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A significant lesson learned during recent military operations (e.g., DESERT SHIELD/STORM and Balkan conflicts) was the difficulty of detecting and forecasting mid-level clouds with conventional meteorological observations and models. Extensive layers of these non-precipitating, mid-level clouds frequently masked target areas, hampered the use of unmanned aerial vehicles (UAV's) , electro-optic sensors and weapons systems. As a result, poorly forecasted and detected mid-level clouds often forced the cancellation of refueling, intelligence and strike missions. Mid-level clouds also present some risk to the civilian aviation community in the form of light-to-moderate turbulence and icing.
The mixed phase structure (i.e., the location, characteristics, and amounts of ice and supercooled water) of mid-level clouds is poorly documented and understood. Their ice-liquid stratification, ratios, temperatures, ice phase form, lifecylce, and horizontal and vertical structure are still largely unknown. More observations and a better understanding of these characteristics are necessary for the proper modeling, forecasting and detection of mid-level clouds.
Because they do not produce severe weather and are typically ignored by climate change scientists, mid-level, non-precipitating clouds are the forgotten clouds of the atmospheric science community. To fill this research void, the DOD Center for Geosciences and Atmospheric Research (CG/AR) at CIRA-CSU is sponsoring an ongoing field program, the Complex Layered Cloud Experiment (CLEX). The CLEX addresses a better physical understanding of mixed-phase non-precipitating clouds in the middle troposphere. In particular, the CLEX strives to document the microphysical, dynamical, and radiative properties of these clouds with the goal of improving their forecasting, modeling and remote detection.
Using in-situ aircraft observations, recent CLEX (e.g., CLEX-5 during Nov-Dec 1999, CLEX-7 during March-April 2000 and CLEX-8 during May-June 2001) have documented the detailed microphysical and radiative structure of eight mid-level clouds (Fleishauer et al., 2001, Carey et al., 2001) and have addressed the question of what causes altocumulus to decay (Larson et al., 2001). These results have provided many insights toward the better forecasting of mid-level clouds.
Herein, we will overview the next field phase (CLEX-9) that is planned for October 2001. We'll review annual and diurnal mid-level cloud climatology over the High Plains and discuss how this has impacted CLEX-9 planning and objectives. We'll review the scientific objectives for CLEX-9 and present the experiment location, observational platforms and mission scenarios that we've identified for achieving these goals.
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In planning for CLEX-9, the annual and diurnal climatology of mid-level clouds over the High Plains was investigated.
The monthly averaged ISCCP D1 mid-level daytime cloud percentages over northeastern Colorado and southwestern Nebraska for both the visible and infrared frequencies exhibited an extended maximum during the late summer and autumn months with an absolute peak during October and November (not shown). Mid-level cloud fractions were 40% to 50% higher over NE CO/SW NE compared to the SGP ARM CART site in central Oklahoma (Fig. 1a,b). For this monthly analyses of ISCCP mid-level daytime cloud percentages, we eliminated all data with >10% high clouds present in the D1 block in order to mitigate any contamination of the "mid-level" cloud classification by thin cirrus.
Fig. 1. Regional mid-level cloud climatolology for the Colorado/Nebraska/Wyoming (CO/NE/WY) and Oklahoma (OK) regions. a) Monthly averaged ISCCP D1 mid-level daytime cloud percentages (when less than 10% of high clouds are present) from climatological visible (VIS) GOES satellite data. b) same as a) except for daytime climatological infrared (IR) GOES satellite data. Removing data when > 10% high clouds are present mitigates the issue of contamination from thin cirrus. Note the peak in mid-level cloud occurrence in October - November. Also note that the mid-level cloud percentage is significantly higher over CO/NE/WY compared to OK.
The diurnal cycle of mid-level cloud coverage over the southwestern Nebraska region (e.g., North Platte) was also investigated (Fig. 2). Using ISCCP D1 data, a "mid-level" cloud was defined as having IR cloud top temperatures from -5° C to -25° C. Utilizing nine years of ISCCP, the October hourly mid-level cloud percentage was calculated.
