# Presentation: 934939

## K. Pfeilsticker, and T. Scholl, IUP, University of Heidelberg, GermanyA. B. Davis, LANL, Los Alamos, USAH. K. Baltink, KNMI, Utrecht, NLS. Crewell, U. Löhnert, and C. Simmer, Met. Institute Bonn, GermanyJ. Meywerk, and M. Qante, GKSS, Geesthacht, Germany

_**Overview**_
**introduction**
**oxygen A-band spectroscopy and retrieval technique**
**some examples**
**Test of **
**photon diffusion in plane-parallel cloud geometry**
**real clouds (anomalous diffusion)****   **
**summary and conclusion**

_**Recent cloudy sky photon path pdf measurements from Heidelberg**_

## Instrumental Set-Up

**spectral resolution (FWHM) is presently limited to 0.013 nm **
**      ****(not line resolving)**
**Integration time: < 15s (previously 900 s, but limited **
**by the spectral  brightness of the sky****)**

## Data Processing

## Measurements during BBC 2001

**Cabauw/NL ****51.971****o ****N, 4.927****o**** E in Sept. 2001 ****together with: **
** ****GKSS 95 GHz Cloud Radar ****             ******** ****Lidar **
** ****Microwave Radiometer ****	****              ******** ****Radio ****probes, ****air****c****raft in-situ instruments**

_**Cloud structure (backscattering ratio measured  by the 95 GHz GKSS Radar) **_
_**on Sept. 17, 2001, UT 9:45 - 10:45**_

## Measured vs Modeled Oxygen A-band spectra

## Cloud Structure and Inferred PDF

**Inferred PDF assuming a ********-type PDF distribution. **

****** ****direct sun PDF**

****** ****inferred cloudy sky PDF**

**Note: The inferred first 2 PDF moments are given in units of a **_**v**_**ertical **_**o**_**ptical **_**d**_**ensity (VOD) for oxygen of the atmosphere**

**<L****tot****> = 2.74 VOD**
******<L****2****tot****> = 2.89 VOD**

## Idealized Scheme  for Cloudy Sky RT

_**Attention: **_**Oxygen A-band absorption measurement integrates over total atmospheric oxygen column ******** hence in cloud pdf studies need corrections for the clear sky absorption !**

**regime (1)**

**regime (3)**

**regime (2)**

## From the total atmospheric paths (<Ltot> and (<L2tot>) to in-cloud paths (<Lc> and (<L2c>) 

**regimes:**
**above the cloud: <L****1****> = (L******** – H ****cloud top ****)/cos(SZA) (typical values  < 1 VOD)**
**< L****c****> (typical values > 2.5 VOD)**
**below the cloud: < L****3**** > = (L****cloud bottom**** – 0**** ****)****·(1+5A****g****R****c****/(1-A****g****R****c****) (typical value < 0.5 VOD)**
_**Corrections:**_
**1st moment: <L****c****> = <L****tot ****> – <L****1****> – <L****3****>**
**2nd moment: <L****2****c****>  = <L****2****tot****> - <L****tot ****>****2****  +  <L****c****>****2**** **

## Testing the pdf solution for photon diffusion through plan-parallel clouds and the anomalous diffusion (Lévy walk) model - the first two moments - 

**1****st**** moment:**

**2****nd**** moment:**

**Parameters:**

**Davis&Marshak (2002)**

**(********-1)**
******(********-1)**

**L****é****vy index 1 ******** ******** ******** 2;****                                                               Davis&Marshak (1997)**

## Measurements over Cabauw on May 22, 2003

** ****radar reflectivites (KMNI, 35 Ghz)**
** ****<L****tot****>, ********<L****2****tot****>, and LWP (KMNI, Uni Bonn)**

## Radar reflectivity measurements (KMNI, 35 Ghz) over Cabauw on May 22, 2003

## Inferred Lévy Indices

## Testing the pdf solution for photon diffusion through plan-parallel clouds and the Levy walk model (Davis&Marshak, 1997) - ratio of 1st two moments - 

**For ******** = 2:**

**Davis&Marshak (2002)**

## Ratio of the 1st two moments of inferred and predicted photon path lengths

## Summary&Conclusion

**photon path PDFs (<L****tot****>, <L****2****tot****>, <L****c****> and <L****2c****o****>, can reliably be derived from oxygen A-band measurements (every 15 s).  **
**a wide range of PDF types occur, depending on the type of cloud cover.**
**Gamma (log-normal) PDF is reasonably good approximations for photon path PDF’s under slab like cloud covers ****(******** = 2)**** .**
**for more complicated cloud covers (c.f. multi-layer, broken cloud covers) anomalous diffusion approximation, c.f. Lévy type photon path PDFs  are better suited ****(<L>~******** ********-1**** **** with ******** < 2)****. **
**Our measurements confirm the numerical values (prefactors) of the Davis&Marshak (2002) diffusion solution for plane-parallel clouds (******** = 2).**