Retrieval of Hydrometeor Profiles in Tropical Cyclones and Convection from Combined Radar and Radiometer Observations

Abstract

A retrieval algorithm is described to estimate vertical profiles of precipitation ice water content and liquid water content in tropical cyclones and convection over ocean from combined spaceborne radar and radiometer measurements. In the algorithm, the intercept parameter N 0 s in the exponential particle size distribution for rain, snow, and graupel are adjusted iteratively to minimize the difference between observed brightness temperatures and simulated ones by using a simulated annealing optimization method. Sensitivity tests are performed to understand the effects of the input parameters. The retrieval technique is investigated using the Earth Resources (ER)-2 aircraft Doppler radar and Advanced Microwave Precipitation Radiometer data in tropical cyclones and convection. An indirect validation is performed by comparing the measured and retrieved 50-GHz (independent channel) brightness temperature. The global agreement shows not only the quality of the inversion procedure, but also the consistency of the retrieved parameters with observations. The direct validation of the ice water content retrieval by using the aircraft in situ microphysical measurements indicates that the algorithm can provide reliable ice water content estimates, especially in stratiform regions. In convective regions, the large variability of the microphysical characteristics causes a large uncertainty in the retrieval, although the mean difference between the retrieved ice water content and aircraft-derived ice water content is very small. The ice water content estimated by a radar-only empirical relationship is higher than those retrieved by the combined algorithm and derived by the aircraft in situ observations. The new combined algorithm contains information that should improve ice water content estimates from either radar-only or passive microwave-only measurements.

On the Differences in Storm Rainfall from Hurricanes Isidore and Lili. Part II: Water Budget

“…All frequencies are measured independently in the horizontal and vertical polarization planes, except the 21.3-GHz channel, which measures the radiance in the vertical polarization plane. Jiang and Zipser (2006) developed a combined radar-radiometer algorithm to estimate the precipitation ice water content (IWC) and liquid water content (LWC) profiles in tropical cyclones and convection for aircraft-based observations. In the algorithm, the intercept parameter, N 0 , in the exponential particle size distribution for rain, snow, and graupel is adjusted iteratively to minimize the difference between observed brightness temperatures (T b 's) and simulated ones by using a simulated annealing optimization method.…”

“…This algorithm was applied to the fourth Convection and Moisture Experiment (CAMEX-4) aircraft-based hurricane and tropical convection dataset and validated by in situ microphysical measurements. Jiang (2004) adapted this algorithm to TMI and PR observations. For each radar reflectivity profile observation, the TRMM PR qualitative algorithm (TRMM 2A23; Awaka et al 1998) is used to determine the height and depth of the melting layer for each rain type.…”

“…However, a statistical study based on the TMI rainfall algorithm (2A12; Kummerow et al 1996) output for the 1-yr tropical cyclone database (Jiang 2004) shows that the cloud water content is between 5% and 20% of the rainwater content. The TRMM 2A12 algorithm is based on the 3D cloud model output.…”

Vertical Structures of Anvil Clouds of Tropical Mesoscale Convective Systems Observed by CloudSat

“…The different effective footprint sizes associated with two algorithms and the beam-filling problem in the retrieving might generate uncertainties about the distance to active rain areas. However, previous work suggests that the 85-GHz channel rather than the lowfrequency channels controls rain retrievals over oceans from basically the same algorithm as in AE_Rain if there is appreciable ice scattering (Jiang and Zipser 2006). However, to what extent this can reduce the overall difference in the effective resolution of resolvable raining elements in the rain rate retrievals over ocean and land is not clear.…”

Vertical profiling of tropical precipitation using passive microwave observations and its implications regarding the crash of Air France 447

“…The sampling frequency of both instruments is poor: TRMM's cross-track-scanning PR has a surface-clutter-limited swath of about 220 km, which results in a revisit frequency of about once every 3 days on average for points near the equator; CPR does not scan at all, and its Sun-synchronous orbit has a ground revisit time of 16 days. Different approaches have been proposed to use the observations of these radars and train microwave radiometers to retrieve precipitation fields at times and locations where no radar data is available, including that of Masunaga and Kummerow [2005], Grecu and Olson [2006], Jiang and Zipser [2006], Viltard et al [2006], and Haddad and Park [2009]. The latter approach, to which we shall refer in this paper as HP09, specifically aims at retrieving the main parameters governing the vertical distribution of precipitation and was evaluated over five different regions in the midlatitudes.…”