Fig. 2. A depiction of the diurnal cycle of mid-level cloud (-5° C to -25° C IR top) coverage over a 280 km x 280 km area near North Platte, Nebraska during the month of October for 9-years of ISCCP (International Satellite Cloud Climatology Project) D1 data. Local time (CST) is given at the top. The ISCCP D1 data allows 3-hour temporal resolution. The blue is the 9-year October mean mid-level cloud coverage. The red line is the IR inferred surface skin temperature.
For all nine years, a clear diurnal signal is exhibited. There is a nocturnal maximum during the early AM hours, typically just before sunrise. The mid-level cloud coverage rapidly decreases after the local sunrise and exhibits a minimum during the late AM - early PM hours, typically centered on local Noon. After local sunset, the mid-level cloud fraction begins to increase again. Please see Kankiewicz et al. (2001) for more details on the analyses procedure and for diurnal mid-level cloud coverage results around the globe. Note that Lazarus et al. (2000) found a similar diurnal cycle in AC clouds using edited cloud reports from synoptic weather observations over the ARM CART site in north-central Oklahoma. Interestingly, this diurnal cycle is consistent with past CLEX forecasting experience with mid-level clouds.
Fig. 3. Depiction of the University of Wyoming King Air (WYKA) Cloud Research Facility and Wyoming Cloud Radar (WCR). a) Associated WYKA instrument locations, including a comprehensive suite of microphysical probes (e.g., PMS 2D-P, 2D-C, 1D-C, Liquid Water Probe, Rosemount Icing rate), radiation probes (up- and down- looking Eppley pyranometers and pyrgeometers and a down-looking Heimann IR radiative thermometer), and the up- and side-looking Wyoming Cloud Radar (WCR, 95-GHz, Doppler and polarimetric). b) Collage of the WYKA and WCR including an Image of the WYKA with side mounted antenna/mirror for the WCR, a depiction of how the horn, lens and mirror system works for side- or up-looking operations and an image of the radar conical horn and associated hardware and waveguide. Images are courtesy of the University of Wyoming.
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CLEX-9, planned for October 2001, will utilize the University of Wyoming King Air (UWKA) research aircraft based out of Laramie, WY (Fig. 3). In addition to a comprehensive suite of microphysics and radiation probes, the UWKA will carry the upward- or side-looking Wyoming Cloud Radar (WCR). The WCR (95-GHz, Doppler, polarimetric) will provide high-resolution observations (e.g., 30 m x 12 m x 15 m resolution volume at 1 km range) of cloud structure, microphysics and kinematics. Since the WCR is the same frequency as that aboard the proposed CLOUDSAT, CLEX-9 will have the opportunity to explore issues surrounding the detection of mid-level, mixed phase clouds from space-based radar.
CLEX-9 will deploy the NOAA-ETL (Radar Meteorology and Oceanography Divsion) dual-frequency microwave radiometer (Fig. 4), the CSU Micropulse LIDAR (Fig. 5), surface shortwave and longwave radiation instrumentation (both flux and spectra) (Fig. 6a,b), the joint University of Massachusetts - University of Wyoming dual-frequency radiometer (Fig. 7), and a supplementary radiosonde system (Fig. 8) on the ground at the North Platte NE Regional Airport (or Lee Bird Field, LBF) (Figs. 9a-d). Between missions, the WYKA can land at LBF to refuel and obtain a weather update from the CSU research trailer where real time weather data and imagery will be available over the Internet.
In addition, the North Platte, NE National Weather Service Forecast Office (Fig. 9e) is also located at LBF, giving us the benefit of local weather expertise and data (e.g., 00z and 12z upper air sounding data of T, Td, and wind). Since most CLEX-9 operations will be in the AM hours, we will attempt to supplement the 12z KLBF sounding with a CSU balloon launch. If the aircraft mission over LBF begins prior to 14z, a CSU balloon will be launched at or prior to 10z. Otherwise, a CSU balloon will be lance at or after 14z. This way we will have a pre- and a post-flight thermodynamic and wind sounding over North Platte.
These airborne and ground based instruments combined will provide an unprecedented view of mid-level clouds.
