Ice-Phase Precipitation Remote Sensing Using <br />Combined Passive and Active Microwave Observations<br />Benjamin T. Johnson<br />UMBC/JCET & NASA/GSFC (Code 613.1)<br />Benjamin.T.Johnson@nasa.gov<br />Gail Skofronick-Jackson<br />NASA/GSFC (Code 613.1)<br />IGARSS 2011 – Vancouver, Canada<br />
Figure 1.: whiteout conditions during a snow storm.<br />2/22<br />
Introduction<br /><ul><li>Midlatitude/Winter precipitation is difficult to measure using radars or radiometers alone.
Precipitating clouds consist of a wide range of particles with variable shape, size, number density, and composition, and microwave radiation is sensitive to these properties
Furthermore, ice clouds, water clouds, and gases and attenuate/emit microwave radiation</li></ul>B. Johnson IGARSS 2011<br />3/22<br />
Physically-based microwave precipitation remote sensing methods require (at least):<br /><ul><li>A physical description of the atmosphere and surface properties
Physical descriptions of hydrometeors (PSD, shape(s), composition)
Appropriate relationships between physical and scattering/extinction/backscattering properties
An inversion method for retrieving the desired physical properties given observations</li></ul>B. Johnson IGARSS 2011<br />4/22<br />
Relevant Key Problems<br /><ul><li>Uncertainties the physical description of the atmosphere: distribution of CLW, WV; particle composition, size distribution, and shape.
No current method for validating MW scattering properties of ice-phase hydrometeors. </li></ul>Present Retrieval Approach<br /><ul><li>Physical method using “consistency matching” -- adjust simulations until consistent with PMW and radar observations across multiple wavelengths (e.g., Meneghini, 1997).
Pros: Simple to implement, works equally over land and water
Cons: “matches” may not represent reality, geometric issues ignored (NUBF, beam matching)
Important note: the uncertainty due to unknown particle shape is orders of magnitude greater than other known sources of uncertainties.</li></ul>B. Johnson IGARSS 2011<br />5/22<br />
Part 1 comments:<br /><ul><li>The basic retrieval works surprisingly well using only constant-density spheres
approx. 5 K RMS error in precipitating regions, simply by adjusting the CLW and particle density.
However, constant-density spheres likely are not representative of the true distribution of mass and sizes of particles within the observed volume of the atmosphere… </li></ul>Improvements:<br /><ul><li>Inclusion of well-known size-density relationships for spheres (following Brown and Ruf, 2007),
Include sets of non-spherical “realistically shaped” hydrometeors</li></ul>B. Johnson IGARSS 2011<br />13/22<br />
(Fixed IWC = 1.0 g m-3)<br />Constant Density Spheres<br />Mass-Density Relationships<br />Magono and Nakamura (1965)<br />Mitchell et al. (1990)<br />Locatelli and Hobbs (1974)<br />Barthazy (1998)<br />UW-NMS (Tripoli, 1992)<br />14/22<br />
Retrieved log10(IWC) [g m-3] using size-density relationships (Brown and Ruf, 2007)<br />15/22<br />