# Presentation: 436153

## NCEP Operational Model Suite

- “Jigsaw puzzle” from 2004 of NCO productions
- Lesson:  Models must be efficient

## Overview of Ferrier microphysics

**Calculates mixing ratios of water vapor, cloud water, rain, and ice (“cloud ice” + “precipitation ice”)**
_**[Flowchart ](slide3.xml)**_**depicting microphysical sources & sinks**
_**[List ](slide4.xml)**_**of microphysical processes**
_**[Precipitation sedimentation ](slide5.xml)**_**-  partitioned between storage in grid box & fall out through bottom of box**
**Only water vapor and total condensate are advected; an **_**[algorithm ](slide6.xml)**_**is used to derive hydrometeors from total condensate using storage arrays**
**Supercooled liquid water allowed to T****ice**** (= -30****°****C)**
**Assumed ice spectra based on global observations of stratiform layer clouds by Ryan (1996, 2000)**
**Other features of scheme are summarized here **
**More info at this ppt talk; also contact Brad.Ferrier@noaa.gov**

## Flowchart of Ferrier Microphysics

- _[return to overview](slide2.xml)_

## List of microphysical processes

| Acronym | Process Description | Source | Sink |
| --- | --- | --- | --- |
| CND | Cloud condensation (>0), evaporation (<0) | Qc | Qv |
| REVP | Rain evaporation | Qv | Qr |
| RAUT | Cloud water autoconversion to rain | Qr | Qc |
| RACW | Cloud water accretion by rain | Qr | Qc |
| DEP | Ice initiation and deposition (>0), sublimation (<0) | Qi | Qv |
| IMLT | Melting of ice | Qr | Qi |
| IACW | Cloud water accretion by ice (riming) | Qi | Qc |
| IACWR | Cloud water accretion by melting ice, shed to rain | Qr | Qc |
| IACR | Rain accretion by ice | Qi | Qr |
| IEVP | Evaporation of (wet) melting ice | Qv | Qi |

**Q****v**** = vapor, Q****c**** = cloud water, Q****r**** = rain, Q****i**** = ice**

- _[return to overview](slide2.xml)_

## Precipitation Sedimentation

**K**

**Height**

**q****K****N**

**(a)**

**(a)  Input: existing precipitation in grid box (q****k****N****) + time-averaged sedimentation from above (P****k-1****N+1****)**

**(b)**

**q****K****N***

**(c)**

**P**

**K**

**N+1**

**q****K****N+1**

**Precipitation Sedimentation**

**(b)  Microphysical sources/sinks based on time-averaged mixing ratio, ****q****K****N***

**(c)  Partition storage (q****k****N+1****) and precipitation through bottom of box (P****k****N+1****) based on thickness of model layer (********∆****z****) & estimated fall distance (****∆****t****·****V****k****)**

- ( )N – Nth time step

- _[return to overview](slide2.xml)_

## Deriving hydrometeors from total condensate

**Cloud water (q****w****), rain (q****r****), cloud ice (q****i****), precip ice (“snow”, q****s****) calculated in microphysics**
**Local, saved arrays store fraction of condensate in form of ice (F****i****), fraction of liquid in form of rain (F****r****).  Assumed fixed with time in column between microphysics calls.   Note that 0 ******** F****i**** , F****r**** ******** 1 .  **
**q****t ****= q****w**** + q****r**** + q****i**** + q****s**** , q****ice**** = q****i**** + q****s****  ********  F****i**** = q****ice****/q****t**** , F****r ****= q****r****/(q****w**** + q****r****)**

**Deriving hydrometeors from total condensate**

- _[return to overview](slide2.xml)_

## Size of “snow” a function of temperature

**Adjust [D] so that  0.1L****-1**** ******** N****s**** ******** 20L****-1**

**HHHP (Washington state)****SMPC (California)****GM (California)****PLATT (multiple locations)****AWSE (Australia)****YL (China)****B, M (Europe)**

**Size of “snow” a function of temperature**

**return to overview**

## Other Features of Microphysics

**Discrimination between cloud ice and “snow” **
**Assume 50 ********m size cloud ice, no fall speeds**
**No cloud ice if T>0********C (melting) ******** only “snow”**
**N****s**** = 0.2·N****i****  (N****s****=snow # conc, N****i****=cloud ice # conc)**
**N****s**** = 0.1·N****i**** if above ice saturation & -8********C < T < -3********C**
**Variable rime density ******** assumes accreted liquid water fills air holes of ice lattice w/o changing volume**
**“****Rime Factor” (3D array) ******
** ****Efficient look-up tables store solutions for:**
**Various particle moments (ventilation, accretion, mass, precipitation rate) at 1 ********m resolution**
**Composite rain & ice fall speed relationships**
**Increase in fall speed of rimed ice  (B****ö****hm, 1989)**

**return to overview**