Fig. 4. Photograph of the NOAA/ETL dual-frequency microwave radiometer (courtesy of NOAA/ETL). The dual-frequency radiometer has passive microwave receivers at 20.6 GHz and 31.65 GHz. The beam is zenith pointing (non-scanning) and has a width of 4°. The radiometer will provide real-time and archived measurements of column integrated cloud liquid water and water vapor at 1-minute intervals. Image courtesy of NOAA/ETL.
Fig. 5. Image of the CSU Micropulse LIDAR 8" telescope and optical driver unit.
Fig. 6. CSU surface radiation instrumentation. a) Image of the CSU surface radiation station that measures the down-welling total solar and infrared hemispheric irradiance. b) Image of the CSU IR interferometer system that measures the down-welling spectral IR irradiance.
Fig. 7. An image of the joint University of Massachusetts (Microwave Remote Sensing Laboratory, MIRSL) - University of Wyoming (Department of Atmospheric Science) dual-frequency (22 and 31 GHz) microwave radiometer. The radiometer will be tested by UMass during CLEX-9 at the LBF ground site for future deployment on the University of Wyoming King Air Research Aircraft. Image courtesy of UMass MIRSL.
Fig. 8. A collage of the CSU supplementary radiosonde system (radiosonde balloon with instrumentation package and the radio theodolite antenna for tracking the balloon).
Fig. 9. Different views of the CLEX-9 observational network. a) Map of the CLEX-9 observational network. The blue triangles are NOAA Wind Profiler sites, the green circles are NWS operational radiosonde sites, the small purple circles are IOP research sounding sites, and the red stars are key CLEX-9 sites. The Wyoming King Air will be stationed in Laramie, WY; the operations and forecasting center will be located at CSU-CIRA in Fort Collins, CO; the primary CLEX-9 observational ground site will be the North Platte, NE Regional Airport (or Lee Bird Field, LBF); and the SGP ARM CART site will be utilized as a secondary observational ground site. b) Aerial view of LBF looking toward the east. The red arrow points to the approximate location of the CSU and NOAA-ETL research trailers at LBF. c) Site plan of LBF with location of CLEX-9 ground site indicated by red arrow. d) Surface image of the CLEX-9 ground site at LBF prior to installation of the research trailers. The GPS coordinates of the research trailers are: LATITUDE: 41 deg, 07.997 min N (41.133 deg); LONGITUDE: 100 deg, 41.744 min W (-100.696 deg); and ELEVATION: 2800 ft. e) View of the National Weather Service Forecast Office in North Platte (KLBF), which is located at the North Platte Regional Airport at a latitude of 41.12 deg and a longitude of -100.67 deg. Image courtesy of the NWS FO at North Platte.
CLEX-9 will continue to increase our sample size and knowledge base of mid-level cloud properties. The ability to take the cloud radar "to the cloud" will allow the CLEX program to dramatically increase its knowledge of cloud-scale morphological, microphysical, and kinematic properties. When combined with the microphysical probe data, radar reflectivity, differential reflectivity, linear depolarization ratio and Doppler measurements will provide detailed information about cloud particle phase (ice vs. water), relative size, ice habit, and degree of aggregation and riming on the cloud scale. The Doppler velocity and spectral width can offer insight into the vertical draft and turbulence structure of clouds.
The NOAA/ETL dual-frequency microwave radiometer, the CSU Micropulse LIDAR, and the CSU radiosonde system located at the North Platte, NE Regional Airport (or Lee Bird Field [LBF], Figs. 4a-c) will nicely complement the airborne WCR in characterizing the larger scale morphology and microphysics of mid-level clouds and in better defining the local atmospheric conditions. The WCR will be most sensitive to the ice content in mixed phase mid-level clouds and may on occasion miss supercooled liquid water cloud, especially if the water contents are very low and the median volume diameter of the droplets are very small. The CSU Micropulse LIDAR and NOAA/ETL microwave radiometer will insure that CLEX-9 does not miss much supercooled liquid water cloud. The LIDAR will provide additional cloud morphology information and the microwave radiometer will give us quantitative information about the path integrated liquid water content.
