Current Near-Surface Humidity Algorithms

March 2008

The current near-surface humidity using AMSU-A and SSM/I collocated observations is

Qa_AMMI = 907.431 + 0.0159161 x Tb_52.8 ^2

- 7.61660 x Tb_52.8

+ 0.236978 x Tb_19v

- 0.229912 x Tb_37v

+ 0.0543359 x Tb_22v

The near surface humidity algorithm using SSM/I and SSM/T-2 collocated observations is

Qa_MIT2 = 87.87 – 9.12175 x Ln (290 – Tb_22v)

- 4.88326 x Ln (290 – Tb_183±7)

+ 3.00728 x Ln (290 – Tb_183±3)

+ 20.6064 x Ln (290 – Tb_37v)

- 27.3020 x Ln (290 – Tb_19v)

The stability correction applied to the Qa retrievals north of 30N is

∆Qa_AMMI = 6.80147 – 0.311378 (SST – Tb_52.8) + 0.401655 x Qa_AMMI

And corrected near-surface observations are obtained by

Qa_AMMIc = Qa_AMMI + ∆Qa_AMMI

Here is description of parameters given above.

Tb_52.8 = AMSU-A 52.8 GHz brightness temperature (K)

Tb_19v = SSM/I 19V GHz brightness temperature (K)

Tb_22v = SSM/I 22V GHz brightness temperature (K)

Tb_37v = SSM/I 37V GHz brightness temperature (K)

Tb_183±3 = SSM/T-2 183±3 GHz brightness temperature (K)

Tb_183±7 = SSM/T-2 183±7 GHz brightness temperature (K)

SST = Sea surface temperature (K)