate and cloud physics for a long time. Therefore we have carried out numerical simulations with the non-hydrostatic regional climate model which has been developed on the basis of Japan Meteorological Agency Non-Hydrostatic Model in order to reveal the change/modification of rainfall-systems around the East Asia during the Baiu season under the global warming climate as well as that in present climate. A semi-cloud resolving model with a horizontal grid of 5 km is nested in Global Climate Model (GCM) which has a horizontal grid of 20 km during 21st May to 29th July for every 10 year. One of the most remarkable changes from the present climate to the global warming climate is the extreme increase of the rainfall amount especially around the southern Kyushu in the Baiu season (Yoshizaki, et al, 2005). It results from not only the extension of the Baiu season but also the intensification of daily rainfall amount of the global warming climate. Three-dimensional structure of rainfall-systems is examined in the global warming climate. Upward sifts of peak levels with 0.5-1.0 km from the present climate are found in the mixing ratios of cloud, snow and rain water. Both time-averaged vertical velocity and peak-values of the mixing ratios of cloud and rain water around the southern Kyushu and its upwind area of the global warming are larger. Interestingly, the layer of large cloud water mixing ratio is much thicker in the global warming climate around the southern Kyushu. These features indicate the high possibility that the structure of rainfall-systems are modified in the global warming climate.
A43A-06 1330h
A decade long aerosol and cloud statistics and aerosol indirect effect at the ARM SGP site
Twelve-year data of MFRSR and MWR have been used to derive aerosol and cloud optical properties at the ARM SGP. Diurnal, monthly, seasonal and interannual variability of aerosol (optical depth and Angstrom coefficient) and cloud (optical depth and effective radius) have been analyzed. We specially focused on aerosol-cloud interactions. We found a signature of indirect aerosol effect for summer data: increased aerosol index has a statistically-significant anti-correlation with mean effective radius. No correlation was found for the other seasons.
A43A-07 1330h
Evaluation of Mid-Latitude Ice Clouds Properties Using MM5 Mesoscale Model and Remote-Sensing Measurements at SIRTA Atmospheric Observatory
The mid-latitude ice clouds properties are evaluated by using MM5 mesoscale model and remote-sensing measurements. The first part of the study uses the model to observation approach: model outputs are compared to long-term meteorological measurements by active remote-sensing (radar and lidar) and passive remote-sensing (infrared and visible fluxes) at SIRTA atmospheric observatory near Paris. The ambition of this first part is to understand which of four available microphysical schemes is best suited to simulate mid-latitude ice clouds. The methodology consists in directly simulating instrument observables from the model outputs without any profile inversion, which allows us to use of fewer assumptions on microphysical and optical properties of ice particles. Results show that when a proper parameterization of the terminal velocity is used, the microphysics schemes allow the MM5 model to simulate the presence of mid-latitude ice clouds in more than 65% of our selection of observed cloud cases. In 35% of the cases, simulated clouds are too persistent whatever the microphysical scheme and tend to produce too much solid water (ice and snow) and not enough liquid water. Among the four schemes compared in the current study, the best observation-to-simulations scores are obtained when the terminal velocity formulation does not directly depends on particle size, and when clouds have medium optical thickness (about 3). The second part of the study uses the observation to model approach. Using several algorithms developed on the SIRTA, it is possible to retrieve a large panel of ice cloud properties with SIRTA remote-sensing instruments: cloud particle size and shape, cloud altitude, temperature and phase, vertical velocity within the cloud, ground shortwave and longwave fluxes (Fground). Cloud microphysical and macrophysical properties are also available using CERES algorithms applied to MSG from June 2004 to now, including the fluxes at the top of the atmosphere (FTOA). All those cloud parameters are also computed using MM5 model with the most performed microphysical scheme (first part study) for all the observation period. Using observation and measurements, the synoptical situations over SIRTA are separated onto four categories that correspond to four categories of FTOA/Fground values. Those four categories are then studied independently: we link all the available parameters using MM5/SIRTA/MSG, in order to understand how microphysical properties vary with the macrophysical ones, and inversely. This allows a better knowledge of the cloud process, and it will be possible to improve the microphysical scheme in mesoscale model.