With these observations, we can build
upon the successful results of CLEX-5 through -8. In particular, a special emphasis
has been placed on improving the remote detection of mid-level clouds. In addition
to practical application (e.g., battlefield planning), better remote detection
is critical to further progress in forecasting and modeling of mid-level clouds
(e.g., physical parameterization, validation and initialization). As a result,
satellite (e.g., GOES, NOAA, DMSP,
and NASA TERRA) satellite
remote sensing data will play a key role in CLEX-9.
CLEX-9 is scheduled for a four week period during 1 Oct - 4 Nov 01 (i.e., either 1 Oct - 28 Oct 01 or 8 Oct - 4 Nov 01, depending on the medium range forecast on 28 Sep 01) over the NE/WY/CO region because of the peak in mid-level cloud coverage over this time and place as discussed above. The North Platte, NE area was chosen as the primary ground observational site for CLEX-9 for several reasons: 1) the area is within easy ferry distance (about 1 hour one-way) of the Wyoming King Air flight facility in Laramie, WY, 2) the region has about 50% higher climatological coverage of mid-level clouds than the SGP ARM CART site in OK (Figs. 1a,b), 3) the air space at mid-levels (5 kft to 22 kft) is much less restricted over the North Platte region than the ARM CART site or northeastern Colorado sites (CSU-CHILL or CSU Pawnee sites), and 4) the clouds are less likely to be under the influence of terrain induced gravity waves at North Platte compared to other potential sites in northeastern Colorado near the foothills and peaks of the Rocky Mountains.
Near sunrise mission start times (sunrise -1 hr to sunrise +3 hrs) will be emphasized during CLEX-9 because of the diurnal cycle of mid-level clouds discussed above. Prior CLEX missions have flown almost exclusively during the local minimum in mid-level cloud coverage (i.e., 0900 to 1500 local). During CLEX-9 the UWKA will often take off prior to sunrise in order to 1) increase our sampling probability during the maxima in mid-level cloud coverage near 0600 local, 2) verify that near sunrise mid-level clouds are similar in structure and physical properties to past CLEX case studies, and 3) investigate the shortwave absorption hypothesis for the post-sunrise dissipation of many mid-level clouds.
4.1 Scientific Objectives
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CLEX has both basic and applied research goals. The basic research objective of CLEX is to observe and understand the morphology, lifecycle, microphysics, dynamics, and radiative properties of non-precipitating mid-level clouds (often mixed-phase and multi-layered). The applied research goals are to improve the 1) satellite detection and nowcasting, 2) numerical modeling, and 3) forecasting of mid-level clouds. CLEX attempts to strike a synergistic balance between the two sets of goals.
Some scientific questions that the CLEX program hopes to address by combining CLEX-9 observations with past CLEX data and results are:
1) Is the cloud-top radiative balance (longwave cooling vs. shortwave warming) the primary force behind the observed diurnal behavior of mid-level cloud coverage (e.g., see Fig. 10)? Do other factors play a significant role (e.g., entrainment, environmental conditions, and water vs. ice)? How do synoptic and mesoscale forcing (ascent or subsidence) at midlevel modulate this behavior?
Fig. 10. Schematic diagram of the primary physical processes occurring in altocumulus clouds (Tulich, 1998).
2) Are the morphology and physical properties of midlevel clouds similar during the nocturnal maximum and daytime minimum in midlevel cloud coverage?
3) Can cloud dissipation be forecasted using satellite remote sensing techniques alone and/or in combination with NWP model (i.e., "cloud dissipation index")?
4) To what extent are midlevel clouds horizontally homogeneous? What is the decorrelation length of various in-situ measured and radar derived microphysical and thermodynamic properties?
5) Can cloud bases and layers be estimated using current and future (e.g., CLOUDSAT) satellite-only techniques?
6) What are the origins of ice in mixed phase midlevel clouds? How does the ice phase evolve in time and space? What are the effects of the ice phase on the morphology and lifecycle of mixed-phase clouds? What are the effects of ice on the satellite remote sensing of mixed-phase clouds? Do numerical cloud models properly parameterize ice in mixed-phase clouds? Is there a better way?
