Aircraft

Research aircraft measurement objectives

The goal of research aircraft operations in the Asir region of Saudi Arabia is to address key scientific questions on the application of weather modification. Research aircraft operations will focus primarily on the characterization the effect of sub–cloud aerosol on the microphysics and dynamics of both natural and seeded clouds through cloud profiling and tracer experiments using two aircraft: an instrumented King Air B200 research aircraft and a Piper Cheyenne II seeding aircraft.

To attain the fundamental purpose of intensive observation period, specific objectives are pursued:

  1. To characterize the boundary layer prior to convection along the Asir escarpment and obtain an understanding on the triggers of first convection (e.g. sea breeze, moisture convergence, orographic lift)
  2. To establish the link between ground based aerosol and sub–cloud aerosol properties within a well mixed boundary layer (under cloudy and cloud-free conditions)
  3. To establish the link between sub–cloud aerosol properties and the initial cloud drop size distribution. We seek this link for clouds of different type (non–precipitating shallow cumulus and deep mixed–phase convection)
  4. To study CCN forced variations on the droplet size distribution and cloud hydrometeor type at various levels above cloud base to determine suitability for cloud seeding under different aerosol loadings
  5. To determine the extent of interaction between the mid–level altocumulus deck and the cloud edges of convective storms that penetrate the altocumulus layer

The research aircraft is the WMI King Air B200 (N825ST) equipped with instruments to conduct in–situ aerosol and cloud microphysical measurements. This aircraft will be dedicated to conduct atmospheric measurements during the observation period, with an additional Piper Cheyenne II aircraft used to conduct seeding trials.

Research aircraft instrumentation

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Figure 1

The WMI King Air B200 (Figure 1) is equipped with specialized instruments that have the capability of measuring aerosol, and microphysical properties of clouds and their thermodynamic environment. These are used to document the composition of clouds and to diagnose the physical processes of precipitation development within them. A list of instruments and integration tasks are listed in Table 1.

Instrument Description
SPEC 2D-S Measures cloud particle size distribution from 10µm to 1280µm
DMT Cloud Combination Probe (CCP) Measures cloud particle size distribution from 2µm to 1550µm
PMS Forward Scatter Spectrometer Probe (FSSP) SPP100 Measures cloud droplet size distribution from 3µm to 47µm
PMS Passive Cavity Aerosol Spectrometer Probe (PCASP) SPP200 Measures aerosol size distribution from 0.1µm to 3µm
DMT CCN-100 Measures cloud condensation nucleus number concentration
Differential Mobility Analyzer (DMA) Measures aerosol size distribution from 0.01µm to 0.4µm
MPS-3 Cascade Impactor system Collects aerosol particles for SEM analysis
Aventech AIMMS-20 Measures temperature, humidity, wind and aircraft attitude
DMT Liquid Water Content (LWC) Measures cloud liquid water content

Table 1