A43A-08 1330h
Implementation of NASA/GSFC GCE Ice Schemes into WRF
WRF is a next-generation mesoscale forecast model and assimilation system, which started with a blank sheet almost seven years ago. The model has since incorporated modern advanced dynamics, numeric and data assimilation techniques, a multiple relocatable nesting capability, and improved physical packages. WRF also adopted an advanced software framework to allow incremental and reasonably rapid development towards full-functionality while maintaining overall consistency on its own architecture and interface. The WRF model can be used for a wide range of applications, from idealized research to operational forecasting, with an emphasis on horizontal grid sizes in the range of 1-10 km. The WRF is a prime candidate to replace existing research and forecast models as MM5 users being strongly encouraged to begin transitioning to it. WRF v2.0.3.1 was recently released in December 2004 with one-way/two-way interactive nesting, Eulerian mass coordinate, WRFSI v2.0 and WRF 3DVAR v2.0. Several improvement are also undergoing among many WRF developer groups. The current WRF includes 1) Lin et al. (1983), Kessler, and Ferrier microphysics schemes; 2) Kain-Fritsch, and Betts-Miller-Janjic cumulus parameterization schemes; 3) Mellor-Yamada-Janjic PBL scheme; 4) GFDL, and Goddard (Chou) shortwave radiation; 5) GFDL, and RRTM long-wave radiation and many other optional physical packages. Our group will implement several ice schemes based on Tao et al. (2003), Goddard radiation (including explicitly calculated cloud optical properties), LIS (including the CLM and NOAH land surface models), rainfall and bogus vortex assimilation techniques and diagnostics into the WRF. We will perform benchmark cases from real case studies. In this meeting, we will present the impact of the first phase of our endeavor resulted from adding several ice schemes (Tao et al. 2003) into WRF.
A43A-09 1330h
Validation of Local-Cloud Model Outputs With the GOES Satellite Imagery
Clouds (visible aggregations of minute droplets of water or tiny crystals of ice suspended in the air) affect the radiation budget of our planet by reflecting, absorbing and scattering solar radiation, and the re-emission of terrestrial radiation. They affect the weather and climate by positive or negative feedbacks. Many researchers have worked on the parameterization of clouds and their effects on the radiation budget. There is little information about ground-based approaches for continuous evaluation of cloud, such as cloud base height, cloud base temperature, and cloud coverage, at local and regional scales. This present article deals with the development of an algorithm for continuous (day and night) evaluation of cloud base temperature, cloud base height and percent of skies covered by cloud at local scale throughout the year. The Vaisala model CT-12K laser beam ceilometer is used at the Automated Surface Observing Systems (ASOS) to measure the cloud base height and report the sky conditions on an hourly basis or at shorter intervals. This laser ceilometer is a fixed-type whose transmitter and receiver point straight up at the cloud (if any) base. It is unable to measure clouds that are not above the sensor. To report cloudiness at the local scale, many of these type of ceilometers are needed. This is not a perfect method for cloud measurement. A single cloud hanging overhead the sensor will cause overcast readings, whereas, a hole in the clouds could cause a clear reading to be reported. To overcome this problem, we have set up a ventilated radiation station at Logan-Cache airport, Utah, U.S.A., since 1995, which is equipped with one of the above-mentioned ceilometers. This radiation station (composed of pyranometers, pyrgeometers and net radiometer) provides continuous measurements of incoming and outgoing shortwave and longwave radiation and the net radiation throughout the year. We have also measured the surface temperature and pressure, the 2-m air temperature and humidity, precipitation, and the 3-m wind and direction at this station. Having the air temperature, moisture, and the measured cloudless incoming longwave (atmospheric) radiation during 1999 through 2004, based upon the ASOS and the algorithm data, we found the appropriate formula (among four reported approaches) for computation of the cloudless-skies atmospheric emissivity. Considering the additional longwave radiation captured by the facing-up pyrgeometer during the cloudy skies, coming from the cloud in the wave band which the gaseous emission lacks (from 8-13 m), we developed an algorithm which provides the continuous 20-min cloud information (cloud base height, cloud base temperature, and percent of skies covered by cloud) over the Cache Valley during day and night throughout the year. The comparisons between the ASOS and the algorithm data during the period of 8-12 June, 2004 are reported in this article. The proposed algorithm is a promising approach for evaluation of the cloud base temperature, cloud base height, and percent of skies covered by cloud at the local scale throughout the year. It also reports the comparison between model outputs and GOES 10 satellite images.