4.2 Mission Priorities
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Mission Priorities for CLEX-9 are as follows
CLEX-9 MISSION PRIORITIES
I. Aircraft + Satellite + Cloud over North Platte, NE (LBF)* Instrumented Ground Site
II. Aircraft + Cloud over LBF* Ground Site
III. Aircraft + Satellite + Cloud
IV. Aircraft + Cloud
V. Cloud over LBF* Ground Site
4.3 Mission Scenarios
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When planning CLEX-9 mission scenarios, there are several factors to consider: 1) Eulerian vs. Lagrangian flight tracks, 2) time of day, and 3) horizontal vs. vertical sampling to name a few.
Eulerian (i.e., operations over a fixed ground site) and Lagrangian (i.e., operations that follow a cloud parcel) will be equally weighted. Each approach has its strengths. When cloud is forecasted over the LBF ground site, Eulerian operations will be given priority because of the limited probability of getting such an event.
Past CLEX have only conducted daytime operations from midmorning to mid-afternoon (0900 to 1500 Local). As shown in Fig. 2, this time period corresponds to the minimum in midlevel cloud coverage during the month of October over the High Plains (As seen in Kankiewicz et al. 2001, this is true for most months over many regions of the globe).
As a result, CLEX-9 will dedicate a significant number of missions to pre-dawn take off times. A pre-dawn take off will allow the UWKA to get on target just prior to or coincident with local sunrise. This will allow CLEX to sample more clouds, investigate cloud dissipation mechanisms, and insure that daytime clouds with unique physical properties do not bias the CLEX midlevel cloud sample. Near sunrise missions would allow CLEX to sample the midlevel cloud coverage maxima. In order to easily identify cloud targets, pre-sunrise missions should be a top priority during the full moon (around 2 October or 1 November). The Wyoming Cloud Radar can also identify clouds by approaching targets from below in upward-pointing mode.
Another decision is whether to stress horizontal or vertical sampling of midlevel clouds. Spiral flight tracks haven proven to be very useful for characterizing the vertical structure of clouds. Upward pointing of the WCR makes most sense if the mission is emphasizing vertical structure. To capture the horizontal morphology and variability in midlevel clouds, missions should emphasize extended racetracks in cloud with horizontal pointing of the WCR and beneath cloud with upward pointing of the WCR. Stacked racetracks of moderate size (20-40 km) can also be utilized to assess both vertical and horizontal structure and variability. A combination of all of these sampling techniques will be utilized during CLEX-9.
4.4 General Cloud Sampling Strategies
4.4.1 Single aircraft missions: University of Wyoming King Air Cloud Research Facility
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With a typical crew and equipment load, the WYKA (tail number N2UW) can be operated at altitudes up to 9.8 km msl (32 kft), at airspeeds of 80-120 m/s, and a maximum rate-of-climb of about 13 m/s (2500 ft/min). Normal measurement/sampling airspeed is 80 m/s. Typical operating altitudes [temperatures] for CLEX are from 2 to 6 km (or about 6,000 to 20,000 feet) [-5° to -30° C]. Occasionally, altitudes up to 28kft (8.5 km) are required.
During CLEX-9, there are five basic flight patterns:
The racetrack is defined by four way points (Fig. 11a). It emphasizes horizontal structure and can be used individually or in a group of stacked racetracks (Fig. 11b) depending on the depth of the cloud and the scientific objective. Racetracks above cloud are utilized for cloud radiation and entrainment measurements. Racetracks below cloud can be used for all of the same plus vertical profiling of the cloud with the Wyoming Cloud Radar. In cloud racetracks will typically number 1 to 3. For cloud microphysical and dynamical studies, a racetrack just above (below) cloud base (top) is useful. The typical length (major axis) of a racetrack will depend on cloud morphology and objectives. For CLEX, typical lengths are roughly 20 to 40 km. For a cloud of thickness on the order of 1 km, 3 in-cloud racetracks can be utilized. Vertical separation between racetracks will typically be 200 - 500 m depending on cloud depth. For cloud less than 1 km thick, use 2 in-cloud race tracks (near cloud top and base). If the cloud is still too thin, see 5) gentle porposing below. A set of stacked racetracks will take an hour or more to complete. If there time is critical and horizontal sampling is still required, consider a set of stacked 2) straight runs below. After completing a set of stacked racetracks, a 4) straight vertical sounding can be utilized to return to cloud top. Radar scanning should be upward pointing during the below cloud track and either side or upward-looking for in-cloud tracks, depending on scientific goals. It would be beneficial to get a mixture of both types in order to document horizontal and vertical cloud morphology.
Fig. 11. Depiction of racetracks. a) The racetrack is defined by four way points. b) Stacked racetracks through a midlevel cloud.
A straight and horizontally level run is defined by two way points (Fig 12a). Practically and scientifically, the straight run is similar to racetracks above except that only one leg is run per vertical level. For stacked straight legs (Fig. 12b), the aircraft executes straight legs once and steps down and make a run of equal length in the opposite direction. This pattern is repeated until the beneath cloud base run is made. To return above cloud top, utilize a 4) straight vertical sounding.
Fig. 12. Depiction of horizontal straight and level runs. a) The straight run or leg is defined by two way points. b) Stacked straight legs through a midlevel cloud.
The slow spiral sounding (usually descending to conserve fuel; Fig. 13) is defined by a radius, a starting and ending altitude and a descent rate. Typical descent rates are 300 - 500 feet per minute. The starting and ending altitude are defined by cloud depth. Be certain to spiral above and below cloud in order to get proper thermodynamic and radiation data above cloud and the same plus vertical radar profiling below cloud. The radius of the spiral will depend on cloud morphology and descent rate. Spiral should be large enough to maintain a gentle bank angle (near horizontal) for ease of interpretation of radar and microphysical data. Typical radius would be about 30 km (20 - 40 km). Radar scanning can be in either upward or side-looking mode until the WYKA is beneath cloud and then upward pointing should be utilized.
Fig. 13. Depiction of a slow descending spiral sounding.
The straight (vertical) sounding (descending [Fig. 14] or ascending) is defined by two way points and a descent rate. A rapid straight sounding is very useful for obtaining quick thermodynamic, microphysical and cloud morphology data. A rapid ascending straight sounding should be used between sets of racetracks, straight runs, or spirals in order to get back above the cloud top.
Fig. 14. Depiction of a descending straight sounding.
Gentle porposing (i.e., sine wave) is defined by a minimum and maximum altitude, two way points, and a descent/ascent rate (Fig. 15a). The choice of these parameters is determined by cloud thickness. This flight pattern is typically utilized to obtain complete horizontal and vertical physical and morphological characteristics of a cloud that is too thin to utilized a spiral or stacked racetracks/straight runs (Fig. 15b). Typically, the WCR should be in side-looking mode. Porposing can be combined with a beneath cloud racetrack (or straight run) that can provide a vertical radar profile of the thin cloud (Fig. 15b).
Fig. 15. Depiction of gentle porposing through cloud. a) Porposing is defined by two way points, ascent/descent rate, and a depth. b) Porposing (and side-looking WCR) can be combined with a beneath cloud racetrack (or straight run) whose purpose is to provide vertical cloud profiling with the WCR.
Any of these flight patterns can be used for either Lagrangian (follow cloud) or Eulerian (local, say over North Platte) measurements. For Lagrangian measurements, the aircraft and hence the flight pattern should drift with the horizontal wind (typically taken at mid-cloud level). Utilize the onboard WYKA Lagrangian sampling "pointer" system. The pointer system predicts air parcel locations by integrating the horizontal wind vector(s) at user-selected locations, then provides continuously updated navigation information to the pilot for repeated passes through the same parcel.
For Eulerian operations over LBF, the WYKA flight scientist can obtain an update on environmental and cloud conditions over LBF as the WYKA approaches North Platte. The CSU trailer at LBF is equipped with two VHF radios so limited communication and coordination with the WYKA should be possible near LBF. At LBF, ground-based remote sensing data (LIDAR, dual-frequency radiometer, surface radiation budget) and a supplementary radiosonde balloon launch will be available. The ground site can pass along thermodynamic and moisture information from the radiosonde balloon launches (both CSU and 12z KLBF launch) and NOAA-ETL radiometer. The NOAA-ETL radiometer and CSU LIDAR data can also be used by the ground manager to pass on cloud morphology and mixed-phase status of clouds above LBF.
Another single aircraft flight scenario is a flight mission with a satellite overpass scientific emphasis. For many of these satellite missions that emphasize cloud top IR and VIS imaging, cloud top morphology and microphysical and radiative behavior should be emphasized (Fig. 16). For satellite platforms with the capability to provide profiling or vertically integrated cloud information (e.g., passive microwave or CLOUDSAT simulations), then the general flight strategies above should be utilized.
Fig. 16. Depiction of above cloud and in-cloud (just beneath cloud top) racetrack sampling during a satellite overpass. The in-cloud track is the most important for horizontal cloud morphology and microphysical information (both probes and side-looking WCR). The above cloud track should be utilized before or after the overpass for documenting the above cloud (IR and VIS) radiative flux.
4.4.2 Dual aircraft missions: Joint UW King Air and SPEC Inc. Learjet Cloud Research Facilities
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During CLEX-9, we have the opportunity on one operational flight day (1 - 2 missions) to run dual aircraft missions utilizing both the University of Wyoming King Air and SPEC Inc. Learjet (LJ, based out of Jefferson County Airport, see Fig. 17). Both aircraft will be outfitted with cloud microphysical probes. During these flights, a minimum vertical separation of 1000 feet will be maintained. The SPEC LJ will operate at altitudes above the WYKA. The scientific objective is to 1) increase horizontal, vertical and temporal microphysical sampling of the clouds and 2) obtain vertically pointing WYKA cloud radar (WCR) data in the vicinity of the SPEC LJ, which will be carrying the Cloud Particle Imager (CPI) and the Nevzorov probe. Both of these instruments are ideally suited for determining the phase (supercooled liquid vs. ice water), amount, and characteristics of cloud hydrometeors in mixed-phase clouds.
Fig. 17. A collage of images of the SPEC Inc. Learjet and associated microphysical instruments. On one mission day, CLEX-9 will run a dual-aircraft mission between the SPEC Learjet and WY King Air aircraft over the North Platte Instrumented Ground Site.
The basic flight strategy will be to fly the SPEC LJ in-cloud in straight and level horizontal runs above the WYKA, which will also run straight runs, over the North Platte/LBF ground site (Fig. 18a). [Alternatively, we may try joint slow spirals with vertical separation if cloud conditions warrant it (Fig. 18b).] The WYKA will either be in-cloud or beneath cloud depending on cloud thickness and the WCR will be utilized in upward-looking mode (Fig. 18a). Although not shown, the SPEC LJ should fly a slightly elongated (say 25%) straight run to account for the differences in operating speed of the two aircraft (WYKA: 160 kts vs LJ: 200 kts). The WYKA flight scientist will be responsible for 1) choosing an appropriate cloud target, 2) providing altitude range and two way points for the SPEC LJ straight runs and 3) communicating this via radio to the SPEC LJ flight scientists. The WYKA will ferry to LBF first in order to profile the cloud(s) over LBF and obtain an update on cloud conditions from the LBF ground manager. The SPEC LJ will arrive on location about 0.5 hr after the WYKA. WYKA (Learjet) one-way ferry time to LBF from Laramie (Jefferson County Airport) is about 1hour (40 minutes)
Ideally, we will call for a dual aircraft mission over the North Platte Municipal airport (LBF) so that we can obtain additional ground-based remote sensing data (LIDAR, dual-frequency radiometer, surface radiation budget) and a supplementary radiosonde balloon launch. The CSU trailer at LBF is equipped with two VHF radios so some communication and coordination with the aircraft should be possible as the aircraft approach the North Platte region. The ground site can pass along thermodynamic and moisture information from the radiosonde balloon launches (both CSU and 12z KLBF launch) and NOAA-ETL radiometer. The NOAA-ETL radiometer and CSU LIDAR data can also be used by the ground manager to pass on cloud morphology and mixed-phase status of clouds above LBF.
A minimum of 1000 feet vertical separation must be maintained at all times. Each plane will request a "box" of air space from air traffic controllers over the target cloud (ideally over North Platte/LBF). The SPEC LJ box will be above the WYKA by at least 1000 feet. The SPEC LJ box should include at least the top half of a thick cloud or the top half of a set of multi-layered clouds. The Before launch, the WYKA and Learjet mission scientists should coordinate on approximate flight levels for each aircraft based on morning sounding, model (and possibly LBF ground data - see next).
Fig. 18. Dual aircraft flight patterns for CLEX-9. a) Vertically separate and stacked straight runs. b) Joint spiral sounding while maintaining vertical separation. The WYKA is beneath the SPEC Learjet. The WCR should be in upward-looking mode in order to document the cloud morphology and microphysical environment sampled by the SPEC microphysical probes (including the CPI and Nevzorov probes).
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CLEX seeks a better fundamental understanding of the physical nature of mid-level clouds in order to better detect, model, and forecast them. In this way, the impact of mid-level clouds on military air missions can be mitigated in the future.
CLEX-9 is planned for October 2001. The primary observational platform will be the University of Wyoming King Air Cloud Research Facility. The UWKA will carry a comprehensive suite of microphysical and radiation probes in addition to the 95 GHz Wyoming Cloud Radar. Additional ground instrumentation, including the NOAA/ETL dual-frequency radiometer and CSU Micropulse LIDAR, will be located near North Platte, NE. An emphasis will be placed on near sunrise flight missions in order to sample the maxima in diurnal mid-level cloud coverage and to better understand the dissipation of mid-level clouds after sunrise.
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Carey, L. D., T. H. Vonder Haar, J. A. Kankiewicz, J. M. Davis, J. M. Forsythe, D. L. Reinke, and K. E. Eis, R. P. Fleishauer, and V. E. Larson, 2001: An Overview of the Next Complex Layered Cloud Experiment. Proceedings of the BACIMO Conference 2001, Fort Collins, CO, July 10 - 12 2001, Hosted by the Army Research Laboratory and the Center for Geosciences/Atmospheric Research at CSU-CIRA.
Fleishauer, R. P., V. E. Larson, T. H. Vonder Haar, 2001: Observed microphysical structure of mid-level, mixed-phase clouds. J. Atmos. Sci., conditionally accepted.
Kankiewicz, J. A., L. D. Carey, D. L. Reinke, and T. H. Vonder Haar, 2001: An ISCCP-Observed Diurnal Cycle in Mid-Level Cloud Cover. Proceedings of the BACIMO Conference 2001, Fort Collins, CO, July 10 - 12 2001, Hosted by the Army Research Laboratory and the Center for Geosciences/Atmospheric Research at CSU-CIRA.
Larson, V. E., R. P. Fleishauer, J. A. Kankiewicz, D. L. Reinke, and T. H. Vonder Haar, 2001: The death of an altocumulus cloud. Geophys. Res. Lett., 28, 2609-2612.
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Acknowledgments. CLEX is funded by the DOD Center for Geosciences/Atmospheric Research at CSU-CIRA. We are especially indebted to Loretta Wilson of CSU-CIRA for managing the CLEX program and helping CLEX-8 and CLEX-9 get off of the ground. We thank Glenn Gordon, Al Rodi, Gabor Vali, Samuel Haimov, Mark Hoshor and the rest of the University of Wyoming Flight Facility staff for their assistance in planning for UWKA and WCR participation in CLEX-9. We thank Brad Orr, Duane Hazen, Brooks Martner, Tim Schneider, and M. J. Post of NOAA/ETL for their help in planning the deployment of the NOAA/ETL dual-frequency microwave radiometer in CLEX-9. We also thank Paul Lawson, Mr. Cleon Biter and the rest of the staff at SPEC Inc. for their assistance in executing CLEX-8 and planning for possible joint SPEC and UWKA flights during CLEX-9. Finally, we acknowledge Jim Jones and Curtis Seaman for their assistance on the CLEX-9 forecasting team.
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